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High-resolution numerical weather prediction (NWP) in the littoral zone remains an outstanding challenge due to the complexity of the surface physical and thermodynamic properties, coastline representation and turbulence quantification. Prevailing approaches to surface flux parameterization in mesoscale NWP are susceptible to error in the littoral zone in part due to the surface heterogeneity and the impact of wind direction on the surface fluxes. The Coastal Land-Air-Sea Interaction (CLASI) project conducted a pilot field campaign during two weeks in summer 2016 around Monterey Bay, California, USA, to collect in-situ and remote measurements of meteorological and oceanographic quantities on-shore, off-shore and slightly inland to capture the cross-shore and along-shore gradient of key atmospheric fields and turbulent fluxes in a variety of conditions. The region was modeled using mesoscale NWP with the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) at horizontal resolutions as fine as 333 m. Whereas COAMPS performed well with predictions of near surface scalar and momentum fields verified by surface mesonet stations 4 to 5 km in-land, the pilot project revealed several sources of error in mesoscale NWP along the coastline. Such errors include a strong positive model bias of surface momentum flux and a lack of sensitivity of surface momentum flux to wind direction, a result expected since surface flux parameterizations are designed for homogeneous conditions. This presentation will show results of new high-resolution NWP model studies performed in preparation for an impending more extensive CLASI field campaign planned for summer 2020 in Monterey Bay. The goal of this latest modeling work is to identify the optimal locations and other constraints for observations needed as part of the larger field campaign objective to develop and validate new NWP model surface flux parameterizations. The COAMPS runs will be compared against large-eddy simulation of

Submesoscale oceanic fronts (SFs), which typically occur on a spatial scale of 0.1–10 km, may have a large influence on the atmospheric surface layer (ASL). However, due to their short temporal-spatial scales, evaluating their direct impact on this layer remains challenging and characterizing the nature of SF-ASL interaction has not been done in the field. To address this, a study of the air-sea response to SFs was conducted using observations collected during the Lagrangian Submesoscale Experiment, which took place in the northern Gulf of Mexico. This manuscript focuses on the meteorological measurements made from a pair of masts installed on the bow of the R/V Walton Smith. This work represents one of the first observation-based investigations into the potential influence that SFs have on the ASL. Contemporaneous measurements from an X-band marine radar, moving vessel profiler, and Lagrangian drifters were also used to analyze the SF dynamics. Systematic surface wind velocity changes over several cross-frontal transects were observed, a process previously associated with mesoscale fronts. A comparison between the eddy covariance and parameterized (COARE 3.5) air-sea fluxes revealed that the directly observed heat flux was 1.5 times larger than the bulk value in the vicinity of the SFs. This suggests that the hydrodynamic processes near the front enhance the local exchange of sensible and latent heat. Given the prevalence of SF over the global upper ocean, these findings suggest that these features may have a widely distributed and cumulative impact on air-sea interactions.

Over the open ocean, the aerodynamic drag coefficient is typically well predicted; however, the impact depth-limited processes have on the drag remains underexplored. A case study is presented here where winds, waves, and currents were simultaneously observed from a mobile platform that repeatedly transected the inner shelf of Monterey Bay, CA. Eddy covariance-derived drag coefficients were compared to several bulk parameterizations, including all of the roughness variations of COARE 3.5 and two explicitly depth-limited models. The analysis demonstrated that the drag was underestimated by O(2–4) times and the variability with wind speed or cross-shore distance was not well predicted. The drag based on a recent depth-limited roughness length model performed substantially better than the rest of the bulk estimates, which were all within 15% of each other and effectively equivalent given typical operational uncertainties. The measured friction velocity was compared to a wave-dependent parameterization and generalizing the model to arbitrary water depth significantly improved the mean observation-model difference to within 30%. Latent variability in the observation-model comparison was associated with stability, wind direction, and wave steepness. The wind stress angle variability was also analyzed. Stress veering was correlated with the alongshore surface current within 2 km from shore (r2 = 0.7–0.95, p < 0.05); offshore of this margin, consistent wind stress veering was observed and may be attributable to a secondary, low-frequency swell system. These results demonstrate that it remains a persistent challenge to accurately predict wind stress variability in the nearshore, especially at locations with complex wave and current fields.