The role of tropopause polar vortices in the intensification of summer Arctic cyclones

Abstract

Abstract. Human activity in the Arctic is increasing as new regions become accessible, with a consequent need for improved understanding of hazardous weather there. Arctic cyclones are the major weather systems affecting the Arctic environment during summer, including the sea ice distribution. Mesoscale to synoptic-scale tropopause polar vortices (TPVs) frequently occur in polar regions and are a proposed mechanism for Arctic cyclone genesis and intensification. However, while the importance of pre-existing tropopause-level features for cyclone development, as well as being an integral part of the three-dimensional mature cyclone structure, is well established in the mid-latitudes, evidence of the importance of pre-existing TPVs for Arctic cyclone development is mainly limited to a few case studies. Here we examine the extent to which Arctic cyclone growth is coupled to TPVs by analysing a climatology of summer Arctic cyclones and TPVs produced by tracking both features in the latest ECMWF reanalysis (ERA5). The annual counts of Arctic cyclones and TPVs are significantly correlated for features with genesis either within or outside the Arctic, implying that TPVs have a role in the development of Arctic cyclones. However, only about one-third of Arctic cyclones have their genesis or intensify while a TPV of Arctic origin is (instantaneously) within about twice the Rossby radius of the cyclone centre. Consistent with the different track densities of the full sets of Arctic cyclones and TPVs, cyclones with TPVs within range throughout their intensification phase (matched cyclones) track preferentially over the Arctic Ocean along the North American coastline and Canadian Arctic Archipelago. In contrast, cyclones intensifying distant from any TPV (unmatched cyclones) track preferentially along the northern coast of Eurasia. Composite analysis reveals the presence of a distinct relative vorticity maximum at and above the tropopause level associated with the TPV throughout the intensification period for matched cyclones and that these cyclones have a reduced upstream tilt compared to unmatched cyclones. Interaction of cyclones with TPVs has implications for the predictability of Arctic weather, given the long lifetime but relatively small spatial scale of TPVs compared with the density of the polar observation network.

The composite development and structure of intense synoptic-scale Arctic cyclones

“…Recent studies have suggested that some Arctic cyclones may have been strongly influenced by TPVs (e.g. Simmonds and Rudeva, 2014;Tao et al, 2017;Gray et al, 2021). Understanding what causes this structural transition of summer Arctic cyclones and why they tend to have longer lifetimes than winter Arctic and extra-tropical cyclones is an area for future research.…”

Spatiotemporal variations in summertime Arctic aerosol optical depth caused by synoptic-scale atmospheric circulation in three reanalyses

“…Regarding the area of >70°N, the higher standard deviation extended from the coast of East Siberian Sea and Beaufort Sea, indicating that the high AOD airs over Northern Eurasia and Northern America were transported toward the North Pole as shown in the section 3.2. The synoptic activity over the Arctic was higher in summer (Clancy et al, 2021;Gray et al, 2021;Serreze and Barrett, 2008; manuscript submitted to Journal of Geophysical Research: Atmosphere 2004); hence, we investigate the contribution of Arctic cyclones on the Arctic AOD variability in summer in the following section.…”

“…The Arctic cyclones (ACs) in summer have a different threedimensional (3D) structure from mid-latitude cyclones (Tanaka et al, 2012) and wintertime ACs (Clancy et al, 2021). Gray et al (2021) presented the difference in the structures of the summertime ACs caused by their relationship to the tropopause polar vortex. Although Xian et al (2022) suggested that the AC frequency might not contribute to the Arctic AOD trend because the AC frequency had no significant trend (Vessey et al, 2020), the AC activity will influence the Arctic aerosol variability on the synoptic timescales; for example, ACs can contribute to the emission, transport, aging, and removal processes (e.g., wet deposition) of Arctic aerosols.…”

Influence of the Thermal Structure on the Intensification of the Extreme Arctic Cyclone in August 2016

“…Arctic Cyclones (ACs) are considered as one of the most dangerous weather systems affecting the Arctic region (Bader et al, 2011), which are synoptic-scale low-pressure systems that form in or move into the Arctic region (Aizawa & Tanaka, 2016). Generally, ACs can be distinguished from extratropical cyclones by latitudes (Gray et al, 2021). Based on the Arctic System Reanalysis (ASR) data set, Tilinina et al (2014) found that 20% of ACs north of 55°N are below 980 hPa during 2000-2010, while the percentage increases to 24% in the Arctic Ocean region.…”