Extensive high-resolution Synthetic Aperture Radar (SAR) data analysis of Tropical Cyclones: comparisons with SFMR flights and Best-Track
|Author(s)||Combot Clement1, Mouche Alexis1, Knaff John2, Zhao Yuan1, Zhao Yuan1, Vinour Leo1, Quilfen Yves1, Chapron Bertrand1|
|Affiliation(s)||1 : Laboratoire d’Océanographie Physique et Spatiale, Institut Français de Recherche pour l’Exploitation de la Mer, Plouzané, France
2 : NOAA/NESDIS Regional and Mesoscale Meteorological Branch, Fort Collins, Colorado, USA
|Source||Monthly Weather Review (0027-0644) (American Meteorological Society), 2020-11 , Vol. 148 , N. 11 , P. 4545–4563|
To produce more precise descriptions of air-sea exchanges under Tropical Cyclones (TCs), spaceborne Synthetic Aperture Radar (SAR) instruments provide unique capabilities to probe the ocean surface conditions, at very high spatial resolution, and on synoptic scales. Using highly-resolved (3 km) wind fields, an extensive database is constructed from Radarsat-2 and Sentinel-1 SAR acquisitions. Spanning 161 tropical cyclones, the database covers all TC intensity categories that have occurred in five different TC basins, and include 29 cases coincident with SFMR measurements. After locating the TC center, a specific methodology is applied to filter out areas contaminated by heavy precipitations to help extract, for each acquisition, the maximum wind speed (Vmax), its associated radius (Rmax), and corresponding outer wind radii (R34/50/64-kt). These parameters are then systematically compared with Best-Track (BTK), and when available, SFMR airborne measurements. For co-located SFMR and SAR observations, comparisons yield root-mean-squares of 3.86 m s−1 and 3 km, for ocean surface wind speeds and TC Rmax, respectively. High correlations remain for category 5 cases, with Vmax exceeding 60 m s−1. The largest discrepancies are found between BTK and SAR Rmax estimates, with Rmax fluctuations poorly captured by BTK, especially for rapidly evolving category 3,4 and 5 TCs. In heavy precipitation (>35 mm h−1), the SAR C-band measurements may be impacted, with local ambiguities associated to rain features, as revealed by external rain measurements. Still, this large dataset demonstrates that SAR measurements have unique high-resolution capabilities, capturing the inner- and outer-core radial structure of the TC vortex, and provide independent and complementary measurements than those used for BTK estimates.