Mesoscale Organizations and Convective Properties of Developing and Nondeveloping Tropical Disturbances over the Northwest Pacific Ocean

Mesoscale convective processes and related dynamic/thermodynamic responses may play an important role in the Tropical Cyclone (TC) genesis, in addition to the favorable environmental conditions. The objective of this study is to determine whether and how unique are mesoscale organizations and convective properties of tropical disturbances prior to TC formation in the Northwest Pacific. Previous studies with a similar goal are based on either a small sample size or limited observational source (e.g., only Infrared). This study identifies over 3000 episodes of developing (Dev) and nondeveloping (Nondev) tropical disturbances and utilizes a large amount of multi-source satellite observations (precipitation, infrared, microwave, spaceborne radar, etc.) to comprehensively compare their convective structures. The Dev and Nondev disturbances were borne in similar large-scale environments such as SST, low-level vorticity, vertical wind shear, except that the Dev tropospheric conditions are slightly moister. However, the frequency, organization, intensities, and ensemble microphysics of the convection are significantly different between Dev (48-96h prior to TC formation) and Nondev. Both Dev and Nondev show very asymmetric distributions of convection with maxima in the down-shear quadrants, but Dev systems have greater areas of precipitation and cold clouds. The embedded individual convective systems of Dev are also more organized, i.e., greater areas and higher stratiform rain fraction. Furthermore, Dev convection is stronger and present greater ice-phase content as indicated by both the passive microwave and spaceborne measurements. Interestingly, Dev disturbances also have markedly higher frequency of shallow warm convection, especially in the up-shear regions, which may help moistening the lower-to-middle troposphere and beneficial for further deep convective developing. In most of the Dev storms, convection rapidly become more organized and deeper during 24-48 prior to the TC genesis. This study further compares the organization and convective properties among Dev systems generated under different types of large-scale flow pattern such as monsoon trough and easterly wave.