Oceanic Convective Systems: ASCAT and NEXRAD Retrieval Analysis

The goal of this research initiative is to study high-impact weather events over the ocean by combining low-earth orbiting scatterometer data with retrievals from coastal NEXRAD sites with dual-polarization capabilities. The Advanced Scatterometer (ASCAT) operating at C-band is implemented as the main scatterometer sensor on board Metop-A and -B, which have a time mean overpass difference of ~49 min during the period of analysis. The ASCAT Level-2 Ocean Surface Wind Vectors Optimized for Coastal Ocean product, with spatial resolution of 12.5 km, are being used throughout the study. NEXRADs provide vertical distribution of hydrometeor identification and low-level single-Doppler retrievals with high temporal and spatial resolution. Several studies have compared scatterometer rain estimates with NEXRAD rain retrievals by collocating and averaging the corresponding cells to match the resolution of the scatterometer. This study identifies oceanic convective storms that produced heavy rainfall based on collocated ASCAT overpasses within view of coastal NEXRADs, and aims to leverage the dual-polarization capabilities to better understand storm development and evolution. In order to compare the datasets in a 1-1 basis, the dual-pol data are re-gridded to match the resolution of the scatterometer. Doppler winds are also re-gridded for comparison with the ASCAT retrievals. A case study in Corpus Christi (TX) on September 23, 2014 is being studied, in which both platforms identify a widespread, long-lived convective storm. Using the re-gridded winds, ASCAT observes a convergence zone at the ocean surface, while aloft the radar observes divergence, which may be an indication of updraft at low levels. Retrieved winds from ASCAT are high (19 m/s max) within the precipitation core, possibly related to the heavy radar-estimated rain rate (130 mm/hr max).  Doppler winds achieved a maximum near 20 m/s, and indicated a sheared environment with ASCAT measuring southeasterly flow near the surface, while the radar measured westerly flow aloft. Liquid Water Path (LWP) revealed that the highest LWP are associated with reduced wind speeds, suggesting attenuation effects on scatterometer wind retrievals. In order to further investigate the life cycle of these storms, more cases will be analyzed and discussed.