Satellite signature of the instantaneous wind response to mesoscale oceanic thermal structures

Abstract

The thermal air‐sea interaction mechanism that modulates the atmospheric mixing by the sea surface temperature (SST) variability is studied with long‐term consistent satellite records. Statistical analyses of daily and instantaneous wind and SST data are performed over the major western boundary currents (WBCs). This wind‐SST coupling, that is mediated by the atmospheric mixing, is found to be very relevant on daily, and even shorter, time scales. Co‐located and simultaneous SST and surface wind fields (from Advanced Very High Resolution Radiometer and Advanced Scatterometer data) reveal that the atmosphere responds instantaneously to the presence of SST structures with a larger coupling coefficient with respect to daily and monthly time averaged fields. The coupling strength varies seasonally over the WBCs in the Northern Hemisphere, with the winter‐time coupling being the lowest. Reanalysis data show that this behaviour is related to the seasonality of the air‐sea temperature difference over the region of interest. Over the Northern Hemisphere WBCs, dry and cold continental air masses drive very unstable conditions, associated with a very weak thermal air‐sea coupling.This article is protected by copyright. All rights reserved.

Atmospheric Fronts Shaping the (Sub)Mesoscale SST‐Wind Coupling Over the Southern Ocean: Observational Case

“…On the front day (between black vertical lines in Figure 7), the daily averaged scale SST‐wind coupling decreased when the atmospheric front passed by (Figure 7a). Concurrently, surface wind speeds increased (Figure 7c), and the air‐sea temperature difference decreased (Figure 7d), both of which are known to enhance SST‐wind coupling (Desbiolles et al., 2023; Foussard et al., 2019; Meroni et al., 2023). This suggests that the influence of atmospheric fronts may counteract the expected enhancement of SST‐wind coupling.…”

“…While it is evident that the atmospheric front contributes to a decrease in SST‐wind coupling, it is important to acknowledge that other factors, such as wind speed and atmospheric stability, can also exert influence (Desbiolles et al., 2023; Foussard et al., 2019; Meroni et al., 2023; O’Neill et al., 2017). Figure 7 shows the regional averaged essential variables variation across the region.…”

“…The SST-wind coupling coefficients are determined by multiple other factors, including the background wind speed, the atmospheric stability, synoptic perturbations, and so on. The distinct SST-wind coupling curve across the global ocean has been well-studied and documented in previous studies (Chelton et al, 2004;Desbiolles et al, 2023;Foussard et al, 2019;Meroni et al, 2023;O'Neill et al, 2012). The synoptic perturbations Journal of Geophysical Research: Atmospheres 10.1029/2023JD039386 (atmospheric front, extratropical cyclones, etc) are used to be regarded as the synoptic noise (Schneider, 2020;Schneider & Qiu, 2015) and thus their role in affecting the coupling has been largely overlooked.…”

Study of Quality Control Methods Utilizing IRMCD for HY-2B Data Assimilation Application

“…Observational data are essential for the assimilation of numerical weather predictions (NWP); however, the acquisition of ocean surface wind (OWS) field data is challenging because of limited observation equipment. Satellite-borne scatterometers are effective in observing wind over the ocean [1][2][3][4][5]. The launch of the HaiYang-2B (HY-2B) satellite equipped with a Ku-band scatterometer (HSCAT-B) improved the capacity to acquire OWS data and is expected to further improve NWP.…”