Revisiting the Relationship between Polar Lows and Weather Regimes

The link between weather regimes (WRs) and polar low (PL) activity is examined over the North Atlantic and North Pacific basins. Compared to earlier studies based on limited, regional PL datasets, our study conducts a more complete evaluation of regional WR-PL relationships using an expanded PL climatology. Our findings show that PL activity is increased over the Norwegian-Barents Seas during the Atlantic Ridge regime and decreased over the former region during the Scandinavian Blocking regime with negative impacts also stretching to the Irminger Sea. Over the Labrador-Irminger Seas, PL activity is modulated strongest by the North Atlantic Oscillation (NAO), with positive impacts during the positive phase and vice versa. Over the North Pacific, the Arctic Low contributes to increased PL activity over most regions, while the opposite is true for the Pacific Wavetrain regime. The variability of PL activity associated with WRs is strongly related to changes in key environmental conditions. In general, regions of enhanced (reduced) PL activity are coincident with anomalous low-level northerly (southerly) flow and reduced (increased) static stability. Further analysis shows that certain persistent WRs can strongly modulate PL activity over some regions, either due to the amplification or propagation of favorable or unfavorable conditions, which cautions the limitation of regarding WRs as stationary patterns. A previously developed PL genesis potential index (PGI) is shown to represent the observed impacts well and is applied to explore the impacts of persistent WRs on the subseasonal predictability of PL activity.