A new generation of Tropical Cyclone Size measurements from space

Combined microwave brightness temperature measurements from recent L- and dual C-band satellite radiometers provide new estimates of surface wind speed structure in Tropical Cyclones which enhances temporal sampling capability for gale (34-knots), damaging (50-knots) and destructive (64-knots) wind radii.Wind radii estimates in Tropical Cyclones (TC) are crucial to help determine the TC wind structure for the production of effective warnings and to constrain initial conditions for a number of applications. In that context, we report on the capabilities of a new generation of satellite microwave radiometers operating at L-band frequency (~1.4 GHz) and dual C-band (~6.9 and 7.3 GHz). These radiometers provide wide swath (> 1000 km) coverage at a spatial resolution of ~40 km and revisit of ~3 days. L-band measurements are almost unaffected by rain and atmospheric effects, while dual C-band data offer an efficient way to significantly minimize these impacts. During storm conditions, increasing foam coverage and thickness at the ocean surface sufficiently modify the surface emissivity at these frequencies, and in turn the brightness temperature (Tb) measurements. Based on aircraft measurements, new geophysical model functions have been derived to infer reliable ocean surface wind speeds from measured Tb variations. Data from these sensors collected over 2010-2015 are shown to provide reliable estimates of the gale-force (34-kt), damaging (50-kt), and destructive winds (64-kt), within the Best-track wind radii uncertainty. Combined, and further associated with other available observations, these measurements can now provide regular quantitative and complementary surface wind information of interest for operational TC forecasting operations