Introducing New Metrics for the Atmospheric Pressure Adjustment to Thermal Structures at the Ocean Surface

• Published in: Journal of geophysical research. Atmospheres 2022-08, Vol.127 (16), p.n/a
• Main Authors: Meroni, Agostino N., Desbiolles, Fabien, Pasquero, Claudia
• Format: Article
• Language: English
• Subjects: air‐sea interactions; meso‐ and sub‐mesoscale; numerical simulations; pressure adjustment; wind response
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2021JD035968

Thermal structures at the sea surface are known to affect the overlying atmospheric dynamics over various spatio‐temporal scales, from hourly and sub‐kilometric to annual and O(1,000 km). The relevant mechanisms at play are generally identified by means of correlation coefficients (in space or time) or by linear regression analysis using appropriate couples of variables. For fine spatial scales, where sea surface temperature (SST) gradients get stronger, the advection might disrupt these correlations and, thus, mask the action of such mechanisms, just because of the chosen metrics. For example, at the oceanic sub‐mesoscale, around 1–10 km and hourly time scales, the standard metrics used to identify the pressure adjustment mechanism (that involves the Laplacian of sea surface temperature, SST, and the wind divergence) may suffer from this issue, even for weak wind conditions. By exploiting high‐resolution realistic numerical simulations with ad hoc SST forcing fields, we introduce some new metrics to evaluate the action of the pressure adjustment atmospheric response to the surface oceanic thermal structures. It is found that the most skillful metrics is based on the wind divergence and the SST second spatial derivative evaluated in the across direction of a locally defined background wind field. Plain Language Summary The ocean surface is characterized by a range of warm and cold structures that are known to influence the overlying atmospheric flow through different mechanisms. One of these mechanisms involves the variation of sea level pressure that can drive secondary wind circulations according to how the sea surface temperature is distributed in space. To assess whether this mechanism is in action, the co‐location of sea temperature maxima (or minima) with zones of wind convergence (divergence) is generally considered. However, the presence of the wind itself has been shown to displace and delay the wind response so that there are cases where the pressure field responds to the sea temperature forcing but this is not detected by the standard metrics. Since pressure variability is generated in all directions, we propose to measure this kind of wind response in the direction perpendicular to the background wind in order to avoid the masking effect of the background wind. Key Points The standard metrics for the pressure adjustment mechanism is adversely affected by advection Three new metrics are introduced and tested The pressure adjustment is detectable