Increased Autumn Cyclone Associated Precipitation Linked to Arctic Sea Ice Loss?

There is broad agreement between global climate model simulations (GCMs) that warming linked to rising concentrations in atmospheric greenhouse gases (GHGs) will lead to increased precipitation in northern high latitudes. This is because of the greater moisture holding capacity of the warmer atmosphere following the Clausis-Claperyon relationship, leading to stronger poleward vapor flux and vapor flux convergence. However, a moister atmosphere may also affect the intensity and precipitation efficiency of extratropical cyclones that generate much of the high latitude precipitation. Some modeling studies suggest little change in cyclone frequency in a warmer climate, but an increase in precipitation output from storms during spring and autumn.

Recently a link between the observed downward trend in September Arctic sea ice and increased strength of September cyclones was noted [e.g. Simmonds and Keay, 2009]. The link is argued in terms of increased enthalpy fluxes associated with more open water. Stronger cyclones likely lead to an increase in their precipitation. Indeed in this study we note an increase in cyclone-associated precipitation in recent years using a cyclone tracking algorithm applied to JRA-25 Atmospheric Reanalysis fields. Yet cause and effect remains unclear. Many studies have shown that changes in sea ice extent are capable of forcing changes in atmospheric circulation and hence precipitation patterns both within and beyond the Arctic. In this study we find that recent changes in cyclone associated precipitation are linked to a shift in atmospheric circulation, with the 2004-2008 pentad of anomalously low summer sea ice extent characterized by deeper penetration of the primary North Atlantic cyclone track into the Arctic.