Utilizing CYGNSS Near Surface Winds to Improve Surface Sensible and Latent Heat Flux Estimates

Surface latent and sensible heat fluxes play an important role in Earth’s climate and weather as they transfer mass, momentum, and energy between the surface and lower troposphere. These fluxes, driven by surface wind and strong vertical gradients of temperature and specific humidity, can increase instability within the boundary layer and have been shown to drive various weather phenomena, like extreme marine cyclogenesis. Though it is difficult to measure latent and sensible heat fluxes directly, we can estimate them by using direct observations of temperature, specific humidity, and surface wind. Though relatively dense observations of these quantities are available over land from numerous in situ observations, there are deficiencies in measurements over the ocean where there is often a sole dependence on space borne instruments. While there are various space borne instruments that can accurately observe temperature and specific humidity in most conditions, current and previous scatterometers, like ASCAT and QuikSCAT, cannot accurately measure surface winds in the presence of precipitation. These inaccuracies can lead to incorrect estimates of latent and sensible heat fluxes.

The Cyclone Global Navigation Satellite System (CYGNSS), launching November 2016, aims to improve current estimates of surface winds over most of the world’s oceans as it will use the GPS L1 channel (1575 MHz, 19-cm wavelength), which does not experience appreciable attenuation in the presence of heavy clouds and precipitation, especially within tropical cyclones. It is our aim to show that CYGNSS’s improved surface wind estimates will lead to better estimates of surface heat fluxes over the oceans in nearly all weather conditions.

The motivation for the work presented here stems from a case study of a strong marine extratropical cyclone (ETC) that occurred in November 2006 off the Atlantic coast of the United States (Crespo and Posselt 2016). Various observations from CloudSat showed a compelling stratiform-to-convective transition in the warm front’s cloud structure and thermodynamic field. Initial examination of reanalysis data indicate large values of surface latent and sensible heat fluxes, correlating with faster surface wind speeds, around the cyclone that could have directly contributed to the cyclone’s intensification and warm frontal convective transition. Though CYGNSS’s mission will be focused in the tropics with its tropical orbit inclination, we will demonstrate its potential ability to observe extratropical cyclones forming in the lower midlatitudes and their associated surface fluxes.