Polar Low Motion and Track Characteristics over the North Atlantic

Abstract

Abstract Polar lows (PLs) are intense mesoscale cyclones over high-latitude oceans. The PL motion and track characteristics over the North Atlantic in the cold season are examined based on ∼1700 PLs during 1979–2016. Our analysis shows that PL motion is mainly controlled by the environmental flow in the lower troposphere. In particular, the steering flow defined over 950–550 hPa within a 450-km radius best matches the PL motion. Meanwhile, 700 hPa is an optimal single level to assess the steering flow. Cluster analysis based on a linear regression mixture model is utilized to describe the PL tracks. Four distinct clusters are identified, and they are characterized by northeastward motion (NE), eastward motion (E), southward motion (S), and slow motion without a dominating direction (SM), respectively. Although PLs in the four clusters have similar lifespans, SM-type PLs have much shorter tracks than the other clusters, due to their slow translation speeds. Further analysis shows that there are no distinctive geographic differences in genesis locations for the four clusters. The track differences can be largely explained by the associated synoptic-scale environmental circulations. Additionally, the S-type PLs tend to develop in a reverse shear environment, the NE-type and E-type PLs are associated with forward shear and left shear environments, respectively, while the SM-type PLs do not show a preference in the environmental shear. The link between the PL tracks and the North Atlantic weather regimes is also investigated. The NAO+ regime is associated with the most frequent PL occurrence over the North Atlantic, while the Scandinavian blocking regime is associated with lowest PL frequency. Significance Statement Polar lows (PLs) are intense mesoscale cyclones and pose hazards to high-latitude coastal areas. A better understanding of polar low motion can help improve polar low forecasts and reduce the hazardous impacts of the storms. Based on a PL track dataset over the North Atlantic basin during 1979–2016, it is found that PL motion is mainly controlled by the environmental flow in the lower troposphere and that the steering flow defined over 950–550 hPa within a 450-km radius best matches the PL motion. In addition, four distinct types of tracks are identified using cluster analysis, and they are characterized by northeastward motion, eastward motion, southward motion, and slow motion without a dominating direction, respectively. The different background flows can largely explain the propagation directions of different track types. Furthermore, the links between the PL motion and the North Atlantic weather regimes are also investigated.