Arctic Ocean or northern and central Canada. At 325 K (upper troposphere), "fresh" stratospheric input was evident on about 80% of the trajectories, most often ...
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 99, NO. D1, PAGES 1793-1804, JANUARY 20, 1994
Stratospheric/troposphericexchangeaffecting the northern wetlands regionsof Canada during summer 1990 A. ScottBachmeier, • Mark C. Shipham, • EdwardV. Browell,• WilliamB. Grant,• and John M. Klassa5'4 The Arctic Boundary Layer Expedition (ABLE) 3B was conductedover the northern wetlands regionof CanadaduringJuly and August 1990. Severalstratospheric/tropospheric exchangeevents were noted by zenith-lookingairbornelidar and in situ measurementsof ozone and other trace gas species. Isentropic trajectories and potential vorticity analyses are utilized to determine the frequency of stratosphericinputs which would have affected the troposphericcolumn over the Moosonceand Scheffervilleregionsand to describethe favored pathwaysof transportof stratosphericair arrivingat theselocations.At the310 K potentialtemperature level (middletroposphere), trajectorieshaving "aged stratospheric"values of potential vorticity at somepoint in their 5-day history arrived at Moosonceor Schefferville roughly40% of the time during the ABLE 3B study period, most often via large-scalesubsidenceenroutefrom" stratosphericinput regions"over the Arctic Oceanor northernand central Canada. At 325 K (uppertroposphere),"fresh" stratospheric input was evident on about 80% of the trajectories,most often associatedwith jet streakswithin the polar and Arctic jet streams. A case study is presentedwhich illustrates both of these general stratosphericinput processes. Even thoughresearchflights were conductedon only 43% of the dayscovering the ABLE 3B period, 68% of thoseflights The NASA Global Tropospheric Experiment/Arctic indicated some degree of stratosphericinput to the tropoBoundary Layer Expedition (GTE/ABLE) 3B was conducted sphere over eastern Canada. The irregular temporal distriover the northern wetlands region of central and eastern bution of flights (interflight periods of up to 5 days) adds Canada during July and August 1990 [Harriss et al., this uncertainty to the representativeness of this stratospheric issue]. A major component of this joint U.S.-Canadian input percentage. Therefore this paper will attemptto quanatmospheric chemistry program was ground-based mitify the frequency of stratosphere/troposphereexchange crometeorological towers near Moosonee, Ontario, and which would have affected the troposphericcolumn over the Schefferville, Quebec. In addition, airborne measurements Moosonee and Schefferville tower site regions during the of trace gases and aerosols were made within the boundary entire study period (including nonflight days). layer and free troposphere (below 6 km) using an instruReiter [1975] identified four processesresponsible for mented Lockheed Electra aircraft. Flight paths often instratospheric/troposphericmass exchange, the two most efcluded slow spirals in the vicinity of the towers to obtain fective being Hadley cell meridional circulations and largedetailed vertical profiles of the lower and middle troposcale eddy transportsin active jet stream regions. Since the sphere. The fluxes of trace gasesmeasuredon a "local" scale Hadley flux can be considerednegligible during summer,the at the tower sites could then be "scaled up" for comparison majority of significant stratosphericinput would result from with "regional" scale measurementsacquired by the aircraft. the meteorological features initiating large-scale eddy Twenty-two flights were conductedon 18 separatedays during the July 6 - August 15 time period. Stratospheric/ transportsnear the tropopause. Previous studieshave docutropospheric exchange events were noted on 15 of the 22 mented the processes of stratospheric intrusions into the flights, based upon airborne lidar [Browell et al., this issue] troposphere via upper tropospheric fronts and tropopause and in situ measurements of ozone and other trace gas folds associatedwith jet streaksIDanielsen, 1968; Danielsen species[Anderson et al., this issue;Talbot et al., this issue]. and Hipskind, 1980; Raatz et al., 1985; Keyser and Shapiro, 1986; Shapiro et al., 1987; O!tmans et al., 1989; Shapiro and Keyser, 1990] or in the vicinity of cutoff lows and polar vortices [Wei, 1987; Vaughan, 1988; Ebel et al., 1991]. In some cases, air of stratospheric origin has been shown to •LockheedEngineeringand SciencesCompany,Hampton,Virhave descended to ground level [Attmannspacher and ginia. 2AtmosphericSciencesDivision, NASA Langley ResearchCen- Hartmannsgruber, 1973; Lamb, 1977; Haagenson et al., ter, Hampton, Virginia. 1981; Johnsonand Viezee, 1981; Viezee et al., 1983; Chung 3College of William and Mary, Williamsburg, Virginia. and Dann, 1985; Wakamatsu et al., 1989]. The proximity of SNowat Alcatel Network Systems,Incorporated,Raleigh, North Carolina. the northern wetlands region to the mean positions of the polar vortex and the polar and Arctic jet streams (Figure 1) Copyright1994 by the AmericanGeophysicalUnion. would therefore contribute to the frequent occurrence of INTRODUCTION
summertime stratospheric intrusions into the lower and middle troposphere over the study area.
Paper number93JD02179. 0148-0227/94/93JD-02179505.00 1793
1794
BACHMEIERET AL..' STRATOSPHERIC/TROPOSPHERIC EXCHANGE Mean 500 hPa Heights (m) - 90070100 - 90081412
334 hPa at Moosonee (--8.5 km) and 322 hPa at Schefferville (-8.8 km). Following previous studies such as Shapiro et al. [ 1987],
potential vorticity valuesin excessof 1 x 10-5KhPa -• s'• were considered "stratospheric values." If potential vorticity values exceeded this threshold at any point along the trajectory, that point was considered to be a potential "stratospheric input," given that the synoptic situation acrossthat particular region was favorable. For example, if the air parcel was too low in the troposphere (pressure >700 hPa or so at 310 K) and no polar vortex or jet streak was in the immediate vicinity, potential vorticity values which reached or barely exceeded the threshold were not classified as stratospheric input regions. This eliminated the consideration of high-potential vorticity values which were found in regions of high static stability, such as temperature inversions associatedwith regions of quasi-stationary high-pressure ridges. It should be pointed out that our use of the term "stratosphericinput" assumesthat isentropic transport sufficiently describes the stratospheric/troposphericexchange process. However, small-scale turbulent processes and diabatic processes such as terrestrial/solar radiation, latent heating/evaporative cooling, and sensible heat exchange violate this isentropic assumption. These turbulent and Fig. 1. Mean 500 hPa height field (meters) for the Arctic Boundary LayerExpedition(ABLE) 3B period(July 1 - August14, 1990).Superim- diabatic processes are difficult to assess using standard posedare the meanpositionsof the 250 hPapolarandArcticjet stream meteorological data and as such are not accountedfor in this axesaswell as a compositeof all ABLE 3B flight paths. study. Since both mandatory and significant level rawinsonde data were utilized to improve the grid point analyses, the ANALYSIS METHODS vertical structure of temperature and wind shear was more An isentropic analysis and trajectory technique devel- accurately represented over regions of North America where opedby Haagenson and Shapiro [ 1979] was usedto compute such sounding data were available. Even though the spatial potential vorticity analyses and trajectories for this study. distribution of rawinsonde data over Canada was rather Analyzed grid point data from the U.S. National Meteorocoarse (often 600-800 km, compared to the typical 350 km logical Center (NMC) provided the initial "first guess"fields over the United States), spot checks of individual sounding of geopotential, temperature, and winds on a 2.5 ø by 2.5 ø profiles indicated that the objective analyses of potential latitude/longitude grid. Rawinsonde data were then introvorticity were very well suited for establishing the air parcel ducedto improve the analysis,using a multiple linear regreslocations relative to the tropopause. sion technique. Trajectories were calculated at 12-hour intervals along the 310 K and 325 K isentropic (constant RESULTS potential temperature) surfaces, backward in time for 120 Compositesof all 310 K and 325 K trajectories arriving at hours(5 days) from both Moosoneeand Schefferville. Maps of objectively analyzed potential vorticity were also gener- Moosonee and Schefferville are shown in Figures 2 through ated at 12-hour intervals. In addition, the NMC gridded data 5. During ABLE 3B the favored avenuesof transportseemed were utilized for the analysis of jet streaks (embedded iso- to be along two general corridors. The "Arctic" corridor comprised flow from the Arctic Ocean, Bering Sea, and tach maxima) within the polar and Arctic jet streams. Jet Queen Elizabeth Islands across the Northwest Territories streams were defined as regions along the 250-hPa pressure and Hudson Bay. The "Pacific" corridor consistedof transsurface (1 hPa = 1 mbar) having wind speedsin excessof 30 port from the Gulf of Alaska and North Pacific Ocean across m s-• [Bluestein, 1986]. the Rocky Mountains. Transport from the central and south-
The 310 K isentropicsurfacewas chosento representthe middle troposphere at levels below the maximum flight altitude of the aircraft. The mean pressuresof the 310 K trajectoriesarriving at Moosoneeand Schefferville were 571 and 548 hPa, respectively. Based upon the subarctic U.S. Standard Atmosphere (1966) for July at 60ø N, these pressurescorrespondto geopotential altitudes of approximately 4.6 and 4.9 km above sea level, respectively. The 325 K surface was representative of the upper troposphere,below the mean summertime jet stream level of 200 hPa [Lau et al., 1981]. Mean pressuresfor the 325 K trajectory arrivals were
ern United
States or the North
Atlantic
Ocean
and Labrador
Sea was less frequent. The long transport paths indicated by many of the trajectories (especially at 325 K) reflect the rapid flow associatedwith the polar and Arctic jet streams, and the cyclonic curvatures over the Gulf of Alaska and Hudson Bay regions reveal the semipermanent areas of low pressure which dominated the tropospheric flow during the period (see Figure 1). Trajectories along the 310 K surface which were subjected to "stratospheric inputs" during their 5-day history are depicted in Figures 6 and 7. Table 1 summarizessome
BACHMEIER ET AL.' STRATOSPHERIC/TROPOSPHERIC EXCHANGE 310K Trajectories, Moosonee (YMO)
1795
325K Trajectories, Moosonee
\
..
\
\
x
/ :.
,,.
/ .o
of all 5-daybackward trajectories alongthe325 Fig.2. Composite of all 5-daybackward trajectories alongthe310 Fig.4. Composite K surface which arrived at Moosoneeduring the study period.
K surfacewhich arrived at Moosoneeduring the studyperiod.
325K Trajectories,Shefferville(YKL)
310K Trajectories,Sheffervi!le(YKL)
/
\
\ /,
/
\
,,
/
/
ß // /
,. .,. ...
Fig.3.Composite ofall5-day backward trajectories along the310 Fig.5.Composite ofall5-day backward trajectories along the325 K surface whicharrivedatSchefferville during thestudy period. K surface whicharrived atSchefferville duringthestudy period.
1796
BACHMEIERET AL.' STRATOSPHERIC/TROPOSPHERIC EXCHANGE YKL
YMO Theta
= 310
Theta = 310
PTheta> I Trajectory
PTheta> I Trajectory
i
! , .....
.,.,,-
•
..
..
/
',• ..
•
/
Fig. 6. Moosonee trajectories along the 310 K surface which were subjectedto stratosphericinputs (large circles) during their 5-day history.
Fig. 7. Schefferville trajectories along the 310 K surface which were subjectedto stratosphericinputs (large circles) during their 5day history.
characteristics of the 310 K trajectories. For the Moosonee trajectories, two primary regions of stratospheric input are evident: the Arctic Ocean/Queen Elizabeth Islands and a swath from the Northwest Territories to Hudson Bay. These input regions were affected by intense polar vortices migrating across the Arctic Ocean or northern Canada and by jet streaks within the Arctic jet. A secondaryinput region over
propagatedthrough the Gulf branch of the polar jet. Trajectories arriving at Schefferville received the majority of their stratosphericinputs along a similar Arctic Ocean/Northwest Territories/Hudson Bay swath, with secondary input regions
the Gulf of Alaska
mum intensity (often > 50 m s'l), leading to the formationof
and western
Canada resulted
from lower-
ing tropopauses near the centers of cutoff Gulf lows and upper tropospheric fronts generated by jet streaks which
over the Gulf of Alaska/western
Canada and the Labrador
Sea/southern Greenland. Inputs across southern Canada occurred when jet streaks within the polar jet reached maxiupper tropospheric frontal zones or tropopause folds.
TABLE 1. Summary of 310 K (Middle Tropospheric) Trajectories Moosonee, Ontario
Schefferville, Quebec YKL
YMO 45%
Percentage of trajectories having stratospheric inputs
39%
Mean altitude of trajectory arrivals having no stratospheric inputs
597 hPa,-4.2
Mean altitude of all trajectory arrivals
571 hPa, N4.6 km
548 hPa,-4.9
Mean altitude of trajectory arrivals having stratospheric inputs
529 hPa,-5.2
524 hPa, -5.2 km
Number of stratospheric inputs
total
km
km
568 hPa, -4.6 km
km
total = 96
= 73
max = 9 per trajectory mean = 2 per trajectory km
max = 9 per trajectory mean = 2 per trajectory
Mean altitude of stratospheric inputs
480 hPa,-5.9
Subsidence of trajectories following strongest stratospheric input
max = 2.5 km mean = 1.2 km
max = 3.3 km mean = 1.3 km
455 hPa, -6.3 km
Percentage of trajectories experiencing subsidencefollowing stratosphericinput
76%
59%
BACHMEIERET AL.' $TRATOSPHERIC/TRoPOSPHERIC EXCIIANGE
\
1797
,,,
ß,
/
Fig. 8. Moosoneetrajectoriesalongthe325 K surfacewhichacquired Fig. 9. Schefferville trajectoriesalong the 325 K surfacewhich acquiredno stratospheric inputsduringtheir 5-day history. no stratosphericinputsduringtheir 5-day history.
The frequentlocationof the 325 K surfacecloseto (or someApproximately onehalf to two thirds of the 310 K stratocontributed to muchhigher values sphericinputsoccurredbetween3 and5 daysprior to arrival timeswithin)thestratosphere at the tower sites, and large-scalesubsidenceprevailed dur- of potentialvorticity, ashigh as 7.16 x 10-5K hPa-• s-• for ing the remainderof a significantportionof thesetransports. Moosoneetrajectoriesand 9.51 x 10-5K hPa'• s-• for those Mean values of subsidence were 1.2 to 1.3 km, with a arriving at Schefferville. Nearly two thirds of the 325 K maximum downward displacement of 3.3 km indicated by trajectoriesexhibited potential vorticity values exceeding one of the trajectories arriving at Schefferville. Most rates the stratosphericthreshold at the time of arrival. These of subsidence following stratospheric inputs were rather
gentle(lessthan 1 km d-• or 1.2 cm s-•),but a maximumrate
values are more characteristic of "fresh" stratospheric air. However, a smaller percentage of the 325 K trajectories
of 1.9 km in 12 hours or 4.4 cm s'• was calculated
for a experiencedsubsidencefollowing stratosphericinputs, and trajectory arriving at Moosonee. Due to subsynopticscale mean values of subsidence were only 0.8 km. Table 2 and turbulent mixing processes[Danielsen, 1968; Shapiro, summarizes some characteristics of the 325 K trajectories. 1980], potential vorticity would not generally be conserved Figures 10 and 11 represent a compositeof all regions duringtransportdownwardthroughthetroposphere.Potential along the 310 K and 325 K surfaceswhere the potential
vorticityvaluesneverexceeded2.98 x 10-5K hPa-•s-• on any
of the 310 K stratosphericinputs,and only about10% of the 310 K trajectories arrived at each of the tower sites still exhibiting potential vorticity values in excessof the stratospheric threshold. Such relatively low values suggestthat thesemiddle troposphericinputs were "aged" stratospheric air.
In contrast to the 310 K trajectories the majority of those at the 325 K level received several stratosphericinputs, with
some trajectories exhibiting stratosphericvalues of potential vorticity at every 12-hourinterval during their entire 5day history. The distribution of stratosphericinputs (not
vorticityvaluesexceeded2 and4 x 10-5K hPa'• s-• duringthe study period. The 2 x 10-5minimum value was chosento filter out any nonstratosphericpotential vorticity regions which may have just reachedor barely exceededthe strato-
sphericthresholdof 1 x 10-5,asdiscussedabove. Thesefiguresdepictthe arealcoverageof theportionof eachisentropic surface which was clearly in the stratosphereat one time or another. The Arctic Ocean, Bering Sea/Gulf of Alaska, and much of Greenland
and the Canadian
Arctic
islands can be
consideredthe principal potentialvorticity sourceregionsat 310 K, as well as HudsonBay and much of Quebec. At 325 K the entire area poleward of the mean polar jet axis (which shown) was similar to that at 310 K, except for a greater includes all of Canada) can be considereda sourceregion of number of inputs over the Gulf of Alaska and the North stratosphericvalues of potential vorticity. Pacific. Those 325 K trajectories having no inputs at all are Comparing Figures 10 and 11 with the mean summer shownin Figures 8 and 9. Most of thesetrajectoriesrepre(June-July-August)potentialvorticity fields at 300 hPa(Figsented slow, lower-altitude transport (below 400 hPa or 7.2 ure 12a) and 500 hPa (Figure 12b) derived by Lau et al. km) originating over the Rocky Mountain region or transport [1981], it canbe seenthat the composite4 x 10-5contoursfor from the eastern North Pacific.
this limited time periodcorrespond wellto themean1 x 10-5
1798
BACHMEIERET AL.' STRATOSPHERIC/TROPOSPItERIC EXCHANGE
Potential Vorticity, 310 K
Potential Vorticity, 325 K
i I
\/
'\ \
"•• ':' ::" Pe->4 x 10'sKhPa '1S'1 • ! Pe_>2x10 'sKhpa'1S'1 •
250 hPa Arctic Jet
•
250hPaPolarJet
.o
potentialvorticity valuesexceeding2 x 10-sK hPa'• s'• and4 x 10's K hPa4 s-LSuperimposedare the mean 250 hPapolar and Arctic jet
Fig. 11. Composite of all regions along the 325 K surface having potentialvorticity valuesexceeding2 x 10'• K hPa't s'• and 4 x 10-s K hPa4 s-LSuperimposedare the mean 250 hPa polar and Arctic jet
stream
stream
Fig. 10. Composite of all regions along the 310 K surface having axes.
(stratospheric threshold) contours. This suggests that the potential vorticity "source regions" defined here by the
axes.
High values of potential vorticity (exceeding 2 x 10'5) were evident on the 310 K composite over Schefferville
composite4 x 10-scontourscan be regarded as representa- (Figure 10), so it is likely that further large-scale subsidence
tiveof theapproximate arealcoverageof meanstratospheric over that region could bring air with a fresher stratospheric values of potential vorticity along quasi-horizontalsurfaces signature to lower altitudes than over the Moosonee region. in the middle (500 hPa) and upper (300 hPa) troposphere In fact, when comparing the 2- to 4-km layers over the two tower sites, Anderson et al. [this issue] found a greater during the summer season.
TABLE 2. Summaryof 325 K (Upper Tropospheric)Trajectories Moosonee, Ontario,
Schefferville, Quebec,
YMO
Percentage of trajectories having stratospheric input Mean altitude of trajectory arrivals having no stratospheric inputs
YKL
77%
83%
392 hPa, -7.4 km
400 hPa, -7.2 km
Mean altitude of all trajectory arrivals
334 hPa,-8.5
km
322 hPa, -8.8 km
Mean altitude of trajectory arrivals having stratospheric inputs
316 hPa, -8.9 km
309 hPa, -9.0 km
Number of stratospheric inputs
total = 459
total
max = 11 per trajectory mean = 7 per trajectory
max = 11 per trajectory mean = 7 per trajectory
km
= 514
300 hPa, -9.2 km
Mean altitiide of stratospheric inputs
295 hPa,-9.4
Subsidenceof trajectories following strongest stratospheric input
max = 2.8 km mean = 0.8 km
max = 2.0 km mean = 0.8 km
Percentage of trajectories experiencing subsidencefollowing stratosphericinput
5i%
44%
BACHMEIERET AL.' STRATOSPHERIC/TROPOSPItERIC EXCHANGE
1799
b) 500hPaPe
300hPaPO
//
./ \ \
,,
/
-r•I A 111#. The •nn lug/ x I0 -vK UUo-, 111# •-, u (!.0 x I0 -sK r•g. 12. Mean summertime•June-July-•ugust) potentialvorticity: (a) at 300 hPaand(b) at 500 UUo hPa4 s-') contour is highlighted [from Lau et al., 1981].
percentage of "stratospheric air" during flights in the Schefferville vicinity. A CAse STUDY: ABLE 3B FLIOItT 2 (JULY 9, 1990)
Flight 2 was a flux survey flight which was conducted over the Hudson Bay lowlands on July 9, 1990, between the
Fig. 13. The 3 ! 0 K Montgomery streamfunction analysis for flight 2, valid July !0, 1990 / 0000 UT, showingthe strongpolar vortex just east of Hudson Bay
hours of 1736 and 2322 UT. A strong polar vortex had intensified as it moved southeastwardacross Hudson Bay during the day (Figure 13). In addition, an eastward moving jet streak within the polar jet reached its maximum intensity
(wind speeds of 60 m s-l) just northeast of Lake Huron (Figure 14). Five-day backward trajectories arriving along
Fig. !4. Location of the 250 hPa polar jet streamduring flight 2, valid July 10, 1990 / 0000 UT.
1800 ;
BACHMEIERET AL.: STRATOSPtlERIC/TRoPOSPHERIC EXCHANGE ?
,
................ t............... +....4
\
',,
Fig. 15. Five-day backward trajectories (310 K) arriving along the flight path during flight 2.
Fig. 16. Five-day backward trajectories (325 K) arriving along the flight path during flight 2.
the flight path are shown for 310 K (Figure 15) and 325 K (Figure 16). The majority of the 310 K trajectories originated over the Arctic Ocean and depict a cyclonic transport aroundthe Hudson Bay vortex. At 325 K a similar transport is indicated for trajectories arriving along the northern portion of the flight region, but the rapid eastward flow associated with the polar jet is evident from the trajectories arriving along the southern portion.
spheric front [Bluestein, 1986]. In situ and remotely sensed data collected during this flight further support the occurrence of the two general processesof stratospheric input to the tropospheric column discussedin the previous section: (1) subsidenceof "aged" stratosphericair in the middle troposphere,as suggestedby the 310 K trajectories; the aircraft directly sampled two regions of stratosphericair between 4.4 and 5.0 km (potenSeveral of the 310 K trajectories received stratospheric tial temperaturesfrom 309 to 314 K), measuringdew points inputs over the Arctic Ocean and Queen Elizabeth Islands 2 as low as -40 øC and ozone mixing ratios around90 parts per to 5 days prior to arrival, but only the one trajectory at the billion by volume; (2) "fresh" inputs of stratospheric air to extreme northwest comer of the flight region exhibited the upper troposphere, as indicated by the 325 K potential potential vorticity values above the stratospheric threshold vorticity increases concurrent with the jet streak arrival; at the time of arrival. At 325 K the "Arctic" trajectories zenith-lookinglidar detectedthe presenceof areasof enhanced received several stratospheric inputs and arrived along the ozonemixing ratio (Plate la.) correlatedwith areasof reduced flight path with a mean potential vorticity of 4.67 x 10-sK relative aerosolbackscattering(Plate lb.) protrudingdownward hPa-• s-•. Such large values of potential vorticity indicate along southernportions of the flight region (closer to the jet that the tropopausehad descendedalong the western fringes streak);alongthe northernportionof the flight region,the tropoof the Quebec polar vortex, placing the 325 K surface in the pauseappearedunperturbed,asdepictedby thehorizontal"wall" lower stratosphere. The "Gulf of Alaska" trajectories, on the on the ozonedistribution(Plate 2a.) and the sharpaerosolledge other hand, received very few inputs during their 5-day (Plate 2b), bothnear 7.5 - 8.0 kin. history, arriving with a mean potential vorticity of only 1.83
x 10-sK hPa-• s-•. However, the potentialvorticities of all 325 K trajectories increased dramatically (by a factor of 2-3) during the day of the flight, concurrent with the approachof the 60 m s'• jet streak. The majority of the 310 K and 325 K trajectories exhibited their strongest subsidence(~1.0 km) during the day of the flight. The location of the core of the velocity maximum was such that the southeast(northwest) portion of the flight track was beneath the right exit (left entrance) region of the jet streak. These are the two regions beneath the jet streak level where sinking motion and divergence would be expected, contributing to the downward advection of stratospheric air through a folded tropopauseor an upper tropo-
CONCLUDING
REMARKS
The isentropic trajectories and potential vorticity analysespresented in this paper provide further verification of the assumed characteristics of upper tropospheric transport in an isentropic framework in the absence of diabatic processes. Since isentropic surfaces usually exhibit a pronounced downward (north to south) slope on the back (western) side of deep cyclonic systems, in addition to a climatological downward (north to south) slope, the results shown in Figures 6 and 7 and in Table 1 are expected. We also note from Figure 12 that transportfrom the north (as indicatedfrom mostof thetrajectoriesin Figures6 and7) wouldtypicallyimply
transportfrom regionsof higherpotentialvorticity.
BACHMEIER ET AL.' STRATOSPI-[ERIC/TROPOSPIIERIC EXCHANGE
FLUX SURVEY ABLE
HUDSON
3B
BAY LOWLANDFLIGHT
1801
KINOSHEO
2
LAKE
9 JUL 90
OZONE MIXING RATIO (PPBV) 0
20
40
60
80
I
I
I
I
I
14:40 14:50 I • I FRASERDALE
,
100 I
UT
15'00 I PT1
i
i
-10
10.
N LAT
E LON
Plate la Distributionof ozonemixing ratio obtainedfrom zenith-lookingairbornelidar overthe southernportionof the flight 2 region.
FLUX SURVEY ABLE
HUDSON
3B
BAY LOWLANDFLIGHT
KINOSHEO
2
LAKE
9 JUL 90
RELATIVE AEROSOL BACKSCATTER (IR) 0 I
, 11-
500
1000
I
1500
I
14:40 14:50 I , I FRASERDALE i
2000
I
I
•
15:00 I
2500 I
UT
,
PT1 i
-11
N LAT
E LON
Plate lb. Distributionof relativeaerosolscatteringobtainedfromzenith-lookingairbornelidar overthe southernportionof the flight 2 region
1802
BACHMEIERET AL..' STRATOSPHERIC/TROPOSPHERIC EXCHANGE
FLUX
SURVEY
ABLE
HUDSON
BAY LOWLAND FLIGHT
3B
- KINOSHEO
2
LAKE
9 JUL 90
OZONE MIXING RATIO (PPBV)
PT1 i
0
20
4o
6o
8o
lOO
I
I
I
I
I
I
15'20 I COAST
15:30 I , KINOSHEO
,
i
15'40 I
15:50 I PT2
,
i
UT
i
10-
-10
