Lecture 3: Global upper troposphere – lower stratosphere (UTLS)• Overview: why is the UTLS interesting?
• Structure of the global tropopause and relation to tracers• Double tropopauses• The tropopause inversion layer

1Global structure of the tropopause:

tropics

midlats

Strong change in stability across the tropopause:•Troposphere: vertically well-mixed; via convection and baroclinic instability•Stratosphere: dynamically stable (mostly); circulation forced by radiation andforcing from troposphere (upward propagating waves)

••

Ozone

Formed in stratosphere (stratospheric source gas)
Strong gradients across tropopause

Ozone column density, DU/km
Satellite climatology in JanuaryOzone••Formed in stratosphere (stratospheric source gas)
Strong gradients across tropopause

Ozone column density, DU/km
Satellite climatology in January

eddy
mixingstratosphere-troposphereexchangemean meridional
circulation

Carbon monoxide (CO)Measurements fromACE-FTS satellite•••

Emitted from combustion (tropospheric source gas)
Photochemical lifetime of ~2 months(useful as a dynamical tracer)
Strong gradients across tropopausetransport frommesosphereStrong gradients in chemical
behavior demonstrates that thetropopause acts as a boundary
separating distinct air masses
H2O exhibits similar behavior

main emissions in NH

Park et al., 2013, J. Geophys. Res.

Atmospheric Chemistry Experiment
Fourier Transform Spectrometer (ACE-FTS)
FTS measurements: 2.2 – 13.3 μm
10+ years of data (Feb. 2004 – present)~ 3,500 occultations /year
Resolution: ~300 km horizontal, 3 km vertical

ACE occultations

measurement pattern:
repeats every year

Low latitudes: 4 samples / year
Randel et al., 2012, J. Geophys. Res.ACE-FTS measurements and retrievals for carbon monoxide (CO)Simulated CO spectrum

ACE-FTSmeasurements

Clerbaux et al., ACP, 2008

microwindows
for CO retrieval
7 also many isotopes
Boone and Bernath, 2009:
The Atmospheric Chemistry Experiment : status and latest results,
5th Atmospheric Limb Conference and Workshop

Other tropospheric hydrocarbons measured by ACE-FTS

Ethane C2H6

Acetelyne C2H2

Hydrogen cyanide HCN

min due toocean loss

lifetime: years

lifetime: 2 weeks

lifetime: 2 months

short-lived species have
sharper cross-tropopause
gradientsPark et al., 2013, J. Geophys. Res.

•but loss due to contact
with oceanDifferent hydrocarbons are often correlated, because of common
sources (i.e. combustion). ACE-FTS data are ideal to study these
relationships.

ratios of tracers withdifferent lifetimes cancharacterize photochemical
age of air

Park et al., 2013, J. Geophys. Res.

In the tropical upper troposphere, CO is closely linked with convective outflow

white lines:
climatologicaldeep convection

Seasonal cycle in upper tropospheredeep tropics 15o N-S:
semiannual variationof CO at 13 km(level nearconvective outflow)

Park et al., 2013,J. Geophys. Res.

WACCM simulation of CO

ACE-FTSmodel includes observed emissions
and full tropospheric chemistry

WACCM

Note: often useful to analyze observational data in combination with model results
Park et al., 2013, J. Geophys. Res.

Model also captures horizontal structure

147 hPa

observations

Park et al., 2013, J. Geophys. Res.

WACCM simulation

Definitions of the tropopause•Lapse rate tropopause (WMO definition)•Cold point (most relevant in the tropics)•Specific value of potential vorticity (PV=2-4)
advantage: continuously valued, useful for dynamics/transport studies

fromdisadvantage: requires meteorological analysis; cannot calculate
temp profiles alone

What processes maintain the tropopause?

tropics:

Mean
upwellingheightcold point
tropopause~17 kmmain convective
outflow ~12 km
Lapse rate fromradiative-convective
equlibrium

T(z)e.g. Thuburn and Craig 2000

What processes maintain the tropopause?
GRL 2001

extra-tropics:‘stirring effect of baroclinic eddies
acting against a smooth thermal relaxation’Colors: lapse rate dashed lines: PV

relaxation
state

equilibrium withbaroclinic eddies
baroclinic eddies organize
flow to give a sharp verticaland horizontal transitions

Cross-section of
extratropical UTLS

mixing above and below jet,but not across jet core

Questions:•Large-scale transport and mixing (when, where and how?)•Seasonal and interannual variablity (processes and trends)•Monsoonal circulations (especially Asian summer monsoon)•Influences of deep convection (continental and tropical)

Gettelman et al 2011

Transport and mixing: when, where and how?
Research aircraft measurements near large tropopause fold

PV=2isosurface

START08 experiment, Pan et al, 2009 200720

Using tracer correlations to understand the chemical transition region

Zahn et al 2000
Hoor et al 2002
Pan et al 2004

Example for individual profile (aircraft measurements):

mixinglayer

statistics frommany profiles:

Pan et al 2004

transition layer or
mixing region

Where is the mixing layer compared to the tropopause?

identify
mixing layer

distribution of
mixing layer
wrt tropopause

result: mixing layer ~2 km think, centered near tropopause
Pan et al., 2004, J. Geophys. Res.

tracer correlations from ACE-FTS satellite data

identifying the mixing
layer from O3 – H2O
correlations

location of
mixing layer
wrt
tropopause

vertical profileof mixing layer

but note vertical resolution of ACE-FTS ~ 2-3 km

Hegglin et al 2009

Using tracer correlations to identify spatial structure of mixing

thin mixing layerheightmixing identified intracer correlations

broad mixing layer on
cyclonic (poleward) side of jet

Jet

latitudePan et al, 200725

2011, JGR

CLaMS simulations

ozoneozone

observations

COCO
simulation of tracer correlations is a sensitive test
for model transport calculations

26

Transport pathways and mixing deduced from CLaMS
Lagrangian transport model
Vogel et al, 2011, JGR

27

Key points:•Tropical tropopause ~17 km, convective-radiative balances•Extratropical tropopause ~ 8-10 km, baroclinic eddies•Strong chemical gradients demonstrate distinct air masses across tropopause•Tropical transport to the upper troposphere via deep convection•Chemical tracers are a powerful tool to diagnose transport and mixing(e.g. spatial structure of mixing layers)

Next: two interesting aspects of the tropopause:
1)double tropopauses
2)tropopause inversion layer

Extratropical temperature profiles often have multiple tropopauses

Randel et al., 2007, J. Geophys. Res.
WMO (1957) tropopause definition:
If above the first tropopause the average lapse rate between
any level and all higher levels within 1 km exceeds 3ºC/km, thena second tropopause can occur.

GPS radio occultation
Basic measurement principle: Deduce atmospheric properties based on
precise measurement of phase delay
Occulting GPSIonosphere

Utility of GPS Radio Occultation:

Neutral atmosphereOcculting LEO

Earth•Long-term stability•All-weather operation•High vertical resolution (< 1 km)•High accuracy: Averaged profiles to< 0.1 Kstatistical distribution of tropopause heightsfrom radiosondes at Charleston 1950-2003

Location of double tropopauses for one day (ERA40 data)

red lines:
PV =1,2,3,4
at 200 hPa(tropopause)(offset)Randel et al., 2007, J. Geophys. Res.

Not a new result: Bjerknes and Palmen (1937); Kochanski (1955); Shapiro (1978), ……

Tropopause structure associated withdeveloping baroclinic wave
Shapiro, 1978 1981

equatorpoledouble tropopauseseasonal variation of profiles with multiple tropopauses

maximumduring winter

2 trops

3 tropsgood agreement between
radiosondes and GPS

Randel et al, 2007., J. Geophys. Res.

GPS climatology: percent of winter (DJF)
soundings with a double tropopause> 60%
maximum insubtropics

Randel, Seidel and Pan, JGR, 2007

Climatological height of tropopauses from GPS datasecondtropopause
close totropical cold point~17 kmRandel et al., 2007, J. Geophys. Res.

Cross-section near Charleston
suggestive of transport
from tropics

static stability N2Randel et al., 2007, J. Geophys. Res.

Double tropopauses and tropospheric intrusions

HIRDLSozone

double tropopause
linked tointrusion above
subtropical jettropopause

staticstability

Pan et al, JGR, 2009

Differences in ozone for single vs. double tropopause
derived from SAGE II satellite data

NHSH-> consistent pattern of less ozone for double tropopauses

Randel et al., 2007, J. Geophys. Res.

Pan et al 2009

Aircraft measurements
during START08 experiment:

Blue: region of tropospheric intrusion

BaircrafttrackAsection along A-B

double tropopause with low lapse rateand low ozone

Pan et al., 2010, Bull. Amer. Meteor. Soc.

Key points:•double tropopauses occur frequently in subtropics, especially during winter•thermal and chemical structure consistent with intrusions from tropics
above subtropical jets

transport above
subtropical jets

JGR 2011

Idealized LC1 life cycle

model generates
double tropopause (red),but in air moving fromhigh latitudes* different fromobservations
imposedinversionlayer???

The tropopause inversion layer (TIL)

Birner, 2002 2003 PhD Thethis,2006 JGR

average vertical structure from high-resolution radiosondes near 45o N,
calculated using ground-based and tropopause-based coordinates
temp

tropopausebased
coordinate

stability

sharp
maximumin N2ground-based
coordinateexamples using GPS data in tropopause-based coordinate

temp

heightrelative to
tropopause

stability

layer ofhighstability

Randel et al, JAS, 2007

Climatology of inversion layer from GPS data
N2 in tropopause
coordinates

DJF

JJA

summer polar
maximum
Randel et al, JAS, 2007

What causes the inversion layer?

profiles of N2 for idealized
cyclonic and anticyclonic circulations,in tropopause-relative coordinates
Wirth 2003

•dynamics?
•cyclone / anticyclones asymmetries?
•radiation or other process?

cyclonic

anticyclonicaverageBalanced dynamical structure (Hoskins et al. 1985)

Cyclonicwarm
isentropes
winds

cold

low
tropopause

Anti-cyclonichightropopause

warmstrong stability(inversion layer)

Study the dependence of tropopause statistics on UTLS circulation-> segregate GPS soundings according to 200 hPa vorticity

200 hPa relative
vorticity Jan 2, 2002

GPS soundingsdependence oftropopause heighton vorticity

anticyclones

cyclones

lower LRT1
for cyclones

profiles binned according to vorticity (~2500 total)(to test hypothesis that climatologicalinversion layer due mainly to anticyclones)
temp

stability
inversion
evident for
all circulation
types

Randel et al., 2007, J. Atmos. Sci.

strength of the inversion vs. circulation

T(ZLRT1+2km) – T(ZLRT1)

Result: inversion exists for cyclones (weaker)
and anti-cyclones (stronger)

systematically stronger
for anticyclonic flow

Randel et al, JAS, 2007

How do radiative processes contribute to the inversion layer?
What is the radiative effect of transition layer?
Vertical profiles in tropopause coordinates

temp changes due to observed H2O and O3(compared to hypothetical dashed curves)transitionlayer

T

H 2O

O3

calculations using
Fixed Dynamical Heating(FDH)
e.g. Forster and Shine 1997

H2O cools

O3 warms

water vapor and ozone both influence thermal structure(especially water vapor near tropopause)

Randel et al., 2007, J. Atmos. Sci.

tropopause inversion layer during polar summer
Radiosonde at Eureka (80o N)high stability
layer

inversion~8K

Static stability• Persistent feature, observed in almost all profiles
during summer in both hemispheres (why?)

Randel and Wu, 2010, J. Atmos. Sci.

Radiosondes and nearby COSMIC soundings

80o N

71o S

COSMIC

sonde

Randel and Wu, 2010, J. Atmos. Sci.

COSMIC allows ~100 times more observations than radiosondes,
to study space-time variability of inversion layer

Radiosondes and nearby COSMIC GPS soundings

80o N

71o S
summer inversion is ubiquitous

COSMIC

sonde

Randel and Wu, 2010, J. Atmos. Sci.
COSMIC allows ~100 times more observations than radiosondes,
to study space-time variability of inversion layer

Strength of polar
tropopause
inversion

COSMIC 70o – 90o N

8K
ArcticT(ztrop+ 2km) - T(ztrop)
daily data from COSMIC,
average over polar cap
COSMIC 70o – 90o S

8K

Randel and Wu, 2010, J. Atmos. Sci.

Antarctic

summer maximum
in both hemispheres

Latitudinal structure of summer inversion

T(ztrop+ 2km) - T(ztrop)

Randel and Wu, 2010, J. Atmos. Sci.

note the remarkable
symmetry betweenhemispheres

What causes the strong polar inversion layer?
* Water vapor near the tropopause *Seasonal vertical profiles
Seasonal cycle at tropopause (9 km)

note tropopausetransition layer (ExTL)
Summermaximum

Polar water vapor measurementsfrom ACE-FTS satellite

Randel and Wu, 2010, J. Atmos. Sci.

tropopause

Summermaximum

Radiative response
to UTLS water vapor

ACE water vapor(input to calculation)

Fixed Dynamical Heating calculations(e.g. Forster and Shine 1997)

Calculated temperature profiles,
changing only the H2O

Enhanced water vapor leads to strong cooling near tropopause• Explains the seasonal cycle, vertical structure and magnitudeof the tropopause inversion
Randel and Wu, JAS, 2010

Similar H2O behavior is seen in the Southern HemisphereH2O at tropopause

summermaximum

Randel and Wu, 2010, J. Atmos. Sci.

Why does this occur during polar summer?
ACE-FTS data

relative verticalgradient in H2O(%/km)

strongest verticalgradients in H2O
across tropopause

Hegglin et al 2009

Key points:• tropopause inversion layer is a ubiquitous feature in extratropics• evident for cyclones and anticyclones; much stronger for anticyclones (as expected)• inversion layer strongest over summer poles; remarkable NH-SH symmetry• radiative calculations show polar inversion layer is a response to strong H2O gradients(and suggests this is a mechanism for other regions)Reference1
•
•
•
•

•

•
•

•

Birner, T., 2003: Die extratropische tropopausenregion, Ph. D. thesis, Fakult ät fürPhysik der Ludwig-Maximilians-Universit ät M ünchen, pp.129.
Birner, T., 2006: Fine - scale structure of the extratropical tropopause region, J.
Geophys. Res., 111, D04104.
Bjerknes, J. and Palmèn, E., 1937: Investigation of selected European cyclones bymeans of serial ascents, Geophys. Publ. 12, 1-62.
Boone, C. and Bernath, P., 2009: The atmospheric chemistry experiment: Status andlatest results, 5th Atmospheric Limb Conference and Workshop (Helsinki, Finland,invited talk).
Clerbaux, C., Boynard, A., Clarisse, L., George, M., Hadji-Lazaro, J., Herbin, H.,
Hurtmans, D., Pommier, M., Razavi, A., Turquety, S., Wespes, C. and Coheur, P.-F.,
2009: Monitoring of atmospheric composition using the thermal infrared IASI/MetOp
sounder, Atmos. Chem. Phys., 9, 6041-6054
Forster, F. and Shine, K.P., 2002: Assessing the climate impact of trends instratospheric water vapor, Geophys. Res. Lett., 29, 10-1-10-4.
Gettelman, A., Hoor, P., Pan, L., Randel, W.J., Birner, T. and Hegglin, M., 2011: Theextra tropical upper troposphere and lower stratosphere, Rev. Geophys., 49,
RG3003.
Haynes, P.H., Scinocca J.F. and Greenslade, M.D., 2001: Formation andmaintenance of the extratropical tropopause by baroclinic eddies, Geophys. Res.
Lett., 28, 4179-4182.

Reference2•••••••

Hegglin, M.I., Boone, C.D., Manney, G.L. and Walker, K.A., 2009: A global view of theextratropical tropopause transition layer from Atmospheric Chemistry Experiment
Fourier Transform Spectrometer O3, H2O, and CO, J. Geophys. Res., 114, D00B11.
Hoor, P., Fischer, H., Lange, L., Lelieveld, J. and Brunner, D., 2002: Seasonalvariations of a mixing layer in the lowermost stratosphere as identified by the CO-O3
correlation from in situ measurements, J. Geophys. Res., 107, ACL 1-1-ACL 1-11.
Hoskins, B.J., McIntyre, M.E. and Robertson, A.W., 1985: On the use andsignificance of isentropic potential vorticity maps, Q.J.R. Meteorol. Soc., 111, 877946.
Kochanski, A., 1955: Cross sections of the mean zonal flow and temperature along
80 W, J. Meteorology., 12, 95-106.
Pan, L., Bowman, K.P., Shapiro, M., Randel, W.J., Gao, R.S., Campos, T., Davis, C.,
Schauffler, S., Ridley, B.A., Wei, C. and Barnet, C., 2007: Chemical behavior of thetropopause observed during the Stratosphere-Troposphere Analysis of RegionalTransport experiment, J. Geophys. Res., 112, D18110.
Pan, L.L., Bowman, K.P., Atlas, E.L., Wofsy, S.C., Zhang, F., Bresch, J.F., Ridley,B.A., Pittman, J.V., Homeyer, C.R., Romashkin, P. and Cooper, W.A., 2010: The
stratosphere - troposphere analyses of regional transport 2008 experiment, Bull.
Amer. Meteor. Soc., 91, 327-342.
Pan, L.L., Randel, W.J., Gary, B.L., Mahoney, M.J. and Hintsa, E.J., 2004: Definitionsand sharpness of the extratropical tropopause: A trace gas perspective, J. Geophys.
Res., 109, D23103.

Reference3•••••••

Pan, L.L., Randel, W.J., Gille, J.C., Hall, W.D., Nardi, B., Massie, S., Yudin, V.,
Khosravi, R., Konopka, P. and Tarasick, D., 2009: Tropospheric intrusions associatedwith the secondary tropopause, J. Geophys. Res., 114, D10302.
Park, M., Randel, W.J., Kinnison, D.E., Emmons, L.K., Bernath, P.F., Walker, K.A.,
Boone, C.D. and Livesey, N.J., 2013: Hydrocarbons in the upper troposphere andlower stratosphere observed from ACE-FTS and comparisons with WACCM, J.
Geophys. Res. Atmos., 118, 1964-1980.
Randel, W.J., Moyer, E., Park, M., Jensen, E., Bernath, P., Walker, K. and Boone, C.,
2012: Global variations of HDO and HDO/H2O ratios in the UTLS derived from ACEFTS satellite measurements, J. Geophys. Res., 117, D06303.
Randel, W.J., Park, M., Wu, F. and Livesey, N., 2007: A large annual cycle in ozone
above the tropical tropopause linked to the Brewer-Dobson circulation, J. Atmos. Sci.,64, 4479-4488.
Randel, W.J., Wu, F. and Forster, P., 2007: The extratropical tropopause inversion
layer: global observations with GPS data, and a radiative forcing mechanism, J.
Atmos. Sci., 64, 4489-4496.
Randel, W.J. and Wu, F., 2010: The polar summer tropopause inversion layer, J.
Atmos. Sci., 67, 2572-2581.
Shapiro, M.A., 1981: Frontogenesis and geostrophically forced secondary circulationsin the vicinity of jet stream-frontal zone systems, J. Atmos. Sci., 38, 954-973.

Reference4•••••Thuburn, J. and Craig, G.C., 2000: Stratospheric influence on tropopause height: Theradiative constraint, J. Atmos. Sci., 57, 17-28.
Vogel, B., Pan, L.L., Konopka, P., Günther, G., Müller, R., Hall, W., Campos, T.,
Pollack, I., Weinheimer, A., Wei, J., Atlas, E.K. and Bowman, K.P., 2011: Transport
pathways and signatures of mixing in the extratropical tropopause region derived
from Lagrangian model simulations, J. Geophys. Res., 116, D05306.
Wirth, V., 2003: Static stability in the extratropical tropopause region, J Atmos Sci.,
60, 1395-1409.
World Meteorological Organization, 1957: Meteorology - A three-dimensional science:
Second session of the Commission for Aerology, WMO Bulletin, 134-138.
von Zahn, U., von Cossart, G., Fiedler, J., Fricke, K. H., Nelke, G., Baumgarten, G.,
Rees, D., Hauchecorne, A. and Adolfsen, K., 2000: The ALOMAR
Rayleigh/Mie/Raman lidar: objectives, configuration, and performance, Ann.
Geophys., 18, 815-833.