Low‐Level Baroclinic Jets Over the New Arctic Ocean
2018
Guest, Peter | Persson, P. Ola G. | Wang, Shouping | Jordan, Mary | Jin, Yi | Blomquist, Byron | Fairall, C. W.
During the Sea State cruise in the fall of 2015, in the Chukchi/Beaufort Sea region, there were five strong (>10 m s⁻¹) surface wind events associated with low‐level atmospheric jets. These jets were analyzed using rawinsonde observations, ship measurements, and a numerical forecast model. The jets occurred when easterly winds aligned with the ice edge, generating low‐level baroclinicity in a direction favorable for increasing the geostrophic wind speed toward the surface. The maximum wind speed usually occurred at the top of the atmospheric boundary layer with wind speeds greater than 8 m s⁻¹ extending through the capping inversion to 2,000–3,000 m elevation, with winds decreasing toward the surface in the boundary layer due to friction. The width (crosswind) dimensions of the jets were 250–400 km and they existed downwind for as long as the winds remained generally parallel to the ice edges, typically several hundred kilometers. Thermal winds calculated from crosswind‐oriented rawinsonde temperature profiles matched the observed vertical wind speed gradients in the inversion regions, indicating that the jets were in quasi‐geostrophic (inversion layer) or quasi‐frictional (boundary layer) balance, with low Rossby numbers. We define these as “baroclinic” type jets, which are distinct from “ice/sea breeze” type jets which flow more down the pressure and density gradients, and have high Rossby numbers. The operational model analyses matched the observations quite well, giving confidence that these types of jets can be simulated and predicted as long as the models have sufficient resolution and accurately parameterize vertical heat fluxes.
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