Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean–atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air–sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air–sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontal-scale air–sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air–sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air–sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air–sea interaction research. Significance Statement: Recent high-resolution satellite observations and climate models have shown a significant impact of coupled ocean–atmosphere interactions mediated by small-scale (mesoscale) ocean processes, including ocean eddies and fronts, on Earth’s climate. Ocean mesoscale-induced spatial temperature and current variability modulate the air–sea exchanges in heat, momentum, and mass (e.g., gases such as water vapor and carbon dioxide), altering coupled boundary layer processes. Studies suggest that skillful simulations and predictions of ocean circulation, biogeochemistry, and weather events and climate variability depend on accurate representation of the eddy-mediated air–sea interaction. However, numerous challenges remain in accurately diagnosing, observing, and simulating mesoscale air–sea interaction to quantify its large-scale impacts. This article synthesizes the latest understanding of mesoscale air–sea interaction, identifies remaining gaps and uncertainties, and provides recommendations on strategies for future ocean–weather–climate research.

Several very large high‐impact fires burned nearly 4,000 km² of mesic forests in western Oregon during September 7–9, 2020. While infrequent, very large high‐severity fires have occurred historically in western Oregon, the extreme nature of this event warrants analyses of climate and meteorological drivers. A strong blocking pattern led to an intrusion of dry air and strong downslope east winds in the Oregon Cascades following a warm‐dry 60‐day period that promoted widespread fuel flammability. Viewed independently, both the downslope east winds and fuel dryness were extreme, but not unprecedented. However, the concurrence of these drivers resulted in compound extremes and impacts unmatched in the observational record. We additionally find that most large wildfires in western Oregon since 1900 have similarly coincided with warm‐dry summers during at least moderate east wind events. These results reinforce the importance of incorporating a multivariate lens for compound extremes in assessing wildfire hazard risk.

We identified anomalously warm sea surface temperature (SST) events during 1980–2019 near the major upwelling center at Punta Lavapié in the central Chile‐Peru Current System, using the European Centre for Medium‐Range Weather Forecasts reanalysis and focusing on time scales of 10 days to 6 months. Extreme warm SST anomalies on these time scales mostly occurred in the austral summer, December through February, and had spatial scales of 1000s of km. By compositing over the 37 most extreme warm events, we estimated terms in a heat budget for the ocean surface mixed layer at the times of strongest warming preceding the events. The net surface heat flux anomaly is too small to explain the anomalous warming, even when allowing for uncertainty in mixed‐layer depth. The composite mean anomaly of wind stress, from satellite ocean vector wind swath data, during the 37 anomalous warming periods has a spatial pattern similar to the resulting warm SST anomalies, analogous to previous studies in the California Current System. The weakened surface wind stress suggests reduced entrainment of cold water from below the mixed layer. Within 100–200 km of the coast, the typical upwelling‐favorable wind stress curl decreases, suggesting reduced upwelling of cold water. In a 1000‐km area of anomalous warming offshore, the typical downwelling‐favorable wind stress curl also decreases, implying reduced downward Ekman pumping, which would allow mixed‐layer shoaling and amplify the effect of the positive climatological summertime net surface heat flux.

We examine the co-variability between the surface wind divergence and vorticity and how it varies with latitude in the Pacific Ocean using surface vector winds from reanalysis and satellite scatterometer observations. We show a strong correlation between divergence and vorticity throughout the extratropical oceans. From this observation, we develop a dynamical model to explain the first-order dynamics which govern this strong co-variability. Our model exploits the fact that for much of the time, the large-scale surface winds are approximately in a steady-state Ekman balance to first order. An angle ${\alpha }^{\prime }$ is derived from Ekman dynamics by utilizing only the surface divergence and vorticity and is shown to succinctly summarize the co-variability between divergence and vorticity. This approach yields insight into the dynamics that shape the spatial variations in the large-scale surface wind field over the ocean; previous research has focused mainly on explaining variability in the vector winds rather than the derivative wind fields. Our model predicts two steady-state conditions which are easily identifiable as discrete peaks in ${\alpha }^{\prime }$ Probability Distribution Functions (PDFs). In the Northern Hemisphere, steady-state conditions can be either (1) diverging, with negative vorticity, or (2) converging, with positive vorticity. We show that these two states correspond to relative high and low sea-level pressure features, respectively. Southern Hemisphere conditions are similar to those of the Northern Hemisphere, except with the opposite sign of vorticity. This model also predicts the latitudinal variations in the co-variability between divergence and vorticity due to the latitudinal variation in the Coriolis parameter. The main conclusion of this study is that the statistical co-variability between the surface divergence and vorticity over the ocean is consistent with Ekman dynamics and provides perhaps the first dynamical approach for interpreting their statistical distributions. The related ${\alpha }^{\prime }$ PDFs provide a unique method for analyzing air–sea interactions and will likely have applications in evaluating the surface wind fields from scatterometers and weather and reanalysis models.

We propose a method to reconstruct sea surface height anomalies (SSHA) from vector surface currents and winds. This analysis is motivated by the proposed satellite ODYSEA, which is a Doppler scatterometer that measures coincident surface vector winds and currents. If it is feasible to estimate SSHA from these measurements, then ODYSEA could provide collocated fields of SSHA, currents, and winds over a projected wide swath of ∼1700 km. The reconstruction also yields estimates of the low-frequency surface geostrophic, Ekman, irrotational, and nondivergent current components and a framework for separation of balanced and unbalanced motions. The reconstruction is based on a steady-state surface momentum budget including the Ekman drift, Coriolis acceleration, and horizontal advection. The horizontal SSHA gradient is obtained as a residual of these terms, and the unknown SSHA is solved for using a Helmholtz–Hodge decomposition given an imposed SSHA boundary condition. We develop the reconstruction using surface currents, winds, and SSHA off the U.S. West Coast from a 43-day coupled ROMS–WRF simulation. We also consider how simulated ODYSEA measurement and sampling errors and boundary condition uncertainties impact reconstruction accuracy. We find that temporal smoothing of the currents for periods of 150 h is necessary to mitigate large reconstruction errors associated with unbalanced near-inertial motions. For the most realistic case of projected ODYSEA measurement noise and temporal sampling, the reconstructed SSHA fields have an RMS error of 2.1 cm and a model skill (squared correlation) of 0.958 with 150-h resolution. We conclude that an accurate SSHA reconstruction is feasible using information measured by ODYSEA and external SSHA boundary conditions.