In relation to INDOEX project, the ultimate goal of this study is to assess the aerosols's effect on cloud microphysics. As the first step, we have developed a retrieval algorithm that retrieves liquid water path and effective radius from collocated microwave and visible observations made by airborne radiometers above cloud top and observations made by radiometers on board TRMM satellite. The aircraft observations were conducted during 1999 INDOEX intensive observation period (January through March) over Indian Ocean by microwave radiometer AIMR (37 and 90 GHz) and Multichannel Radiometer MCR (0.63 micron among others). Data from similar frequencies (wavelength) of TMI and VIRS on TRMM satellite were used for the satellite version of the algorithm. The algorithm first determines liquid water path from microwave data. A lookup table to find effective radius from liquid water path and visible reflection function is generated using a radiative transfer model. Given a collocated pair of retrieved liquid water path and observed visible reflection function, the effective radius is determined from the lookup table.

The retrieval and data analysis are conducted for the period of January to March of 1999 over the northen Indian Ocean using both the aircraft and satellite measurements. The observed clouds are mostly low level cumulus and stratocumulus. Based on the typical atmospheric conditions in this region, error analysis has been done using a Monte Carlo procedure. Results show that on average, cloud depth, retrieved liquid water path and effective radius, and observed anthropogentic aerosol concentration all have noticable North-South gradients in this region during this time period. We are analyzing the retrievals to evaluate how (or whether) these parameters are interrelated. This analysis will help us better understand the aerosols' effect on influencing cloud microphysics,which further affects cloud albedo.