Low‐Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn

Abstract

Low‐level wind jets (LLJs) and strong surface winds are frequently observed near the sea ice edge in the presence of strong thermal contrast between open water and sea ice. Two LLJ cases near the sea ice edge in the Beaufort Sea are examined using dropsonde observations made from Seasonal Ice Zone Reconnaissance Survey flights. Ensembles of Polar Weather Research and Forecast simulations with and without sea ice demonstrate the contribution of the surface thermal contrast to the boundary layer structure, the LLJ, and surface ice edge jets. Because the surface temperature contrast only influences the lower most hundreds of meters in the atmospheric boundary layer, its contribution to the temperature gradient and wind speed at the level of the LLJ is limited. The sea ice does strengthen the LLJ by extending the LLJ northward over sea ice and increasing the maximum LLJ wind speeds by up to 13% and as much as 29% further north at a lower altitude. However, the primary reason for the observed strong winds in these two cases are the synoptic interactions between anticyclones and approaching cyclones. The effect of the surface thermal contrast on surface winds is controlled by a separate mechanism. The cold and stable boundary layer over sea ice prevents the momentum transport from the LLJ to the surface. This leads to weaker surface winds over sea ice and confines the strong surface winds close to the sea ice edge. This mechanism contributes to the frequent occurrence of the surface “ice edge jets.”

The evolution of a shallow front in the Arctic marginal ice zone

“…For example, recent work suggests that in an energetic sea state the damping of short waves by ice in the MIZ may decrease the effective transfer velocity from wind to ocean (Smith and Thomson, 2019). Overlaid on the complicated picture of wind stress transfer to the ocean in MIZs are localized weather patterns, such as low-level jets, which may result from the transitions of atmospheric properties across the MIZ (e.g., Guest et al, 2018;Liu and Schweiger, 2019). The use of the COARE algorithms has been shown previously as insufficient for predicting surface fluxes in the MIZ (Yu et al, 2017); however, in this case the strong match between the wind stress estimated with COARE versus that calculated using the inertial dissipation method (Figure 6c) suggests that the COARE results here are valid.…”