Probing the Spatiotemporal Structure of Hydrometeors in Indian Monsoon Depressions

Indian monsoon depressions are synoptic scale events typically spun up in the Bay of Bengal. They usually last 4-6 days, during which they propagate northwestward across the Indian subcontinent before dissipating over West India or Pakistan. They can have a significant effect on monsoon precipitation, particularly in primarily agrarian North India, and therefore quantifying their structure and variability and evaluating these in NWP and GCMs is of critical importance. In this study, satellite data from the CloudSat and recently concluded TRMM missions are used in conjunction with an independently evaluated tracking algorithm to form a three-dimensional composite image of cloud structure and precipitation within monsoon depressions. Comprising 34 depressions from the 1998-2014 TRMM regime and 12 from the 2007- CloudSat regime, this composite is statistically robust and allows significant probing of the spatiotemporal characteristics of the moisture and hydrometeor fields. Among the key results of this work are the discovery and characterisation of a bimodal, diurnal cycle in surface precipitation; the first picture of the structure of cloud type and density in depressions; the first composite picture of vertical hydrometeor structure in depressions; and novel discussion on drop size distributions and resulting latent heat profiles. Time permitting, the first cross-examination of this study with contemporaneous NWP data will also be presented.