Meridional ozone gradients in the African upper troposphere

This study presents regular observations from the MOZAIC data base over Africa (1994–2004) to highlight the role of Hadley cells in tropical ozone production. We show the presence in the African upper troposphere (9–12 km) of a minimum of ozone and of a maximum of relative humidity that both follow the meridional migration of the Inter‐Tropical Convergence Zone (ITCZ). We suggest that mechanisms contributing to meridional ozone gradients (0.3 to 1.5 ppbv deg−1) on both sides of the ozone minimum in the 20°S–20°N latitude band are (1) the vertical transport of relatively poor ozone air masses by tropical convection, and (2) the photochemical production of ozone in upper‐level branches of the Hadley circulation. Depending on the season and on the meridional side of the ITCZ, ozone precursors injected in the ascending branch of the ITCZ include biomass burning, biogenic, lightning and anthropogenic emissions.

[1]  John A. Pyle,et al.  Measurement of ozone and water vapor by Airbus in-service aircraft: The MOZAIC airborne program, an overview , 1998 .

[2]  D. Jacob,et al.  Origin of ozone and NOx in the tropical troposphere: A photochemical analysis of aircraft observations over the South Atlantic basin , 1996 .

[3]  B. Doddridge,et al.  A tropical Atlantic Paradox: Shipboard and satellite views of a tropospheric ozone maximum and wave‐one in January–February 1999 , 2000 .

[4]  A. Thompson,et al.  Ozone over southern Africa during SAFARI‐92/TRACE A , 1996 .

[5]  D. Kley,et al.  Calibration and performance of automatic compact instrumentation for the measurement of relative humidity from passenger aircraft , 1998 .

[6]  V. Thouret,et al.  Enhanced view of the “tropical Atlantic ozone paradox” and “zonal wave one” from the in situ MOZAIC and SHADOZ data , 2006 .

[7]  Anne M. Thompson,et al.  Convective transport of biomass burning emissions over Brazil during TRACE A , 1996 .

[8]  J. Warner,et al.  Daily global maps of carbon monoxide from NASA's Atmospheric Infrared Sounder , 2005 .

[9]  C. Mari.  African Monsoon Multidisciplinary Analysis-Atmospheric Chemistry ( AMMA-AC ) : A new IGAC Task , 2005 .

[10]  K. Suhre,et al.  Atlantic subtropical potential vorticity barrier as seen by Measurements of Ozone by Airbus In‐Service Aircraft (MOZAIC) flights , 1998 .

[11]  J. Lamarque,et al.  Tropospheric ozone over the tropical Atlantic: A satellite perspective , 2003 .

[12]  V. Thouret,et al.  Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data , 2004 .

[13]  Georgiy L. Stenchikov,et al.  Lightning-generated NOX and its impact on tropospheric ozone production: A three-dimensional modeling study of a Stratosphere- Troposphere Experiment: Radiation, Aerosols and Ozone (STERAO-A) thunderstorm , 2005 .

[14]  H. Christian.  Global Frequency and Distribution of Lightning as Observed From Space , 2001 .

[15]  H. Levy,et al.  A model analysis of the tropical South Atlantic Ocean tropospheric ozone maximum: The interaction of transport and chemistry , 2000 .

[16]  M. Rodwell,et al.  A Model of the Asian Summer Monsoon. Part I: The Global Scale , 1995 .

[17]  Randall V. Martin,et al.  Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model , 2003 .

[18]  Valerie Thouret,et al.  Comparisons of ozone measurements from the MOZAIC airborne program and the ozone sounding network at eight locations , 1998 .

[19]  A. Thompson,et al.  Linking horizontal and vertical transports of biomass fire emissions to the Tropical Atlantic Ozone Paradox during the Northern Hemisphere winter season: 1999 , 2002 .

[20]  A. Kitoh,et al.  Trend and interannual variability of Walker, monsoon and Hadley circulations defined by velocity potential in the upper troposphere , 2004 .

[21]  Toshihiro Ogawa,et al.  Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 2. Tropospheric variability and the zonal wave-one , 2003 .

[22]  Jean-Pierre Cammas,et al.  c ○ European Geosciences Union 2003 Atmospheric Chemistry and Physics Discussions , 2003 .

[23]  J. Peixoto,et al.  Physics of climate , 1984 .

[24]  A. Marenco,et al.  Study of ozone formation and transatlantic transport from biomass burning emissions over West Africa during the airborne Tropospheric Ozone Campaigns TROPOZ I and TROPOZ II , 1998 .

[25]  A. Thompson,et al.  Tropical ozone as an indicator of deep convection , 2002 .