Upper Tropospheric humidity from Megha-Tropiques : A humidity-convection study

Upper tropospheric humidity (UTH) and rainfall estimates are produced operationally from Megha-Tropiques observations since its launch on October 12th, 2012. With its low inclination (20°) orbit, this indo-french satellite offers a frequent revisit of the tropical belt giving 3 to 5 passes every day. This configuration provides an interesting sampling of the convective systems during their life that allows studies of their evolution, from their precipitation core to their close environment. The UTH is computed for the 3 upper channels of SAPHIR (±0.2 GHz, ±1.1 GHZ and ± 2.8 GHz) following a well established method applied to water vapor channels (6.3μm: e.g. Soden and Bretherton, 1993; 183 GHz: e.g. Spencer and Braswell, 1997) which gives an idea of the vertical distribution of the relative humidity in the upper part of the troposphere. The CINDY/DYNAMO international campaign that took place over the equatorial Indian Ocean from the 1st October 2011 to the 31 March 2012 aimed to study the conditions for the development of active convection in the context of the MJO (Madden-Julian Osillation). Thanks to a large deployment of ground instruments (SPol-Ka polarimetric radar, Smart-R radar, radiosoundings) and airborne measurements (SAPHIR-Falcon 20, NOAA-P3) it is possible to describe quite thoroughly the whole state of the atmosphere while the Megha-Tropiques satellite (mainly SAPHIR and MADRAS instruments) overpasses. This offers an ideal opportunity to study the relationship between convection and its moist environment. A few case studies are selected from the CINDY/DYNAMO observations and explored with the Megha-Tropiques estimations of rainfall and UTH: a simple eulerian approach is used over the area of activity of the cloudy systems and the distribution of UTH is analyzed and associated to the rainfall rate which is a good signature of the intensity of convection