A high resolution analysis of polar low types: Structural and dynamical comparisons to tropical cyclones

Using the Arctic Surface Reanalysis data set (30km resolution) provided from The Ohio State University, we will study the structure and dynamics associated with polar lows of differing basic state baroclinicities. The dataset was chosen for its focus on the north polar region as well as the fact that the dataset is relatively new at the time of this research. The case of minimal basic state baroclinicity will be represented through the 18–21 December 2002 “hurricane-like” polar low event in the Barents Sea; which exhibited spiraliform convective bands, a near-axisymmetric form, and a cloud-free eye. We will also look at the more baroclinic-type polar low, which we will represent with the 6 December 2011 polar low that was situated north of Scotland.

The non-baroclinic polar low of mid-late December 2002 formed in the Barents Sea as a result of upper-level potential vorticity anomalies triggering a baroclinic energy conversion process. The initial environment of the eventual polar low was highly baroclinic in the 900–600 hPa layer with the thickness gradient oriented southward, and a strong frontal wind field from a residual synoptic-scale low. Due to the strong winds, the environment would almost completely lose its baroclinicity as more a cyclonic surface flow was induced via the upper-level PV anomaly. The surface winds on the western side of the system pulled Arctic air off the sea ice to the north over relatively warm water (a cold air outbreak), triggering massive surface energy fluxes that exceeded 1kW/m2 off the water near the center of the storm. Sensible heat fluxes were a large part (~66%) of the total surface energy fluxes off the water. The energy fluxes caused a deepening of the polar low to about 961 mb, which in turn strengthened the storm's wind field and increased the surface energy fluxes. Maximum near-surface winds of about 24 m/s were located around the storm's cloud-free eye. The polar low developed and maintained a hybridized core structure with a shallow warm core present from the surface to about 850 mb.

In the baroclinic-type polar low in early December 2011, the wind field about the storm is more comparable to the occluded front of a mature baroclinic low. The polar low is situated quite far to the south, but a cold air outbreak in the region is apparent by the cloud streets seen in visible satellite imagery during the event. Near-surface winds of roughly 24 m/s were observed on the western side of the storm's center. We will compare the dynamics and structure of this polar low type with the December 2002 polar low, which exhibited limited baroclinicity.