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Impact des phénomènes de surface sur la TTL

Impact des phénomènes de surface sur la TTL. P. Ricaud, B. Barret, J.-L. Attié, E. Le Flochmoën Laboratoire d’Aérologie, Toulouse, France H. Teyssèdre, V.-H. Peuch Centre National de Recherches Météorologiques, Toulouse, France. TTL (Tropical Tropopause Layer). TTL : ~14  ~18 km

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Impact des phénomènes de surface sur la TTL

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  1. Impact des phénomènes de surface sur la TTL P. Ricaud, B. Barret, J.-L. Attié, E. Le Flochmoën Laboratoire d’Aérologie, Toulouse, France H. Teyssèdre, V.-H. Peuch Centre National de Recherches Météorologiques, Toulouse, France

  2. 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)

  3. 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

  4. 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

  5. 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

  6. Tropical Tropopause Layer (TTL) From Liu and Zipfser, JGR, 2005 • 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

  7. Overshootings OPF : Overshooting Precipitation Features Liu and Zipser, JGR, 2005

  8. Variation diurne OPF OPF : Overshooting Precipitation Features Liu and Zipser, JGR, 2005

  9. MOCAGE: 15 & 17 km N2O CH4 Vertical Flux CO

  10. 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

  11. The H2O distribution HALOE MOCAGE ECMWF TEMPERATURE • 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

  12. MOCAGE EQUATORIAL BAND: 10°S-10°N S America Indonesia W Pacific OLR Africa CO • 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 20 km N2O Altitude 0 km CH4 H2O Anom Temp Anom -180 180 Longitude

  13. Transports dans la TTL

  14. 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 (?)

  15. 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

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