Austin and Midgley [1994] pointed out the episodic nature of cyclones and associated ...... 20 25 30 35 40 45 50 55 60 ⢠0.0E+00. Figure 15. Latitudinal cross ...
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. D14, PAGES 16,935-16,951, JULY 27, 1998
Case studies of tropospheric ozone events observed at the summit of Mount Fuji Yukitomo Tsutsumi, 1Yasuhito Igarashi, 2YujiZaizen, 1andYukioMakino 1 Abstract. Tropospheric ozoneeventsobservedat the summitof Mount Fuji (3776 rn abovesea level) were analyzedas casestudies. The ozone,intrudingfrom the lower stratosphere by the cutofflow or thetropopause fold overthe Asiancontinent,is transported to the middletroposphere overJapanevenin summer. The subtropical jet, whichis intensifiedover Japan,alsocontributes to the summerintrusionfrom the stratosphere. A longstratospheric streamer,as described previouslyby Appenzelleret al. [ 1996], bringsabouta persistent ozoneenhancement at the summit of Mount Fuji. The largevariationof summerozoneover Japanis attributableto the alternate overspreading of theseozone-richstratospheic air massesandthe ozone-depleted subtropical maritimeair mass. In contrast,winter ozonevariationis relativelysmallat the summitof Mount Fuji. The steeppotentialtemperaturegradientbetween500 hPa and300 hPa in the winter cutoff low, whichrestrainsverticalmixing in the uppertroposphere, possiblycauseslessinfluenceof the stratospheric air masson the middletroposphere in winter,sincemixingprocesses arounda cutoff low playan importantrole in air massexchangebetweenthe stratosphere andthe troposphere.
1. Introduction
Stratospheric air intrudesinto the tropospherea variety of ways [Shapiro, 1980], but main processesare thoughtto be due to tropopausefolds and cutoff lows near the upper layer trough. Frontal downdrafts or postfrontal subsidencethen transports stratosphericozone to ground level [Lamb, 1977; Derwent et al., 1978; Johnsonand Viezee, 1981]. Davies and Schuepbach [1994] pointedout that the rapiddescentof ozone-richair behind a cold
front
was
the
mechanism
of
transfer
to
the
lower
Mount Fuji in other seasonsthan during winter [Tsutsumiet al., 1994]. In particular, enhancedozone events lasting half a day to 2 days are sometimesobservedfrom june to September. This durationis too longfor a tropopausefold passingover Mount Fuji, but the enhanced ozone may be related to stratosphere/troposphere exchange in summer. This paper summarizescasestudiesof the troposphericozone at the summit of Mount Fuji to showthe causeof short-termozonevariationand its relationship to stratosphere/troposphere exchange and to suggestthe causeof the smallerozonevariationin winter.
troposphereand brought about short-livedozone spikes at a mountainsite. We have beenmeasuringthe troposphericozone at the summitof Mount Fuji sinceAugust 1992. Tsutsumiet al. 2. Analysis [1994] clarified the seasonalozone variation at the summit of We use ultraviolet (UV) absorptionat 254 nm to measure Mount Fuji. Austinand Midgley [1994] pointedout the episodic ambientozone at the summit of Mount Fuji (35.4øN, 138.7øE, nature of cyclones and associatedtropospheric/stratospheric3'I76 m abovesealevel) (Figure1). The systemwasdescribed in exchangearoundJapan. Aircraft measurements were conducted detail by Tsutsumiet al. [1994]. The Japan Meteorological to observethe troposphericozone aroundJapan [Muramatsuet Agency(JMA) has a meteorologicalweatherstation(samesite as al., 1984; Hatakeyamaet al., 1995; Tsutsumiand Makino, 1995], for ozoneobservation)at the summitof Mount Fuji, and we used but they were sporadic. Mount Fuji is an isolated dormant meteorologicalfactors (pressure, temperature,humidity, wind konide volcanowhoseheight is 3776 m above sea level and the direction,wind speed,global solarradiation)observedroutinely at highestmountainin Japan. The small mountaintop (800 m in this station. diameter) and the steep mountain slope, whose differential elevation is more than 2000 m, result in restraint of the mountain
and valley winds, as described by Tsutsumi et al. [1994]. Typical troposphericozoneeventsare thereforeobserveddirectly
Tomeasure a cosmogenic radionuclide, 7Be(T1/2:54d),aerosol
was collected on a quartz fiber filter by using a high-volume sampler(Sibata HVC-1000N) during the specialcampaignfrom
and continuously atthe summit ofMount Fuji.Short-lived highJuly 26toJuly 30,1994. More than 150 m3airwas sampled ozone concentration spikes canbeobserved atthesummit of thermoelectric, every 4 hourso Since thesampier's flowmonitor is pressurecompensationis required to obtain a precisesampledvolume. So far, however,we were unable to
•Atmospheric Environment and AppliedMeteorology Researchconductthe experimentbecauseof the lack of proper facilities. Department, Meteorological Research Institute, Tsukuba, Ibaraki,Japan. The7Beconcentration is thusexpressed in arbitrary units. Two 2Geochemical Research Department, Meteorological Research Institute, setsof datawere lost dueto a poweroutage.
Tsukuba,Ibaraki,Japan.
Copyright1998by theAmericanGeophysical Union. Papernumber98JD01152. 0148-0227/98/98JD-01152509.00
Backward trajectoriesof air massesalong isentropic surface were calculatedfrom the summit of Mount Fuji using objective analysisdata from the JMA. The vertical levels for objective analysisdata were 1000, 850, 700, 500, 400, 300, 250, 200, 150, and 100 hPa. The longitudinal and latitudinal resolution 16,935
TSUTSUMIEL AL.:TROPOSPHERIC OZONEEVENTSAT MOUNTFUJI
16,936
was 1.875ø. We calculated the air masspositionevery6 hoursby
interpolating objective analysis datawhose timeresolution was originally 12hours (0900and2100JST(Japan standard time)). Theobjective analysis datahasnotalways fullyreflected thereal atmosphere, especially whena vertical distribution ofwindhasa singular point, thenthecalculated trajectory could haveanerror.
i 6040•:;~'••-
638 •
5-•'.'7"• 642•
20
634
Potentialvorticity(PV) is a conservative quantityunderan 0
630
4
38
•
5
•
340
•
•
(
8
..... humidity (%) - windspeed (m/s) 360
_
_-- 315
iTsukuba
,•
7
ozone(ppbv) pressure (hPa)
Sea ofJapan •
6
-
z- 270
330 '•_
Tokyo • .... k
_
z- 225
_
,•,
E
_
_
180
3:0 _
135
35
z- 90
310 '• -
_-- 45
_
300
34
4
33
.... 134
• .... 136
I .... 138
I ....
longitude (øE)
5
6
7
8
potential temperature (K)
wind direction(o)
140
0
IIIIIIlilllllllllllllll[1111111[lllllll
142
100 km
Figure2. Hourlyvariationin ozone,pressure, humidity, windspeed,andwinddirection at thesummit of Figure1. Geographical mapshowing theareaaround Mount temperature, MountFujifromSeptember 4 to 8, 1992.
Fuji(35ø21'N,138ø44'E). 10000 6000 2000
70
60
50
40
30
20
90
100
110
120
longitude (Eø)
130
140
150
o
c•
o
alitude (m)
Figure 3. Backward trajectories fromthesummit of Mount Fujiandhighpotential vorticity (PV)areas. Backward trajectories started from 2100JSTonSeptember 4 at315K level (solid line)and2100 JSTonSeptember 5 (thinline)at312K level. Symbols ontrajectories indicate positions ofairparcels every 6 hours. Shaded areas indicate theregion where potential vorticity (PV)exceeded 1.0X10.6m2s'•Kkg'• at312K isentropic level. Uppercase letters indicate thedate andtimeofhigh PVareas andlowercase letters those onthetrajectory. A,a: 0900JST,September 2;B,b:2100JST,September 2;C,c:0900 JST,September 3;D,d:2100JST,September 3; E, e:0900JST,September 4; F, f: 2100JST,September 4.
TSUTSUMI EL AL.: TROPOSPHERIC OZONE EVENTS AT MOUNT FUJI
200•?•:%•/•4 !i••:.:.?:.•.?:.: ii:•i:i•i•:.. •:•_
•
16,937
2.0E-06
•=: 550 450........ ": .......... :." .......................................... •///. ..... •':':' .... )"•:"' :-'i•.............................. •' '/•::; '"'[':
900 950 ._•.• I '"::"' I I ",....:z.:2•ii•?:•::;'!?!•!•;:!:! I ...... :........... '.... ' .... ........ 2.5E-07
1000
O.0E+O0
20
25
30
35
40
45
50
55
60
latitude(øN)
Figure4. Latitudinal crosssectionchartof PV (m2s41.•kg 4) along118øEat 2100 JSTon September 3, 1992. Solid linesindicatethe isoplethof wind speed(m/s). The circle indicateswherethe backwardtrajectory,starting from 2100 JST on September5, passedthrough.
adiabaticconditionand the PV in the stratosphere is higherthan that in the troposphere. Reed [1955] usedthe PV as a tracer for the stratosphericair mass. Shapiro [1974] found a close relationshipbetweenthe PV and the ozone concentrationin the barecliniczone beneaththe jet stream. We calculatedthe PV from objective analysis data to identify the air mass origin. However,the time and spatialresolutionof the objectiveanalysis datais not enoughto be alwaysableto catchthe shorttime or fine structure
events.
3. Results
and Discussion
3.1. Drastic Ozone Variation and Continuanceof High OzoneConcentrationin Late Summer(September4-8, 1992) Drastic variation in the ozone concentration sometimes occurs in
shortperiodsat the summitof Mount Fuji from summerto early autumn. The ozoneconcentration, whichwasabout10 ppbv on September 4, 1992, increasedabruptlyto 70 ppbvon September5
7O
•: • ba'• )I •
20 60
70
c• 80
90
- ß ---•100
110
I
120
longitude(øE)
130
140
150
o o o (•1
o o o ,,o
o o o o
altitude(m)
Figure5. Backward trajectories fromthe summitof MountFuji, startingfrom2100 JSTon September 6 (thick solidline), 2100 JST on September 7 (thin line), and2100 JST on September 8 (thin solidline) at 315 K level. Symbolson trajectories indicatepositionsof air parcelsevery6 hours.Lowercaselettersindicatethe dateandtime on the trajectory(a: 0900 JST, September3; b: 0900 JST, September4; c: 0900 JST, September5 d: 0900 JST, September6).
16,938
TSUTSUMI EL AL.: TROPOSPHERIC OZONE EVENTS AT MOUNT FUJI 60--
(a)
(b)
1.5E-06
m
20 / " I "" I "I .... r I' ""1' ' ' ..... 90 100 110 120 130 140 150
90
100
longitude (øE)
110
120
130
140
1.3E-06
150
1.0E-06
longitude (øE)
7.5E-07
5.0E-07 .
.
2.5E-07
0.0E+00
90
100
110
120
130
140
150
90
100
longitude (øE) Figure 6.
110
120
130
140
150
longitude (øE)
Parcelpositionson the backwardtrajectoryfrom the summitof Mount Fuji and the horizontalPV
distributions (m2s-IKkg-l) at 315K isentropic levelfromSeptember 3 to 6. A, B, andC showpositions of theair parcelthat startedfrom 2100 JST on September6, 2100 JST on September7, and 2100 JST on September8. (a): 0900 JST,September 3; (b): 0900 JST,September 4; (c): 0900 JST,September 5; (d): 0900 JST, September 6.
(Figure 2)
This ozone enhancementlasted about 84 hours. Pacific Ocean (solid line in Figure 3).
The humidityand the ozone clearlyshow negativecorrelation except for the afternoon of September5. The backward trajectorystartingfrom 2100 JST on September 4 showsthat the low ozone air mass came from the subtropicalarea over the
The low ozone concentration overthe subtropicalPacificOceanwaspointedout by many aircraft observations[Kondo et al., 1993; Tsutsumiet al.; 1996; Gregory et al., 1996; Singh et al., 1996] and ship observations[dohnsonet al., 1990; Piotrowicz et al., 1991].
80.
1.5 x10
-4
= -- Ozone
•
70
•
60
----•---Water
vapor x5
1 x10-4
•., •" 50 •
•
40
0
•-
30
5 xlO
-s
:Z
•o
o
o 7/25
7/26
7/27
7/28
7/29
7/30
7/31
Date
Variationof 7Be,ozoneand watervapor
Figure 7. Timevariations in7Be, ozone, andwater vapor atthesummit ofMount FujifromJuly26to30,1994. Ozone andwatervapor arehourly averages, and7Beisa 4 houraverage. Cross symbols indicate that7Bedataare lacking.
TSUTSUMI EL AL.' TROPOSPHERIC OZONE EVENTS AT MOUNT FUJI
16,939
6000
4000 '----------'•:'• ..... '•, '.__? 2000
'
I
'
{
'
I
'
I
50
lO
,
110
130
120
140
150
160
longitude(øE)
altitude(m)
Figure 8. Backwardtrajectoriesfrom the summitof Mount Fuji, startingfrom 0900 JST on July28 at 320 K level (solid line) and 0900 JST on July 29 at 318 K level (faint line). Symbolson trajectoriesindicatepositionsof air parcelsevery6 hours.Lowercaselettersshowthe dateandtime on trajectories(a: 0900 JST, July 18; b: 0900 JST, July 19; c: 0900 JST, July20; d: 0900 JST, July 21; e: 0900 JST, July 22; f: 0900 JST, July 23; g: 0900 JST, July 24; h: 0900 JST,July25; i: 0900 JST, July26; j: 0900 JST,July27; k: 0900 JST,July28).
smallcutoff low in this areabroughtaboutthe intrusionof high PV into the lower troposphere(Figure 4), and the trajectory passedthis high PV region. Stratospheric air intrudesinto the troposphere aroundcutofflows [Hoskinset al., 1985]. The high Pacific Ocean. ozone air massintrudingfrom the stratosphere was transported The thin line in Figure 3 showsthe backwardtrajectoryfrom over Japanin late summer. Tsutsumiand Makino [1995] also 2100 JSTon September 5 whenthe highozoneconcentration was showed that the high ozone peaks over Japan, which were observedat the summitof Mount Fuji. The trajectorypassed observedby the aircraft measurements,originated from the over the Asian continent. The high humidity at closed to thehighPV region(- 1.0x 10-6m2s4K kg4) around stratosphere 46øN, 118øE("D" in the figure)at 2100 JST on September3. A 2100 JST on September5 was probablycausedbecausethe air
Thusthe low ozoneconcentration on September4 was causedby the intrusionof a maritimeair massfrom the subtropicalPacific Ocean. The crookedair masstrajectorywas due to air masses beingtransported alongthe limb of the anticyclonecenteredin the
100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
------------------
20
2.0E-06 1.8E-06 ß . 1.5E-06
i -3E'06 ß 1.0E-06 7.5E-07
ii5'0E'07 i. 2.5E-07
• O.OE+00 25
30
35
40
45
50
55
60
latitude (øN) Figure9. Latitudinal cross section chartofPV (m• S-!K kg'!) along114øEat 0900JSTonJuly18,1994.Solid linesindicateisoplethof windspeed(m/s).The circleindicates wherethebackward trajectory,startingfrom0900 JST on July28, passedthrough.
16,940
TSUTSUMI EL AL.' TROPOSPHERICOZONEEVENTSAT MOUNT FUJI
-'.::-:-:-:-:-:..--:-:-.--:-:-:-:,--: ........... :........... -'......... :::-.--....'-•___•.:•!-...---'*• g---.-.,•". ......... •-••....-•••.. •i..,_.' :-.'..,,.':::?:.-,.-':::'-..•:::. ======================================================================== ".:-:-:-.
..... 1.8E-06 ß
ß
_!i:iii:i:i:i:!:::•!•!::::•d:':,' 2•.:A:'_..i'"'" :.... ::::•..':i.................. •::'• ............ ::::: ........ .......... :':•• '"*'---' ßß -'.'•[,",'-.-':•:!::'-.-':-'-'-•:::--':-':•:•-'-'::'•,.•:'•'g••!.•.-.'.-'.:-'::::::::-".-'.:::::::::::::::-'-'"-•.:..."". -•.."-':.',•: :;•-:•: ,'.-'.-'.:: :•i•(-':•ji •'":
45_: ................... ::::::::::::::::::::::::::: ...... :••. .............. .,.'"••" •
*
_'--'.:•
'":-..:-'.'•i '..::?..::::-'-'::-:::::i::: '" :':::::::':'::.::"&::.•5 _-'?_-:-'_."_:õ :::::::::::::::::::::::
;;iiiii?•i 1.5E-06 .:.:.:.:.:
:::':•'"":•i 1.3E-06
"•)..:j ')..:?:, 1.0E-06
5i:!:; :.,.':s .•(.. •!! •;..'•5'. '..::'(-'si.:.::::isisisiii! '"'-'•:,,"?.'5!5i:i:i5i5!555::,. -'::":'"':--ß ::::.-:.-':5': .•::".'. '•....'. -.'-.j.:..:..'• ?"' '"••'"'-'-'••••'..:'-:,.-'i5 '•,-'• '""ß ß
ß.'5::::::::.:• :..'..,.'::•:'..-: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :i:i:i:i::' ..:.x..-....::.::.:..:-$•.•:: .i i:!:.::?:':ii::':q. ::•.:•::::•::•::•
20 90
. .:.:--
•::y?::::.•.::............ . .:......
...... •••'"•'"•"t'""t"'• ••!••••i •••• I.•
1 I0
120
130
140
150
lO
longitude (øE) o
Figure13. Horizontal windspeed distribution {m/s)at200hPaat2100JSTonAugust 26, 1993.
16,942
TSUTSUMI EL AL.: TROPOSPHERIC OZONE EVENTS AT MOUNT FUJI
330
320
310
30
2O
9'0
100
1 I0
120
130
140
150
ongituae(øE) Figure 14. Horizontaldistribution of totalcolumnozone(DU) onAugust26, 1993.
backwardtrajectorystarting points. The final positions,which werereversedfor 10 days,rangedonly within 0.055ø in longitude and 2.5ø in latitude. This smalldispersiveresultmeansthat the trajectoryerror from the wind shearwas relatively small. The latitudinal cross section of PV along 114øE shows that an intrusion from the stratospherecould have occurred at 40øN (Figure 9). A cutoff low was locatedat 40øN, 114øE, and the trajectorypassedthroughthe high PV region(circlein Figure9). Although the trajectorydid not passany high PV region from July 19 to 22, the air masshasanotherpossibilityto be affectedby the stratosphericozone. A stationarycutoff low was located around55øN, 150-165øEduringJuly 21-28 from the view of the
The air masswas actually locatedon the edge of a region with
enhanced PV (>0.5x 10-6m2s-l K kg4) from2100JSTonJuly22 to 2100 JST on July 25 from the horizontalPV analysisat 320 K potentialtemperature level (Figure 10). Beryllium 7 has its sourcein the upper troposphereand lower stratosphere[Lal et al., 1958; Brost et al., 1991] and could be thereforeused as a tracer for stratosphericair [e.g., Viezeeand Singh, 1980; Raisbecket al., 1981; Kritz et al., 1991; Dibb et
al., 1992]. A highozoneconcentration at the uppertroposphere has two possiblesources:the stratosphereand photochemical production by anthropogenicgases. The coincidence of
enhanced ozoneand7Beat thesummit of MountFujion July
500 hPaweatherchart. The air masson thebackwardtrajectory 28, 1994, indicatesthat the air massorigin is the stratosphere over remainedat the southwestside of the cutoff low from July 22 to 25, althoughthe intervalto the cutofflow wascomparativelylong. The intrusionfrom the stratosphere on the southwestside of the cutoff low is known to be active [Price and Vaughan, 1993].
the Asian continentor north of Japan. Although the detailed process is not certain, irreversible vortexes in small-scale turbulence,as pointedout by Shapiro [1980], or stratospheric slenderstreamer,whichcouldnot be displayedwith the objective
I00
300.•..:•.•.;;•, 350 ....... .•.XX.....: ........... X..½-..'":.,,•..'"•'.:• "•('.:.-I •f'•'•:}'•. 2.5E•6
• 600 . -.•....?:....•.......;.:..::. 650
i
.,i•: """:"•::: 'Z.•:g"'....':•." '?• _!•:•:: ........... -
-:,•-::::• 1.5E•6
.....-.
900
-
1ooo 20
-'....
.... 25
30
35
40
45
50
55
60 • 0.0E+00
Figure15. Latitudinal crosssection cha• of PV (m• s'•K kg'•) along137øEat 2100JSTon August28, 1993. Solidlinesindicatethe isoplethof wind speed(•s). MountFuji is locatedat 35.4øNand 138.7øE.
TSUTSUMI EL AL.' TROPOSPHERIC OZONE EVENTS AT MOUNT FUJI 100 _ 90 _ 80 _ 70
16,943
650
analysisresolution,may play an importantrole. It is obvious, however,that the stratosphere/troposphere exchangecan occurin
645
summer in eastern Asia.
60
640
5O
3.3. SummerOzoneIntrusion from Upper Troposphere
4O 30
(August 1993)
635
20 10
ßI
0
11
--
iI
I ! I I I I I I I I I I I I 12
ozone(ppbv)
'
I I I I I I
A typhoontraversedover Japanon August27, 1993, and then an anticycloneoverspreadJapan from August 28 to 29. The ozoneconcentration increasedfrom 40 ppbv to above60 ppbv, but the humiditydecreasedrapidly aroundnoon on August28 (Figure 11). The ozone concentrationindicatedmaximum(80 ppbv) at 1600 JST on August28 and the enhancedozone(60-70 ppbv)lasteduntil 1900JSTon August29. Backwardtrajectories startingfrom 2100 JST on August28 and0900 JST on August29 (Figure 12) show that air massescame from central Russia,
630
13
-'-
humidity(%)
..... pressure (hPa)
windspeed(m/s)
36O
340 _-
2- 315 _
subsiding froma higheraltitude(-0.9 cm/sof the averagevertical speed). The 5700 m contourlinesat 500 hPa level (thick dashed linesin Figure12) showthattrajectories movedtogetherwith the southwest sideof theupperlayerpressure trough. The horizontal PV distribution at 318 K potentialtemperature level showshigh
_-• 270
330 --
2- 225 --
180
320 _
135 _
_-- 90
310 _
_--45
_
300
II I I I I II I I I I II I
I I I I I II
PV areas(>0.75x10'6m2 s-•K kg'•) werelocatedcloseto the
0
Figure 16. Hourly variationin ozone,pressure,humidity,wind speed,potentialtemperature,and wind directionfrom August11
trajectoriesduring transport(Figure 12). From the horizontal distributionof wind speedat 200 hPa at 2100 JST on August 26, 1993 (Figure13), thejet waslocatedalongthe southwest side of theupperlayerpressure troughandrotatingcyclonically around the points"B" in Figure 12. The high PV areasoccurredaround this point. The total column ozone distributionon August 26, 1993,fromtotal ozonemappingspectrometer (TOMS) version
to 13, 1993.
7 shows that the total ozone content exceeded 300 Dobson unit
11
12
13
potentialtemperature (K)
+ wind direction(o)
lOOOO 2000 70
G
lO 70
80
90
100
110
120
longitude(øE)
130
140
150
•
•
•
•
'•
E
altitude(m)
A: 2100 JST, August10 ......... C: 2100 JST, August8
B' 2100 JST, August9 D: 2100 JST, August7
Figure 17. Backwardtrajectories fromthe summitof Mount Fuji and5700 m contourlinesat 500 hPa level from August7 to 10. Backwardtrajectoriesstartedfrom 0900 JST on August11 (circlesandthick solidline), 2100 JST on August11 (rectangles andthin solidline), and0900 JST on August12 (diamondsandfaint line) at 318 K level. Symbolson trajectoriesindicatepositionsof the parcelsevery6 hours.Lettersindicatethe date and time of the closedsymbolpositions.
16,944
TSUTSUMIELAL.' TROPOSPHERIC OZONEEVENTSAT MOUNTFUJI 60
60
5O
4O
40 -• _
_
_
30
30• _
_
_
_
2O
20 9O
100
110
120
130
140
150
II I I[IIII[IIII[ItI I[IIII 90
100
110
120
130
IIII
140
150
longitude(øE)
longitude(øE)
Figure 18. Surfacepressure distribution (hPa)at 0900 JST on
Figure20. Contourmapat 500 hPaat 0900 JST on June12,
June 12, 1995.
1995.
downward at 35øN(Figure15). The (DU) (1 DU = 2.69 x 10'16molecules cm-2) at 35øN,115øE m2 s-lK kg-l) stretched potentialtemperature riseat 1600 JST on August28 reinforcesair masssubsidence by the cutoff low (Figure 11). Similar ozone enhancementoccurred on August 11, 1993. After a typhoon traversedthe Sea of Japan south to north on August 11, an anticyclone overspread Japan. The ozone concentrationincreasedto 80 ppbv from the noon of August 11 to 12 (Figure 16). Pressureand potentialtemperatureincreased and humidity decreased with increasing ozone. From the backward trajectory analysis (Figure 17), the air mass, which showed low ozone and high humidity in the morning on 45øN, 135øE,and the latitudinal crosssectionof PV along 137øE August 11, camefrom the subtropicalareaover the Pacific Ocean. shows thatthehighPV region (>1.0X10-6m2s-I K kg-l) intruded In contrast,the air mass, which showed high ozone and low to900hPalevelat45øNandanother highPV branch (>0.5x 10-6 humidity in the afternoonon August 11 and in the morningon August 12, came from the central Asian continentto Japan, subsidingfrom the uppertroposphereto lower troposphere. A stationarycutoff low was locatedaround50øN, 110ø-120øEfrom August 6 to 10. The 5700 m contour lines at 500 hPa 120 650 (Figure 17) show that backwardtrajectories,which startedfrom 100 --• • ß;,,, .. 648 2100 JST on June 11 and 0900 JST on June 12, movedtogether 80 646 with the southwestside of the cutoff low from August7 to 10, 60 644 subsidingfrom 8000 m to 4000 m. The averagedownwardspeed 40 642 of thesetrajectoriesfrom August 8 to 10 was 2.3 cm/s, and it 20 640 becamesloweras the trajectoryapproachedJapan. The air mass
(Figure14). The relationship betweentotal columnozoneand tropopause break is well established by Shapiroet al. [1982], Uccelliniet al. [1985], Rodgerset al. [1990], and Gougetet al. [1996]. Thus the causeof ozone enhancement which lasted about33 hoursfrom August28 to 29 is air masssubsidence from the uppertroposphereat the southwestside of the upper layer troughovertheAsiancontinentandtransport to overJapan. The ozone peak at 1600 JST on August 28, 1993, may be ascribed to stratospheric ozoneintrusionrelatedto thepresence of a cutoff low. This day, the cutoff low was located over
0
638
11
(m/s)
12
..... pressure (hPa) wind speed (m/s) I ....humidity (%) -- ozone(ppbv) i
:%.:
330
360
_
2- 315
_
:-:-.:•. 40
_
320 •
_---270 _
_:-225 _:- •8o
310 --
c
g?.:.• 30
_
_
_-- 135 _
300
_--90
_
30
_
_--45
_
-
290
o
20 90
potentialtemperature (K) wind direction(o)
100
110
120
130
longitude(øE)
140
150
........... lo ;::::::::: ::::::5::: ,..........
•':'• 0
Figure 19. Hourly variationin ozone,pressure, humidity,wind Figure 21. Horizontalwind speeddistribution(m/s) at 200 hPa speed,potentialtemperature, andwind directionfrom June11 to at 0900 JST on June 12, 1995. 12, 1995.
TSUTSUMI EL AL.: TROPOSPHERICOZONE EVENTS AT MOUNT FUJI
16,945
•: 1.5E-06 ::::5 ,:.:.:
..:..
'::::.
*•iil 1-0E-06
'"':•il 7.5E_07 5.0E-07
2.5E-07
90
100
110
120
130
140
ii?i•i?i O. OE+00
150
longitude(øE) Figure22. Horizontal PV distribution (m2s4 K kg4) at 500hPalevelat 0900JSTonJune12, 1995.
over the Asian continent does not usually approachJapan in midsummer,becausea semipermanent anticyclonecenteredin the Pacific Ocean is dominantover Japan. However, in this case,a southeastwardflow by the typhoon brought the continental air massto Japan. Consequently,summerair mass subsidenceobviously occurs over the Asian continentaroundupper layer trough and a cutoff low, resultingin the summerozone enhancementin the middle troposphere over Japan. Price and Vaughan [1992] and Beekmannet al. [1994] pointedout that many cutoff lows appear in Europe from June to July, contributing to the stratosphere/troposphere exchange. Cut-off lows also play an
move from June 11 to 12, overspreadJapan(Figure 18). The ozone concentrationincreased with increasing pressure and potentialtemperatureat the summitof Mount Fuji from June 11 to noon on June 12, and the maximumconcentrationof 108 ppbv wasrecordedat 1300 JST on June12, whereashumiditydecreased from the evening on June 11 (Figure 19). The coincidenceof pressureand potential temperatureincreasesand the humidity decrease suggests air masssubsidence from the uppertroposphere. A ridge was locatedover Japanand a cutoff low was locatedwest of Japanat 0900 JST on June12 from the 500 hPa contourmap (Figure 20). The horizontalwind speeddistributionat 200 hPa level,wherea jet is usuallylocated,showsthatthejet wasdivided important role in summerstratosphere/troposphere exchange over into the polar front jet and the subtropicaljet at 45øN, 95øE, and jet was intensifiedat the southandthe westpart of easternAsia. Wakamatsuet al. [1989] suggestedthat ozone the subtropical Japan (Figure 21). This strong subtropicaljet resulted in the intrudingfromthe stratosphere is transported to a lowerlayerby theanticyclone. They indicatedthatthe intrudingozonetook2-3 intrusionof the stratosphericair massnorth of it. The horizontal days to enhance ozone at ground level, and our results are PV distributionat 500 hPa level alsoshowsthat the high PV area was locatedat the southand the west part of Japan(Figure 22). consistent with theiranalysis. The longitudinalcross sectionof PV showsthat the high PV
region(>0.75X 10-6m2s-•K kg4) intruded from350 hPa,130øE
3.4. Intrusion Around Subtropical Jet in Early Summer (June 12, 1995)
Although a stationaryfront was located from west to east at 25øN from June 11 to 12, 1995, an anticyclone,which did not
100 150
200
to 500 hPa, 140øEat 0900 JST on June 12 (Figure 23). Similar stratospheric ozone intrusionby the subtropicaljet was reported by the aircraftmeasurement over the AtlanticOcean[Gougetet al., 1996].
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