Linkages Between the Equatorward Transport of Tropopause Polar Vortices and the Development of Cold Air Outbreaks

Coherent vortices in the vicinity of the tropopause, referred to as tropopause polar vortices (TPVs), may be extracted from high latitudes in conjunction with high-latitude upper-level ridge amplification. Once extracted, TPVs may interact with and strengthen midlatitude jet streams, as well as act as precursor disturbances for the development of intense midlatitude cyclones. Arctic air surges that accompany TPVs as they are transported to middle latitudes may lead to widespread cold air outbreaks (CAOs) and significant socioeconomic impacts. CAOs can further enhance baroclinicity throughout the troposphere, providing additional dynamical support for the development of intense midlatitude cyclones. The purpose of this study is to investigate 1) the mechanisms responsible for the extraction of TPVs from high latitudes and their transport to middle latitudes, and 2) the relationship between the equatorward transport of TPVs and the development of CAOs. It is hypothesized that 1) the large-scale flow configuration plays an important role in allowing TPVs to be transported from high latitudes to middle latitudes, and 2) TPVs serve as catalysts for CAOs as surface-based pools of arctic air found beneath and behind TPVs surge equatorward while TPVs are transported to middle latitudes.

The frequency of TPVs and the geographical regions favorable for their extraction from high latitudes and transport to middle latitudes will be investigated by constructing a 1979–2015 climatology of TPVs utilizing the 0.5° ERA-Interim dataset. The frequency of TPVs transported to middle latitudes that are associated with CAOs over North America will be determined from this climatology. TPV-relative composite analyses and illustrative case studies of TPVs associated with CAOs over North America will be conducted to identify factors and diagnose processes that support the equatorward transport of TPVs and the concomitant development of CAOs. Preliminary case studies of TPVs associated with CAOs over North America have shown that the large-scale flow configuration may play an important role in the equatorward transport of TPVs to middle latitudes. The preliminary case studies have also shown that the interaction between TPVs and the large-scale flow may play an important role in the concomitant development of CAOs. It is anticipated that the to-be-conducted TPV-relative composite analyses and illustrative case studies of TPVs associated with CAOs over North America will show that the results of the preliminary case studies can be generalized.