Effects of Storms on Microwave Brightness Temperatures and its Application to Estimate Cloud Parameters from AMSU-B

Abstract

The goal of this thesis is to understand the effects of storms on microwave brightness temperatures (mainly in the frequency range of 90-190 GHz, the Advanced Microwave Sounding Unit (AMSU)-B channels) and to explore the retrieval of cloud parameters from them.Four observation cases (two over ocean and two over land), analyzed using aircraft passive microwave measurements in the frequency range of 10 to 220 GHz in conjunction with aircraft radar measurements, show that the high frequencies are sensitive to ice scattering in the upper layers of storms, especially the three water vapor channels around 183.3 GHz (183.3±7, 183.3±3, and 183.3±1 GHz). The observations at these frequencies are found to depend crucially on the variations in particle size distribution, ice water path, phase transitiontemperature, and cloud structure.The different sensitivities to altitude and amount ofhydrometeors suggest a method to estimate the canting angle and tilt direction of tilted convective cloud using brightness temperatures at 183.3±1 and 183.3±7 GHz. The method provides a possibility to estimate the vertical displacement of cloud structure and thereby toestimate the accurate location of surface rainfall.Methods to detect deep convective clouds and convective overshooting from measurements at the three water vapor channels of AMSU-B are developed. The averaged deep convective cloud fraction is about 0.3% in the tropics and convective overshooting contributes about 22% to this.Algorithms to estimate the ice water paths in the upper layers of tropical deep convective clouds are developed using the three water vapor channels around 183 GHz of AMSU-B. Although the average amount of deep convective cloud fraction in the tropics is only about 0.3%, itcontributes about 34% to the total ice water path.