Abstract
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.
Highlights
Warm precipitating cloud (WPC) refers to the cloud producing rain with cloud top temperature above 273 K
We begin by presenting the geographic distributions of various quantities that characterize the total, EL-warm precipitating cloud (WPC) and extreme-heavy warm precipitating cloud cloud (EH-WPC) from macrophysical and microphysical characteristics, observed by both
It is clear that the total WPC mainly occurs in the North-west Pacific, and South Pacific Convergence Zone (SPCZ), accounting for approximately 22% of the total detected pixels
Summary
Warm precipitating cloud (WPC) refers to the cloud producing rain with cloud top temperature above 273 K. If the particles grow large enough, they fall as drizzle or rain Cloud parameters, such as the cloud effective radius, optical depth and so on, are the key indicators of this cloud phase and process. The low clouds could reduce the net radiation balance on a globally annually averaged basis by nearly 15 W m−2 , and these low clouds of mid-latitude stratus have a very strong impact on the net radiation budget with summer values of cloud forcing lower than −100 Wm−2 [6] Knowledge of these important properties of WPCs has been enabled by the significant progress in satellite observations in the past several decades. From joint CloudSat and MODIS observations, Suzuki et al [36] investigated the microphysical process of warm rain from cloud to precipitation on the global scale They found that the slope of CloudSat reflectivity changes with MODIS optical depth to provide a gross measure of the collection efficiency factor.
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