The role of stratosphere vortex downward intrusion in a long-lasting late-summer Arctic storm

Storm activities have recently exhibited intensification over the Arctic, potentially impacting air–ice–sea interactions and contributing to rapid changes in the Arctic climate and environment. In this study, the spatial and temporal structures and driving mechanisms of a long-lasting storm occurring in September 2010 over the Arctic Ocean have been investigated using modelling experiments. The storm dominantly demonstrates an equivalent barotropic structure from the surface to the lower stratosphere, and an upper troposphere–lower stratosphere warm and mid–low troposphere cold temperature anomaly distribution throughout its entire development period, showing large differences from those that are predominantly driven by baroclinic instability. The stratosphere vortex downward intrusion and the resultant upper troposphere–lower stratosphere positive potential vorticity (PV) anomaly play a decisive role in the storm's intensification and long-lasting duration, though a merged surface baroclinic front also makes contributions at the initial time period. Although both increased static stability and positive vorticity due to the thermal structure anomaly and resulting cyclonic jet are two contributors to PV, we found that the former predominantly governs the PV anomaly evolution and, in turn, determines the storm's intensity and lifetime. In particular, our new finding shows an out-of-phase occurrence in time between the maximum upper warm and lower cold temperature anomalies, which sustains the intensity and persistence of the PV anomaly and, in turn, the storm over an extended time period. The results here may have significant implications for enhancing Arctic storm prediction capability, and improving understanding of the physical mechanisms of large-scale climate variability and changes and their linkage to synoptic storms.