JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 105, NO. D3, PAGES 3757-3769, FEBRUARY
16, 2000
A casestudy of transport of tropical marine boundary layer
and lower troposphericair massesto the northern
midlatitude upper troposphere
WilliamB. Grant,• EdwardV. Browell,• CarolynF. Butler,2 MartaA. Fenn,2
MarianB. Clayton,
2 JohnR. Hannan,
3 HenryE. Fuelberg,
• DonaldR. Blake,4
NicoiaJ. i•iake,• tSera•c•
L. Gregory,BriantJ. Heikes,-Gienw. Sachse,HanwantB. Singh,
7 JulieSnow,s andRobertW. Talbots
Abstract. Low-ozone
(< 20 ppbv)air masses
wereobserved
in theuppertroposphere
in
northern midlatitudesover the eastern United Statesand the North Atlantic Ocean on
severaloccasions
in October1997duringtheNASA Subsonic
Assessment,
Ozoneand
Nitrogen
OxideExperiment
(SONEX)mission.Threecases
of low-ozone
air masses
wereshownto haveoriginated
in thetropicalPacificmarineboundary
layeror lower
troposphere
andadvected
poleward
alonga warmconveyor
beltduring
a synoptic-scale
disturbance.
The tropopause
waselevated
in theregionwiththelow-ozone
air mass.
Stratospheric
intrusions
accompanied
thedisturbances.
Onthebasisof stormtrackand
stratospheric
intrusion
climatologies,
suchevents
appear
to bemorefrequent
from
September
throughMarchthantherestof theyear.
1. Introduction
above normal 36.9% of the time, normal ozone 56.0% of
the time, and below normal 7.1% of the time. When
There have been a number of observations of low-ozone
air massesin the northern midlatitudes that have been traced
anticyclonic
weatherpatternswith southerlyflow existed,
total ozone was below normal 28.5 % of the time, normal
to transportfrom the tropicalmarineboundarylayer or 66.8% of the time, and above normal 4.7% of the time.
lowertroposphere.
Table1 givesa summary
of a number When only flow direction was considered,above-normal
of suchobservations,as well as somefor which the source
total ozonewas observed30.1% of the time for northerly
regionwas not identified. Sincesuchdata are generally flow, while below-normal ozone was found 26.5% of the
reported
duringintensive
fieldcampaigns
or othershort-term
time for southerlyflow.
measurement
programs,they cannotbe usedto developa
The SubsonicAssessment,
Ozone and NitrogenOxide
climatology
of low-ozoneevents. However,theydo help
Experiment
(SONEX)
mission
providedan opportunityto
establishthat suchtransportdoesoccur.
obtain
more
information
regarding
the transportof lowIn addition, total ozone over central Europe has been
ozone air from the tropics to northernmidlatitudes. The
studied as a function of weather pattern [Kalvova and
purpose of SONEX was to study the upper tropoHalenka, 1995;DubrovskyandKalvova,1997]. The obsersphere/lowerstratospherein and near the North Atlantic
vation was madethat when cyclonicweatherpatternswith
flight corridor to better understandthis region of the
northerly flow at 500 hPa existed, total ozone there was
atmosphere
andhow civilianair travelmightbe affectingthe
atmosphericchemistry [Singh et al., 1999]. Bases of
]AtmosphericSciencesResearch,NASA Langley Research operationsincludedNASA Ames(Moffett Field), California
Center, Hampton, Virginia.
(37.4øN, 122.1ø-W);Bangor, Maine (44.8øN, 68.8øW);
2ScienceApplications
International
Corporation,
Hampton, Shannon,Ireland (52.7øN, 8.9øW); and Lajes, Terceira
Virginia.
Island, Azores (38.8øN, 27.1øW). It took place from
3Department
of Meteorology,
FloridaStateUniversity,
Tallahas-
October 13 to November 12, 1997.
see.
4Chemistry
Department,
University
of California,Irvine.
5Center
for Atmospheric
Chemistry
Studies,Graduate
Schoolof
2.
Low-Ozone
SONEX
6AerospaceElectronicSystemsDivision,NASALangley
Oceanography,Universityof RhodeIsland, Narragansett.
ResearchCenter, Hampton, Virginia.
Air
Masses
Observed
Oil
Low-ozoneair masseswere observedon four flights
7NASAAmesResearch
Center,Moffett Field, California.
Slnstitute
for theStudyof Earth,Oceans,
andSpace,
University duringSONEXfromOctober13to 23, 1997(seeTable2).
of New Hampshire,Durham.
Copyright2000 by the AmericanGeophysical
Umon.
Papernumber! 999JD901022.
0148-0227/00/1999
JD901022 $09.00
Platei showsa pronounced
exampleof low-ozoneair in the
uppertroposphere,
observed
onthetransitflightfromNASA
AmesResearchCenterto Bangor,Maine, on October13.
Thisatmospheric
crosssection
of ozonewasobtained
using
a combination
of datafrom the NASA LangleyResearch
Center'sairborneUV differential
absorption
lidar (DIAL)
3757
3758
GRANT
ET AL.:
TROPOSPHERIC
TRANSPORT
FROM
TROPICS
TO MIDLATITUDES
Table 1. Observations
of Low-Ozone
Air Masses
Transported
FromtheTropicalMarineBoundary
LayerandLowerTroposphere
to the
UpperTroposphere
at NorthernMidlatitudes.
Dates
Latitude,Longitude
Altitude,
Instrument
km
Ozone
Authors
Concentration,
ppbv
Midtroposphere
Tropicalsoumeregion,
observed in Ariantie Ocean
32.3øN, 64.8øW
11-12
52.S,øN,4. løW
11-12
35øN-59øN,9øW-92øW 6-15
ECC sonde
ECC sonde
UV DIAL
18
2
18
27øN, 139øE
12-14.5
UV DIAL
<20
35.4øN,138.7øE
3.8
UV absorpt. 18
Koike et al. [1997]
Tsutsumiet al. [ 1998]
Unknownsourceregion
May 2, 1993
May 29, 1997
August4, 27, 1993
38.8øN, 27.1øW
47.5øN, 11.1øE
32.3øN, 64.8øW
7-9*
3-5//
10-14'
ECC sonde
UV DIAL
ECC sonde
Oltmans et al. [1996]
Eisele et al. [1999]
Oltmanset al. [1996]
Lower troposphere
September16, 1991
48øN, 133øE
1.5-2.5
UV DIAL
26.9øN,128.3øE
0.02
UV absorpt. 20-25
April 23, 1993
Juy
October 13-23, 1997
Oltmans et al. [1996]
Davies et al. [ 1998]
presentstudy
Tropical sourceregion,
observed in Pacific Ocean
March 4, 1994
August 11, 1993
October
9, 1991
20-30
20-30
20-30
Browell et al. [ 1996]; Merrill [ 1996]
Aldmotoet al. [1996]
* nobackward
trajectory
analyses
wereperformed
todetermine
whether
thelowozone
hadcomefromthetropics.
//backwardtrajectorycalculations
determined
thattheair masscamefrom25øN,60øW.
system
[Browell, 1989;Richteretal., 1997;Browelletal.,
the intersection
of the tropospheric
background
ozonevalue
with the trend in the stratospheric
ozone. This generally
occursnear a value of 100 ppbv. The groundto 18 km
evidentin themiddleof thelow-ozone
region.Moretypical ozonecolurn variesfrom 65 Dobsonunits(DU) outsidethe
ozonevaluesfor this time and placeare 40-55 ppbv, as low-ozoneair massregionto 20 DU inside. Note that 1 DU
measured most of the time on the SONEX mission. A
representsa milliatmosphere
cm of ozoneat 760 torr and
pronounced
stratospheric
intrusionis alsoevident
justto the 293 K.
eastof the Rocky Mountains. As will be discussed
below,
The UV DIAL/in sireozoneprofilesfor October15 and
a synoptic-scaledisturbancewas associatedwith both the 20 were similarto thatfor October13. The tropopause
in
southerly
transportof the tropicalmarineboundary
layer thelow-ozoneregionwasnear 15 kin, andstratospheric
air
(MBL) air and the descentof the stratospheric
air. The was observedon one or bothsidesdownto 3-4 km, with the
elevated
ozonein thelowertroposphere
between
Pittsburgh, 100-ppbvcontourdroppingto 6 km on October15 and9 km
Pennsylvaxfia,and Albany, New York, is attributedto on October20. On October23, only the latitudinalrange
photochemical
smog[Grant et al., 1998]. The Total Ozone 55ø-58øN
wassampled,anda 2-kmlayerof low ozone(22MappingSpectrometer
(TOMS)imagefor thatday(Plate2) 40 ppbv)wasfound,alongwithoccasional
valuesashighas
clearly showshigh column ozone associatedwith a low 65 ppbvin the 6-8 km region. The TOMS imagefor this
tropopause
nearthe RockyMountainsandlow columnozone day showsincreasedcolumnozone to the northeastof the
associated
witha hightropopause
to theeastof that. Figure flight track. The ozonecolurn from the groundto 16 km
1 showsthe UV DIAL/in situtropospheric
columnozone for October 15 varied from 20 DU to 90 DU, while the
andthesurface
to 18km columnozoneaswellasthetropo- ozone column from the groundto 17 km on October20
1998] and in situ measurements
[Gregoryet al., 1996]
onboardthe NASA DC-8. Valuesas low as 18 ppbvare
pauseheightalongtheOctober13 flighttrack. Thetropopauseheightwascalculated
fromtheUV DIAL data,being
varied from 8 DU to 70 DU.
Severalapproaches
wereusedto verify thatthelow-ozone
Table2. Parameters
of Low-Ozone
Observations
andComparisons
During$ONEX
Flight
Date
Latitude
Longitude
Altitude,M'mimum
O3,
km
ppbv
Negative
PV*
3
Oct. 13
39ø46.5øN
92ø-64øW
6-14
18
yes
4
6
7
Oct. 15
Oct. 20
Oct. 23
54ø-55øN
35ø43øN
55ø-59øN
60ø42øW
9ø-12øW
9øW
5-13
7-15
9-12
22
18
22
yes
yes
*The valuesarejust slightlynegative.
no
GRANT
ET AL.:
TROPOSPHERIC
TRANSPORT
FROM
TROPICS
TO MIDLATITUDES
3759
Ames to Bangor
SONEX
13 Oct 97
Flight 3
Ozone (ppbv)
20
40
60
I
16:00
I
17:00
I
I
I
18:00
!
I
,I
19:00
=
80
I,
,
I
100
I
I
20:00
,
,
,.I
21:00
,
,
,
I
22:00
I i
UT
.
Pittsburgh Albany Bangor
20--
--2O
--0
38.13
39.58
39.29
38.68
41.71
45.37
46.49
N Lat
-95.12
-84.65
-76.17
-67.68
-63.68
E Lon
!
-116.19
-105.67
Plate 1. UV DIAL and in situ ozonedataobtainedon October13, 1997, duringthe flight from NASA
Ames, California, to Bangor, Maine. The vertical and horizontalresolutionsare 300 m and 70 km,
respectively,and the measurement
precision/accuracy
is 5 ppbvor 10g3,whicheveris larger. The black
regionsrepresentozonein the stratosphere
(concentration> 100 ppbv);the white regionsindicatemissing
data. The dottedline at the bottom is the surfaceelevation. There is a stratospheric
intrusioncentered
near 95øW.
air seenin northernmidlatitudesoriginatedin the tropical
MBL: backwardtrajectoryanalysis;examinationof potential
vorticity levels; and comparison of molecular species
concentrations
foundat midlatitudecomparedto the tropical
MBL.
3. Backward Trajectories
hPa. Thedataare processed
usinga cubicsplineprocedure
within the trajectorymodelin orderto interpolate
the data
to equally spaced5-hPa increments. Dependingon the
flight, 6-8 pressurelevelssomewhere
in the rangeof 100
hPato 400 hPa (flight 7), 500 (flight6), 550 (flight3), or
600 (flight 4) hPa wereused. Data pointswerecalculated
each15 minutesof flight time (-•210 km). The backward
trajectories
wentback 10 days,with an arrow indicating
Backwardtrajectoriescan be usedto indicatewhere the eachday.
air massesoriginated. Backwardtrajectorycalculations
Figure 2 showsthe backwardtrajectories
calculatedfor
were run at Florida StateUniversityusinginputsfrom the
along
EuropeanCentre for Medium-RangeWeather Forecasts flight 3 on October13, 1997. All of theair masses
of
0ECMWF)in a kinematicanalysisinvolvingtheu, v, andw the flight track west of 70øWhad originsequatorward
componentsof the wind [Fuelberg et al., 1996]. The 20øNandat severalpressure
levels. Thebackward
trajectoECMWF data are suppliedwith a horizontalresolutionof ries for arrival at 300 hPa all showascentnear 10øN, which
zone(ITCZ), while at
2.5øby 2.5ø and 15 pressure
levelsin theverticalup to 100 is nearthe intertropicalconvergence
3760
GRANT
ET AL.'
TROPOSPHERIC
TRANSPORT
FROM
TROPICS
TO MIDLATITUDES
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GRANT ET AL.:
TROPOSPHERIC
TRANSPORT FROM TROPICS TO MIDLATITUDES
3761
Plate 3. GOES-8 imagefor October13, 1998, with PV modeloverlay.
The injectionof ozone-richair into the troposphere
via
< 150 hPa (not shown),therewasgenerallydescent.These
intrusions
hasbeenextensively
studied[Danielbackwardtrajectoriesalongwith the stratospheric
intrusion stratospheric
shown in Plate 1 are consistent with the slantwise baroclinie
motion which dominatesmidlatitudesynoptic-scale
disturbances. GOES-8 water vaporimageryfor thisday (Plate3)
showsan elongatedband of cloudinessassociatedwith the
leadingedgeof a majortrough-ridgesystemat approximately 90øW (1830 UT). The troughaxis is characterizedby
confluenceof descendingdry stratospheric
air to the west
and ascendingmoist convectiveboundarylayer air to the
east [Browning, 1990]. The lfigh ozone mixing ratios
encounteredat 10 kin and 1800 UT are found within the dry
stratosphericintrusionwhile the broadbandof low-ozone
mixing ratios encounteredat 10 kilometersbetween1900
and 2200 UT is found within the ascendingair.
Cooper et al. [1998] also reported stratospheric
air
comingdownto meeta "warmconveyorbelt" (WCB). The
GOES imagein their Plate 1 clearlyshowsa WCB off the
east coast of the United States with a cold front to the west
of it. They foundthat stratospheric
air was generallyfound
behind a cold front, but not ahead of the front.
Harrold
[1973] presented
an earlyanalysisof theWCB. SuchWCBs
typically have a width of 100-1000km, a depthof a few
kin, and initially flows parallel to and in advanceof a
surface cold front. Precipitationis also formed in an
extensivemidtropospheric
flow.
sen and Mohnen, 1977; Danielsen, 1980; Browell et al.,
1987]. Danielsen and Mohnen [1977] statethat ozone-rich
air is transportedinto the tropospherewith each major
cyclonicdevelopment.
However, the transport of ozone-poorair from the
convectiveboundarylayer into theuppertropospherevia the
WCB has received less attention [Bethan et al., 1998]. This
transport occurs along the WCB of northward moving,
saturated
mature
air
which
mid-latitude
lies ahead
disturbances.
of the confluence
line
in
The southern end of the
WCB lies within the convectiveboundarylayer while the
northern end extendsinto the upper troposphere. Latent
heat releaseassociatedwith frontal precipitationresultsin
diabatic ascent of the saturatedboundary layer air along
surfacesof constantequivalentpotentialtemperature. On
October13 the WCB extendsfrom Baja California(20øN)to
centralOntario(55øN)(seePlate3). The origin of the lowozonemixing ratiosshownin Plate 1 is likely to be within
the convectiveboundarylayer at the southernend of the
WCB.
Most of the backwardtrajectoriesfor flight 4, October
15, originatedequatorwardof 20øN, this time associated
with a strongconvective
updraftassociated
with the300-hPa
air mass5 daysprior to arrival, followedby moregradual
3762
GRANT
ET AL.'
100
- Ozone
TROPOSPHERIC
TRANSPORT
FROM
TROPICS
TO MIDLATITUDES
Column
-
2O
8O
15
E
D 60
o 40
N
o
2O
o
15
16
17
18
19
20
21
22
23
Time, UT
Figure 1. Troposphericozone colurm•sand tropopause
heightdeterminedby the UV DIAL/in situ
instrumentsonboardthe DC-8 for the SONEX October13, 1997 flight.
ascents.For flight 6, October20, someof the flighttracks 1996;$inghetal. , 1996;NewelletaL, 1997;BrowelletaL,
originated
below20øN,whilefor flight7, October23, only 1998; Fenn et aL, 1999]. This is dueto net ozonedestruca few of the backwardtrajectorieshad suchorigins.
tion resultingfrom photolysisof ozone and water vapor
duringhigh UV irradianceand the production
of peroxy
radicalsthroughreactions
withcarbonmonoxide
or methane
4. Potential Vorticity (PV)
in an atmosphere
low in precursors
for ozoneformation
Potentialvorticitycan alsobe usedto help identifythe [Thompson
et al., 1993;Monkset al., 1998].
originof the low-ozoneair masses.As shownby Browell
Concentrations
of othertracespecies
canprovideaddi-
et al. [1987, 1996], Beckmannet al. [1994], Newell et al. tional evidence that the low-ozone air massesobserved in
[1997], Fennet al. [1999], and referencestherein,thereis northern
midlatitudes
hadtropicalMBL origins.ThePEMa highcorrelation
betweenthePV andozoneof stratospheric TropicsA data set (southern
Pacificfrom August30 to
origin in the troposphere. Both PV and ozoneare well
October
6,
1996)
[Fennet
al.,
1999]includes
tracespecies
conservedin the lower stratosphere.However,the correlaconcentrations
in thetropicalMBL. Thecategory
of neartion decreasesat lower altitudesin the troposphere[Beck- surface(NS) air includesdata obtainedwithin 3 km of the
mannet al., 1994]. Plate 3 hasPV modelproductsoverlaid oceansurface,with abouthalf of thedatacomingfromthe
on the GOES-8 image, clearly showingthat the two hightropicsand the otherhalf from southern
mid andhigh
column-ozone
regionsin the TOMS imagewere relatedto latitudes.Another
category
calledreference
(REF)includes
high PV at 238 hPa. In addition,sincethe sign of PV
datawhichare within20% of the reference
ozoneprofile
changesfrom positivein the northernhemisphere
(NH) to and did not havehigh aerosolloading. It did not include
negativein the southernhemisphere
(SH), any findingof data from the MBL. The values for the NS and REF cases
negativePV wouldalsobe indicativeof transportfrom the are included in Table 3. Some comments can be made about
tropicsto northernmidlatitudes.In fact, sometransportof theagreement
betweenthePEM-Tropics
A NS andSONEX
air masses from the NH
to SH was found in the Pacific
low-ozoneair masses.The threeshort-lived(2 days)ocean
sourcespecies,CH3I, CHBq, and CHIC1, had the best
agreement
withtheSONEXvalues,asmightbeexpected
for
rapid transportfrom the tropics to midlatitudes. The
peroxidesconcentrations
were muchlower in SONEX than
in PEM-TropicsA, which is reasonable
sincethey are
water-soluble.
Theotherspecies
for whichcomparisons
can
be made had higher concentrations
for SONEX than for
5. Concentrationsof Molecular Species
PEM Tropics-A. Peroxyacetyl
nitrate(PAN), whichhasa
Ozonemixing ratiosin the tropicalMBL are low, on the highsourcein thestratosphere,
wasmuchhigherin SONEX
order of 5-20 ppbv [Routhieret al., 1980;Browellet al., air masses
thanin PEM-TropicsA NS air masses,
suggestExploratoryMission-TropicsA (PEM-TropicsA) data set
[Fennet al., 1999]. For SONEX, severalflightsincluding
that of October13 showednegativevaluesof PV (seeTable
2). Modified PV citedhere was from the GoddardSpace
Flight Center/Data Assimilation Office (GSFC/DAO)
assimilationmodel [Thompsonet ai., i999].
GRANT ET AL.'
a)
TROPOSPHERIC TRANSPORT FROM TROPICS TO MIDLATITUDES
3763
60
40
2o
- 140
b)
200
,
,
- 120
,
- 100
-80
-60
,
,
,
,
,
,
96
120
144
'
168
'
192
'
216
300
4OO
5OO
600
700
8OO
9OO
b
1000
0
•
24
'
48
'
72
240
Hours Back
Figure2. (a)Backward
trajectories
forflight3, October
13,1997,at300hPa(9.2km)showing
thatmuch
of theairmass
sampled
hadorigins
in thetropical
Pacific
Ocean.
(b)Same
asla, butshowing
thevertical
motion of the air masses.
ing thattherewassignificant
mixingfrommid andupper to northernmidlatitudes.They obtainedbottlesamplesas
well asmeasuring
CO, NO, andNO• at 46.4øN,10.6øWfor
troposphere
in the SONEX air masses.
Comparisons
canalsobe madewithdatafromNS and an aircraftaltitudeof 4 km. Their values,reportedin their
background
air masses
fromPEM-WestA [Browellet al., Tables 1 and 2, while lower for short-livedspeciesthanthe
1996]. ThePEM-WestA valuesweresometimes
higherand adjacentair mass,are generallymuchhigherthanobserved
sometimeslower thanthe PEM-TropicsA values.
duringSONEX. This suggests
thatthe air masses
reported
Bethanet al. [1998] alsomeasuredconcentrations
of trace by Bethanet al. may have alreadymixedwith preexisting
species
in an air masstransported
fromthesubtropical
MBL mid-latitude air.
3764
GRANT
ET AL.:
TROPOSPHERIC
o
TRANSPORT
FROM
TROPICS
TO MIDLATITUDES
GRANT ET AL.: TROPOSPHERICTRANSPORTFROM TROPICSTO MIDLATITUDES
3765
6. Synthesis
highestozonevalueswhile the period from Septemberto
April or May hasthe highestvariability[seealsoThouretet
Thus, three ways were usedto checkthat the low-ozone al., 1998]. Thusthe SONEX periodoccurredduringa time
air seenin northernmidlatitudesoriginatedin the tropical with aboutaveragevariability. Note thatmostof the ozone
Pacific MBL: backward trajectories;PV analysis;and excess and deficit cases occur within 2-4 km of the seasonal
concentrationsof trace speciesin comparisonwith those averagetropopauseheight. This is consistentwith the ozone
found earlier in the tropical MBL. Backwardtrajectory distributionshown in Plate 1 in which a synoptic-scale
calculationsand PV could each be used independentlyto disturbance
involvesbotha stratospheric
intrusionandlongdeterminethe presenceof tropicalMBL air in the northern rangetransportof low-ozoneair from the tropicalMBL.
mid-latitudeupper troposphere. Concentrationsof trace
specieswas mostusefulfor oceansourcespecieswith short 7.2. Storm Track Climatologies
residencetimes, CH3I, CHBr3, and CH3C1. Together,the
Storm track climatologiescan also be used to suggest
three approaches
make an strongcasethat the air masses
camefrom the tropicalPacificOceanwith the tropicalMBL
when WCB transport of tropical MBL air to northern
midlatitudesmight occur. Blackmonet al. [1977] provided
propertiesintact.
an early analysisof NH Atlantic and Pacific Oceanstorm
tracks, which generally occur during fall and winter.
7. ClimatologiesRelated to Low-Ozone
Hoskinsand Valdes [1990] point out that the warm oceans
Transport From the Tropical MBL and Lower
Troposphere
off the east coasts of the cold North
American
and Asian
continentsprovide the conditionsin which winter storm
tracks are inevitable. However, suchconditionsare lacking
in the SH so storm tracks are more extended (130ø in
7.1. Ozonesonde Results
longitudeover the Atlantic) and less deftmite[Jamesand
Ozonesondes
can be usedto provideclimatologicaldata Anderson, 1983].
Chang [1999] examined the characteristicsof wave
regarding the occurrenceof low ozone in the northern
packets
in theuppertroposphere
for seasonal
andhemisphermidlatitudes. Austin and Follows [1991] used the 20-year
ozonesonderecord at Payerne,Switzerland,finding that the ic variations. The 300-hPa zonal wind was muchhigher in
frequencyof stratospheric
intrusionsat 300 hPa was maxi- the NH in winter (> 60 m s'l) thansummer(> 20 m s't),
and standard deviations of the 300-hPa v' for 1980-1993
was
mizedin late winter/earlyspringand minimalduringthe
summer. Beckmannet al. [1994] providedtropospheric highin the NH in winter,with the highestvaluesextending
ozoneclimatologies
usingBrewer-Mastozonesonde
datafor from the mid PacificOceanto northernEurope. Meridional
theObservatorie
deHauteProvence,
southern
France(44øN, groupvelocitieswere muchhigherin theNH for winterthan
6øE). The ozonein the5-10-kmregionwaslowestduring for summer. This analysisalso supportswinter as having
October-March,droppingbelow 40 ppbv on average, more troposphericpolewardtransportthan summer.
compared
with over60 ppbvduringthemiddleof theyear.
Similarresultswere shownfor otherEuropean
ozonesonde 7.3. Stratosphericintrusion climatologies
stations. Also, the heightof the 120 ppbv contourwas
Sincethe threelongflighttrackobservations
of upper
shownto be highestfrom September
thoughNovember, tropospheric
low ozonemasses
transported
fromthetropics
rising above 12 kin.
the early 1990s. The only low-ozoneoccurrences
of note
occurredin conjunctionwith stratospheric
intrusions,it
seems
thatsuchcoupling
maybefrequent.Thisassumption
is supported
by Danielsenand Mohnen[1977]. Thusthe
climatologyof stratospheric
intrusionsis a secondarea of
arepresented
in Table1. A tropicalsource
wasindicated
by
backwardtrajectories
for the April 23, 1993Bermuda
data
investigation.
Cooper et al. [1998] reviewed a numberof studieson
Oltmanset al. [1996]provideozonesonde
dataplotsfor
several stations in the Atlantic Ocean from 32øN to 65øN in
[Oltmanset al. , 1996].
stratosphere
intrusions,
findingthatmostof the papers
The electrochemical
concentration
cell (ECC) ozonesonde reported
a higherfrequency
of stratospheric
intrusions
in the
data for WallopsIsland, Virginia (37.5øN/75.3øW)for the
periodJanuary5, 1979 to December22, 1992 [Pierceand
Grant, 1998;Thouretet al., 1998]werealsoreprocessed
to
fall-to-spring
period
intheNH. Johnson
andViezee
[1981]
foundozone
intrusions
in vimudly
everytrough
thatthey
sampled
overthecentral
United
States
inthefallandspring
developa climatology
of low-ozone
air masses
overa point of 1978. Beckmann
et al. [1997]reported
the seasonal
in the easternUnited States. The WallopsIslandozone- variation
of stratospheric
air injections
at the Zugspitze
sondes
wereusedsincethereis a longperiodof continuous (2964m abovesealevel(asl))andWank(1780m asl)
measurements,
and sinceit representsnortherncontinental
mountain
stations
in Germany.Duringtheperiodfrom
September
toApril,Wankhada highnumber
ofevents
per
study. Figure3 showsthemeanozonemixingratiobelow month
(7-12permonth,
median
equal
to8)asdidZugspitze
the actualtropopause
with the dataaveragedmonttfiy,as (13-28permonth,
median
equalto 17),whileduring
the
midlatitudes.
A total of 425 ozonesondes were used in the
well asthefrequency
of ozoneexcesses
anddeficitsgreater period
Mayto August,
Wankhada lownumber
(1-4per
than30% from themonthlymean. The 100-ppbvcontour month),
whileZugspitze
hada moderate
number
(9-15per
line is lowerduringthemiddleof theyearthanat theendof month).
the year, and is significantly
belowthe meantropopause Beckmannet al. [1997] also showthe distributionof the
heightin the middleof the year, but aboveit at the endof
annualmeandistribution
of the globaltropopause
folding
the year. The period from April to Septemberhas the activityfor 1984-1993with a 10ø grid spacing.The loca-
20
'
'
'
I
'
'
'
I
'
'
'
I
'
'
'
I
'
'
'
I
'
'
'
A
-
15
v
lO
0
2
4
6
Time (months)
8
10
2
20 'B ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' '
--35--
5
0
2
4
6
Time (months)
8
10
12
Figure3. (a) Themeanozone
mixing
ratiobelowtheactual
tropepause
withthedataaveraged
monthly
usingECCozonesondes
forWallops
Island,
Virginia.Thedarklineis themonthly
meantropepause
height.(b)Thefrequency
ofozone
excesses
• 30%above
themonthly
mean.(c)Thefrequency
ofozone
deficits < 30% below the monthly mean.
GRANT ET AL.'
TROPOSPHERIC TRANSPORT FROM TROPICS TO MIDLATITUDES
3767
20
15
•
25
•
6
8
10
Time (months)
Figure 3. (continued)
tions with > 50 events/yearin the NH are foundprimarily
from easternNorth America to centralEuropepolewardof
about35ø, with a few more southof Alaska but north of 50ø.
The region of eastern Asia from 35ø-55øNhad >40
events/year. In general, the oceanshad more events/year
thandid the continents. The locationsof the higherfrequenciesof troposphericfoldingactivitygenerallycorrespond
to
the locationsof high stormtrack activity.
While there are a numberof caseswhere stratospheric
intrusionswere associatedwith WCB transportfrom the
foundto be associated
with the WCB transport
andappear
to be generallycoupledto WCB transportin suchsynopticscale disturbances.
Futurework to more firmly establishthe climatologyof
transportfrom the tropical MBL to northernmidlatitudes
might involve the use of TOMS daily globaltotal ozone
maps, GOES water vapor images and wind fields.
In
addition,PV contourmaps couldbe usedto establishthe
link with stratospheric
intrusions.A preliminaryinspection
tropicsto midlatitudes,
thetwoprocesses
arenotnecessarily of TOMS imagesindicatesthat coupledlow/high ozone
linked. In general,the WCB is associated
with a mature dipoles in which the low-ozoneregion moves from the
directionandeventually
midlatitudecycloneor synoptic-scale
disturbance. The tropicspolewardin a northeasterly
are fairly frequentin the September-March
period.
WCB is situatedahead of a cold front. Stratospheric dissipate
intrusionsare associated
with jet strea•, whichmay or may
Acknowledgments.
The authors
thankA. Notaft(SAIC), L. W.
not be coupledto the midlatitudecyclones.
Overbay,W. J. McCabe, andJ. A. Williamsfor technicalsupport
of the UV DIAL systemduringSONEX. The authorsalsothank
M.
A. Owens(HamstonUniversity),A.M. Thompson(NASA
8. Summary and conclusion
GoddardSpaceFlight Center), and two anonymous
refereesfor
Low-ozoneair masseswere found in the upper tropo- helpful commentson the manuscript. The authorsthankR. B.
dataanalysis,A.D. Frolov
sphereof northernmidlatitudesbetween13.IøW and91. løW Piemefor the Wallopsozonesonde
(University
of
Maryland)
for
the
TOMS
image,and L. Pfister
on four flightsduringthe SONEX missionin October1997.
(NASA
Ames
Research
Center),
T.
L.
Kuesera
(StevenMyer and
Using a variety of techniques,suchas backwardtrajectory
Associates,
Corp. at NASA GoddardSpaceFlightCenter)andA.
calculations,PV analysis, and concentrations
of various M. Thompsonfor the GOES-8image.
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H. E. FuelbergandJ. R. Hannan,Departmentof Meteorology,
Florida StateUniversity,Tallahassee,FL 32306.
B. G. Heikesand J. Snow,Centerfor Atmospheric
Chemistry
Studies,GraduateSchoolof Oceanography,
Universityof Rhode
Island, Narragansett,Pd 02882.
O. W. Saehse,AerospaceElectronicSystems,NASA Langley
ResearchCenter,Hampton,VA 23681-0001.
H. B. Singh, NASA Ames ReserehCenter, Moffett Field, CA
94035.
D. R. BlakeandN.J. Blake,ChemistryDepartment,University
of California, Irvine, CA 92717.
R. W. Talbot, Institute for the Study of Earth, Oceans, and
Space,Universityof New Hampshire,Durham,NH 03824.
E. V. Browell, W. B. Grant, and G. L. Gregory,Atmospheric
SciencesResearch,NASA LangleyResearchCenter,Hampton,VA
23681-0001 (w.b.grant@lare.nasa.gov).
C. F. Butler,M. B. Clayton,andM. A. Fenn,ScienceApplica28, 1999;accepted
tionsInternationalCorporation,NASA LangleyResearchCenter, (ReceivedApril 5, 1999;revisedSeptember
September30, 1999.)
Hampton,VA 23681-0001.