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Impact des phénomènes de surface sur la TTL

P. Ricaud, B. Barret, J.-L. Attié, E. Le FlochmoënLaboratoire d’Aérologie, Toulouse, France

H. Teyssèdre, V.-H. PeuchCentre National de Recherches Météorologiques, Toulouse, France

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TTL (Tropical Tropopause Layer) TTL : ~14 ~18 km 2 idées fortes :

Transport ascendant dans systèmes convectifs jusqu’à la base de la TTL puis transport lent par échauffement radiatif jusque dans la basse stratosphère (Sherwood and Dessler, 2000) et transport horizontal sur de longues distances (Gettelman et al., 2002)

« Fontaine stratosphérique » au Pacifique Ouest corrélée au minimum de température (Newel) avec des nuages convectifs plus élevés là où l’OLR est la plus faible

1 idée émergente Overshooting jusqu’à 18 km (Liu and Zipser, 2005)

principalement au-dessus des continents (surtout l’Afrique) avec une forte variation diurne (plus intense l’après-midi)

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Aim

Diagnose tropospheric and stratospheric processes that play a key role in the distribution of long-lived species measured by space-borne sensors in the Tropical Tropopause Layer (TTL)

Layer between the tropopause and 380 K

2 mechanisms are widely accepted Convection upto the base of the TTL around 14 km

followed by a slow uplift through radiative heating (Sherwood and Dessler, 2000)

Overshooting above continental convective systems (Danielsen, 1993)

Focus on a weakly documented period, namely the March-April-May (MAM) 2002-2004 period

Comparisons with 3D CTM Troposphere-Stratosphere MOCAGE

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Data sets

Satellite data Odin: N2O at 17 km HALOE CH4 and H2O at 17 km MOPITT CO at 850 and 150 hPa Fire counts from TRMM Outgoing Longwave Radiation from AVHRR

Model data 3D CTM MOCAGE: N2O, CH4, CO, H2O, T/P, Flux Run 2000-2005 for climate studies 5°x5° Troposphere-stratosphere

ECMWF Temperature & Winds from ECMWF

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Outgoing Longwave Radiation (OLR)

Strong convective outflow is defined by low values of OLR (< 220 W.m-2) Western Africa Western Pacific Indonesia South America

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Tropical Tropopause Layer (TTL)

17 km ~ 370 K ~ 100 hPa 15 km ~ 150 hPa High values of N2O, CH4

and CO over Western Africa, Indonesia and South America induced by strong convective outflows

Low values of Western Pacific

Overshootings above 14 km (Liu and Zipfser, 2005):

Africa, Indonesia & S. America

From Liu and Zipfser, JGR, 2005

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Overshootings

Liu and Zipser, JGR, 2005

OPF : Overshooting Precipitation Features

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Variation diurne OPF

Liu and Zipser, JGR, 2005

OPF : Overshooting Precipitation Features

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MOCAGE: 15 & 17 km

N2O CH4

CO VerticalFlux

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Tropospheric Processes

Fire pixels in Western Africa (onset of the African monsoon), and Northern South America

Emissions of CO at 850 hPa associated with the biomass burnings

From IPCC [2001], emissions from biomass burning represent 30%, 10% and 1% of total emissions for CO, CH4 and N2O

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The H2O distribution

Dehydrated area at 17 km over Africa (HALOE & MOCAGE) associated with strong convective outflow

Lows in Temperature over Africa

< 200 K @ 15 km < 190 K @ 17 km

HALOE MOCAGE

ECMWF TEMPERATURE

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MOCAGE

Afr

ica

Ind

onesi

a

W P

aci

fic

S A

meri

ca

CO

N2O

CH4

EQUATORIAL BAND: 10°S-10°N

3 sources of CO: Africa, Indonesia & South America

2 sources of CH4: Africa & Indonesia, but none in South America

None of N2O (as expected) Lows of H2O at 17 km

associated with Lows of Temperature below and convection over Africa and South America

Convective outflows stop: 14 km over S. America 17 km over W. Africa &

Indonesia

Alt

itud

e

0 km

20 km

H2OAnom

TempAnom

-180 180Longitude

OLR

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Transports dans la TTL

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Synthesis

In MAM 2002-2004, tropospheric air masses characterized by high concentrations of CO, CH4 and N2O are uplifted into the top of the TTL at 17 km by strong continental convective systems

over Western Africa, Indonesia and Northern South America

The emission of CO and CH4 associated with biomass burning modifies even more the distribution of these species

above Western Africa and Northern South America

Over Western Pacific, the absence of long-lived species local maxima demonstrates that convective processes do not uplift rapidly tropospheric air masses into the lower stratosphere

Over Western Africa, the rapid vertical outflows coincident with low temperatures are also responsible for a more intense dehydration of the lower stratosphere than elsewhere

The 3D CTM MOCAGE reproduces almost all of the features except the maxima over South America: sources of CH4 and/or convection (?)

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Projets Très court terme :

Jeux de données de CO dans l’UTLS provenant de sondeurs au limbe (AURA/MLS, Odin/SMR)

Assimilation avec MOCAGE-PALM Court Terme

Rajouter les jeux de données de CO troposphérique provenant de sondeurs au nadir (MOPITT et AIRS)

Puis rajouter METOP/IASI CO