Arctic cyclones have become more intense and longer-lived during the last seven decades, which are attributed to increased surface/lower-troposphere baroclinic instability, amplified winter jet streams associated with the weakened stratospheric polar vortex, and strengthened summer lower-stratospheric Arctic vortex.
Arctic cyclones are a fundamental dynamic driver for transient heat and moisture transport including atmospheric rivers and cloud formation and redistribution, which accordingly contribute to and alter the Arctic energy and water budgets and pathways. They also dynamically drive the occurrence of extreme weather and climate events, such as heat waves, heavy precipitation, strong winds, ocean wave surges, sea ice breakup and rapid movement, coastal flooding, and coastal erosion, influencing infrastructure and daily life.
Intense cyclones driving extreme Arctic weather and climate events have been more frequently observed during recent years, causing dramatic environmental and socioeconomic impacts. However, inconsistencies have emerged about long-term changes in Arctic cyclone activity. Here we analyze multiple reanalysis datasets covering a multidecadal period with improvements to the cyclone tracking algorithm and the integrated cyclone activity metric. The results indicate an intensification of Arctic cyclone activity over the last seven decades. There has been a long-term shift of the maximum cyclone counts from weaker to stronger cyclones and a pronounced lengthening of the duration of strong cyclones. Spatial analysis shows increased strong cyclone frequency over the Arctic, driven by enhanced lower troposphere baroclinicity, amplified winter jet stream waves over the North Atlantic, and a strengthened summer tropospheric vortex over the Arctic. The stratospheric vortex has also intensified the tropospheric waves and vortex with distinct dynamics between winter and summer. Recently enhanced baroclinicity over large areas of the Arctic and midlatitudes suggests more complicated atmospheric dynamics than what is hypothesized with Arctic-amplification-induced decrease in meridional temperature gradients.