The Upscale Growth of Convective Systems over Tropical Oceans

Abstract:

Mesoscale Convective Systems (MCSs) account for significant proportions of rainfall and produce spatially broad, top-heavy latent heating profiles, which have critical impacts upon global weather and climate, and their future projections. While the growth of convection into MCSs (upscale growth) over land and especially in the mid-latitudes is reasonably well understood, the processes that lead to upscale growth over tropical oceans are not. This problem is compounded by a severe lack of data over tropical oceans, especially for quantifying the temporal changes in MCSs. This research seeks to answer two questions regarding the upscale growth of tropical oceanic MCSs: (1) Where and when does it occur? (2) What environmental conditions are conducive for upscale growth to occur?

We quantify the temporal variability of tropical oceanic MCSs by tracking precipitation systems in the Integrated Multi-SatellitE Retrievals for GPM (IMERG). We show that upscale growth predominantly occurs in the ITCZ with little spatial variability throughout the ITCZ. Further, there is a weak diurnal cycle that peaks in the early morning hours. MCS environments are characterized using various satellite measurements and multiple reanalyses. Correlations are drawn between time-series of these environments and an index that quantifies upscale growth using MCS rain volume and area.