Evaluating cloud cover as a link between high pressure systems and Greenland melt
Lily Hahn, Geosciences
In the past two decades, persistent high pressure, atmospheric blocking conditions have become more frequent over Greenland, contributing to record-breaking melt events and a warming trend since the mid-1990s. Proposed mechanisms connecting blocking to enhanced melt include adiabatic warming of air via sinking motion; the advection of warm, southerly air onto western Greenland; or, more recently, the radiative impact of cloud cover changes associated with high pressure systems.
Here we use reanalysis data and a regional climate model to analyze the influence of high pressure systems on Greenland cloud cover, and the impact of these cloud changes on the surface energy budget and melting. We find that high pressure anomalies promote northerly winds over central Greenland which interact with Greenland orography in the northeast to promote stronger upslope flow and therefore increased cloud cover, while in the south promoting stronger downslope flow and reduced cloud cover.
The increase of cloud cover at height and the high ice sheet albedo promote a dominant longwave warming impact in the northeast, while in the south the reduction of cloud cover at lower altitudes combined with the lower albedo in this region allows shortwave warming to dominate. This link between blocking and cloud cover differs from the previously suggested mechanism of large-scale sinking, with the surface energy balance strongly dependent on the vertical and lateral distribution of cloud cover changes.
Further work to understand factors promoting Greenland melt will be essential for predicting the effects of freshwater fluxes and sea level rise globally.