Cloud-Precipitation Parameters and Radiative Forcing of Warm Precipitating Cloud over the Tropical Pacific Ocean Based on TRMM Datasets and Radiative Transfer Model

An approach is proposed for combining observations from the Precipitation Radar (PR) and the Visible and Infrared Scanner (VIRS) onboard the TRMM (Topical Rainfall Measuring Mission) satellite to investigate the climatology of warm precipitating cloud (WPC) microphysical properties, such as cloud effective radius (Re), cloud optical depth (Tau), and liquid water path (LWP) in the tropical Pacific Ocean (20° S–20° N) from 1998 to 2012. The WPCs are captured by VIRS/PR and categorized into two extreme (light and heavy) rain rate types (EL-WPC, EH-WPC). Their radiative effects are also simulated by the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) radiative transfer model. The results indicate that total, EL-WPC and EH-WPC reach their highest occurrence frequencies of 22%, 1.6% and 2.0% in the North-west Pacific, Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ), respectively. Most of the EL-WPC has higher ratio to total WPC in the Pacific warm pool with warmer sea-surface temperature (SST), while the higher ratio for EH-WPC is located in SPCZ associated with deep convection. WPC has an average Re of 15.6 μm, Tau of 20, and LWP of 200 g m−2. EL-WPC is a little larger average Re than EH-WPC, and larger Re is distributed with higher echo top height (H). Moreover, for EH-WPC, the increased Re by the collision-coalescence process in lower H (<3.5 km) generates a stronger rain rate. In addition, although the H of EH-WPC decreases along the increased brightness temperature at 10.8 μm (BT4), this is not obvious in EL-WPC possibly due to a certain echo height to generate a light precipitation. With an increased rain rate of WPC, Re becomes larger in EL-WPC and smaller in EH-WPC. EL-WPC induces a cooling of approximately −0.5 W m−2 for radiative forcing, which is −3.0 W m−2 less than the EH-WPC.