Articles | Volume 9, issue 24
Atmos. Chem. Phys., 9, 9647–9660, 2009

Special issue: TROCCINOX - Tropical convection and its impact on the troposphere...

Special issue: SCOUT-O3 Tropics

Special issue: AMMA Tropospheric Chemistry and Aerosols

Atmos. Chem. Phys., 9, 9647–9660, 2009

  23 Dec 2009

23 Dec 2009

Hydration and dehydration at the tropical tropopause

C. Schiller, J.-U. Grooß, P. Konopka, F. Plöger, F. H. Silva dos Santos, and N. Spelten C. Schiller et al.
  • Forschungzentrum Jülich GmbH, ICG-1, 52425 Jülich, Germany

Abstract. High-resolution water measurements from three tropical airborne missions in Northern Australia, Southern Brazil and West Africa in different seasons are analysed to study the transport and transformation of water in the tropical tropopause layer (TTL) and its impact on the stratosphere. The mean profiles are quite different according to the season and location of the campaigns, with lowest mixing ratios below 2 ppmv at the cold point tropopause during the Australian mission in November/December and high TTL mixing ratios during the African measurements in August. We present backward trajectory calculations considering freeze-drying of the air to the minimum saturation mixing ratio and initialised with climatological satellite data. This trajectory-based reconstruction of water agrees well with the observed H2O average profiles and therefore demonstrates that the water vapour set point in the TTL is primarily determined by the Lagrangian saturation history. Deep convection was found to moisten the TTL, in several events even above the cold point up to 420 K potential temperatures. However, our study does not provide evidence for a larger impact of these highly-localised events on global scales.

Final-revised paper