A Cloud Resolving Simulation of a Polar Low Over the Labrador Sea

Polar lows, high latitude mesoscale marine cyclones, remain one of the most enigmatic of meteorological phenomena. They can be often observed on satellite imagery as spiral cloud systems whose striking organization belies the significant threat they represent to maritime activity as a result of the hurricane force associated with them. Their small horizontal scale, often less than 500km, short life time, typically less than 24 hours, and their tendency to form in data sparse regions make them a challenge to forecast. Polar lows are often associated with significant fluxes of heat and moisture between the atmosphere and ocean that act to modify both fluids. In the atmosphere, the fluxes act to warm and moisten the boundary layer resulting in the formation of 2D roll and 3D cellular convection. In the ocean, fluxes act to densify the surface waters and may contribute to the preconditioning phase of deep ocean convection. The presence of sea ice often introduces a spatial heterogeneity into the air-sea flux fields, In this talk, we will present a numerical simulation of a polar low that formed over the Labrador Sea on February 8 1997 during the Labrador Sea Deep Ocean Convection Experiment. A flight on that date with an instrumented aircraft collected data on the cloud-scale structure of the polar low and its associated air-sea interaction. The simulation was performed with a cloud resolving mesoscale forecast model in a domain with a horizontal scale of 500 km by 400 km at a horizontal resolution of 500m. The high spatial resolution and large domain allowed for an explicit representation of both the cloud-scale and larger-scale circulations associated with the polar low. In addition, the model included an explicit representation of the heterogeneity associated with the Labrador Sea's marginal ice zone. A comparison with satellite and in-situ observations indicate that the simulation is able to capture many of the cloud-scale and large-scale features of this polar low. In particular, the simulated cloud field bears a close resemblance to that associated with the low.