The Impact of Assimilating CYGNSS Ocean Surface Winds on Momentum and Energy Fluxes in Hurricane Boundary Layers

The NASA Cyclone Global Navigation Satellite System (CYGNSS) has been planned for launch in October 2016. The satellite system will make frequent and accurate measurements of ocean surface winds throughout the life cycle of tropical storms and hurricanes. This will enable scientists to probe key air-sea interaction processes that take place near the core of the storms – processes that are rapidly changing and play a critical role in the genesis and intensification of hurricanes. In this study, the impact of assimilation of CYGNSS ocean surface wind data on momentum and energy fluxes at the air-sea interface within the core of hurricanes is assessed. The NCEP operational hurricane weather research and forecasting (HWRF) model is used in a regional Observing System Simulation Experiments (OSSE) framework with the NCEP gridpoint statistical interpolation (GSI) 3DVAR data assimilation system for this investigation. The regional nature run developed by RSMAS/University of Miami and NOAA/AOML is used for generating the simulated observations and verification purpose. A series of simulated CYGNSS ocean surface winds have been provided by University of Michigan. The ECMWF nature run data at T511 horizontal resolution was used to provide the first guess, initial and boundary conditions for the OSSEs. Various data assimilation and sensitivity experiments have been conducted for developing and intensification phase of a hurricane during 28 July to 11 August 2005 over the Atlantic Ocean. The preliminary results show that the assimilation of CYGNSS ocean surface winds improves the momentum and energy flux in the hurricane inner-core region during the whole 72-h simulation period as the momentum flux, latent heat and sensible heat flux are all enhanced. Because of these improvements, the heating transportations in horizontal and vertical direction are also enhanced, leading to a better hurricane intensity forecast. Further analysis is on going to explain why and through which processes the assimilation of CYGNSS sea surface wind speeds can improve the energy and momentum fluxes. Related results will be presented in the symposium.