Journal Article

Observations Reveal Intense Air‐Sea Exchanges Over Submesoscale Ocean Front

Li, Mingkui, Ma, Ke, Sun, Shantong, Cai, Wenju, Chen, Zhaohui, Gan, Bolan, Wu, Lixin, Cai, Jinzhuo, Ma, Xiaohui, Sun, Bingrong, Yang, Haiyuan, Jing, Zhao

2024

Overview

Air‐sea exchanges across oceanic fronts are critical in powering cloud formation, precipitation, and atmospheric storms. Oceanic submesoscale fronts of scales 1–10 km are characterized by strong sea surface temperature (SST) gradients. However, it remains elusive how submesoscale fronts affect the overlying atmosphere due to a lack of high‐resolution observations or models. Based on rare high‐resolution in situ observations in the Kuroshio Extension region, we quantify the air‐sea exchanges across an oceanic submesoscale front. The cross‐front SST and turbulent heat flux gradients reaches 2.4°C/km and 47 W/m2/km, respectively, far stronger than that typically found in mesoscale‐resolving products. The stronger SST gradient drives substantially stronger air‐sea fluxes and vertical mixing than mesoscale fronts, enhancing cloud formations. The intense air‐sea exchanges across submesoscale fronts are confirmed in idealized model simulations, but not resolved in mesoscale‐resolving climate models. Our finding provides essential knowledge for improving simulations of cloud formation, precipitation, and storms in climate models. Plain Language Summary Oceanic fronts, characterized by large sea surface temperature (SST) gradients, are ubiquitous in the global ocean. Through intense heat and moisture release, these oceanic fronts induce large horizontal gradient of sea level pressure or increasing vertical mixing intensity in the lower atmosphere, are critical in powering cloud formation, precipitation, and atmospheric storms, but are sensitive to SST gradients. Oceanic submesoscale fronts of spatial scales 1–10 km are characterized by strong SST gradients. However, our knowledge of how the submesoscale fronts affect the overlying atmosphere is by and large void, due to a lack of high‐resolution observations or models. Here, based on high‐resolution in situ observations and model simulations, we show that submesoscale fronts drive much stronger air‐sea exchanges and vertical mixing as compared to mesoscale fronts, with significant implications for marine atmosphere boundary layer changes and cloud formations. Limited by the coarse resolution, the intense air‐sea exchanges across submesoscale fronts are not resolved in mesoscale‐resolving climate models. These results highlight the importance of submesoscale air‐sea interactions and call for a proper representation of submesoscale air‐sea exchanges in the next generation of climate models. Key Points Observations show strong gradient in sea surface temperature and turbulent heat flux across a submesoscale oceanic front Submesoscale fronts drive substantially stronger air‐sea fluxes and vertical mixing than mesoscale fronts The intense air‐sea exchanges across submesoscale fronts are not resolved in mesoscale‐resolving climate models

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Air / Air-sea interaction / Air‐sea exchanges / Atmosphere / Atmospheric models / Boundary layers / Climate / Climate models / Cloud formation / Clouds / Heat flux / Heat transfer / In situ observation / Lower atmosphere / Mesoscale phenomena / Ocean models / Oceanic fronts / Oceanic submesoscale front / Oceans / Precipitation / Sea level pressure / Sea surface / Sea surface temperature / Simulation / Storms / Surface temperature / Temperature gradients / Turbulent heat flux / Vertical mixing