Dayside proton aurora associated with magnetic ... - Wiley Online Library

Click Here

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, A04301, doi:10.1029/2009JA014760, 2010

for

Full Article

Dayside proton aurora associated with magnetic impulse events: South Pole observations Y. Ebihara,1 R. Kataoka,2 A. T. Weatherwax,3 and M. Yamauchi4 Received 12 August 2009; revised 9 November 2009; accepted 16 November 2009; published 1 April 2010.

[1] We present, for the first time, auroral hydrogen emission at 486.1 nm (proton aurora) associated with a magnetic impulse event (MIE) or a traveling convection vortex (TCV). The MIE (or TCV) is a transient phenomenon (∼5–15 min) characterized by a large amplitude (>50 nT) in the magnetic field disturbance occurring at 70°–80° magnetic latitudes (MLATs). Optical observations at the South Pole Station (−74.3° MLAT) showed a clear spot‐like brightening of proton auroral emissions associated with MIEs. These spots of the proton aurora were ∼300–500 km in length and ∼150–200 km in width at an altitude of 150 km and lasted for ∼1–2 minutes. The spot drifted antisunward with a speed of ∼3–5 km/s but did not always drift. Quasi‐stable spots coincided with poleward moving multiple arcs at 630.0 nm. There was no clear one‐to‐one correspondence between the spots and the power of the ground magnetic field in the Pc1 range. The variety of proton auroral emissions associated with MIEs may be a visible manifestation of the variety of processes that take place near the region generating a pair of field‐aligned currents that drives MIEs. Citation: Ebihara, Y., R. Kataoka, A. T. Weatherwax, and M. Yamauchi (2010), Dayside proton aurora associated with magnetic impulse events: South Pole observations, J. Geophys. Res., 115, A04301, doi:10.1029/2009JA014760.

1. Introduction [2] Transient (∼5–15 min) and large‐amplitude (>50 nT) magnetic field disturbances have occasionally been observed at 70°–80° magnetic latitudes (MLATs), as documented by Lanzerotti et al. [1986] from magnetometer records at the South Pole Station. These phenomena are called magnetic impulse events (MIEs). Friis‐Christensen et al. [1988] and Glassmeier et al. [1989] interpreted them as tailward traveling Hall current (or convection) vortices (traveling convection vortices (TCVs)) driven by a pair of field‐aligned currents [Friis‐Christensen et al., 1988; Glassmeier et al., 1989; McHenry et al., 1990a, 1990b; Lühr et al., 1993; Vogelsang et al., 1993]. Hereafter, the term TCV is referred to as MIE to avoid terminological confusion. The vortices are usually separated by about 600–1000 km in the east–west direction and move tailward at about 3–10 km/s. Statistical studies show that MIEs tend to occur in prenoon hours [Glassmeier et al., 1989; Lanzerotti et al., 1991; Lin et al., 1995; Sibeck and Korotova, 1996; Zesta et al., 2002; Kataoka et al., 2003]. Vogelsang et al. [1993] confirmed that MIEs are indeed associated with filaments of field‐aligned currents. Lyatsky et al. [1999b] compared the equivalent current derived from ground magnetic field observation with 1

Institute for Advanced Research, Nagoya University, Aichi, Japan. Interactive Research Center of Science, Tokyo Institute of Technology, Tokyo, Japan. 3 Department of Physics, Siena College, Loudonville, New York, USA. 4 Swedish Institute of Space Physics, Kiruna, Sweden. 2

Copyright 2010 by the American Geophysical Union. 0148‐0227/10/2009JA014760

the ionospheric convection obtained from the Super Dual Auroral Radar Network radars. Some noticeable discrepancies between them were found, possibly due to the inhomogeneity of ionospheric conductivity [Zhu et al., 1997]. Yahnin and Moretto [1996], Yahnin et al. [1997], and Moretto et al. [2002] found that the foci of MIEs and their trajectories lay within the plasma sheet. On the basis of ground‐based networks of magnetic field observation, snapshots of equivalent currents have been revealed [Murr et al., 2002; Amm et al., 2002]. Murr et al. [2002] showed that the system of the current is confined to a narrow region (∼3° in latitude) in which 1–10 keV electrons that correspond to the characteristic energy of the central plasma sheet are present. After surveying 18 MIE events, Lam and Rodger [2004] found that the intensities of the magnetic perturbations are similar in the conjugate points in both Northern and Southern hemispheres. This most likely indicates that the current circuit is located within the magnetosphere. [3] There are two major questions regarding the formation of MIEs: What is the external driver that deforms or perturbs the magnetopause boundary? How does this deformation or perturbation of the magnetopause boundary drive the field‐aligned currents that are observed as they are closed in the ionosphere? To answer the first question, following mechanisms have been suggested: (1) flux transfer events [Russell and Elphic, 1978; Haerendel et al., 1978; Cowley, 1982; Lanzerotti et al., 1986], (2) Kelvin‐ Helmholtz instability at the inner edge of the magnetospheric boundary layer [McHenry et al., 1990a, 1990b; Bristow et al., 1995], and (3) indentation of the magnetopause due to a pressure pulse in the solar wind [e.g., Kivelson and

A04301

1 of 8

A04301

EBIHARA ET AL.: PROTON AURORA AND MAGNETIC IMPULSE EVENT

Southwood, 1991; Lühr et al., 1996; Murr and Hughes, 2003], a change in the polarity of the interplanetary magnetic field (IMF) [e.g., Lühr et al., 1996], or a hot flow anomaly and/or small‐scale pressure pulses generated within the foreshock [e.g., Sitar et al., 1998; Sibeck et al., 1999, 2003; Kataoka et al., 2001, 2003]. [4] To answer the second question, the following mechanisms have been suggested: (1) elongated plasma clouds [Wei and Lee, 1990], (2) flow vorticity in the vicinity of the indentation of the magnetopause [e.g., Kivelson and Southwood, 1991], (3) density gradient inside the magnetopause [e.g., Lühr et al., 1996; Moretto et al., 2002], and (4) inertial currents, associated with in‐and‐out plasma acceleration, converted into field‐aligned current due to a curvilinear effect and/or the gradient of Alfvén speed [e.g., Kataoka et al., 2004]. [5] Auroral emissions associated with MIEs have been observed. Mende et al. [1990] demonstrated that an overhead aurora appeared at the onset of an MIE. The aurora expanded over a large region equatorward from the main auroral oval. Lühr et al. [1996] found that, except for one event, there were no discrete auroras at 557.7 nm associated with MIEs. Using images from the Polar satellite, Sitar et al. [1998] observed the intensification of auroral emissions associated with an MIE. Weatherwax et al. [1999] found that a localized intensification of energetic electron precipitation (427.8 nm auroral emission and riometer absorption) was observed at the South Pole Station but not at the nominally conjugate locations in the Northern Hemisphere. Vorobjev et al. [2001] analyzed auroral transient events (ATEs) observed by the ultraviolet imager on Polar. Prenoon ATEs generally appear as bright spots of auroral luminosity in the area from 0800 to 1000 magnetic local time (MLT). Their bright auroras quickly expand westward (antisunward) and poleward and are accompanied by MIEs. Mende et al. [2001] found that dayside auroral optical events, which are initiated equatorward of the preexisting main aurora and propagated poleward, were always accompanied by MIEs. In many cases, the majority of auroral activity takes place in the 630.0 nm emission, with short‐ lived activity taking place in the 427.8 nm emission. Kataoka et al. [2001] found that an MIE had upward field‐ aligned currents with soft electron precipitation located near the trailing edge of the Hall current loop. Murr et al. [2002] show that an MIE‐associated auroral arc at 427.8 nm had a width between 50 and 100 km and a minimum length of ∼600 km. [6] Arnoldy et al. [1996] showed that approximately 70% of MIEs are associated with bursts of pulsation activity in the Pc1 range. These Pc1 bursts are known to be a manifestation of electromagnetic ion cyclotron waves and have demonstrated good correlation with the auroral hydrogen emission (proton aurora) [e.g., Sakaguchi et al., 2007; Yahnin et al., 2007; Yahnina et al., 2008]. It is thus readily expected that MIEs might be accompanied by proton auroral emission. However, to the best of our knowledge, no auroral emission due entirely to precipitating protons has been reported in association with MIEs. The aim of this paper is to report, for the first time, proton auroral emissions associated with MIEs on the basis of magnetic field and optical observations performed at the South Pole Station. At that

A04301

location, the Sun is more than 12° below the horizon for ∼4 months during the austral winter season, allowing for the continuous measurement of faint proton auroral emissions 24 h/d during the austral winter with reduced interference by solar radiance.

2. Data [7] We used data from the Japanese all‐sky imager (ASI) installed at the South Pole Station (−74.3° corrected geomagnetic latitude) [Ejiri et al., 1999; Ebihara et al., 2007]. The ASI consisted of a 180° field‐of‐view fish‐eye lens ( f = 6 mm, F = 1.4), an automated filter changer, and a back‐ illuminated, air‐cooled CCD camera with a resolution set at 512 × 512 pixels for an electron aurora and 256 × 256 pixels for a proton aurora. In 2005, the exposure times of the 557.7 nm emission [O I], 630.0 nm emission [O I], and 486.1 nm emissions (Hb) were 4, 4, and 16 s, respectively. It took 51 s to complete each cycle of observation. For the proton aurora, we employed a narrow‐band‐pass interference filter with a full width at half maximum of 1.7 nm and center wavelength of 486.15 nm in order to distinguish the hydrogen emission from other emissions. [8] Some corrections, including those for the van Rhijn effect, atmospheric extinction, and the nonuniform sensitivity of the optics, were made. Another factor, related to the Doppler shift and Doppler broadening of the hydrogen emission, remains to be resolved [e.g., Jasperse and Basu, 1982; Kozelov, 1993]. The Doppler shift depends not only on the energy distribution of energetic hydrogen, but also on the geometry between an observer’s line of sight and the direction of the energetic hydrogen. When looking at the magnetic zenith, an observer measures an asymmetric spectral profile with a strong red‐shifted wing and a weak blue‐shifted wing [Lummerzheim and Galand, 2001]. The blue‐shifted wing is simply understood to be from incident hydrogen atoms. Lummerzheim and Galand [2001] suggested that collisional angular redistribution results in upward moving hydrogen [Kozelov, 1993] and hence a slight Doppler broadening toward red in a spectrum. Lummerzheim and Galand [2001] also found that the spectral shape of the blue‐shifted wing, rather than the location of the spectral peak, provides a true measure of the mean energy of incident protons. The effect of the Doppler shift is expected to be maximized at the magnetic zenith and becomes negligible at the large magnetic zenith angles. [9] It should be noted that the imaging of a hydrogen emission might be contaminated by electron‐excited emissions, such as continuum emission, the N2 Vegard‐Kaplan (2, 15) emission band, or electron‐excited hydrogen emission [Rees, 1989; Takahashi and Fukunishi, 2001]. Such contamination by electron‐excited emissions makes it difficult to identify proton precipitation. On the basis of our experience, we believe that a hydrogen emission satisfying the following criteria can be regarded as being entirely due to precipitating protons: (1) The auroral forms in the hydrogen emission are quite different from those at 557.7 nm, and (2) the auroral forms have a broadly shaped structure. Because an incident proton is known to spread due to multiple

2 of 8

A04301


A04301

Figure 1. Summary of magnetic field and optical observations at the South Pole Station on 5 July 2005. (a–c) The H, D, and Z components of the magnetic field (right‐handed coordinate system). (d) A time‐ averaged power spectrogram of the H component of the magnetic field. (e) A keogram of the emission at 486.1 nm as a function of time and magnetic latitude. (f) A keogram at 630.0 nm. (g) A keogram at 557.7 nm. An arrow indicates possible brightening due entirely to precipitating protons. In Figure 1d, fast Fourier transform analysis was performed on the windowed envelope having length of 51.2 s. charge exchange, proton auroral structures are broadly shaped [Jasperse and Basu, 1982].

3. Observation 3.1. The 5 July 2005 Event [10] Figure 1 summarizes the magnetic field and optical observations performed at the South Pole Station on 5 July 2005 during a 2 h period (1050–1250 UT) when the station was located in the late morning sector (MLT ≈ UT − 3.5 h). In Figures 1a–1c, the magnetic fields in the H, D, and Z components are presented (in the right‐handed coordinate system), which indicate that an MIE event commenced at ∼1150 UT. The peak‐to‐peak amplitude reached ∼200 nT in the H component magnetic field. Figure 1d shows the dynamic fast Fourier transform (FFT) power spectrum of the H component magnetic field, in which the time‐averaged global spectrum is subtracted to enhance the spectral peak. There is no clear enhancement in the power spectra in conjunction with the MIE event, except for a faint enhancement

at ∼0.2–0.3 Hz at ∼1200 UT. Figures 1e–1g show meridional slices of the intensity of the emission (a keogram) at 486.1, 630.0, and 557.7 nm, respectively. The two‐dimensional images were sliced along the magnetic meridian that intersects the magnetic zenith. The magnetic South Pole is to the top. It is easy to visually identify four transient enhancements at 486.1 nm during the MIE event at 1150–1210 UT. However, enhancements of the 486.1 nm line do not always mean enhancements of precipitating protons. In fact, the first and third enhancements at 486.1 nm are similar to those at 557.7 nm and 630.0 nm, while the second and fourth ones are isolated from those at 557.7 nm or 630.0 nm. Our best speculation at present is that the second and fourth enhancements at 486.1 nm (indicated by white arrows in Figure 1f) result entirely from precipitating protons, not electrons. In Figure 1f, a few dispersed stripes are shown to appear at 630.0 nm. Each stripe, as indicated by a white arrow, was initiated equatorward of the main oval and propagated poleward. At a fixed MLAT, the interval of the stripes is almost a constant at ∼3–6 min. A similar auroral

3 of 8

A04301


A04301

Figure 2. Example of stationary spot‐like proton aurora taken from 1158:55 to 1201:28 UT on 5 July 2005. Successive two‐dimensional images at wavelengths of (top) 486.1 nm, (middle) 557.7 nm, and (bottom) 630.0 nm in the geographic coordinates. Geographic longitude 0° is at the top and 90° is to the right. The center of the image is at 90°S in geographic coordinates, that is, zenith of the South Pole Station. The outer circle corresponds to a geographic latitude of −83°. White lines indicate a constant corrected geomagnetic latitude and magnetic local time. Emission from the Milky Way is shaded by the gray rectangle. structure was observed on closed field lines on the dayside [e.g., Lyatsky et al., 1999a; Mende et al., 2001; Milan et al., 2001; Kozlovsky and Kangas, 2002]. Lyatsky et al. [1999a], Milan et al. [2001], and Kozlovsky and Kangas [2002] suggested that the poleward propagating structure can be explained by a field‐line resonance [e.g., Hughes, 1983; Samson et al., 1996]. [11] According to the high‐resolution OMNI data (http:// omniweb.gsfc.nasa.gov/) [King and Papitashvili, 2005] the ACE satellite observed a solar wind dynamic pressure that remained almost constant at approximately 0.8–1.2 nPa during the MIE. The ACE satellite was located at (235, −41, 21) RE in the GSE coordinates. As mentioned above, a pulse of the solar wind dynamic pressure is suggested to be not a necessary condition for generating MIEs [e.g., Kataoka et al., 2001; Sibeck et al., 2003]. Of course, we cannot deny the possibility that the ACE satellite missed a structured pressure pulse in the solar wind. Murr and Hughes [2003] found clear evidence of solar wind drives of MIEs using data from the Geotail satellite just upstream of the bow shock. [12] Figure 2 shows successive auroral images at wavelengths of 486.1, 557.7, and 630.0 nm from 1158:55 UT

to 1202:06 UT on 5 July 2005. The MLT ranges from approximately 0700 to 0930 h. The images are mapped to the geographic coordinates (top to the geographic longitude 0°) at altitudes of 150, 120, and 220 km for 486.1, 557.7, and 630.0 nm, respectively. The mapping altitude for 486.1 nm is determined following Sigernes et al. [1996], who showed that the maximum volume emission rate of a hydrogen emission takes place at an altitude of ∼145 km in the low‐latitude boundary layer. The outer circle corresponds to the geographic latitude of −83°. The white lines in Figure 2 indicate the geomagnetic coordinates (MLT and MLAT). A spot‐like structure of the emission at 486.1 nm, as indicated by a white arrow, emerged at about −73 to −75 MLAT during the interval from 1159:46 to 1200:37 UT. The spot was ∼150–200 km in width and ∼500 km in length and was spread toward the magnetic east and west. The centroid seems to remain fairly stable during its appearance of about 2 min. The spot‐like emission is believed to result from proton precipitation for two reasons. First, the proton aurora was diffusive in shape and the spot did not have a small‐scale structure. Second, the spot is well isolated from emissions at 557.7 and 630.0 nm.

4 of 8

A04301


A04301

Figure 3. Same as Figure 1, except for the period from 1630 to 1830 UT on 4 July 2005.

3.2. The 4 July 2005 Event [13] Figure 3 summarizes the magnetic field and optical observations from 1630 to 1830 UT on 4 July 2005 during which the South Pole Station was located in the early afternoon sector. An MIE with a peak‐to‐peak amplitude of ∼150 nT in the H component magnetic field commenced at ∼1728 UT on 4 July 2005. The dynamic FFT power spectrogram of the H component magnetic field shows that the pulsation activity in the Pc1 range had already intensified since 1702 UT (Figure 3d). However, there is no clear one‐ to‐one correspondence between the MIE event and the power of the magnetic pulsation in the Pc1 range. A white arrow in Figure 3e indicates a transient spot of the proton aurora that appeared just equatorward of the main oval, identified by the auroral emission at wavelengths at 630.0 nm. According to the high‐resolution OMNI data (http://omniweb. gsfc.nasa.gov/), the ACE satellite observed a solar wind dynamic pressure that remained almost constant at approximately 1.2 nPa during the MIE. The ACE satellite was located at (236, −42, 21) RE in the GSE coordinates. [14] Figure 4 demonstrates sequential auroral images at wavelengths of 486.1, 557.7, and 630.0 nm from 1736:24 to 1739:35 UT on 4 July 2005. A bright auroral spot emerged at −76 to −78 MLAT at the western edge of the imager’s

field of view. As time proceeded, the bright spot drifted toward the magnetic east (antisunward) and disappeared around 1738:56 UT. The drift speed is estimated to be ∼3– 5 km/s, which is consistent with a typical traveling speed of the current system associated with MIEs [e.g., Friis‐ Christensen et al., 1988]. The spot is ∼150–200 km in width and ∼500 km or larger in length. Although there is a slight possibility that the drifting spot of the proton aurora resulted from precipitating electrons, we believe that the drifting spot is most likely a manifestation of precipitating protons for the following two reasons. First, the auroral spots at 557.7 and 630.0 nm have small‐scale structures, whereas the auroral spot at 486.1 nm is diffusive. Second, there were some auroral structures at 557.7 and 630.0 nm in the region where no significant 486.1 nm emission was present. Note that the exposure time of the 486.1 nm emission is 16 s. When the spot propagates with a speed of ∼3–5 km/s, there is some smearing in the direction of its propagation. This has to be ∼50–80 km. Thus, the length of the spot may be a bit overestimated. 3.3. Other Events [15] Proton auroral spots were also observed in association with MIEs in the 2005 austral winter season. A quasi‐

5 of 8

A04301


A04301

Figure 4. Example of a drifting spot‐like proton aurora taken from 1736:24 to 1738:56 UT on 4 July 2005. The format is the same as in Figure 2. Emission from the Milky Way is shaded by the gray rectangle. stationary spot that resembles the 5 July 2005 event was observed during the two MIE events that occurred at ∼1300 UT on 5 June 2005 and at ∼1040 UT on 3 August 2005 (data not shown). These two spots were also found to be in the vicinity of the poleward traveling multiple arcs in the images at 630.0 nm. A drifting spot that resembles the 4 July 2005 event was observed during the MIE event that occurred at 1745 UT on 31 July 2005 (data not shown).

4. Discussion and Summary [16] Major characteristics of the spot‐like proton aurora associated with MIEs can be summarized as follows. [17] 1. The spot‐like proton aurora moved antiearthward with a speed of ∼3–5 km but did not always track the traveling current system associated with MIEs. [18] 2. One of the spot‐like proton auroras coincided with poleward moving multiple arcs at 630.0 nm. We cannot prove causal relationship between them. [19] 3. There was no clear one‐to‐one correspondence between the spot‐like proton aurora and the power of the ground magnetic field in the Pc1 range. [20] 4. IMF Bz was close to zero or slightly positive. The solar wind dynamic pressure remained almost constant at the position of the ACE satellite.

[21] Our best speculation is that the spot‐like proton auroras result entirely from precipitating protons. Possible sources of the proton precipitation are as follows. (1) Protons were precipitated from the magnetosphere probably due to a localized compression of the magnetosphere [e.g., Meurant et al., 2003; Yahnina et al., 2008] or diamagnetic decompression propagating antiearthward. (2) Protons escaped from the opposite hemisphere [e.g., Frahm et al., 1986; Yamauchi et al., 2005]. (3) Protons directly entered from the magnetosheath [e.g., Lemaire and Roth, 1978; Carlson and Torbert, 1980; Sonnerup et al., 1981; Heikkila, 1982, 1989; Lundin, 1988; Woch and Lundin, 1991, 1992; Sauvaud et al., 1998; Sandahl et al., 1999; Stenuit et al., 2001; Lundin et al., 2003; Yamauchi et al., 2003; Lu et al., 2004]. There is no clear evidence that supports any of the above mechanisms. We leave this issue for future work. A variety of proton auroral emissions responding to MIEs might be visible manifestations of a variety of causation mechanisms of MIEs. We expect that proton auroral images will help us more deeply understand the cause–effect relationships among the magnetosheath, the magnetosphere, and the ionosphere. [22] Acknowledgments. The Japanese all‐sky imager project at the South Pole Station was initiated by Masaki Ejiri and Sho‐ichi Okano in 1997 and performed under an agreement of cooperation between the National Institute of Polar Research and the U.S. National Science Foundation

6 of 8

A04301


between 1997 and 2005. We appreciate the wintering science research associate Jeanne Edwards for taking care of the instrument. YE thanks Shigeru Fujita, Yoshizumi Miyoshi, and Yosuke Matsumoto for their valuable discussions. The OMNI data were obtained from GSFC/SPDF OMNIWeb at http://omniweb.gsfc.nasa.gov/. The work of YE was supported by the Program for Improvement of Research Environment for Young Researchers from the Special Coordination Funds for Promoting Science and Technology (SCF), which was commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. The work of RK was supported by a research fellowship of the Special Postdoctoral Research Program at RIKEN. At Siena College, we gratefully acknowledge support from NSF award ANT‐0638587. We further thank Louis Lanzerotti at the New Jersey Institute for Technology for his support and guidance with regard to the South Pole Station fluxgate magnetometer observations. [23] Wolfgang Baumjohann thanks Alan Rodger and another reviewer for their assistance in evaluating this manuscript.

References Amm, O., M. J. Engebretson, T. Hughes, L. Newitt, A. Viljanen, and J. Watermann (2002), A traveling convection vortex event study: Instantaneous ionospheric equivalent currents, estimation of field‐aligned currents, and the role of induced currents, J. Geophys. Res., 107(A11), 1334, doi:10.1029/2002JA009472. Arnoldy, R. L., M. J. Engebretson, J. L. Alford, R. E. Erlandson, and B. J. Anderson (1996), Magnetic impulse events and associated Pc 1 bursts at dayside high latitudes, J. Geophys. Res., 101(A4), 7793–7799, doi:10.1029/95JA03378. Bristow, W. A., et al. (1995), Observations of convection vortices in the afternoon sector using the SuperDARN HF radars, J. Geophys. Res., 100(A10), 19,743–19,756, doi:10.1029/95JA01301. Carlson, C. W., and R. B. Torbert (1980), Solar wind ion injections in the morning auroral oval, Geophys. Res. Lett., 85(A6), 2903–2980. Cowley, S. W. H. (1982), The cases of convection in the Earth’s magnetosphere: A review of developments during the IMS, Rev. Geophys. Space Phys., 20(3), 531–565, doi:10.1029/RG020i003p00531. Ebihara, Y., Y.‐M. Tanaka, S. Takasaki, A. T. Weatherwax, and M. Taguchi (2007), Quasi‐stationary auroral patches observed at the South Pole Station, J. Geophys. Res., 112, A01201, doi:10.1029/2006JA012087. Ejiri, M., et al. (1999), Japanese research project on Arctic and Antarctic observations of the middle atmosphere, Adv. Space Res., 24(12), 1689– 1692, doi:10.1016/S0273-1177(99)00335-X. Frahm, R. A., P. H. Reiff, J. D. Winningham, and J. L. Burch (1986), Banded ion morphology main and recovery storm phases, in Ion Acceleration in the Magnetosphere and Ionosphere, Geophys. Monogr. Ser., vol. 38, edited by T. Chang et al., pp. 98–107, AGU, Washington, D. C. Friis‐Christensen, E., M. A. McHenry, C. R. Clauer, and S. Vennerstrøm (1988), Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind, Geophys. Res. Lett., 15(3), 253–256, doi:10.1029/GL015i003p00253. Glassmeier, K.‐H., M. Hönisch, and J. Untiedt (1989), Ground‐based and satellite observations of traveling magnetospheric convection twin vortices, J. Geophys. Res., 94(A3), 2520–2528, doi:10.1029/ JA094iA03p02520. Haerendel, G., G. Pachmann, N. Sckopke, H. Rosenbauer, and P. C. Hadgecock (1978), The frontside boundary layer of the magnetosphere and the problem of reconnection, J. Geophys. Res., 83(A7), 3195–3216, doi:10.1029/JA083iA07p03195. Heikkila, W. J. (1982), Impulsive plasma transport through the magnetopause, Geophys. Res. Lett., 9(2), 159–162. Heikkila, W., T. Jorgensen, L. Lanzerotti, and C. Maclennan (1989), A transient auroral event on the dayside, J. Geophys. Res., 94(A11), 15,291–15,305, doi:10.1029/JA094iA11p15291. Hughes, W. J. (1983), Hydromagnetic waves in the magnetosphere, Rev. Geophys., 21(2), 508–520, doi:10.1029/RG021i002p00508. Jasperse, J. R., and B. Basu (1982), Transport theoretic solutions for auroral proton and H atom fluxes and related quantities, J. Geophys. Res., 87 (A2), 811–822, doi:10.1029/JA087iA02p00811. Kataoka, R., H. Fukunishi, L. J. Lanzerotti, C. G. Maclennan, H. U. Frey, S. B. Mende, J. H. Doolittle, T. J. Rosenberg, and A. T. Weatherwax (2001), Magnetic impulse event: A detailed case study of extended ground and space observations, J. Geophys. Res., 106(A11), 25,873– 25,889, doi:10.1029/2000JA000314. Kataoka, R., H. Fukunishi, and L. J. Lanzerotti (2003), Statistical identification of solar wind origins of magnetic impulse events, J. Geophys. Res., 108(A12), 1436, doi:10.1029/2003JA010202. Kataoka, R., H. Fukunishi, S. Fujita, T. Tanaka, and M. Itonaga (2004), Transient response of the Earth’s magnetosphere to a localized density

A04301

pulse in the solar wind: Simulation of traveling convection vortices, J. Geophys. Res., 109, A03204, doi:10.1029/2003JA010287. King, J. H., and N. E. Papitashvili (2005), Solar wind spatial scales in and comparisons of hourly wind and ACE plasma and magnetic field data, J. Geophys. Res., 110, A02104, doi:10.1029/2004JA010649. Kivelson, M. G., and D. J. Southwood (1991), Ionospheric traveling vortex generation by solar wind buffeting of the magnetosphere, J. Geophys. Res., 96(A2), 1661–1667, doi:10.1029/90JA01805. Kozelov, B. V. (1993), Influence of the dipolar magnetic field on transport of proton–H atom fluxes in the atmosphere, Ann. Geophys., 11(8), 697– 704. Kozlovsky, A., and J. Kangas (2002), Motion and origin of noon high‐ latitude poleward moving auroral arcs on closed magnetic field lines, J. Geophys. Res., 107(A2), 1017, doi:10.1029/2001JA900145. Lam, M. M., and A. S. Rodger (2004), A test of the magnetospheric source of traveling convection vortices, J. Geophys. Res., 109, A02204, doi:10.1029/2003JA010214. Lanzerotti, L. J., L. C. Lee, C. G. Maclennan, A. Wolfe, and L. V. Medford (1986), Possible evidence of flux transfer events in the polar ionosphere, Geophys. Res. Lett., 13(11), 1089–1092, doi:10.1029/GL013i011p01089. Lanzerotti, L. J., R. M. Konik, A. Wolfe, D. Venkatesan, and C. G. Maclennan (1991), Cusp latitude magnetic impulse events, 1, Occurrence statistics, J. Geophys. Res., 96(A8), 14,009–14,022, doi:10.1029/ 91JA00567. Lemaire, J., and M. Roth (1978), Penetration of solar wind plasma elements into the magnetosphere, J. Atmos. Terr. Phys., 40(3), 331–335, doi:10.1016/0021-9169(78)90049-1. Lin, Z. M., E. A. Bering, J. R. Benbrook, B. Liao, L. J. Lanzerotti, C. G. Maclennan, A. N. Wolfe, and E. Friis‐Christensen (1995), Statistical studies of impulsive events at high latitudes, J. Geophys. Res., 100(A5), 7553–7566, doi:10.1029/94JA01655. Lu, G., T. G. Onsager, G. Le, and C. T. Russell (2004), Ion injections and magnetic field oscillations near the high‐latitude magnetopause associated with solar wind dynamic pressure enhancement, J. Geophys. Res., 109, A06208, doi:10.1029/2003JA010297. Lühr, H., W. Blawert, and H. Todd (1993), The ionospheric plasma flow and current patterns of travelling convection vortices: A case study, J. Atmos. Terr. Phys., 55(14), 1717–1727. Lühr, H. W., M. Lockwood, P. E. Sandholt, T. L. Hansen, and T. Moretto (1996), Multi‐instrument ground‐based observations of a travelling convection vortices event, Ann. Geophys., 14(2), 162–181, doi:10.1007/ s00585-996-0162-z. Lummerzheim, D., and M. Galand (2001), The profile of the hydrogen Hb emission line in proton aurora, J. Geophys. Res., 106(A1), 23–31, doi:10.1029/2000JA002014. Lundin, R. (1988), On the magnetospheric boundary layer and solar wind energy transfer into the magnetosphere, Space Sci. Rev., 48(3–4), 263– 320, doi:10.1007/BF00226010. Lundin, R., et al. (2003), Evidence for impulsive solar wind plasma penetration through the dayside magnetopause, Ann. Geophys., 21(2), 457– 472. Lyatsky, W. B., G. J. Sofko, A. V. Kustov, D. André, W. J. Hughes, and D. Murr (1999a), Traveling convection vortices as seen by the SuperDARN HF radars, J. Geophys. Res., 104(A2), 2591–2601, doi:10.1029/ 1998JA900007. Lyatsky, W. B., R. D. Elphinstone, Q. Pao, and L. L. Cogger (1999b), Field line resonance interference model for multiple auroral arc generation, J. Geophys. Res., 104(A1), 263–268, doi:10.1029/1998JA900027. McHenry, M. A., C. R. Clauer, E. Friis‐Christensen, P. T. Newell, and J. D. Kelly (1990a), Ground observations of magnetospheric boundary layer phenomena, J. Geophys. Res., 95(A9), 14,995–15,005, doi:10.1029/ JA095iA09p14995. McHenry, M. A., C. R. Clauer, and E. Friis‐Christensen (1990b), Relationship of solar wind parameters to continuous, dayside, high latitude traveling ionospheric convection vortices, J. Geophys. Res., 95(A9), 15,007–15,022, doi:10.1029/JA095iA09p15007. Mende, S. B., R. L. Rairden, L. J. Lanzerotti, and C. G. Maclennan (1990), Magnetic impulses and associated optical signatures in the dayside aurora, Geophys. Res. Lett., 17(2), 131–134, doi:10.1029/GL017i002p00131. Mende, S. B., H. U. Frey, J. H. Doolittle, L. Lanzerotti, and C. G. Maclennan (2001), Dayside optical and magnetic correlation events, J. Geophys. Res., 106(A11), 24,637–24,649, doi:10.1029/2001JA900065. Meurant, M., J.‐C. Gérard, B. Hubert, V. Coumans, C. Blockx, N. Østgaard, and S. B. Mende (2003), Dynamics of global scale electron and proton precipitation induced by a solar wind pressure pulse, Geophys. Res. Lett., 30(20), 2032, doi:10.1029/2003GL018017. Milan, S. E., N. Sato, M. Ejiri, and J. Moen (2001), Auroral forms and the field‐aligned current structure associated with field line resonances, J. Geophys. Res., 106(A11), 25,825–25,833, doi:10.1029/2001JA900077.

7 of 8

A04301


Moretto, T., M. Hesse, A. Yahnin, A. Ieda, D. Murr, and J. F. Watermann (2002), Magnetospheric signature of an ionospheric traveling convection vortex event, J. Geophys. Res., 107(A6), 1072, doi:10.1029/ 2001JA000049. Murr, D. L., and W. J. Hughes (2003), Solar wind drivers of traveling convection vortices, Geophys. Res. Lett., 30(7), 1354, doi:10.1029/ 2002GL015498. Murr, D. L., W. J. Hughes, A. S. Rodger, E. Zesta, H. U. Frey, and A. T. Weatherwax (2002), Conjugate observations of traveling convection vortices: The field‐aligned current system, J. Geophys. Res., 107 (A10), 1306, doi:10.1029/2002JA009456. Rees, M. H. (1989), Antarctic upper atmosphere investigations by optical methods, Planet. Space Sci., 37, 955–966, doi:10.1016/0032-0633(89) 90050-0. Russell, C. T., and R. C. Elphic (1978), Initial ISEE magnetometer results: Magnetopause observations, Space Sci. Rev., 22(6), 681–715, doi:10.1007/BF00212619. Sakaguchi, K., K. Shiokawa, A. Ieda, Y. Miyoshi, Y. Otsuka, T. Ogawa, M. Connors, E. F. Donovan, and F. J. Rich (2007), Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes, J. Geophys. Res., 112, A04202, doi:10.1029/2006JA012135. Samson, J. C., L. L. Cogger, and Q. Pao (1996), Observations of field line resonances, auroral arcs, and auroral vortex structures, J. Geophys. Res., 101(A8), 17,373–17,383, doi:10.1029/96JA01086. Sandahl, I., et al. (1999), First results from the hot plasma instrument PROMICS‐3 on Interball‐2, Ann. Geophys., 17(5), 659–673, doi:10.1007/s00585-999-0659-3. Sauvaud, J. A., H. Barthe, C. Aoustin, J. J. Thocaven, J. Rouzaud, E. Penou, D. Popescu, R. A. Kovrazhkin, and K. G. Afanasiev (1998), The ion experiment onboard the Interball‐Aurora satellite: Initial results on velocity‐ dispersed structures in the cleft and inside the auroral oval, Ann. Geophys., 16, 1056–1069, doi:10.1007/s00585-998-1056-z. Sibeck, D. G., and G. I. Korotova (1996), Occurrence patterns for transient magnetic field signatures at high latitudes, J. Geophys. Res., 101(A6), 13,413–13,428, doi:10.1029/96JA00187. Sibeck, D. G., et al. (1999), Comprehensive study of the magnetospheric response to a hot flow anomaly, J. Geophys. Res., 104(A3), 4577– 4593, doi:10.1029/1998JA900021. Sibeck, D. G., N. B. Trivedi, E. Zesta, R. B. Decker, H. J. Singer, A. Szabo, H. Tachihara, and J. Watermann (2003), Pressure‐pulse interaction with the magnetosphere and ionosphere, J. Geophys. Res., 108(A2), 1095, doi:10.1029/2002JA009675. Sigernes, F., et al. (1996), Calculations and ground‐based observations of pulsed proton events in the dayside aurora, J. Atmos. Terr. Phys., 58(11), 1281–1291, doi:10.1016/0021-9169(95)00113-1. Sitar, R. J., J. B. Baker, C. R. Clauer, A. J. Ridley, J. A. Cumnock, V. O. Papitashvili, J. Spann, M. J. Brittnacher, and G. K. Parks (1998), Multi‐ instrument analysis of the ionospheric signatures of a hot flow anomaly occurring on July 24, 1996, J. Geophys. Res., 103(A10), 23,357–23,372, doi:10.1029/98JA01916. Sonnerup, B. U. Ö., G. Paschmann, I. Papamastorakis, N. Sckopke, G. Haerendel, S. J. Bame, J. R. Asbridge, J. T. Gosling, and C. T. Russell (1981), Evidence for magnetic field reconnection at the Earth’s magnetopause, J. Geophys. Res., 86, 10,049–10,067, doi:10.1029/ JA086iA12p10049. Stenuit, H., J.‐A. Sauvaud, D. C. Delcourt, T. Mukai, M. Fujimoto, N. Y. Buzulukova, R. P. Lin, and R. P. Lepping (2001), A study of ion injections at the dawn and dusk polar edges of the auroral oval, J. Geophys. Res., 106(A12), 29,619–29,631, doi:10.1029/2001JA900060.

A04301

Takahashi, Y., and H. Fukunishi (2001), The dynamics of the proton aurora in auroral breakup events, J. Geophys. Res., 106(A1), 45–63, doi:10.1029/2000JA002013. Vogelsang, H., H. Lühr, H. Voelker, J. Woch, T. Bösinger, T. A. Potemra, and P.‐A. Lindqvist (1993), An ionospheric travelling convection vortex event observed by ground‐based magnetometers and by Viking, Geophys. Res. Lett., 20(21), 2343–2346, doi:10.1029/93GL02703. Vorobjev, V. G., O. I. Yagodkina, D. G. Sibeck, K. Liou, and C.‐I. Meng (2001), Polar UVI observations of dayside auroral transient events, J. Geophys. Res., 106(A12), 28,897–28,911, doi:10.1029/2000JA000396. Weatherwax, A. T., H. B. Vo, T. J. Rosenberg, S. B. Mende, H. U. Frey, L. J. Lanzerotti, and C. G. Maclennan (1999), A dayside ionospheric absorption perturbation in response to a large deformation of the magnetopause, Geophys. Res. Lett., 26(4), 517–520, doi:10.1029/ 1999GL900017. Wei, C. Q., and L. C. Lee (1990), Ground magnetic signatures of moving elongated plasma clouds, J. Geophys. Res., 95(A3), 2405–2418, doi:10.1029/JA095iA03p02405. Woch, J., and R. Lundin (1991), Temporal magnetosheath plasma injection observed with Viking: A case study, Ann. Geophys., 9(2), 133–142. Woch, J., and R. Lundin (1992), Signatures of transient boundary layer processes observed with Viking, J. Geophys. Res., 97(A2), 1431–1447, doi:10.1029/91JA02490. Yahnin, A. G., and T. Moretto (1996), Travelling convection vortices in the ionosphere map to the central plasma sheet, Ann. Geophys., 14(10), 1025–1031, doi:10.1007/s005850050363. Yahnin, A. G., V. G. Vorobjev, T. Bösinger, R. Rasinkangas, D. G. Sibeck, and P. T. Newell (1997), On the source region of traveling convection vortices, Geophys. Res. Lett., 24(3), 237–240, doi:10.1029/96GL03969. Yahnin, A. G., T. A. Yahnina, and H. U. Frey (2007), Subauroral proton spots visualize the Pc1 source, J. Geophys. Res., 112, A10223, doi:10.1029/2007JA012501. Yahnina, T. A., H. U. Frey, T. Bösinger, and A. G. Yahnin (2008), Evidence for subauroral proton flashes on the dayside as the result of the ion cyclotron interaction, J. Geophys. Res., 113, A07209, doi:10.1029/ 2008JA013099. Yamauchi, M., R. Lundin, O. Norberg, I. Sandahl, L. Eliasson, and D. Winningham (2003), Signature of direct magnetosheath plasma injections onto closed field‐line regions based on observations at mid‐ and low‐altitudes, in Earth’s Low‐Latitude Boundary Layer, edited by P. Newell and T. Onsager, pp. 179–188, AGU, Washington, D. C. Yamauchi, M., L. Eliasson, R. Lundin, and O. Norberg (2005), Unusual heavy ion injection events observed by Freja, Ann. Geophys., 23(2), 535–543. Zesta, E., W. J. Hughes, and M. J. Engebretson (2002), A statistical study of traveling convection vortices using the Magnetometer Array for Cusp and Cleft Studies, J. Geophys. Res., 107(A10), 1317, doi:10.1029/ 1999JA000386. Zhu, L., P. Gifford, J. J. Sojka, and R. W. Schunk (1997), Model study of ground magnetic signatures of traveling convection vortices, J. Geophys. Res., 102(A4), 7449–7459, doi:10.1029/96JA03682. Y. Ebihara (corresponding author), Institute for Advanced Research, Nagoya University, Aichi 464‐8601, Japan. ([email protected]‐u.ac.jp) R. Kataoka, Interactive Research Center of Science, Tokyo Institute of Technology, Tokyo 152‐8550, Japan. A. T. Weatherwax, Department of Physics, Siena College, Loudonville, NY 12211, USA. M. Yamauchi, Swedish Institute of Space Physics, Kiruna SE‐981 28, Sweden.

8 of 8