Putrasahan, D. A., A. J. Miller and H. Seo, 2013:
Isolating mesoscale coupled ocean-atmosphere interactions in the Kuroshio Extension region.
Dynamics of Atmospheres and Oceans, 63, 60-78.
Abstract.
The Kuroshio Extension region is characterized by energetic oceanic mesoscale and frontal
variability that alters the air-sea fluxes that can influence large-scale climate variability in the
North Pacific. We investigate this mesoscale air-sea coupling using a regional eddy-resolving
coupled ocean-atmosphere (OA) model that downscales the observed large-scale climate
variability from 2001-2007. The model simulates many aspects of the observed seasonal cycle of
OA coupling strength for both momentum and turbulent heat fluxes. We introduce a new
modeling approach to study the scale-dependence of two well-known mechanisms for the surface
wind response to mesoscale sea surface temperatures (SST), namely, the .vertical mixing
mechanism. (VMM) and the .pressure adjustment mechanism. (PAM). We compare the fully
coupled model to the same model with an online, 2-D spatial smoother applied to remove the
mesoscale SST field felt by the atmosphere. Both VMM and PAM are found to be active during
the strong wintertime peak seen in the coupling strength in both the model and observations. For
VMM, large-scale SST gradients surprisingly generate coupling between downwind SST
gradient and wind stress divergence that is often stronger than the coupling on the mesoscale,
indicating their joint importance in OA interaction in this region. In contrast, VMM coupling
between crosswind SST gradient and wind stress curl occurs only on the mesoscale, and not over
large-scale SST gradients, indicating the essential role of the ocean mesocale. For PAM, the
model results indicate that coupling between the Laplacian of sea level pressure and surface wind
convergence occurs for both mesoscale and large-scale processes, but inclusion of the mesoscale
roughly doubles the coupling strength. Coupling between latent heat flux and SST is found to be
significant throughout the entire seasonal cycle in both fully-coupled mode and large-scale
coupled mode, with peak coupling during winter months. The atmospheric response to the
oceanic mesoscale SST is also studied by
comparing the fully coupled run to an uncoupled
atmospheric model forced with smoothed SST prescribed from the coupled run. Precipitation
anomalies are found to be forced by surface wind convergence patterns that are driven by
mesoscale SST gradients, indicating the importance of the ocean forcing the atmosphere at this
scale.
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