Large-Scale Environmental Impacts on Organization of Precipitation Systems
Tropical convection is often organized into clusters. But due to the insufficient understanding of the mechanisms behind, description of convective organization is still missing in GCMs, and it is even more challenging to represent its feedbacks on the convection development. To identify the favorable thermodynamical and dynamical large-scale environmental conditions for the convective organization, a 15-yr Tropical Rainfall Measuring Mission (TRMM) Precipitation Feature (RPF) database is combined with ERA-Interim reanalysis. Based on sizes and maximum echo top heights, RPFs between 36°S-36°N are classified into shallow isolated, shallow organized, deep isolated and deep organized. Firstly, we show the global distribution of these four types of RPFs, and quantify their contribution to total precipitation. Secondly, in combination with the meteorological variables from the ERA-Interim, we differentiate the environmental properties favoring these four types of RPFs to understand what factors benefit the convective organization. A series of analyses show that moisture convergence at surface, mid-level (700-300hPa) moisture, low-level (1-3km) wind shear and upper level vertical velocity play important roles in clustering the convection. Organized systems occur more likely in the environment with stronger surface moisture convergence, higher mid level relative humidity and strong low-level wind shear. However, there are large regional and seasonal variations in the influences of these factors. Generally, systems are relatively easier to be organized over ocean than over land.