P51     Low-level jets in the Autumnal Marginal Ice Zone: Sensitivity to sea ice extent and the influence of coupling on surface turbulent heat fluxes.

Hughes, Mimi, Ola Persson, Amy Solomon, CIRES, University of Colorado, Boulder and NOAA/ESRL/PSD and Janet Intrieri, NOAA/ESRL/PSD

Low-level jets (LLJs) transport moisture, impact surface fluxes, and ultimately impact sea ice evolution in the marginal ice zone (MIZ) of the Arctic Ocean. We investigate a very shallow, off-ice LLJ in the MIZ of the Beaufort Sea north of Alaska for a case study during the Sea State campaign of October 2015. The LLJ was associated with significant thermal gradients near the edge of the advancing, thin, first-year ice. Our study uses unique observations taken from the ship R/V Sikuliaq as well as model output from the Weather, Research, and Forecasting (WRF) model, in control and perturbed sea ice configurations, and from the Coupled Arctic Forecasting System (CAFS). We first compare the WRF control and CAFS simulations to the ship observations to test the models’ ability to represent this LLJ, including its thermal and kinematic structure. We use the model simulations to help discriminate between spatial and temporal changes in the observations, and provide evidence suggesting the LLJ is driven in part by density current mechanisms. Results also suggest that the models’ difficulties for representing clouds and associated radiative effects impact the thermal gradient near the ice edge.  Then we conduct sensitivity experiments with WRF to test the roles of different forcing mechanisms for the LLJ evolution. In particular, we eliminate the local temperature gradient across the sea ice edge in idealized experiments (through modification of the sea ice concentration) to test what role shallow baroclinicity due to the temperature gradient induced by the presence of sea ice plays compared to the baroclinicity caused by the passage of transient cyclones and anti-cyclones. Finally, we demonstrate improvements in the representation of surface turbulent fluxes in CAFS compared with WRF.