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A Lagrangian Perspective on Deep Convective Tropical Raining Systems

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February 15, 2013
David Duncan
Hosted by Chris Kummerow (advisor), Dave Thompson, Steven Reising (Electrical and Computer Engineering)

Abstract

Deep convective precipitating systems are categorized, tracked, and analyzed in the Tropical Ocean. Precipitating systems are tracked via an algorithm applied to the high-resolution CPC Morphing technique (CMORPH) precipitation product. Systems are categorized with an objective method, using data from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and a K-means clustering algorithm that exploits the consistency and similarity of tropical precipitation regimes. Propagation characteristics of these systems are found to be remarkably similar between ocean basins. The raining system’s geographic center is calculated at each time step, allowing various ancillary datasets to be co-located with these systems to permit analysis of the effect of deep convective raining systems on local oceanic environments. The ancillary fields examined comprise elements of the water and energy budgets, as well as cloud field information from the International Satellite Cloud Climatology Project (ISCCP).

The biggest determinant of a system’s environmental impact is its propagation speed. This finding is corroborated by analysis of cloud fields which show that slow-moving systems and their associated deep clouds persist longer in a given location and therefore have a greater impact on the local environment than systems that move through more quickly. In the mean, sea surface temperature (SST) drops by ~0.15°C and total precipitable water (TPW) increases by 5-7kg/m2 due to the passage of a deep convective raining system, but impacts vary depending on system speed and ocean basin. The existence of a possible precipitation feedback based on system propagation speed is also explored.