Tropopause Polar Vortex Climatology and Linkages with Rossby Wave Initiation

Abstract:

Tropopause Polar Vortices (TPVs) are coherent vortices along the tropopause, identified by a local minimum in temperature and local maximum in potential vorticity along the dynamic tropopause. TPVs are most often found in high latitudes poleward of 60ºN, are primarily transported into the midlatitudes via northern Canada and Siberia and are important features in midlatitude and polar synoptic meteorology, associated with cyclogenesis, cold air outbreaks, and Rossby Wave initiation (RWI). RWI events occurr most frequently over the western North Pacific Ocean and are associated with an upstream wave train propagating over Asia, antecedent downstream ridge, and increased moisture transport along an initially zonal midlatitude jet, which is subsequently perturbed.

Prior studies describe the climatology of TPV location and structure, but are relatively lacking for climatological analyses of TPV transport from polar regions into midlatitudes and whether there is an association with RWI events. In this study, a climatology of TPV transport into midlatitudes is created, identifying TPV linkages with RWI events with the expectation that TPVs are located poleward of the RWI location acting as positive potential vorticity anomalies that perturb the initially zonal jet. Analysis of December through February TPV tracks and RWI locations based on the ERA-Interim (ERA-I) reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) reveals that about 22 percent of all wintertime TPVs are identified as having been transported into the midlatitudes. The most common pathways for TPV transportation into the midlatitudes are via northern Canada and northern Siberia and smaller maxima over northern Scandinavia and over western Alaska. An objective algorithm to identify physically based TPV-RWI linkages will also be discussed to assess characteristics associated with RWIs with a physically linked TPV compared against RWIs without a physically linked TPV.