Tropical Ice Water Amount and Its Relations to Other Atmospheric Hydrological Parameters as Inferred from Satellite Data

Abstract

An over-ocean ice water path (IWP) algorithm, using satellite Special Sensor Microwave Water Vapor Sounder (SSM/T-2) data, is presented for clouds during the Tropical Oceans Global Atmosphere Coupled Ocean?Atmosphere Response Experiment. In developing the retrieval algorithm, clouds are first divided into 10 classes based on their top temperatures and microwave radiative properties. Radiative transfer model simulations are then performed for the different classes to establish a relation between IWP and the depression of 150-GHz brightness temperature. Correction to the effect of supercooled liquid water is done by incorporating data of liquid water path (LWP) retrievals from Special Sensor Microwave/Imager (SSM/I) and relative humidity profiles from the European Centre for Medium-Range Weather Forecasts analyses. The algorithm retrievals are compared with the analyses in the International Satellite Cloud Climatology Project (ISCCP) dataset. By using collocated SSM/T-2, SSM/I, and ISCCP data, the relations among IWP and other atmospheric hydrological properties including cloud-top temperature, LWP, rainfall rate, and precipitable water are investigated. The results indicate that IWP tends to increase with the decrease of cloud-top temperature and this correlation is particularly evident for precipitating clouds. LWP retrieved for nonprecipitating clouds has a similar tendency but only for those with top temperatures warmer than 0°C. There is no clear relation between IWP and LWP. The ratio of IWP to total condensed water (IWP + LWP) for nonprecipitating clouds seems to be negatively correlated with cloud-top temperature on an average of a large data volume, but this relationship differs substantially among individual cases. Rainfall rate has a strong correlation with IWP. High values of IWP and LWP are always associated with high precipitable water although high precipitable water does not automatically correspond to high IWP or high LWP.