Use of Sentinel-1 C-Band SAR Images for Convective System Surface Wind Pattern Detection
Résumé
Convective systems (CS) through their downdrafts hitting the sea surface may produce wind patterns (or cold pools) with wind intensity exceeding 10–25 m s−1. The latter for a long time have been significant for weather forecast and meteorological studies, especially in the tropical regions like the Gulf of Guinea since it is hard to detect the CS-associated wind patterns. Based on Sentinel-1 images [C-band Synthetic Aperture Radar (SAR)] with high spatial resolution and large swath, the current study proposed the detection of surface wind patterns through wind speed estimation by C-band model 5.N (CMOD5.N; for vertically polarized images) and two models proposed by Sapp and Komarov (for horizontally polarized images). Relative to the X-band SAR, the effects of precipitation on C-band radar backscattering are negligible, and thereby it has little impact on wind speed estimation from Sentinel-1 images. The detected surface wind patterns include a squall line and a bow echo at the mesoscale (>100 km) and many submesoscale (<100 km) convection cells. They are accompanied by various degrees of precipitation (from light to heavy rain). This study also used Meteosat infrared images for monitoring and detection of deep convective clouds (with low brightness temperature) corresponding to surface wind patterns. The agreement in location and sometimes in shape between them strengthened the assumption that the CS downdrafts may induce the sea surface patterns with high wind intensity (10–25 m s−1). In particular, because of the Sentinel-1 high spatial resolution, the pattern spots with high winds (20–25 m s−1) are detected on the illustrated images, which was not reported in the literature. They are located close to the coldest convective clouds (about 200-K brightness temperature).