A New Generation of Tropical Cyclone Size Measurements from Space

Legend: Wind radii estimates from (left) the best track and from (right) the merged SMOS/SMAP/AMSR-2 surface wind dataset retrieved along the tracks of Hurricanes (a),(b) Jimena; (c),(d) Ignacio; and (e),(f) Kilo. All wind radii estimates are shown at every satellite intercepts time with 34-, 50-, and 64-kt wind radii being displayed in blue, cyan, and red, respectively. After Reul et al., 2017

Wind radii estimates in tropical cyclones (TCs) are crucial to helping 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 (>1,000 km) coverage at a spatial resolution of ∼40 km and revisit of ∼3 days. The 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 2010–15 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.

These results are detailed in the following publication:

Reul Nicolas, Chapron Bertrand, Zabolotskikh E., Donlon C., Mouche Alexis, Tenerelli Joseph, Collard F., Piolle Jean-Francois, Fore A., Yueh S., Cotton J., Francis P., Quilfen Yves, Kudryavtsev V. (2017). A new generation of Tropical Cyclone Size measurements from space . Bulletin Of The American Meteorological Society , 98(11), 2367-2386 . Publisher's official version : https://doi.org/10.1175/BAMS-D-15-00291.1 , Open Access version : https://archimer.ifremer.fr/doc/00376/48758/