Ocean, Ice, Atmosphere Seminar

Methods to detect deep convective clouds and convective overshooting from measurements at the three water vapor channels (183.3+/-1, 183.3+/-3, and 183.3+/-7 GHz of the Advanced Microwave Sounder Unit (AMSU)-B are presented. Thresholds for the brightness temperature differences between the three channels are suggested as criterion to detect deep convective clouds, and an order relation between the differences is used to detect convective overshooting. The procedure is based on an investigation of the influence of deep convective cloud systems on the microwave brightness temperatures at frequencies from 89 to 220 GHz using the simultaneous aircraft microwave and radar measurements over two tropical deep convective cloud systems, taken during the Tropical Rainfall Measuring Mission (TRMM) Large Scale Biosphere-Atmosphere Experiment (LBA) campaign. Furthermore, a microwave radiative transfer model and simulated mature tropical squall line data derived from the Goddard Cumulus Ensemble (GCE) model are used to adapt the criteria to the varying viewing angles of AMSU-B. These methods are employed to investigate the distributions of deep convective clouds and convective overshooting in the tropics (30S to 30N) for the four three-month seasons from March 2002 to February 2003. The distributions show a seasonal variability of shifting from the winter hemisphere to the summer hemisphere. The distributions of deep convective clouds follow the seasonal patterns of the surface rainfall rates. The deep convective clouds over land penetrate more frequently into the tropical tropopause layer than those over ocean. The averaged deep convective cloud fraction is about 0.3% in the tropics and convective overshooting contributes about 22% to this.