Schedule May 24, 2018
Mesoscale Air-Sea Interaction
Frank Bryan (NCAR)

The Earth system models that have been used in climate change research in recent years typically have horizontal resolution in the atmospheric and oceanic components of approximately 100 km. This resolution is sufficient to capture the flow instabilities of the midlatitude atmospheric jet streams that give rise to weather. However, the resolution is insufficient to capture the dynamical analog of weather in the ocean, referred to as mesoscale eddies, arising from instabilities of the major current systems such as the Gulf Stream, Kuroshio, and Antarctic Circumpolar Current. While the feedback and transport effects of the ocean mesoscale eddies on the interior of the ocean are parameterized in ocean models, this source of variability in surface properties and air-sea interaction is missing from nearly all climate simulations. Using climate simulations with ocean model resolution sufficient to explicitly represent mesoscale eddies, and recently available global high-resolution satellite observations, it has become apparent that there is a significant dynamical coupling between small-scale features in the sea surface temperature field and the flow level atmospheric winds. The primary mechanism is through the influence of SST on the static stability of the atmospheric planetary boundary layer. The result is the predominance of stronger winds over small-scale warm SST features, and weaker winds over cold. This is opposite to the sense of the co-variability on larger-scales. There are indications that this coupling can impact larger scales in the global climate system through scale interactions in both the free atmosphere and interior ocean.

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