Sea Spray and Air-Sea Fluxes: Key Elements in Earth System Modeling of Weather and Climate

Air-sea fluxes of mass, heat, and momentum have a profound impact on global weather and climate. Water vapor evaporated from the oceans is a major source of moisture for global precipitation, and salt and organic aerosols produced from the oceans provide cloud nucleation sites and participate in microphysical processes. Transfer of latent and sensible heat between the atmosphere and ocean drives the atmospheric circulation and modulates the global water and energy cycle. Wind friction at the ocean surface induces turbulent mixing and transport in the upper ocean and atmospheric boundary layer. Although the air-sea transfer processes occur on small scales, their impact on weather and climate is global. Progress toward accurate modeling of air-sea fluxes has been limited in part because of the complex physical processes controlling the air-sea fluxes and the lack of observations, especially in high-wind conditions such as hurricanes and winter storms, in which extreme wind-induced surface waves and sea spray push the existing air-sea flux formulations into untested territories.

The goal of this study is to develop an air-sea interface module which accounts for the effects of sea spray on air-sea fluxes to improve prediction of weather and extreme weather events. Following prior examples for calculation of spray-mediated fluxes and feedback effects of spray, this work will create a physically-based interface module in which spray-mediated fluxes are computed in fully coupled atmosphere-wave-ocean model that can represent realistic wind and wave characteristics. The coupling framework has been developed and tested in the Unified Wave INterface-Coupled Model (UWIN-CM, see Chen et al. 2013; Chen and Curcic 2016). This air-sea interface module is now built to be compatible with the NASA GMAO modeling framework, with the intent of eventually being incorporated into GMAO modeling system to make Earth System model predictions. The model simulations with the new air-sea fluxes module are evaluated and validated using NASA satellite data, e.g., surface wind products of the Ocean Vector Winds Science Team (OVWST), gridded air-sea fluxes (OAFlux), and surface waves data from the Cyclone Global Navigation Satellite System (CYGNSS), and on-going aircraft measurements.

The new air-sea interface module is fully tested in the regional high-resolution coupled atmosphere-wave-ocean model, i.e., UWIN-CM simulations of high-impact weather systems such as hurricanes and winter storms, and tested in the global GMAO GEOS-5 model for simulations up to 1-2 months. The air-sea flux module will also be designed to facilitate future augmentation with additional physics. The result will be a product which may be incorporated into the next generation of weather prediction tools, advancing NASA Earth Science Research Program’s goal of improving the capability to predict weather and extreme weather events. Results from UWIN-CM and GEOS-5 will presented at the conference.