Using “Rapid Revisit” CYGNSS Wind Speed Measurements to Detect Convective Activity

The Cyclone Global Navigation Satellite System (CYGNSS) is a spaceborne GNSS-reflectometry mission, which was launched on December 15, 2016 for ocean surface wind speed measurement. CYGNSS includes eight small satellites in the same low earth orbit, so that the mission provides wind speed products having unprecedented coverage both in time and space to study multitemporal behaviors of oceanic winds. The nature of CYGNSS coverage results in some locations on earth experiencing multiple wind speed measurements within a short period of time (a “clump” of observations in time) resulting in a “rapid revisit” series of measurements. Such observations seemingly can provide indications of regions experiencing rapid changes in wind speeds, and therefore serve as an indicator of convective activity. An initial investigation of this concept using simulated and on-orbit CYGNSS measurements is provided in this paper. The temporally “clumped” properties of CYGNSS measurements are examined, and the results show that clump durations and spacing vary with latitude. For example, the duration of a clump can extend as long as a few hours at higher latitudes, with gaps between clumps ranging from 6 to as high as 12 h depending on latitude. Initial examples are provided to indicate the potential of changes within a clump to detect convective activity through a comparison with convective activity indicators derived from model datasets. The results at present are limited by the ongoing calibration of CYGNSS wind speed retrievals, so that future work will be required to obtain a more complete assessment, but nevertheless clearly indicate the potential utility of the method for studies of atmospheric convection.