MAVEN observations of the Solar Cycle 24 ... - Wiley Online Library

MAVEN observations of the Solar Cycle 24 space weather conditions at Mars 1

1

2

3

4

C.O. Lee , T. Hara , J.S. Halekas , E. Thiemann , P. Chamberlin , F. 3

1

1

1

4

Eparvier , R.J. Lillis , D.E. Larson , P.A. Dunn , J.R. Espley , J. 4,5

1

1

3

Gruesbeck , S.M. Curry , J.G. Luhmann and B.M. Jakosky

C.O. Lee, [email protected] 1

Space Sciences Laboratory, University of

California, Berkeley, CA 94720, USA. 2

Department of Physics and Astronomy,

University of Iowa, Iowa City, IA 52242, USA. 3

Laboratory for Atmospheric and Space

Physics, University of Colorado, Boulder, Colorado, USA. 4

NASA Goddard Space Flight Center,

Greenbelt, MD 20771, USA. 5

Department of Astronomy, University of

Maryland, College Park, Maryland, USA. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/2016JA023495

c ⃝2017 American Geophysical Union. All Rights Reserved.

Abstract.

The Mars Atmosphere and Volatile EvolutioN (MAVEN) space-

craft has been continuously observing the variability of solar soft x-rays and EUV irradiance, monitoring the upstream solar wind and interplanetary magnetic field conditions, as well as measuring the fluxes of solar energetic ions and electrons since its arrival to Mars. In this paper, we provide a comprehensive overview of the space weather events observed during the first ∼1.9 years of the science mission, which includes the description of the solar and heliospheric sources of the space weather activity. To illustrate the variety of upstream conditions observed, we characterize a subset of the event periods by describing the Sun-to-Mars details using observations from the MAVEN solar Extreme Ultraviolet Monitor (EUVM), Solar Energetic Particle (SEP) instrument, Solar Wind Ion Analyzer (SWIA), and Magnetometer (MAG) together with solar observations using near-Earth assets and numerical solar wind simulation results from the Wang-Sheeley-Arge (WSA)-Enlil model for some global context of the event periods. The subset of events include an extensive period of intense SEP electron particle fluxes triggered by a series of solar flares and coronal mass ejection (CME) activity in December 2014, the impact by a succession of ICMEs and their associated SEPs in March 2015, and the passage of a strong corotating interaction region (CIR) and arrival of the CIR-shock accelerated energetic particles in June 2015. However, in the context of the weaker heliospheric conditions observed through-


out Solar Cycle 24, these events were moderate in comparison to the stronger storms observed previously at Mars. Keypoints: • We present a comprehensive overview of the first 1.9 years of MAVEN space weather conditions measured upstream at Mars • We characterize a subset of Mars-impacting events due to an extensive period of SEP electrons, a succession of ICMEs, and a strong CIR • We discuss the space weather implications of the weaker Solar Cycle 24 heliospheric conditions on the events observed by MAVEN


1. Introduction MAVEN has been continuously monitoring the local space weather conditions around Mars since 16 November 2014. Relevant observations from the instrument suite include solar flare activity based on solar irradiance measurements by the solar Extreme Ultraviolet Monitor (EUVM), the fluxes of energetic particles accelerated locally at the Sun and in the heliosphere from the Solar Energetic Particle (SEP) instrument, the solar wind plasma parameters by the Solar Wind Ion Analyzer (SWIA), and the vector measurements of the interplanetary magnetic field (IMF) by the Magnetometer (MAG). Such a comprehensive set of observations at Mars will allow the better characterization of the local EUV and solar wind conditions during active space weather periods and analysis of the response of the Martian system to the upstream disturbances. Some of the Mars-impacting space weather events observed by MAVEN include the heating of the neutral atmosphere triggered by large flares [Thiemann et al., 2015], the perturbation of the Martian system and ion escape enhancements due to the passage and interaction of an interplanetary coronal mass ejection (ICME) [Jakosky et al., 2015b], and the triggering of diffuse auroral emission in the lower Martian atmosphere due to the precipitation of electrons during a SEP event [Schneider et al., 2015]. With MAVEN completing nearly one Mars-year (∼1.9 Earth years) of its science observations, the purpose of this paper is to present a comprehensive overview of the space weather event periods observed by MAVEN over the course of the prime science phase and to illustrate the variety of upstream space weather activity observed by MAVEN through our ‘Sun-to-Mars’ characterization for a selection of event periods. For a given


space weather event of interest, our characterization involves looking at the solar activity from coronagraph images and movies together with 3D numerical simulations of the heliospheric solar wind conditions as well as utilizing ground- and space-based Earth observations. Thus, the material presented here will be useful to those who study the response of the Mars to the local space weather activity and wish to understand the solar and heliospheric context for observations made in the near-Mars environment by MAVEN and other missions such as Mars Express (MEX) and Mars Odyssey, as well as Mars Science Laboratory (MSL). The content presented in this study will also be useful to the solar-heliospheric community, for example, to study the propagation and evolution of CMEs and their associated SEPs beyond Earth at 1 AU. Because MAVEN does not have a solar imager or a solar coronagraph, we utilize near-Earth monitors to fill in the observation gaps during our analysis and characterization of the event periods. We also take advantage of and utilize routine simulations of the heliospheric solar wind conditions to obtain the global context for the single-point MAVEN measurements and to better connect the MAVEN observations to the near-Earth solar observations. We will not present the analyses regarding how the Martian system responded to the energetic inputs (e.g. Jakosky et al. [2015b]) for the event periods presented in this paper since it is beyond the scope of this paper. In Section 2 we describe the data sets that are used in the study. In Section 3 we present observations obtained through the science phase of the MAVEN mission, of the solar irradiance, differential energy fluxes of SEPs, upstream solar wind speed, density and dynamic pressure as well as the total IMF magnitude. We also present a table that summarizes the solar and heliospheric sources of the space weather activity observed


upstream of Mars. A subset of these events are characterized in Sections 4 to 7. In Section 8 we briefly discuss the weaker heliospheric conditions of Solar Cycle 24 and their space weather implications at Mars and comment on the broader research applications of the MAVEN upstream observations by the heliospheric research community.

2. Data used in this study MAVEN orbits Mars in a ∼4.5 hour orbit, with periapsis at ∼150 km and apoapsis at ∼6200 km above the surface. The highly elliptical orbit allows for in situ measurements of the plasma conditions from the solar wind regions, Martian bow shock, and all the way down to the lower boundary of the thermosphere and ionosphere (see Figure 2 in Jakosky et al., this issue; see also Figures 16 and 18 in Jakosky et al. [2015b]). In addition, the orbit precesses around the planet for MAVEN to measure the relevant plasma regimes within the Martian magnetosphere and, because of planetary rotation, to visit all geographic locations. The MAVEN observations shown in this study are from the following the instruments: EUVM [Eparvier et al., 2015], SEP [Larson et al., 2015], SWIA [Halekas et al., 2015], and MAG [Connerney et al., 2015a, b]. EUVM measures at a 1-second cadence the variability of the solar EUV and soft x-ray irradiance including flares. Shown throughout this study are the level 2 (L2) measurements from the EUVM science channel B (hereafter, EUVM-B) radiometer, which is sensitive to the 0.1–7 nm range of solar emissions from the hot solar corona and responds to flares in a similar manner as the NOAA Geostationary Operational Environmental Satellites (GOES: Aschwanden. [1994]) 0.1–0.8 nm channel for soft x-rays. At the time of this writing, EUVM-B was calibrated for measuring non-flaring irradiance and over-estimates irradiance during solar flares. c ⃝2017 American Geophysical Union. All Rights Reserved.

The SEP instrument consists of two identical sensors, SEP 1 and SEP 2, each consisting of a pair of double-ended solid state telescopes (referred to as A and B) to measure 20– 1000 keV electrons and 20–6,000 keV ions in four orthogonal look directions. The data shown here are L2 data in the form of energy fluxes measured by the SEP1 sensor in the ‘1F’ look direction (see Figure 3 of Larson et al. [2015]) that typically views the Parker spiral direction except during specific spacecraft maneuvers at periapsis, surface assets relay, and Earth communication. The measurement cadence ranges from 1 second to 32 second, depending on the MAVEN altitude and spacecraft data rate. SWIA is a toroidal electrostatic analyzer with deflectors, which covers ion energies per charge from 25 eV to 25 keV, with an angular field of view of 360◦ ×90◦ , of which a 45◦ ×45◦ portion is pointed toward the Sun to measure the solar wind. The MAG instrument consists of two triaxial fluxgate magnetic field sensors, one at the end of each solar panel, and measures the magnetic fields at 32 Hz with 0.015 nT resolution. To select the data measured during the solar wind intervals, an algorithm is used together with the SWIA onboard moments data and MAG measurements to compute the averages of the solar wind quantities over the upstream segment of each MAVEN orbit (shown in Sections 4 to 6) and also over ∼45-second intervals (e.g., Figure 2). Additional details describing the algorithm can be found in Section 3.1 of Halekas et al. [2016]. Data gaps in the observations occur when the spacecraft is in safe mode and during scheduled observation campaigns, which require off-pointing. In addition, there are gaps in the SEP data when the instrument attenuators close at altitudes below 500 km, all the time through October 2015 and only when the SEP field of view sees the ram direction thereafter. EUVM also have data gaps for some orbits below 500 km as well as when


MAVEN is in eclipse with Mars. For the upstream SWIA and MAG observations, the data gaps exist for the times when the orbit did not extend outside the Martian bow shock due to the precession of the MAVEN orbit in Mars’ gravity field. To identify the solar origins of the space weather activity at Mars, we utilize white light observations from the SOlar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric COronagraph (LASCO: Brueckner et al. [1995]), namely the C2 and C3 coronagraphs, which image the solar corona from 1.5 R⊙ to 6 R⊙ and 3.7 R⊙ to 30 R⊙ , respectively. In addition, we utilize images of the solar atmosphere in multiple wavelengths from the Solar Dynamic Observatory [Pesnell et al., 2012] Atmospheric Imaging Assembly (SDO/AIA: Lemen et al. [2012]) and images of the solar photosphere from the SDO Helioseismic and Magnetic Image (SDO/HMI: Scherrer et al. [2012]). To obtain some global context for the solar and heliospheric sources of the local space weather conditions at Mars, we use 3D numerical simulations of solar wind density and speed from the Wang-Sheeley-Arge (WSA)-Enlil coupled solar corona-solar wind model (hereafter, WSA-Enlil: Arge et al. [2004]; Odstrcil [2003]).

The low resolu-

tion simulations are routinely generated by the NASA Space Weather Research Center (SWRC) and archived at the integrated Space Weather Analysis (iSWA) website (iswa.ccmc.gsfc.nasa.gov). The simulation movies and time snapshots are valuable for getting a better understanding of the propagation (i.e. timing and direction) of the solar wind structures that are predicted to impact Mars. During event periods when the stormy upstream conditions at Mars are triggered by multiple heliospheric disturbances (e.g., a series of Mars-impacting CMEs discussed in in Section 5.2), the WSA-Enlil simulations to-


gether with the SDO and LASCO observations are valuable for potentially distinguishing the individual sources of space weather activity.

3. Overview of the Mission-long Observations To date, the MAVEN prime science mission spans the end of the maximum phase through the declining phase of Solar Cycle 24 (Figure 1). Figure 2 shows an overview of the upstream conditions observed during the period from 16 November 2014 through 31 May 2016. From top to bottom, the panels show EUVM Channel B solar irradiance data, differential energy fluxes [keV/cm2 /s/sr/keV] for the SEP ions and electrons, the orbitaveraged SWIA upstream solar wind speed, density, and dynamic pressure measurements, and the total IMF magnitude from MAG. The EUVM observations show the frequency of the flare activity (spikes) and the baseline irradiance values declining with the activity cycle of the Sun. Note that the solar irradiance reached a baseline minimum value (∼0.1 mW m−2 ) in mid-October 2015. The peaks and troughs that repeat roughly every 26.4 days (a ‘Carrington rotation’ viewed at Mars) are variations due to the solar rotation. The data gaps shown throughout are due to the periods when EUVM was not pointed toward the Sun. SEPs are accelerated by the shocks in the corona during eruptive events or by the propagating interplanetary shock ahead of the CME ejecta. With the decline in solar eruptive activity, the second and third panels show that the frequency of the SEP activity and the measurements of the higher energy SEPs (e.g., >1 MeV ions) also declined with the activity cycle. The panels also show that the longer-duration and more intense SEP activity were observed earlier in the mission. In addition, there were particularly large periods of time in mid-July through September 2015 and in mid-January through midc ⃝2017 American Geophysical Union. All Rights Reserved.

May 2016 when the SEP activity was at a minimum due to a lack of solar eruptive events directed toward Mars. Of note are the discrete periods of fluxes for ions with measured energies of ≤ 100 keV that are seen throughout the SEP ion data set. One example can be seen toward the end of May 2016 (far right of second panel in Figure 2; also can be seen in more detail in Figure 10 of Section 7). These measured fluxes are due to the detection of oxygen pickup ions (PUIs) that are created in the distant upstream region of the hot atomic oxygen (neutral) exosphere at Mars, picked up by the solar wind and accelerated downstream toward Mars (and as seen by the forward-facing detectors of the SEP instrument). Details regarding the detection of PUIs by the MAVEN SEP can be found in Rahmati et al. [2015]. The bottom four panels show the time series of the ∼45-s averaged upstream solar wind plasma and total IMF observations from SWIA and MAG. (For a more complete presentation and discussion of mission-long upstream plasma moments and vector magnetic field time series, we refer the interested readers to Halekas et al. [2016], specifically Figure 4 and Section 3.1). For the solar wind speed (fourth panel), density (fifth panel), dynamic pressure (sixth panel), and total IMF magnitude (bottom panel), MAVEN observed median values of ∼391 km s−1 , ∼2.7 cm−3 , ∼0.7 nPa, and ∼3.2 nT. To examine the effects of the declining solar cycle activity on these parameters, we calculate the median values for the observations obtained during the maximum phase (16 November 2014 to 30 November 2015; red segment in Figure 1) and during the declining phase (starting on 1 December 2015; blue segment in Figure 1). The start of the solar cycle declining phase is based on the NOAA monthly sunspot number (SSN) value dropping below 55, which was the value for the local minimum observed between the double maximum peaks in 2012 and


2014, when the northern hemisphere reached solar maximum before the southern hemisphere. The median values for the solar wind speed, density, dynamic pressure, and IMF magnitude are ∼384 km s−1 , ∼2.8 cm−3 , ∼0.7 nPa, and ∼3.5 nT for the maximum phase observations, while the declining phase values are ∼400 km s−1 , ∼2.3 cm−3 , 0.6 nPa, and 2.6 nT. Therefore, the relative changes for these values between the maximum declining phase observations are about +4%, −20%, −14%, and −32%. The small increase in the median speed during the less active phase of the solar cycle is due to the increase in the high-speed stream activity, which is observed more regularly during the declining phase observations than the maximum phase observations for the solar wind speed. In general, recurrent streams are much more prominent during the solar cycle declining phase due to the persistence of mid-to-low latitude solar coronal holes (source of the high-speed streams) over several solar rotations [Richardson, 2004]. The streams may be observed to recur one or more times at intervals of a solar rotation period as viewed from Earth. Thus as we approach the solar cycle minimum period, we expect the high-speed stream activity to dominate the MAVEN upstream observations. The more significant decreases in the solar wind density, dynamic pressure, and IMF magnitude are in part due to the changing heliocentric distance of Mars, which varies between 1.38 AU (perihelion) and 1.67 AU (aphelion). This will effect the observed values by r−2 for the solar wind density and dynamic pressure and r−1 for the IMF magnitude. If we scale these solar wind measurements by the perihelion distance, the relative changes in the median values for the maximum and declining phase observations are −1%, +7%, and −19% for the solar wind density, dynamic pressure, and IMF magnitude. Thus, the decrease in the solar wind density is small while the larger decrease in the IMF magnitude


follows the decreasing trend of the sunspot numbers and therefore the solar activity cycle (see for example Figure 4 in McComas et al. [2013]). The modest increase in the solar wind dynamic pressure is attributed to the increase in the solar wind speeds during the solar cycle declining phase. Table 1 lists the space weather events observed during the first ∼1.9 years of its science mission. The table lists by row an ‘event period’ (Column 2), during which MAVEN observed solar flares, measured upstream solar wind plasma and IMF disturbances due to the passage of an ICME and/or solar wind stream interaction region, and/or detected particle fluxes of SEPs (ions, electrons). A description of the table columns is as follows: Columns 3–5 list the GOES-classification for the flare event, NOAA active region (AR) number, and time (in UT) of the peak intensity measured by MAVEN EUVM-B. The given flare classification is the magnitude irradiance increase in the NOAA GOES X-Ray Sensor (XRS) channel B instrument [Bornmann et al., 1996]. For the cases when the flare was only observed by MAVEN, a scaling is used that converts EUVM-B irradiance measurements to GOES XRS-B values that are determined from a set of flares when both instruments made simultaneous observations [Thiemann et al., submitted, this issue]. Similarly, the reported flare peak time is the peak of the GOES XRS-B, when available, or the peak of the EUVS-B measurements. When the active region of the solar flare can be viewed from Earth, the longitude of the centroid of the active region is recalculated for the Mars vantage point and is listed in Column 6 (‘Solar Location’) together with the latitude of the active region. EUVM does not have imaging capabilities to determine the location for the flares on the solar farside of Earth that are viewed only from MAVEN.


The ϕ values listed in Column 7 are the relative solar longitude angle between Earth and Mars during the event periods, obtained using ephemerides data for Earth and Mars maintained by NASA HelioWeb (http://omniweb.sci.gsfc.nasa.gov/coho/helios/planet.html). The following convention for ϕ is adopted in this study: looking down on the solar ecliptic plane (north is pointing out of the page) ϕ is in the clockwise direction. Positive ϕ means that Mars is leading Earth in the solar ecliptic plane, whereas negative ϕ means that Mars is trailing Earth in the solar ecliptic plane. When Mars and Earth are at the same heliolongitude (i.e., Mars is located along the Sun-Earth line), ϕ is 0◦ , and when Mars is in solar conjunction (‘behind’ the Sun from the Earth point of view), ϕ is 180◦ . Columns 8–10 list the LASCO observation time for when the bright CME loop or halo first enters the C2 field of view, ICME shock arrival time observed by SWIA, and the peak dynamic pressure associated with the shock arrival. For the CMEs that do not impact Mars (e.g., a CME that erupted near the western solar limb form the Mars perspective), the shock arrival time is labeled as ‘no impact’. In addition, for the times when MAVEN orbit did not extend out of the bow shock and into the solar wind, the shock arrival time and peak dynamic pressure values are labeled with ‘NU’, or no upstream. Columns 11–12 list the arrival time of the solar wind stream interaction region (SIR) and the peak dynamic pressure, as determined from the SWIA measurements for the solar wind speed and density. The stream interaction region is the compression region that forms due to the fast speed solar wind stream running into the slow speed stream ahead [Pizzo, 1978; Gosling and Pizzo, 1999]. Within this region, the solar wind dynamic pressure reaches its peak value. Note that the more familiar term, corotating interaction


region (CIR), is not distinguished from SIRs in this table. A more detailed description of CIRs is provided in Section 6. To coincide with the data panels to be shown (eg., Figure 3), the orbit-averaged upstream solar wind data set was used to determine the shock arrival times and peak dynamic pressure values that are listed in Columns 9–12 and throughout the paper in the forthcoming sections. The peak values for the dynamic pressure (and in general other peak solar wind values) may therefore be underestimated by the averaging. Moreover, unusual solar wind intervals may be excluded in the averaged data set generated by the Halekas et al. [2016] algorithm, such as periods when the solar wind fluctuations are high or when the Mach numbers are really low. Thus, the excluded data may contain solar wind values that are higher and observed at different times than those reported in this study. For details regarding the caveats and limitations in using the upstream solar wind data, we refer the interested reader to Section 3.1 in Halekas et al. [2016]. The remaining columns, 13 and 14, list the arrival times of the SEP ions and electrons. The arrival times for SEP ions are based on when differential fluxes for measured ion energies of > 100 keV are > 102 [keV/cm2 /s/sr/keV] (blue on the color scale in the data panels), which is about one order of magnitude above the background values (purple/black). The >100 keV threshold was chosen since the pickup oxygen ions are typically measured at and below this energy range (as discussed earlier; also see Rahmati et al. [2015] for details). For the SEP electron, the start times are based on when the differential fluxes for measured electron energies of an arbitrary threshold of > 40 keV are > 102 [keV/cm2 /s/sr/keV] (blue) above the background values. During the event periods when there are multiple shock sources of SEPs, for example, a succession of ICMEs


propagating toward Mars over a several-day period, the arrival times of SEPs from each individual shock source may be ambiguous to identify. We therefore state ‘continued from previous’ in the SEP columns for the multi-source event period to indicate that MAVEN continued to observe SEPs since the initial arrival of SEPs that is listed in the prior row(s). In the following sections we will characterize a selection of Mars-impacting space weather event periods that are shown in Figure 2 and listed in Table 1. We will describe the Sunto-Mars details for the events, using observations from the MAVEN instruments (EUVM, SEP, SWIA, MAG), together with observations of the Sun from near-Earth assets (e.g., SDO AIA and HMI, SOHO LASCO C2) and numerical simulation results of the solar wind from WSA-Enlil-cone for some global context of the event periods. Our selection of the events will showcase the variety of space weather conditions at Mars that MAVEN observed so far since the science phase of the mission began.

4. Observation of a Major SEP Electron Event Period On 16 December 2014 the SEP detector observed the start of an extended period of solar energetic electron and ion fluxes (number 1, Dec ‘14 event period in Table 1). Figure 3 (second panel) shows that the > 100 keV ions SEP ions were initially detected ∼ 10:00 UT on 18 December 2014, with differential energy flux (keV/cm2 /s/sr/keV) levels of > 103 (green) lasting for several days until ∼ 04:00 UT on 24 December 2014. The third panel of this figure shows that the SEP electrons arrived almost two days earlier (16:00 UT on 16 December 2014) than the SEP ions with measured differential fluxes observed through ∼08:00 on 29 December 2014. The most intense levels of differential fluxes (> 104 , orange) were detected for the 20–70 keV electrons measured by the SEP detector, from ∼ 02:00 UT on 18 December 2014 through ∼ 14:00 UT on 21 December 2014. Note c ⃝2017 American Geophysical Union. All Rights Reserved.

that the measurement of the SEP electrons were coincident with the observation of diffuse aurora by the MAVEN IUVS instrument, as reported by Schneider et al. [2015]). The arrival times of the SEP electron and ion events occurred after a series of solar flare and CME activity at the Sun. The top panel in Figure 3 shows that EUVM observed a series of flares during 13–18 December 2014. The most intense flare observed by EUVM, which peaked around 04:42 UT on 17 December 2014, was classified at Earth from GOES observations as an M8.7 class flare event. Based on SDO/HMI observations, the M8.7class flare erupted from active region (AR) 12242. This active region also produced an M1.6 class flare event (19:33 UT on 14 December 2014) and was likely the source region for a CME eruption that was observed over the solar east limb by SDO/AIA and first entered the LASCO C2 field of view (FOV) at 18:36 UT on 14 December 2014. The source of the most intense fluxes (orange-red, >104 keV/cm2 /s/sr/keV) observed for the 20–70 keV electrons during 18–21 December may largely be due to the 17 December M8.7 class flare. From the perspective at Mars, which was located ∼106◦ in heliolongitude ahead of the Sun-Earth line (as illustrated in Figure 4a), AR 12242 was located just over the solar west limb for a magnetic field line connection to Mars. The bottom five panels in Figure 3 show the solar wind plasma and IMF conditions around the SEP activity period, obtained by SWIA and MAG during the orbital passes into the solar wind. MAVEN observed the IMF in a typical Parker Spiral geometry (ϕIM F ∼120◦ ) from 11 December through 17 December, shown in Figure 3 (fourth panel). At the same time, the solar wind speed, density, dynamic pressure, IMF components and total magnetic field were at the background levels. When the onset of the highest SEP electron fluxes occurred, MAG observed the crossing of the heliospheric current sheet (HCS) at


around 22:40 UT of 17 December, when the IMF changed from an anti-sunward sector (ϕIM F ∼120◦ ; -Bx , +By vector components) to a sunward sector (ϕIM F ∼300◦ ; +Bx , -By vector components). Shortly after the HCS crossing, SWIA observed a small shock, as indicated by a peak in the solar wind density (14.6 cm−3 ) and the corresponding dynamic pressure (2.5 nPa) at around 02:00 UT on 18 December, followed by a modest rise in the solar wind speed (peak of ∼385 km s−1 at around 12:00 UT). Around the same time, MAG observed the rotations of the x- and y-components of the magnetic field and a peak in the IMF magnitude (∼ 9 nT) for about two days, as shown in the bottom two panels of Figure 3. The solar wind plasma and IMF values decreased toward the background levels over the next few days, concurrently with the decrease in the fluxes for the SEP ions and electrons. Around 23 December 2014 a disturbed solar wind structure was observed, based on the measurements of the high and fluctuating solar wind density and total magnetic field values over a five day period. Upon the return of the solar wind density and total magnetic field toward the background values, the solar wind speed increased and peaked at ∼600 km s−1 on 28 December 2014. The SEP activity for the ions were relatively low during this time for the ions with measured energies of >1 MeV (differential fluxes of < 102 , blue) but the differential energy fluxes for the < 100 keV SEP electrons were elevated (> 103 , green) during the passage of the high speed, low density solar wind structure. A summary of the information presented for this event period that is related to the solar flares, CMEs, solar wind, and SEPs are listed in Table 1 (number 1, Dec ’14 event period). To put the MAVEN observations into context, Figure 4a shows a time snapshot of the WSA-Enlil-cone simulation of the heliospheric solar wind densities and cone CME


shock front (labeled ‘CME’) for the event period. The figure shows that the simulated 14 December CME propagated west of the Sun-Mars line and that the eastern flank of the ICME shock front passed Mars at around 18:00 UT of 18 December. At the same time, the simulated ICME merged behind the HCS (solid white line) embedded in the dense (and slow) solar wind stream (green) to produce moderate compression. The simulation of the solar wind and ICME is qualitatively consistent with the MAVEN observations around the 18 December 2014 time frame, specifically the crossing of the HCS followed by the passage of the ICME flank. The extended period of SEP electron activity and the higher fluxes detected in comparison with the SEP ions may be explained. As AR 12242 rotated on the solar disk toward Earth, it continued to produce a number of flares, including an X-class flare at 00:27 UT on 20 December (see http://www.lmsal.com/solarsoft/latest events archive.html), as well as several CMEs. Given its heliolongitude location and based on the WSA-Enlil simulations of the solar wind conditions for this event period, Mars may have been magnetically connected via the Parker spiral to the source region(s) of the solar flaring activity and possibly to the shock fronts of the CMEs as the respective ejecta propagated radially away from the Sun toward Earth. Such a continuous sequence of solar activity and connectivity may have produced the extensive SEP activity, particularly the SEP electrons, observed by MAVEN.

5. Major Periods of Disturbed Space Weather Conditions 5.1. Mid-February of 2015 The most stormy set of space weather conditions observed by MAVEN by the time of writing this study occurred during mid-February through mid-March of 2015. Figure 5 c ⃝2017 American Geophysical Union. All Rights Reserved.

shows a series of M-class flare activity observed by EUVM (top panel), intense fluxes of SEP ions and electrons by the SEP detector, and disturbed upstream solar wind and IMF conditions (bottom five panels) throughout this period. The first set of activity began on 9 February 2015 (number 2, event period Feb ‘15a in Table 1). MAVEN EUVM detected an M2.2 class flare with the intensity peaking around 23:46 UT. The flare erupted from AR 12282, as seen by SDO/AIA, and was also observed by GOES. With Mars at ∼127◦ in heliolongitude ahead of the Sun-Earth line, AR 12282 was estimated to be near the west limb of the solar disk as viewed from Mars. Around the time of the flare activity, a CME erupted near the same active region as seen in the SDO/AIA observations. This CME first entered the LASCO C2 field of view at 23:24 UT over the west solar limb. Given the western source location of this CME, the ejecta did not impact Mars. However, Mars was magnetically connected to the shock front accelerating ahead of the CME during the early phase of the event such that SEPs were detected by MAVEN. The second and third panels of Figure 5 show modest levels of differential energy fluxes (cyan, between 102 to 103 ) detected for the SEP ions with measured energies of ∼100 keV to ∼1 MeV at ∼02:00 UT on 11 February 2015 (after the series of large data gaps in Figure 5, second panel), followed by the arrival of the lower energy ions (measured energies of < 100 keV) between 12 to 17 February 2015. SEP electrons with measured energies of < 100 keV were also detected by MAVEN, but at lower differential energy flux levels (blue, ∼102 ). Over the next several days from 18 to 23 February, brief periods (∼1-2 days) of SEP activity were observed for < 100 keV ions and electrons. Local disturbances in the upstream solar wind plasma and magnetic field conditions, likely due to the passages of solar wind stream structures and crossings of the HCS, were


observed by MAVEN during this time period. The fourth panel in Figure 5 shows that the ϕIM F was fluctuating between a radial (ϕIM F ∼360 or 0◦ ) and Parker spiral (ϕIM F ∼300◦ ) configuration (sector toward the Sun) during 11 to 17 February. Shortly after MAVEN observed the crossing of the HCS on 18 February when ϕIM F switched from ∼300◦ to ∼120◦ (sector away from the Sun). The IMF remained in a Parker spiral configuration until 22 February when the configuration again became more radial (ϕIM F ∼360◦ or 0◦ ). The solar wind speeds (fifth panel in Figure 5) remained low throughout this period (< 360 km s−1 ), while the solar wind density fluctuated, with peak values of ∼18 cm−3 and ∼24 cm−3 occurring around the time of the IMF reconfigurations during 18 and 22 February, respectively. Note that the particle fluxes detected for the SEP ions and electrons (second and third panels) around the same time periods of the peak solar wind densities and IMF reconfigurations. 5.2. Late February through March of 2015 Following this period of relatively moderate activity, a series of solar flare and CME activity occurring at the end of February through early March triggered an extensive period of stormy conditions at Mars, including one of the strongest ICME events observed by MAVEN thus far. The latter have been previously reported by Jakosky et al. [2015b], who discussed the response of the upper and lower Martian atmosphere to the impact of the ICME as observed by MAVEN on 8 March 2015. In addition, Lillis et al. [2016] discussed in detail the variability of the observed SEP fluxes during this event period. Here, we will focus on characterizing in more detail the upstream conditions and providing additional context to the time period leading up to the strong ICME impact described by Jakosky et al. [2015b]. c ⃝2017 American Geophysical Union. All Rights Reserved.

The series of storms began with a CME eruption on 24 February 2015 at 10:09 UT over the south east limb of the Sun as observed by SDO/AIA. Subsequently, a bright CME loop entered the LASCO C2 field of view over the southeast quadrant of the coronagraph image around 10:24 UT. The active region of this CME was beyond the east limb from the perspective at Earth and therefore could not be identified for this event period (number 3, event period Feb ‘15b in Table 1). The sixth and eighth panels of Figure 5 show that MAVEN observed the ICME shock arrival early in 27 February 2015, with the peak solar wind density (∼23 cm−3 ) and dynamic pressure (∼4.5 nPa) as well as the total IMF (∼11 nT) peaking around 02:30 UT. Around the same time, MAG observed a rotation in the xand y-components of the IMF (seventh panel). Only a modest increase in the solar wind speed ( 393 km s−1 ) was observed by MAVEN during that time. Detection of the 1 MeV SEP ions arrived first (08:00 UT on 7 March) followed by the lower energy particles, while the SEP electrons arrived soon after the solar flare and first CME eruption, at around 09:15 UT on 6 March (third panel). The peak fluxes for the SEP ions (>104 keV/cm2 /s/sr/keV) remained constant for over a day and occurred around the time of a shock passage, indicating that the merged CME ejecta headed directly toward Mars for a fairly constant connection to the nose of the shock. MAVEN observed a single peak enhancement at 21:00 UT on 8 March for the solar wind speed (∼815 km s−1 ), density (∼11.4 cm−3 ), dynamic pressure (∼12.5 nPa) and total IMF magnitude (∼11.7 nT). As


the merged ejecta passed over Mars, MAVEN observed a rotation in the in the IMF vector (seventh panel). Note that although the solar source locations for these events were located on the backside of the Sun from the perspective at Earth, the active region may be AR 12297. This active region rotated over the east solar limb as viewed at Earth and produced an M8.9 class flare that was observed by MAVEN EUVM and GOES on 7 March 2015. As this active region rotated toward the direction of Earth on the solar disk, it produced a number of flares and CMEs, including the activity that triggered first super geomagnetic storm of Solar Cycle 24 at Earth (‘St. Patrick’s Day Storm’; Wu et al. [2016]). It is worth mentioning here the M3.0 flare event that was observed by EUVM on 24 March 2015 (number 5, Mar ‘15b event period in Table 1) is of particular interest because the measured irradiance peaked (at around 08:48 UT) while MAVEN was making in situ measurements on the Martian dayside, providing the opportunity to study the ionosphere and thermosphere flare response. For example, Thiemann et al. [2015] showed that this flare caused significant thermospheric heating. 5.3. January 2016 In January 2016, MAVEN observed a period of disturbed upstream conditions that was triggered by a series of solar and heliospheric activity (number 17, Jan ‘15 event period in Table 1). Starting at around 11:27 UT through 14:03 UT on 28 December 2015, SDO/AIA observed a long-duration flare and magnetic loop activity in the southwest quadrant of the solar disk (not shown), around AR 12473. At Mars, EUVM observed a M1.8 class flare with the peak intensity observed at around 13:00 UT (leftmost flare in the top panel of Figure 6). An Earth-directed CME was observed by LASCO, with c ⃝2017 American Geophysical Union. All Rights Reserved.

the bright CME material appearing in its field of view starting at around 12:12 UT. During this event period, Mars was trailing Earth in the orbital plane by ∼77◦ such that the CME propagation direction would be east of the Sun-Mars line. From the WSAEnlil-cone event simulation for this event period, the flank of the ICME shock front was predicted to impact at around 00:00 UT on 2 January 2016. The disturbed upstream conditions observed around this time by MAVEN suggest for such a flank impact. At ∼20:00 UT on 1 January 2016 (second panel), MAVEN detected particle fluxes for the SEP ions. As the solar wind speed (fifth panel) started to increase on 2 January 2016, there were fluctuations in the solar wind density and dynamic pressure (sixth panel), with the peak dynamic pressure of ∼3.4 nPa observed at ∼ 03:50 UT. At the same time, the IMF (bottom panel) increased to ∼12.3 nT in magnitude (bottom panel), with a large -By component (∼ -11.9 nT) that was observed for almost one day. The upstream solar conditions remained disturbed for several days due to an impact of another ICME that arrived on 6 January. SDO/AIA observations showed CME activity around the same active region in the southwest quadrant of the solar disk, with the bright CME material appearing over the west in LASCO C2 field of view starting at around 23:36 UT on 1 January 2016. Following the CME, MAVEN observed an M-class flare at 00:28 UT on 2 January. These solar events triggered the early arrival of low energy (< 100 keV) SEP electrons to Mars, which were initially detected at around 15:30 UT. The < 1 MeV SEP ions were detected several days later with the arrival of the ICME. Although WSA-Enlil-cone simulation predicted a direct impact of the ICME around 4–5 January (Figure 4c), the MAVEN observations show that the ICME shock arrived later, at around 02:40 UT on 6 January when the density and dynamic pressure reach ∼5.5 cm−3 and ∼3 c ⃝2017 American Geophysical Union. All Rights Reserved.

nPa. Shortly after, at around 07:20 UT the Bx and By components of the IMF rotated and the peak IMF was observed to be ∼6.4 nT. While the upstream solar wind returned to more quiescent conditions over the next several days, MAVEN detected the arrival of > 100 keV electrons at 14:50 UT on 6 January followed by the arrival of >1 MeV ions at 02:00 UT on 7 January. The second panel shows that the most energetic SEP ions (>1 MeV) arrived first followed by the lower energy ions. In addition, the flux levels at all measured SEP ion energies remained relatively constant (green, around 103 keV/cm2 /s/sr/keV). The SEPs were likely accelerated by the moving shock source of a CME shortly after it erupted from the Sun. From the perspective at Earth, the source location of the CME eruption was over the solar west limb, such that the event was a backsided one. We note that the activity region of the CME eruption was observed on the solar farside by the EUV instrument on the Solar TErrestrial RElations Observatory (STEREO) [Kaiser , 2005] Ahead (A) spacecraft, which at the time was located at about 167◦ in heliolongitude along the 1-AU orbit ahead of Earth. The slow eruption of the CME began at around 12:35:30 UT near the southeast limb of the solar disk from the STEREO A perspective. Near Earth, the bright CME material first appeared in the LASCO C2 field of view at around 14:24 UT. Although it is unclear where the source of the CME eruption is located from the perspective of Mars, given that there was no detection of an ICME shock by MAVEN during the several days following the CME eruption at the Sun, the source location is inferred to be near the west solar limb based on the MAVEN/SEP and LASCO C2 observations. The WSA-Enlil-cone simulation for this event (not shown) further supports this, as the CME was predicted to propagate west of the Sun-Mars line with no impact of the ICME on Mars.


This space weather activity period concluded with the passage of a stream interaction region preceding a high speed solar wind stream. On 13 January 2016, one of the highest values for the solar wind density and the related dynamic pressure were observed by MAVEN at around 15:20 UT. The sixth panel shows that during this time, the peak density and dynamic pressure values were ∼25 cm−3 and ∼7.4 nPa. Around the same time, the bottom panel shows that the peak IMF magnitude was measured at ∼ 10 nT. The second panel shows the detection of SEP ions at measured energies of ≤ 200 keV.

6. Observations of CIRs As the solar cycle activity continued to ramp down during the tail end of the maximum phase, MAVEN began to observe some recurrent high speed solar streams and the related stream interaction regions. A stream interaction region (SIR) is the compression region that forms due to the high speed solar wind stream running into the slow speed stream preceding it [Pizzo, 1978; Gosling and Pizzo, 1999]. This region is characterized by the high solar wind density and corresponding dynamic pressure as well as high magnetic field strength [Smith and Wolfe, 1976; Mason and Sanderson, 1999]. If the streams recur for more than one solar rotation, they are called corotating interaction regions, or CIRs [Smith and Wolfe, 1976]. Observations have shown that the high speed streams that drives the CIRs typically follows the magnetic sector boundaries [Gosling et al., 1978; Crooker et al., 1999; Lee et al., 2010] and the solar wind rarefaction region forms in the declining speed region of the high speed stream. During May through July 2015, a number of mid-to-low latitude coronal holes persisted for several solar rotations and produced recurrent high speed solar wind streams and the associated CIRs in the heliosphere. Figure 7 shows the composite images of the persistent c ⃝2017 American Geophysical Union. All Rights Reserved.

coronal hole structure, taken on 14 May, 10 June and 6 July 2015 by SDO/AIA. The composite images shown were taken at the 17.1 nm, 19.3 nm, and 21.1 nm wavelength channels. The CIR associated with this coronal hole source of high speed solar wind was strong enough to trigger a G2-class (‘moderate’) geomagnetic storm on 7 June and a G1class (‘minor’) geomagnetic storm on 4 July 2015 when the coronal hole rotated toward Earth during these periods. As the coronal hole source rotated toward Mars in June and July 2015, the high speed wind stream and the related CIR was observed by MAVEN. The fifth and sixth panels of Figure 8 show the arrival of a high speed stream on 22 June 2015 (number 9, Jun ‘15(b) event period in Table 1). During this time, Mars was in solar conjunction with Earth, as shown in Figure 4d. The arrival time of the high speed stream on 22 June is consistent with the estimated arrival based on the solar rotation period for the coronal hole source. Assuming to a first approximation that the rotation period for the coronal hole source is about 27.3 days (a Carrington rotation), with Mars located at 1.56 AU and in solar conjunction with Earth the solar wind stream would arrive ∼15.5 days later (half a Carrington rotation plus another ∼2.5 days if we assume a 400 km s−1 -solar wind to propagate from 1 AU to 1.56 AU) after the observation at Earth on 7 June. SWIA observed the peak solar wind density and dynamic pressure values to be ∼38 cm−3 and ∼14 nPa at around 16:45 UT on 22 June. At the same time, MAG measured the peak IMF to be ∼8 nT (bottom panel) and observed the switching of the magnetic sector from positive (-Bx , +By ) to negative (+Bx , -By ) (panel seven). This is illustrated in Figure 4d, which shows the HCS (white solid line, labeled ‘HCS’) separating the positive IMF polarity sector (red outline of the circular panel) from the negative polarity sector


(blue outline) that follows. The fourth panel of Figure 8 shows that the IMF configuration was predominantly a Parker spiral configuration (ϕ ∼120◦ , away sector) before crossing the HCS. Upon this crossing the IMF configuration fluctuated between the Parker spiral (ϕ ∼300◦ , toward sector) and radial configuration (ϕ ∼360◦ or 0◦ ). The solar wind speed reached ∼750 km s−1 at around 09:00 UT on 23 June 2015, as the densities returned to the ambient values. This was the second highest solar wind speed value recorded by MAVEN to date, and the peak dynamic pressure is comparable to the value observed for the 8 March ICME event (number 4, Mar ’15(a) event period). The coronal hole shown in Figure 7 continued to produce a high speed solar wind stream that triggered the geomagnetic activity observed at Earth on 4 July. Given that Mars was trailing Earth in heliolongitude by ∼ -164◦ , the estimated arrival for the high speed stream associated with this coronal hole would be about 15 days later, around 19 July (number 10, Jul ‘15(b) event period in Table 1). The fifth panel in Figure 9 shows the arrival of this high speed stream starting at around 12:00 UT on July 17 and reaching a peak value of ∼ 522 km s−1 at around 19:00 UT on 19 July. The observed peak density, dynamic pressure, and total IMF during this event period were 5.7 cm−3 , 1 nPa, and 9.2 nT. As with the 22 June event period, the magnetic sector was observed to switch from positive, away from the Sun (-Bx , +By ; ϕ ∼120◦ ) to negative, toward the Sun (+Bx , -By ; ϕ ∼300◦ ). We note there was another coronal hole source of high speed solar wind stream that also persisted for several solar rotations (not shown). This source produced the high speed solar wind streams observed by MAVEN on 28 June (fifth panel in Figure 8) and 27 July (fifth panel in Figure 8).


6.1. CIR-accelerated energetic particles The shocks associated with CIRs can accelerate solar wind particles and produce energetic particles. Typically, these shocks form beyond 1 AU and can accelerate energetic particles that stream into the inner heliosphere [Barnes and Simpson, 1976; van Hollebeke et al., 1978]. However, CIR shocks can also form at and within 1 AU [Gosling and Pizzo, 1999; Forsyth and Marsch, 1999; Jian et al., 2006]. The CIR-related energetic ions are found in the high-speed portion of the solar wind stream (see Figure 2 in Mason and Sanderson [1999] or Figure 1 in Lee et al. [2010]), consistent with the particles being accelerated at the reverse shock and streaming into the inner heliosphere inside the high speed stream. The second and third panels of Figure 8 show the energetic ion and electron particles accelerated by the CIR observed on 22 June 2015. The energetic electrons arrived at around 14:00 UT on 21 June followed by the arrival of the energetic ions at 18:00 UT on 22 June. The arrival of the energetic ions occurred after passage of the compression region (peak density, dynamic pressure and magnetic field) and during the arrival of the high speed stream. The SEP detector measured energies up to ∼ 3 MeV for the ions at moderate flux levels (green, ∼103 keV/cm2 /s/sr/keV) with the highest fluxes (red) measured at for the < 100 keV ions, the latter which likely have some flux contribution by PUIs (see Section 3). The energetic particle activity observed by the SEP detector for the July 17 and 27 CIR event periods (Figure 9) were more modest in comparison to the June 22 event period. MAVEN/SEP detected fluxes for the energetic ions at measured at energies of ≤ 200 keV, while no significant levels of energetic electron fluxes were detected. In both cases, the


energetic ions occurred in the high speed portion of the solar wind stream that preceded the compressed interaction region. The observations by MAVEN of the overall weaker space weather conditions observed around 17 July compared to 22 June is consistent with the weaker geomagnetic storm activity observed at Earth on 4 July. Note that Figure 8 shows that MAVEN/SEP detected moderate levels of SEP ion and electrons fluxes starting at 15:00 UT on 19 June and 19:00 UT on 18 June respectively (number 9, Jun ‘15b event period in Table 1). The source of these SEPs is the CME that erupted over the west solar limb from the perspective at Mars. The CME activity were first seen by SDO/AIA near the east limb at around 17:10 UT on 18 June 2015, followed by the appearance of the bright CME loop at 17:24 UT in the LASCO C2 field of view. During the early phase of the CME event, Mars was magnetically connected to the moving shock front of the CME. Such a connection would allow SEPs accelerated by the CME shock front near the Sun to stream along the field line toward Mars. The WSA-Enlil-cone event simulation illustrates this remote connection scenario (Figure 4d).

7. Periods of SEP Activity Without Upstream Solar Wind Measurements The bottom four panels in Figure 2 show a number of large (> 1 month) data gaps in the upstream solar wind plasma and magnetic field observations. This is due to the MAVEN orbit not extending beyond the bow shock because apoapsis is near the solar terminator or on the Martian night side. Thus for periods when SEP activity was detected by MAVEN, there were no upstream observations to associated with the observed SEP events. Table 1 lists three time periods during which SEP ions and/or electrons were observed but no upstream (NU) observations were available to characterize the SEP event periods, such as the identification of the shock source (ICME, CIR), shock arrival time and strength. c ⃝2017 American Geophysical Union. All Rights Reserved.

These time periods are March 2015 through May 2015 (numbers 5 to 7 in Table 1), October through November 2015 (numbers 14 to 16), and April through May 2016 (numbers 20 to 21). Observations of the flare event details by EUVM are provided (if available) along with the LASCO C2 observations of the CMEs. To fill in these data gaps, future studies that examine the SEP event periods and their impacts (of any) on the Martian system may utilize penetrating proton data from SWIA to obtain estimates for the solar wind velocity (see [Halekas et al., 2016]), and/or use model data from WSA-Enlil-cone for estimates of the overall solar wind conditions. For the latter, there is ongoing research activity to improve the modeling accuracy of WSA-Enlil-cone for upstream conditions at Mars and validate the results with existing upstream solar wind observations (e.g., Falkenberg et al. [2011]; Dewey et al. [2016]). In the meantime, to characterize the heliospheric conditions for these event periods, we use the WSA-Enlil-cone simulations that are routinely available at the CCMC iSWA site together with SDO AIA and/or SOHO LASCO observations to determine whether the SEP activity observed at Mars are due to ICME shock sources and to what extent the ICME may impact Mars. One such example event period is when MAVEN observed the arrival of SEPs May 2016 (Figure 10). The bottom two panels show that the SEP electrons arrived first, at ∼22:00 UT, before the arrival of the SEP ions almost half a day later at ∼14:00 UT. The flux levels for the SEP ions and electrons at all measured energies remained fairly steady (green, around 103 keV/cm2 /s/sr/keV) throughout the event period. The sources of the SEPs are due to the CME and/or flare activity that occurred around AR 12542 as seen in the SDO AIA observations. The top panel shows that MAVEN


EUVM detected a C3.2 class flare with the peak intensity occurring around 16:03 UT on 15 May. Meanwhile, the CME was seen in the LASCO C2 field of view starting at 15:36 UT. At the time, Mars was trailing behind Earth by only 3.5◦ in heliolongitude and therefore was nearly radially aligned along the Sun-Earth line (see panel e of Figure 4). From the Mars and Earth vantage points the solar activity occurred near the west solar limb. Not surprisingly, the flare and CME events also triggered SEP activity near Earth. The ACE Real Time Solar Wind (RTSW) observations (not shown) from http://www.swpc.noaa.gov/products/ace-real-time-solar-wind showed that the Electron Proton Alpha Monitor (EPAM) [Gold et al., 1998] measured fluxes of SEP electrons and protons for the same time period as the MAVEN observations. Based on the WSA-Enlil-cone simulation for this event period, the ICME propagated westward of Sun-Mars (and Sun-Earth) line, as shown in panel e of Figure 4. Although the ICME did not impact Mars (or Earth), the SEPs were detected because of the connection along the Parker spiral field line to the ‘nose’ of the accelerating shock front of the ejecta (gray portion of the outlined CME contour) during the early stage of the ICME event, as shown in the snapshot of the WSA-Enlil cone simulation. This event period, along with the SEP events observed on 18-19 June 2015( event number 9; Section 6.1) and 6-7 January 2016 (event number 17; Section 5.3) may make good case studies for examining the impact of SEPs at Mars without the added complexities of an ICME ejecta disturbing the Martian system. In all three event periods, Mars was magnetically connected to the moving shock front during the early phase of the CME event such that the highest energy SEP ions arrived first followed by arrival of the lower


energy ones. Moreover, the lighter SEP electrons began to arrive soon after the solar eruption activity.

8. Discussion and Conclusion Since its arrival to Mars, MAVEN EUVM, SEP, SWIA and MAG instruments have been continuously observing the variability of solar soft x-rays and EUV irradiance, measuring the fluxes of solar energetic ions and electrons, and monitoring the upstream solar wind and interplanetary magnetic field conditions. In this paper, we provided a comprehensive overview of the space weather conditions observed by MAVEN during the first ∼1.9 years of its science mission. This period of observations overlapped with other orbiter missions at Mars, such as MEX and Mars Odyssey, which do not have onboard instruments to directly measure EUV, SEP, or the IMF. Thus for the first time at Mars, observations from the upstream monitoring of the solar EUV, SEPs, and solar wind plasma and IMF are available from MAVEN to provide additional contextual information of the near-Mars space weather disturbances, including their solar and heliospheric sources, for analyzing the in situ observations made in the Martian ionosphere, atmosphere or at the surface by these missions. For example, the list of SEP events provided in this study will be useful for examining periods of increased background count rates detected by imagers and other instruments onboard the Mars orbiters. To investigate the extent by which the upstream space weather activity impacted the Martian ionosphere down to the surface, observations from MAVEN, MEX, Mars Odyssey, and/or MSL can be used together. For example, MAVEN observations for event periods in which SEPs and/or CMEs impacted Mars can be compared with the surface measurements of the radiation dose rates by the MSL Radiation Assessment Detector (RAD; Hassler et al. [2012]) to examine and c ⃝2017 American Geophysical Union. All Rights Reserved.

characterize the observations for Forbush decreases and dose rate enhancements [Hassler et al., 2014] [Lee et al., manuscript in preparation]. The strongest space weather events observed by MAVEN, as reported in this paper, occurred during the maximum phase of Solar Cycle 24. In terms of the solar wind speed, density, dynamic pressure, and total IMF, the highest peak values (based on the orbitaveraged upstream observations) were observed in March 2015 when a succession of ICMEs impacted Mars (815 km s−1 , 11.4 cm−3 , 12.5 nPa and 11.7 nT) and in June 2015 during the passage of a CIR and corresponding high speed solar wind stream (750 km s−1 , 38 cm−3 , 14 nPa, and 8 nT). Moreover, the event periods in which MAVEN observed the highest differential energy fluxes of SEPs occurred in December 2014 for the 20–70 keV electrons (> 104 keV/cm2 /s/sr/keV) and in March 2015 for the > 1 MeV ions (> 103 keV/cm2 /s/sr/keV). It remains to be seen whether MAVEN will observe upstream disturbances related to space weather events that are stronger (i.e. higher peak values) than those reported in this study. As the CME rate declines with the solar activity level, we expect to observe upstream disturbances associated with CIRs together with the recurrent fast solar wind streams that drive them as well as energetic particles accelerated by the CIR shocks. In the context of Solar Cycle 24, it is important to discuss here that the upstream disturbances triggered by solar storms have been moderate in comparison to the stronger storms observed previously at Mars. For example, the peak dynamic pressure derived by proxy using magnetic field measurements from Mars Global Surveyor (MGS) was ∼33.4 nPa during the 2003 Halloween super storm [Crider et al., 2005], when an ICME with an average speed of 1340 km s−1 impacted Mars. The heliospheric conditions during


Solar Cycle 24 have been weaker overall compared to Solar Cycle 23, including the solar wind speed, density, dynamic pressure and total IMF strength. In particular, the solar wind density and dynamic pressure remained very low through the Cycle 24 maximum [McComas et al., 2013] since the initial values were reported for the extended Cycle 23 minimum period [McComas et al., 2008; Smith and Balogh, 2009; Lee et al., 2009], while the total IMF values observed in Cycle 24 have only risen to the levels observed during the Cycle 23 declining phase [McComas et al., 2013]. The overall heliospheric total pressure (magnetic+plasma) have therefore been significantly reduced, by ∼40% as reported by Gopalswamy et al. [2014], between Cycles 23 and 24. Some implications of the weaker heliospheric conditions for space weather are the diminished strength, or effectiveness, of the Cycle 24 CMEs to produce strong magnetic storms and the efficiency of the CME shocks to accelerate SEPs to very high energies. At Mars, this will influence the strength of the magnetic field draping around the Martian dayside, compression of the ionosphere, ionization of the atmosphere, rates of ion escape, and radiation enhancements by SEPs at the surface, to name several examples. Generally speaking, the lower total heliospheric pressure allowed the Cycle 24 CMEs to expand more rapidly earlier in the event phase, resulting in larger CME widths for a given CME speed [Gopalswamy et al., 2014]. As such, the effectiveness of a CME to produce a strong magnetic storm is reduced in part because of the diluted magnetic energy content attributed to the greater expansion but also because the lower IMF resulted in weaker compressed CME sheath fields [Gopalswamy et al., 2014, 2015b]. The weaker heliospheric conditions also affected the speeds of the CMEs. In a statistical study of 1-AU observations of magnetic clouds (MCs) during the rising and maximum phases of Cycles 23 and


24, Gopalswamy et al. [2015b] reported that the average MC and ICME shock speeds in Cycle 24 were both reduced (by ∼15% and ∼17%) due to the wider CMEs propagating into the slower ambient solar wind and therefore were subjected to a larger drag force. The weaker ambient fields and the slower shock speeds also affected the efficiency of the CME shocks to accelerate SEPs to very high energies (>500 MeV protons) [Gopalswamy et al., 2014] (and references therein). Thus far, the MAVEN observations of the space weather impacts and effects on Mars have been reported for a few event periods (e.g., Jakosky et al. [2015b]; Thiemann et al. [2015]; Schneider et al. [2015]; Lillis et al. [2016]), adding to the existing literature regarding how the Martian plasma environment responded to the impacts of solar flares (e.g., Fallows et al. [2015]), strong ICMEs and the associated SEPs (e.g., Crider et al. [2005]; Espley et al. [2005]; Morgan et al. [2014]; Futaana et al. [2008]; Ulusen et al. [2012]; Nemec et al. [2013]; Lillis et al. [2012]), and passages of CIRs (e.g., Dubinin et al. [2009]; Edberg et al. [2010]), as well as how the radiation environment at the Martian surface is influenced by the SEP and CME events (e.g., Hassler et al. [2014]; Guo et al. [2015]). Detailed analysis regarding the response of Mars to additional event periods, in terms of the atmospheric escape rates, variability and heating of the Martian atmosphere, solar wind-magnetospheric dynamics, etc., are beyond the scope of this study and will be presented in separate studies. Given the more moderate space weather events observed by MAVEN in light of the weaker heliospheric conditions, future studies may include the comparison of the Mars response to the different space weather events (ICMEs, SEPs, CIRs, flares) observed throughout the MAVEN mission period versus the events observed prior to the MAVEN mission.


The MAVEN observations also provide a unique and comprehensive data set that may be used to study the heliospheric conditions beyond the 1-AU orbit of Earth and STEREO. Such studies may include understanding the dynamics and evolution of CMEs and CIRs from the Sun out to Mars or comparing the space weather effects observed at 1 AU and 1.5 AU for a given solar-heliospheric event period and radial alignment or Parker spiral geometry of the Mars and 1-AU observer. Comparative conditions at Earth and Mars are of special interest to those who are planning crewed missions to Mars since the two orbital locations are separated by the interplanetary region where most solar wind stream interaction regions develop [van Hollebeke et al., 1978]. These regions alter the propagation of solar-heliospheric disturbances, including the interplanetary CME-driven shocks that create the space radiation (via SEPs) that are hazardous to humans. Acknowledgments. This research has been supported by NASA through MAVEN Project subcontracts to the authors, managed by LASP, University of Colorado under the direction of the MAVEN Principal Investigator, B.M. Jakosky. The MAVEN mission has been made possible through NASA sponsorship and the dedicated efforts of NASA Goddard Space Flight Center, LASP, Lockheed project management, and the MAVEN Technical and Science Teams. The MAVEN data shown are publicly available at the NASA Planetary Data System (PDS) website (http://ppi.pds.nasa.gov). This research also makes use of the WangSheeley-Arge (WSA)-Enlil low resolution solar wind simulations that are routinely generated and archived by the NASA Space Weather Research Center (SWRC) and archived at the integrated Space Weather Analysis (iSWA) website. In addition, this research uses observations from the SOlar and Heliospheric Observatory (SOHO) Large Angle and c ⃝2017 American Geophysical Union. All Rights Reserved.

Spectrometric COronagraph (LASCO) C2 and C3 coronagraph images, Solar Dynamic Observatory Atmospheric Imaging Assembly (SDO/AIA), and Geostationary Operational Environmental Satellites (GOES) x-ray sensor (XRS). We thank the two reviewers for their careful reading of this manuscript and for providing constructive feedback to improve its content. C. Lee thanks T. McEnulty, R.A. Hock-Mysliwiec J. van Tilborg, S. Xu, and A. Rahmati for their insights and helpful discussions.

References Arge, C.N., Luhmann, J.G., Odstrcil, D., Schrijver, C.J., Li, Y.: 2004, Stream structure and coronal sources of the solar wind during the May 12th, 1997 CME, J. Atm Solar Terr. Phys., 66, 1295–1309. Aschwanden, M.J.: 1994, Irradiance observations of the 1–8 A solar soft X–ray flux from GOES, Solar Phys. 152, 53–59. Barnes, C.W., Simpson, J.A.: 1976, Evidence for interplanetary acceleration of nucleons in corotating interaction regions, Astrophys. J., 210, L91–L96. Bornmann, P. L., Speich, D., Hirman, J., Matheson, L., Grubb, R., Garcia, H. A., Viereck, R.: 1996, GOES X-ray sensor and its use in predicting solar-terrestrial disturbances, In: SPIE 1996 International Symposium on Optical Science, Engineering, and Instrumentation, International Society for Optics and Photonics, 291-298. Brueckner, G.E., Howard, R.A., Koomen, M.J., Korendyke, C.M., Michels, D.J., Moses, J.D., Socker, D.G., Dere, K.P., Lamy, P.L., Llebaria, A., Bout, M.V., Schwenn, R., Simnett, G.M., Bedford, D.K., Eyles, C.J.: 1995, The Large Angle Spectroscopic Coroc ⃝2017 American Geophysical Union. All Rights Reserved.

nagraph (LASCO), Solar Phys. 162, 357–402. Cane, H.V.: 2000, Coronal mass ejections and Forbush decreases, Space Sci. Rev. 93, 55–77. Cane, H.V., Reames, D.V., von Rosenvinge, T.T.: 1988, The role of interplanetary shocks in the longitude distribution of solar energetic particles, J. Geophys. Res. 93, 9555–9567. Connerney, J. E. P., J. Espley, P. Lawton, S. Murphy, J. Odom, R. Oliversen, D. Sheppard.: 2015a, The MAVEN magnetic field investigation, Space Sci. Rev., 1-35, doi: 10.1007/s11214-015-0169-4. Connerney, J. E. P., J. R. Espley, G. A. DiBraccio, J. R. Gruesbeck, R. J. Oliversen, D. L. Mitchell, J. Halekas, C. Mazelle, D. Brain, and B. M. Jakosky: 2015b, First results of the MAVEN magnetic field investigation, Geophys. Res. Lett., 42, doi: 10.1002/2015GL065366. Crider, D.H., Espley, J., Brain, D.A., Mitchell, D.L., Connerney, J.E.P., Acuna, M.: 2005, Mars Global Surveyor observations of the Halloween 2003 solar superstorm’s encounter with Mars, J. Geophys. Res. 110, A09S21, doi:10.1029/2001JA010881. Crooker, N.U., Gosling, J.T., Bothmer, V., Forsyth, R.J., Gazis, P.R., Hewish, A., Horbury, T.S., Intriligator, D.S., Jokipii, J.R., Kota, J., et al.: 1999, CIR morphology, turbulence, discontinuities, and energetic particles, Space Sci. Rev., 89, 179 ? 220. Dewey, R.M., Baker, D.N., Mays, M.L., Brain, D.A., Jakosky, B.M., Halekas, J.S., Connerney, J.E.P., Odstrcil, D., Luhmann, J.G., Lee, C.O.: 2016, Continuous Solar Wind Forcing Knowledge: Providing Continuous Conditions at Mars with the WSAENLIL+Cone Model, J. Geophys. Res. 121, 6207–6222, doi:10.1001/2015JA021941.


Dubinin, E., Fraenz, M., Woch, J., Duru, F., Gurnett, D., Modolo, R., Barabash, S, Lundin, R.: 2009, Ionospheric storms on Mars: Impact of the corotating interaction region, Geophys. Res. Lett, 36, doi:10.1029/2008GL036559. Edberg, N. J. T., Nilsson H., Williams, A. O. , Lester, M., Milan, S. E., Cowley, S. W. H., Franz, M. , Barabash, S. Futaana, Y.: 2010, Pumping out the atmosphere of Mars through solar wind pressure pulses, Geophys. Res. Lett., 370, L03107, doi: 10.1029/2009GL041814. Eparvier, F.G., Chamberlin, P.C., T.N. Woods, Thiemann, E.M.B.: 2015, The Solar Extreme Ultraviolet 308 Monitor for MAVEN, Space Science Reviews, 195, 293–301. Espley, J., Cloutier, P.A., Crider, D.H., Brain, Acuna, M.: 2005, Low-frequency plasma oscillations at Mars during the October 2003 solar storm, J. Geophys. Res. 110, A09S33. Falkenberg, T. V., A. Taktakishvili, A. Pulkkinen, S. Vennerstrom, D. Odstrcil, D. Brain, G. Delory, and D. Mitchell: 2011, Evaluating predictions of ICME arrival at Earth and Mars, Space Weather, 9, S00E12, doi:10.1029/2011SW000682. Fallows, K., Withers, P., Gonzalez, G.: 2015, Response of the Mars ionosphere to solar flares: Analysis of MGS radio occultation data, J. Geophys. Res. 120, 9805–9825. Forsyth, R.J.,Marsch, E.: 1999, Solar origin and interplanetary evolution of stream interfaces, Space Sci. Rev., 89, 7–20. Futaana, Y., Barabash, S., Yamauchi, M., McKenna-Lawlor, S., Lundin, R., Luhmann, J.G., Brain, D., Carlsson, E., et al.: 2008: Mars Express and Venus Express multi-point observations of geoeffective solar flare events in December 2006, Planetary and Space Science, 56, 873.


Gold, R.E., Krimigis, S.M., Hawkins, S.E., III, Haggerty, D.K., Lohr, D.A., Fiore, E., Armstrong, T.P., Holland, G., Lanzerotti, L. J.: 1998, Electron, Proton, and Alpha Monitor on the Advanced Composition Explorer spacecraft, Space Sci. Rev. 86, 541– 562. Gopalswamy, Yashiro, S., Liu, Y., Michalek, G., Vourlidas, A., Kaiser, M.L., Howard, R.A.: 2005, Coronal mass ejections and other extreme characteristics of the 2003 October-November solar eruptions, J. Geophys. Res., 110, A09S15, doi: 10.1029/2004JA010958. Gopalswamy, N., Akiyama, S., Yashiro, S., Xie, H., Makela, P, Michalek, G.: 2014, Anomalous expansion of coronal mass ejections during solar cycle 24 and its space weather implications, Geophys. Res. Lett., 41, 2673–2680. Gopalswamy, N., Xie, H., Akiyama, S., Makela, P, Yashiro, S., Michalek, G.: 2015a, The Peculiar Behavior of Halo Coronal Mass Ejections in Solar Cycle 24, ApJ. Lett., 804, L23(1–6). Gopalswamy, Yashiro, S., Xie, H., Akiyama, S., Makela, P.: 2015b, Properties and geoeffectiveness of magnetic clouds during solar cycle 23 and 24, J. Geophys. Res., 120, 9221–9245. Gosling, J.T., Pizzo, V.J.: 1999, Formation and Evolution of Corotating Interaction Regions and Their Three Dimensional Structure, Space Sci. Rev., 89, 21–52. Gosling, J.T., Asbridge, J.R., Bame, S.J., Feldman, W.C.: 1978, Solar wind stream interfaces, J. Geophys. Res., 83, 1401–1412. Guo, J., Zeitlin, C., Wimmer-Schweingruber, R.F., Rafkin, S., Hasller, D.M., Posner, A., Heber, B., Kohler, J., Ehresmann, B., Appel, J.K., Bohm, E., Bottcher, S., Burmeister,


S., Brinza, D.E., Lohf, H., Martin, C., Kahanpaa, H., Reitz, G. : 2015, Modeling the variations of dose rates measured by RAD during the first MSL Martian Year: 2012– 2014, ApJ, 810, 24, 10pp, doi:10.1088/0004-637X/810/1/24 . Halekas, J. S., E. R. Taylor, G. Dalton, G. Johnson, D. W. Curtis, J. P. McFadden, D. L. Mitchell, R. P. Lin, B. M. Jakosky: 2015, The Solar Wind Ion Analyzer for MAVEN, Space Sci. Rev., 195, 125–151. Halekas, J. S., S. Ruhunusiri, Y. Harada, G. Collinson, , D. L. Mitchell, C. Mazelle, J. P. McFadden, J.E.P. Connerney, J.R. Espley, F. Eparvier, J.G. Luhmann, B. M. Jakosky: 2016, Structure, Dynamics, and Seasonal Variability of the Mars-Solar Wind Interaction: MAVEN Solar Wind Ion Analyzer Inflight Performances and Science Results, J. Geophys. Res., accepted. Hassler, D.M., et al.: 2012, The Radiation Assessment Detector (RAD) Investigation, Space Sci. Rev., 170, 503-558. Hassler, D.M., et al.: 2014: Mars’ surface radiation environment measured with the Mars Science Laboratory’s Curiosity Rover, Science, 343. Jakosky, B.M., et al.: 2015a, The Mars Atmosphere and Volatile Evolution (MAVEN) Mission, Space Sci. Rev., doi:10.1007/s11214-015-0139-x. Jakosky, B.M., et al.: 2015b, MAVEN observations of the response of Mars to an interplanetary coronal mass ejection from the Sun, Science, 350, doi:10.1126/science.aad0210. Jian, L., Russell, C.T., Luhmann, J.G., Skoug, R.M.: 2006, Properties of stream interactions at one AU during 1995–2004, Solar Phys. 239, 337–392. Kaiser, M.: 2005, The STEREO mission: an overview, Adv. Space Res., 36, 1483–1488.


Larson, D.E. R.J. Lillis, Lee, C.O., K. Hatch, M. Robinson, D. Glaser, J. Chen, D.W. Curtis, C. Tiu, R.P. Lin, J.G. Luhmann, B.M. Jakosky: 2015: The MAVEN Solar Energetic Particle Investigation, Space Sci. Rev., 195, 153–172. Lee, C.O., Luhmann, J.G., Zhao, X.P. Liu, Y., Riley, P., Arge, C.N., Russell, C.T., de Pater, I.: 2009, Effects of the weak polar fields of Solar Cycle 23: Investigation using OMNI for the STEREO Mission Period, Solar Phys., 256, 345–363. Lee, C.O., Luhmann, J.G., de Pater, I., Mason, G.M., Haggerty, D., Richardson, I.G., Cane, H.V., Jian, L.K., Russell, C.T., Desai, M.I.: 2010, Organization of Energetic Particles by the Solar Wind Structure During the Declining to Minimum Phase of Solar Cycle 23, Solar Phys., 263, 239–261. Lemen, J.R., et al.: 2012, The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), Solar Phys., doi:10.1007/s11207-011-9776-8. Lillis, R. J., C. O. Lee, D. E. Larson, J. G. Luhmann, J. S. Halekas, J. E. P. Connerney, B. M. Jakosky: 2016, Shadowing and Anisotropy of Solar Energetic Ions at Mars measured by MAVEN during the March 2015 solar storm, J. Geophys. Res., 121(4), 2818-2829. Lillis, R. J.,Brain, D.A., Delory, G.T., Mitchell, D.L., Luhmann, J.G., Lin, R.P.: 2012, Evidence for superthermal secondary electrons produced by SEP ionization in the Martian atmosphere, J. Geophys. Res., 117, E03004, doi:10.1029/2011JE003932. Mason, G.M., Sanderson, T.R.: 1999, CIR associated energetic particles in the inner and middle heliosphere, Space Sci. Rev. 89, 77–90. McComas, D.J., Ebert, R.W., Elliott, H.A., Goldstein, B.E., Gosling, J.T., Schwadron, N.A., Skoug, R.M.: 2008, Weaker solar wind from the polar coronal holes and the whole Sun, Geophys. Res. Lett., 35, doi:10.1029/2008GL034896.


McComas, D.J., Angold, N., Elliott, H.A., Livadiotis, G., Schwadron, N.A., Skoug, R.M., Smith, C.W.: 2013, Weakest solar wind of the space age and the current Mini solar maximum, ApJ, 770, 2–11. Mewaldt, R.A., Looper, M.D., Cohen, C.M.S., Haggerty, D.K., Labrador, A.W., Leske, R.A., Mason, G.M., Mazur, J.E., von Rosenvinge, T.T.: 2012, Energy Spectra, Composition, and Other Properties of Ground-Level Events During Solar Cycle 23, Space Sci. Rev., 171, 97-120. Morgan, D.D., Dieval, C., Gurnett, D.A, Duru, F., Dubinin, E.M., Franz, M., Andrews, D.J., Opgenoorth, H.J., Ulusen, D., Mitrofanov, I., Plaut, J.J.: 2014, Effects of a strong ICME on the MARtian ionosphere as detected by Mars Express and Mars Odyssey, J. Geophys. Res., 119, 5891–5908, doi:10.1002/2013JA019522. Nemec, F., Morgan, D.D., Dieval, C., Gurnett, D.A., Futaana, Y.: 2013, Enhanced ionization of the Martian nightside ionosphere during solar energetic particle events, Geophys. Res. Lett, 41, 793–798. Odstrcil, D.: 2003, Modeling 3D solar wind structure, Adv. Space Res., 32, 497–506. Pesnell, W. D., B. J. Thompson, and P. C. Chamberlin: 2012, The Solar Dynamics Observatory (SDO), Solar Phys., doi:10.1007/s11207-011-9841-3. Pizzo, V.: 1978, A three-dimensional model of corotating streams in the solar wind: 1. Theoretical foundations, J. Geophys. Res. 83, 5563–5572. Pizzo, V. J.: 1991, The evolution of corotating stream fronts near the ecliptic plane in the inner solar system: 2. Three-dimensional tilted dipole fronts, J. Geophys. Res., 96, 5405–5420, doi:10.1029/91JA00155.


Rahmati, A., Larson, D.E., Cravens, T.E., Lillis, R.J., Dunn, P.A., Halekas, J.S., Connerney, J.E., Eparvier, F.G., Thiemann, E.M.B., Jakosky, B.M.: 2015: MAVEN insights into oxygen pickup ions at Mars, Geophys. Res. Lett., 42, doi:10.1002/2015GL065262. Richardson, I.G.: 2004, Energetic particles and corotating interaction regions in the solar wind, Space Sci. Rev., 111, 267–376. Scherrer, P., Schou, J., Bush, R.I., Kosovichev, A.G., Bogart, R.S., Hoeksema, J.T., Liu, Y., Duvall Jr., T.L., Zhao, J., Title, A.M., Schrijver, C.J., Tarbell, T.D., Tomczyk, S.: 2012, The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO), Solar Phys., 275, 207–227, doi:10.1007/s11207-011-9834-2. Schneider, N., Deighan, J.I., Jain, S.K., Stiepen, A., Evans, J.S., Stewart, A.I.F., Larson, D., Mitchell, D.L., Lee, C.O., Lillis, R., Brain, D., Stevens, M.H., et al.: 2015, The discovery of diffuse aurora on Mars, Science, 350, doi:10.1126/science.aad0313. Smith, E.J. and Balogh, A.: 2008, Decrease in heliospheric magnetic flux in this solar minimum: recent Ulysses magnetic field observations, Geophys. Res. Lett., 35, Cite ID L22103, doi:10.1029/2008GL035345. Smith, E. J., and Wolfe, J.H.: 1976, Observations of Interaction Regions and Corotating Shocks, Geophys. Res. Lett., 3, 137–140. Thiemann, E. M. B., Eparvier, F. G., Andersson, L. A., Fowler, C. M., Peterson, W. K., Mahaffy, P. R., Deighan, J. I.: ( 2015, Neutral density response to solar flares at Mars, Geophys. Res. Lett., 42(21), 8986–8992. Ulusen, D., Brain, D.A., Luhmann, J.G., Mitchell, D.L.: 2012, Investigation of Mars’ ionospheric response to solar energetic particle events, J. Geophys. Res., 117, A12306, doi:10.1029/2012JA017671.


van Hollebeke, M.A.I., McDonald, F.B., Trainor, J.H., von Rosenvinge, T.T.: 1978, The radial variation of corotating energetic particle streams in the inner and outer solar system, J. Geophys. Res., 83, 4723–4731. Wu, C.C., Liou, K., Lepping, R.P., Hutting, L., Plunkett, S., Howard, R.A., Socker, D.: 2016: The first super geomagnetic storm of solar cycle 24: ‘The St. Patrick’s day event (17 March 2015)’, Earth, Planets, and Space, 68, doi:10.1186/s40623-016-0525-y.



Dec ’14

1

Mar (a)

Mar ’15 (b) Apr ’15

May ’15

5

7

6

’15

’15

4

3

Feb (a) Feb (b)

2

’15

Event Period

#

12242

12242

M1.1

M8.7

backside

backside backside

12297

X1.2

—

M2.6

M1.5

M8.9

backside backside

—

—

backside

backside

—

M1.0

backside

—

backside

backside

M6.2

M3.0

backside

M2.6

12282 over south east limb backside

—

M2.2

12241

backside

M1.8

M6.9

12242

NOAA AR

M1.6

GOESClass

Flare

Solar Locationb

—

—

—

04/29/15 — 00:40

—

—

—

03/24/15 — 08:48 — —

03/07/15 S17W69 22:32

03/06/15 — 05:50 03/06/15 — 08:23

03/01/15 — 12:44 — —

02/28/15 — 04:57 02/28/15 — 21:29

02/09/15 N12W66 23:46 — —

12/17/14 over 04:42 west limb 12/18/14 S09W90 21:58

12/17/14 S09W72 01:50

12/14/14 S17W60 19:33 12/16/14 — 00:12

Peak Time

160

155

153

153

153

144

137

137

137

135

135

134

134

133

127

107

106

106

105

104

EarthSunMars ϕ (deg)

04/30/15 02:24

03/29/15 18:36 04/14/15 02:48 04/14/15 11:48 04/14/15 15:36 04/19/15 12:48

03/07/15 22:24

03/06/15 04:49 03/06/15 07:12

03/01/15 12:48 03/03/15 15:48

02/28/15 05:24 02/28/15 21:48

02/09/15 23:24 02/24/15 10:24

—

—

—

LASCO C2 Detection 12/14/14 18:36 —

CME

NU

NU

NU

NU

NU

NU

03/04/15 04:40 merged with previous? 03/07/15 04:00 merged with previous? 03/08/15 21:00 merged with previous no impact

02/27/15 02:30

no impact

—

—

—

12/18/14 02:00 —

Shock Arrivalc

NU

NU

NU

NU

NU

NU

—

—

12.5

—

4.5

—

6.5

4.5

—

—

—

—

—

Peak Pdyn c (nPa) 1.6

—

—

—

—

—

NU

—

—

—

—

—

—

—

—

—

—

—

—

—

—

SIR Arrivalc

Solar Wind

—

—

—

—

—

NU

—

—

—

—

—

—

—

—

—

—

—

—

—

Peak Pdyn c (nPa) —

Table 1: Solar Wind Transient and Energetic Particle Event Periods Observed by MAVEN, Dec 2014–May 2016 a Ar-

03/03/15 11:30 continued from previous 03/07/15 08:00 continued from previous continued from previous 03/28/15 09:00 04/16/15 21:00 04/23/15 07:00 04/24/15 21:00 continued from previous 05/03/15 23:00

not well defined not well defined

02/11/15 02:00 02/27/15 01:40

—

—

—

12/18/14 10:00 —

Ions

SEP rival

05/02/15 18:30

—

—

—

03/02/15 06:30 continued from previous 03/06/15 09:15 continued from previous continued from previous 03/25/15 18:00 —

not well defined not well defined

12/16/14 16:00 continued from previous continued from previous continued from previous continued from previous 02/15/15 00:00 02/27/15 02:40

Electrons


Oct (b)

Nov ’15

Jan ’16

Feb (a) Feb (b)

15

16

17

18

19

’16

’16

’15

’15

Oct (a)

14

13

12

11

Jul ’15 (a) Jul ’15 (b) Jul ’15 (c) Sep ’15

’15

10

9

Jun (a) Jun (b)

8

’15

Event Period

#

over east limb

—

backside —

M1.4

—

—

backside backside

C-series

C-series

12488

12473

M1.8

C3.3

over west limb 12473

—

backside

M3.5

12422

M1.0

backside

12422

M1.3

M1.4

12423

12415

—

—

M1.3

M1.1

—

—

backside

—

—

M1.0

—

12365

—

M1.3

12358

backside

M1.3

—

NOAA AR

GOESClass

Flare

Table 1. (continued)

Solar Locationb

—

—

S20E52

S19E48

—

—

—

S25E08

S23E66

(series)

—

01/29/15 N07E06 21:57 (series) —

12/28/15 13:00 01/02/16 00:28 01/06/16 15:30 —

10/05/15 — 11:48 10/08/15 — 17:24 — —

over east limb 09/30/15 S20E87 11:14

09/20/15 18:11 09/28/15 04:02 09/29/15 05:22

—

07/04/15 — 05:21 — —

—

06/01/15 — 13:30 06/18/15 over 01:00 east limb — —

—

05/01/15 — 18:37

Peak Time

-46

-46

-56

-68

-72

-75

-77

-108

-122

-123

-126

-128

-128

-133

-160

-164

-171

-177

-179

-179

174

161

161


01/29/16 21:28 02/20/16 14:36 02/21/16 11:48

10/07/15 07:48 11/02/15 20:57 12/28/15 12:12 01/01/16 23:36 01/06/16 14:24 —

—

—

09/30/15 09:48

—

—

—

07/01/15 14:36 —

06/18/15 17:24 —

06/01/15 14:00 06/18/15 01:25

05/01/15 19:24

LASCO C2 Detection 05/01/15 18:12

CME

no impact

02/04/16 06:05 no impact

—

01/02/16 03:50 01/06/16 02:40 no impact

NU

NU

—

—

10/06/15 17:30

—

—

—

07/06/15 20:00 —

—

no impact

no impact

—

NU

NU

Shock Arrivalc

—

—

3.3

—

—

3.0

3.4

NU

NU

—

—

3.5

—

—

—

—

2.1

—

—

—

—

NU

Peak Pdyn c (nPa) NU

—

—

NU

—


—

1.9

3.2

1.0

—

—

—

—

—

—

—

—

—

—

—

01/13/16 7.4 15:20 — —

—

—

—

—

—

—

—

10/05/15 4.2 13:00

07/17/15 10:30 07/27/15 02:00 09/22/15 06:30 —

06/22/15 14 16:45 — —

—

—

NU

—

—

SIR Arrivalc

Solar Wind

Ar-

10/17/15 10:00 11/04/15 10:00 01/01/16 20:00 01/05/16 00:00 01/07/16 02:00 01/13/16 08:00 02/03/16 17:00 02/23/16 07:00 continued from previous

06/19/15 15:00 06/22/15 18:00 07/06/15 14:00 07/19/15 00:00 07/27/15 06:00 09/21/15 13:00 10/03/15 00:00 continued from previous continued from previous —

continued from previous continued from previous 06/02/15 11:00 —

Ions

SEP rival

—

—

—

01/02/16 15:30 01/06/16 14:50 —

11/03/15 10:40 —

—

09/21/15 13:00 10/02/15 16:00 continued from previous continued from previous —

—

06/18/15 19:00 06/21/15 14:00 07/03/15 17:00 —

—

continued from previous continued from previous —

Electrons


Apr ’16

20

12529

—

—

C5.8

NOAA AR

GOESClass —

Peak Time —

Solar Locationb -45


04/16/16 N13W26 -17 19:58 M6.7 12529 04/18/16 N12W46 -16 00:29 21 May ’16 C3.2 12542 05/15/16 N10W75 -3.5 16:03 a All times are in UT. b As viewed from Mars. c The values are determined solar wind observations available.

Event Period

#

Flare

Table 1. (continued)

—

Shock Arrivalc


Peak Pdyn c (nPa) 02/22/16 3.5 20:00

SIR Arrivalc

Solar Wind

Ar-

continued from previous —

Ions

SEP rival

—

Electrons

04/16/16 no impact — NU NU 04/16/16 20:36 21:00 04/18/16 no impact — NU NU — 04/18/16 00:48 00:50 05/15/16 no impact — NU NU 05/16/16 05/15/16 15:36 14:00 22:00 from the orbit-average resolution upstream solar wind data set. ‘NU’ means there were no MAVEN upstream

LASCO C2 Detection —

CME

250

Monthly SSN

200 150 100 50 0 1995

Figure 1.

1998

2001

2004 2008 Year

2011

2014

2017

NOAA monthly mean sunspot numbers (SSN) for the last two solar cycles. The

MAVEN science observations began on 16 November 2014 (black dashed vertical line), during the end of the maximum phase of Solar Cycle 24. The MAVEN observations that were made during the maximum and declining phases of the solar cycle are indicated by the red and blue segments, respectively.


1.0 0.1

105 104

1F ions (keV)

1000

103

103 102 101 1000 800 600 400 200 10 1

10.0

Total IMF (nT)

Ram Pressure (nPa)

102 101 105 104

100

Density (cm-3)

Velocity (km s-1)

1F electrons (keV)

100

keV/cm2/s/sr/keV

0-7 nm (mW/m2)

10.0

1.0 0.1 10 1

R (AU) Month

Figure 2.

1.38 Jan 2015

1.50 May

1.63 Sep

1.66 Jan 2016

1.55 May

MAVEN observations from November 2014 to the end of May 2016. From top

to bottom, the panels show the EUVM irradiance, SEP ions and electrons, SWIA solar wind proton velocity, density, dynamic pressure, and MAG IMF magnitude. Note that the ∼45second resolution upstream data are used for the observations shown in the bottom four panels. A description of the data gaps in the observations can be found in Section 2. Additional labels indicate the heliocentric distance of Mars in AU.


104

1000

103 100

102

104

100

103 102

Velocity (km s-1)

101 360 300 240 180 120 60 0

90 60 30 0 -30 -60 -90 800

phi (deg)

IMF the (deg)

1F electrons (keV)

101 105

keV/cm2/s/sr/keV

1F ions (keV)

105

keV/cm2/s/sr/keV

0-7 nm (mW/m2)

3.0 2.5 2.0 1.5 1.0 0.5

600

Total IMF (nT)

IMF (nT)

-3

Density (cm ) Pressure (nPa)

400 200 25 20 15 10 5 0 15 10 5 0 -5 -10 15

Bz By Bx

10 5 0

Date 2014

Figure 3.

Dec 11

Dec 21

Dec 31

2014 December event period (Event 1 in Table 1). The panels from top to bottom

show the EUVM 0.1-7nm solar irradiance data, differential energy fluxes for the SEP ions and electrons, and the orbit-averaged upstream data from SWIA for the solar wind velocity, density and dynamic pressure and from MAG for the interplanetary magnetic field. c ⃝2017 American Geophysical Union. All Rights Reserved.

Figure 4.

WSA-Enlil simulation snapshots illustrating the magnetic field line connection of

Mars to ICMEs and heliospheric solar wind structures. The panels show the solar ecliptic view of the modeled solar wind densities (colors) out to 2 AU. The event snapshots are shown for the times listed at the top of each panel. Shown in the lower right of this figure are the symbols used for the inner planets and orbiting spacecraft. Earth is shown as a yellow filled circle and is fixed to the right side of each panel at 0◦ heliolongitude (Sun-Earth line). Also labeled are various features described in the text.


104

1000

103 100

102

1F electrons (keV)

101 105 104

100

103 102 101 360 300 240 180 120 60 0

Velocity (km s-1) IMF (nT)

-3


600

Total IMF (nT) Date 2015

Figure 5.

phi (deg)

IMF the (deg)

90 60 30 0 -30 -60 -90 1000

keV/cm2/s/sr/keV

105

keV/cm2/s/sr/keV

0-7 nm (mW/m2) 1F ions (keV)

5 4 3 2 1 0

200 30 20 10 0 20

Bz

10

By

0 -10 25 20 15 10 5 0 Feb 01

Bx

Feb 11

Feb 21

Mar 03

Mar 13

Same as Figure 3 but for the 2015 February to March 2015 event periods (Events

2–4 in Table 1).


1.0

105 104

1000

103 100

102 101 105 104

100

103 102

Velocity (km s-1)

101 360 300 240 180 120 60 0

90 60 30 0 -30 -60 -90 800

phi (deg)

IMF the (deg)

SEP 1F Electrons Diff Energy Flux

SEP 1F Ions Diff Energy Flux

0.0

keV/cm2/s/sr/keV

0.5

keV/cm2/s/sr/keV

0-7 nm (mW/m2)

1.5

600

200 30 25 20 15 10 5 0 10 5 0 -5 -10 -15 15

Total IMF (nT)

IMF (nT)

-3


400

Bz By Bx

10 5 0

Date

Figure 6.

Dec 31 2015

Jan 10 2016

Jan 20

Same as Figure 3 but for the December 2015 to January 2016 event period (Event

17 in Table 1).


Figure 7.

SDO/AIA composite images of the Earth-facing disk of the solar corona at wave-

length channels of 17.1 nm, 19.3 nm, and 21.1 nm. The left, middle, and right panels show a persistent low-latitude coronal hole in the observations taken on 14 May 2015 (left), 10 June 2015 (middle), and 6 July 2015 (right). Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.


104

1000

103 100

102 101 105 104

100

103 102 101 360 300 240 180 120 60 0

phi (deg)

600 200 50 40 30 20 10 0 10

Bz

0

By

IMF (nT)

-3


Velocity (km s-1)

IMF the (deg)

90 60 30 0 -30 -60 -90 1000

keV/cm2/s/sr/keV

105

keV/cm2/s/sr/keV



0-7 nm (mW/m2)

1.0 0.8 0.6 0.4 0.2 0.0

Bx

Total IMF (nT)

-10 10 5 0 Date 2015 Jun

16

21

26

Figure 8. Same as Figure 3 but for the June 2015 event period (Event 9 in Table 1).


0-7 nm (mW/m2)

103 100

102 101 105 104

IMF (nT)

-3


Velocity (km s-1)

103 102 101 360 300 240 180 120 60 0

90 60 30 0 -30 -60 -90 600

phi (deg)

IMF the (deg)

100

keV/cm2/s/sr/keV

104

keV/cm2/s/sr/keV

105

1000



1.0 0.8 0.6 0.4 0.2 0.0

400 200 15 10 5 0 10

Bz

0

By Bx

Total IMF (nT)

-10 15

Date 2015

10 5 0 Jul 01

Jul 11

Jul 21

Jul 31

Figure 9. Same as Figure 3 but for the July 2015 event period (Events 10–12 in Table 1).


1F ions (keV)

0.1

105 104

1000

103 100

102

1F electrons (keV)

101 105 104

100

103 102 101

Date 2016 May

11

16

keV/cm2/s/sr/keV keV/cm2/s/sr/keV

0-7 nm (W/m2)

1.0

21

Figure 10. EUVM and SEP observations for the May 2016 event period (Event 21 in Table 1).
