Polar lows – moist-baroclinic cyclones developing in four different vertical wind shear environments

Abstract. Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety of their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify lows. The method is applied 370 north-eastern Atlantic, which were obtained matching from ERA-5 reanalysis registered STARS dataset Norwegian Meteorological Institute. reproduces most We identify five different polar-low configurations characterised vertical wind shear vector, change horizontal-wind vector with height, relative propagation direction. Four categories feature a strong orientations whereas fifth category contains conditions weak shear. This confirms relevance previously identified categorisation into forward- reverse-shear expand right- left-shear propagate towards colder warmer environments, respectively. For strong-shear categories, organises moist-baroclinic dynamics systems. apparent low-pressure anomaly tilting height against main updrafts occurring along warm front located forward-left direction vector. These contribute through latent heat release typically associated comma-shaped clouds. Polar-low situations shear, often spirali-form clouds, occur mainly at decaying stages development. thus find no evidence for hurricane-like propose instead clouds seclusion process.