Analysis of the Thermodynamics and Dynamics of Tropical Mesoscale Convective Systems

The Tracked IMERG Mesoscale Precipitation Systems (TIMPS), combined with ERA5 reanalysis product and TRMM/GPM are used to identify the thermodynamic and dynamic controls that govern the progression and occurrence of mesoscale convective systems (MCSs). Composites are made of MCSs occurring broadly within the tropics (30ºS to 30ºN) during a period extending from 2014-2016, excluding those associated with tropical cyclones. The life of an MCS is divided into three stages: growth or initiation, propagation and maturity, and then eventual decay. The growth stage shows low level convergence and mid-level divergence. The divergence layer near 500 hPa is characterized by warm and dry anomalies, indicative of a stable layer that caps convection. The propagation and maturity stage is distinguished from the other two life cycle phases in exhibiting a cool and moist lower troposphere. Above this point, moisture and temperature anomalies are negligible. The third stage exhibits low level divergence and convergence in the mid-troposphere and further aloft at the tropopause, indicative of anvil remnants constituted by elevated stratiform clouds and upper-tropospheric cirrus. In contrast to the developing and propagating stages, decay is characterized by a cool and moist mid-layer with elevated moisture sustained through the column above the boundary layer. Surface levels during decay are markedly dry with temperatures averaging a little lower than the lifetime average. The evolution of vertical movement through the full lifecycle is compared to that of buoyancy and the precipitation rate. Greatest buoyancy was observed in the first stage whereas the greatest vertical motion and precipitation rate was observed in the second stage. This temporal gap suggests impacts from gravity waves and their dissipation rate may play a larger role in the development of MCSs than previously thought.