Extreme Greenland Blocking and Moisture Transport: Historical and Future Perspectives

Abstract:

Atmospheric blocked flows over the North Atlantic Arctic (NAA) and Greenland are oftentimes characterized by an anomalous ridge that deflects traveling cyclones from their usual tracks. Atmospheric blocking regularly produces a strong equatorward deflection of polar air on the eastern flank of the anticyclone, including severe cold episodes in winter, and a poleward deflection on the western flank, leading to severe droughts and heat waves in summer. Recent changes in low-frequency atmospheric circulation around Greenland have increased sensible heat and moisture advection from the mid-latitudes into the region.

In this study, we explored the frequency and seasonality of extreme Greenland blocking in both past and future climates. We also explored the relationship between extreme blocking and moisture transport (quantified as integrated vapor transport, IVT) into and over the region. We quantified historical atmospheric flow blocking over Greenland using the Greenland Blocking Index, and extreme blocking was defined from 1980 to 2019 at the 90th, 95th, 97th, and 99th percentiles for both summer (June to August) and winter (December to February) seasons. Future blocked flows were defined using a similar metric that we calculated using model output taken from different members of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). Moisture transport over Greenland was defined by calculating daily IVT over the region from 15° to 85°W and 55° to 80°N. Historical moisture transport was calculated from the ERA-Interim reanalysis, and future moisture transport was calculated from model output from CMIP6 members. Recent trends of the frequency of historical extreme blocking over Greenland were contrasted with CMIP6 predictions of trends in future extreme blocking. In addition, historical trends of IVT over Greenland during periods of extreme blocking were compared with future predictions of the same from CMIP6 members. These findings are analyzed in context of other work on extreme weather and climate events, and future work is suggested on the role of moisture transport in developing or sustaining blocks over Greenland.