Case study of a long-lived Siberian summer cyclone that evolved from a heat low into an Arctic cyclone

Abstract. Extratropical cyclones are known for strongly influencing mid-latitude weather in particular during the cold season and for their association with high-impact weather such as destructive winds and heavy precipitation. Cyclones occur typically in the oceanic storm track regions, and most studies about cyclone dynamics focused on cyclones that developed over the ocean. In this study, we investigate a particularly long-lived example of a lesser known Siberian summer cyclone. Starting with a climatological analysis of Siberian summer cyclone tracks in ERA5 reanalyses during the period 1979–2021, we focus on 9 events which are initially identified as typical heat lows. While there is a large variability in surface cyclogenesis conditions of Siberian summer cyclones, the Siberian heat lows form in very dry and hot environments and exhibit deep, convectively well-mixed boundary layers at genesis. In a detailed case study of a long-lived Siberian summer cyclone in July 2021, we show how the cyclone forms as a heat low during a heat wave in Kazakhstan. The cyclone then interacts with an upper-level trough, propagates across the Asian continent and evolves into an Arctic cyclone that experiences rapid intensification and produces a warm conveyor belt whose outflow almost reaches the North Pole and leads to the formation of a tropospheric potential vorticity cutoff in the Arctic. This case is unusual since subtropical heat lows are not known to propagate far from their location of origin. This unusual cyclone has a track length of almost 4000 km and it is associated with a heatwave initially, heavy precipitation during intensification, and an important upper-level flow anomaly in the Arctic. Comparison with the other Siberian heat lows shows that a similar development can be observed for the other cases, although not as pronounced and long-lived. This extraordinary case study also indicates how compounding high-impact events in different locations may be related to one single weather system.