Examination of tropical variability with organization metrics applied to large-scale convective systems identified by hybrid cloud-precipitation regimes

Abstract:

Large-scale tropical convective systems often grow larger than 100,000km² sizes and play a significant role in tropical weather and climate. Previously, we identified synoptic scale convective systems using tropical cloud regimes (TCRs) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations. In this study, the TCRs are enhanced by embracing Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation data. The resulting hybrid tropical cloud-precipitation regimes (TCPRs) exhibit greater skill over previous TCRs in terms of “seamless” identification of convective systems and their organization.

In order to assess organization and evaluate its role in physical processes, we use various convective organization metrics previously developed, namely: (1) Convective Organization Potential (COP), (2) Organization index (I_org), (3) Simple convective aggregation index (SCAI), and (4) Modified SCAI (MCAI). We apply the above metrics to TCPR aggregates (contiguous areas of the most convective TCPRs) in the tropical Indo-Pacific warm pool region. With the obtained time series of 4 organization metrics, we examine the variability of convective organization at different time scales, i.e. diurnal cycle, intra-seasonal, and interannual variability. Using standard temporal correlation analysis, we find that for the same TCPR aggregations, each organization metric signifies different variability corresponding to the above time scales. For example, one metric co-varies better with Madden-Julian Oscillation (MJO) activity indicators, while another corresponds better to El Niño-Southern Oscillation (ENSO) strength. We investigate possible causes of such different behaviors of organization metrics and explore different aspects of the generalized variability of convective systems at various time scales.