Environmental Control of Wind Response to Sea Surface Temperature Patterns in Reanalysis Dataset

Abstract

Abstract Sea surface temperature (SST) is characterized by abundant warm and cold structures that influence the overlying atmospheric boundary layer dynamics through two different mechanisms. First, turbulence and large eddies in the lower troposphere are affected by atmospheric stability, which can be modified by local SST, resulting in enhanced vertical mixing and larger surface winds over warmer waters. Second, the thermodynamic adjustment of air density to the underlying SST structures and the subsequent changes in atmospheric pressure drive secondary circulations. This paper aims to disentangle the effects of these processes and explore the environmental conditions that favor them. Two main environmental variables are considered: the large-scale air–sea temperature difference (proxy for stability) and wind speed. Using 5 years of daily reanalyses data, we investigate the 10-m wind response to SST structures. Based on linear regression between wind divergence and SST derivatives, we show that both mechanisms operate over a large spectrum of conditions. Ten-meter wind divergence is strongly impacted by the local SST via its effect on vertical mixing for midwind regimes in slightly unstable to near-neutral conditions, whereas the secondary circulation is important in two distinct regimes: low wind speed with a slightly unstable air column and high background wind speed with a very unstable air column. The first regime is explained by the prolonged Lagrangian time that the air parcel stays over an SST structure while the second one is related to strong heat fluxes at the air–sea interface, which greatly modify the marine atmospheric boundary layer properties. Location and frequency of the environmentally favorable conditions are discussed, as well as the response in low-cloud cover and rainfall. Significance Statement The main objective of this study is to explore the wind response to thermal structures at the sea surface under different environmental conditions using the latest atmospheric reanalysis. Recent literature suggests that fine-scale air–sea interactions affect a large spectrum of atmospheric dynamics, from seasonal to weather-type regimes. It is thus important to characterize the atmospheric response to ocean surface variability. Our findings describe the environmental conditions for which the two main physical processes through which the atmosphere responds to sea surface temperature structures are active the most and can guide the development of high-resolution observing missions and campaigns in specific geographical locations and seasons to retrieve data that can be used to improve parameterization in models.