Abstract
Processes at the air-sea interface govern the climate mean state and
climate variability by determining the exchange of momentum, heat, and
water between the atmosphere and ocean. Traditional climate models
compute those exchanges across the air-sea interface by assuming an
ocean surface with roughness determined by wind and stability
conditions, essentially assuming ocean surface waves are in equilibrium
states. In reality, that is rarely the case. Such effects have been
emphasized in numerical weather predictions for weather systems like
tropical cyclones. An accurate representation of ocean surface waves
requires a prognostic ocean surface wave model. The addition of
WAVEWATCH III (WW3) to the Community Earth System Model 2 (CESM2) makes
it possible to parameterize the impacts of ocean surface waves on
momentum and energy exchange. This study documents our implementation of
a wave-state-dependent surface flux scheme in CEMS2. Our scheme
considers the effects of waves on ocean surface roughness and those of
sea spray on surface sensible and latent heat. We found that the new
scheme significantly impacts the mean atmospheric circulation and the
upper ocean. The errors in mean atmospheric circulation and surface
temperature patterns are reduced. The modified surface flux lowers the
eddy-driven jet speed and weakens the Hadley circulation. Global mean
sea surface temperature (SST) warm bias is reduced due to the cooling of
the Southern Ocean and eastern boundary currents. In particular, the
eastern Pacific exhibited a weak cooling trend in the historical
simulation for the recent decades, reducing the existing SST trend bias
in CESM2.