Tropical Cloud Cluster Variability and Genesis Productivity

Tropical cloud clusters (TCCs) are large areas of deep convection and associated cirrus outflow that occur over tropical oceans. They play a critical role in the energy balance of the tropics, releasing large amounts of latent heat high in the troposphere. If conditions are favorable, TCCs can develop into tropical cyclones (TCs), which put coastal populations at risk. Previous work, usually connected with large field campaigns, has investigated TCC characteristics over small areas and time periods. Recently, developments in satellite reanalysis and global best track assimilation has allowed for the creation of a much more extensive database of TCC activity.

We use the TCC database to produce an extensive global analysis of TCCs, focusing on TCC variability and genesis productivity (GP) over a 28-year period (1982-2009). We show that global TCC frequency was fairly consistent over the time period, with relatively small interannual variability and no noticeable trend. However, regional analyses show a high degree of interannual variability among the world's ocean basins with clear trends in some regions. Approximately 1600 TCCs develop around the globe each year; 7% of those develop into TCs. The East Pacific Basin (EPAC) produces the highest number of TCCs (per unit area) in a given year, but the West Pacific Basin (WPAC) has the highest GP (~12%). Annual TCC frequency in some basins exhibits a strong correlation to the sea surface temperature (SST), particularly the EPAC, North Atlantic (NATL), and WPAC. However, GP is not as sensitive to SST, supporting the idea that tropical cyclogenesis is controlled primarily by atmospheric dynamical considerations.