Tropopause Polar Vortex Intensity Linkage to Polar Low Development

Polar lows (PLs) are intense mesoscale cyclones that develop in marine polar airmasses poleward of the midlatitude waveguide. They are typically short-lived, with an average lifetime of approximately 20 hours, and are capable of substantial societal and marine hazards due to their intense snowfall and wind. PLs’ small temporal and spatial scales make them a predictability challenge, especially those on the smaller end of this spectrum. High latitudes are additionally frequently inhabited by tropopause polar vortices (TPVs), which are sub-synoptic scale vortices along the tropopause. TPVs are commonly much longer-lived than their PL counterparts and are known to aid in facilitating surface cyclogenesis. Given the abundance of TPVs and PLs in the Arctic, and the known role of TPVs in surface cyclogenesis, we hypothesize TPV intensity can have significant impact on PL development.

To test this hypothesis, we use high-resolution Model for Prediction Across Scales (MPAS) simulations with 3.75 km mesh spacing and ERA5 initial conditions to analyze two PL cases with TPV linkages which had poor short term forecast skill. Initial simulations show the lack of predictability beyond a short-range window is attributable to mesoscale uncertainties in the ERA5 initial state in the environment surrounding the TPV. We further test our hypothesis by running two sets of MPAS ensembles initialized from 10 ERA5 ensemble members, one set of control simulations and another set of simulations applying a heating tendency in the upper troposphere below the TPV core to weaken the vortex. These sets of ensembles are then used to compare the isolated impact of the TPV intensity to broader initial condition uncertainty on the PL development and subsequent evolution.