Hurricane Boundary Layer Observations from Dropsondes and COSMIC GPS Radio Occultation

One of the primary challenges hindering the continued improvement of forecasted tropical cyclone track and intensity is the lack of understanding of hurricane boundary layer (HBL) dynamics and structure. Numerical simulations often rely on boundary layer assumptions in parameterizations that tend to disintegrate in tropical cyclone situations. Additionally, in situ observations are limited to sparse radiosonde, GPS dropwindsonde (dropsonde), and aircraft data, primarily from field campaigns and scheduled NOAA Hurricane Hunter flights. Conventional satellite measurements have been very helpful in discerning the nature of hurricanes. However, the lack of cloud penetrating capability of the passive infrared sounders and the low vertical resolution of the passive microwave sounders in tropical cyclone environments prevent us from obtaining the vertical structure of tropical cyclones. This study uses GPS radio occultation (RO) from the Constellation Observation System for Meteorology, Ionosphere and Climate (COSMIC), which offers high vertical resolution boundary layer structure observations in all-weather conditions. GPSRO profiles collocated with storm tracks from IBTrACS (Knapp et al. 2010), dropsondes, and radiosondes allow us to discern specific HBL properties, such as boundary layer thickness, based on patterns of refractivity, temperature, and moisture. The radial vertical profile structure of a tropical cyclone is also extracted. In observing the HBL both in and around tropical cyclone environments, a conceptual model of radial HBL properties will be created to aid in determining parameterization choices for numerical simulations, and improve existing boundary layer parameterizations such that forecast tracks and intensities could improve.