Examining Atmospheric Dynamical Forcing of Greenland Ice Sheet Surface Mass Loss Within the Context of Arctic Amplification

Abstract

The current period of Arctic amplification has been characterized by a pronounced reduction in high-latitude snow and ice cover that is reflective of rapidly changing thermodynamic environment. Given this change in the local background conditions, it is not surprising that the Greenland Ice Sheet (GrIS) has undergone drastic surface mass loss since the turn of the century; however, research has shown that the recent acceleration of runoff from the GrIS is strongly linked to a shift in the large-scale atmospheric circulation over the same period that has brought more frequent and intense bouts of summer Greenland blocking. While this atmospheric dynamical change may merely be a manifestation of internal variability, there is growing evidence that widespread changes in surface cover and near-surface thermal gradients under Arctic amplification may favor persistent extremes such as the episodes of Greenland blocking that have encouraged melt of the ice sheet.Here, we explore whether the change in summer atmospheric circulation over Greenland may be a dynamical response to Arctic amplification and attendant snow cover loss. Our results suggests that low North American spring snow cover and a weakened meridional temperature gradient combine to encourage the high-amplitude Omega blocking patterns that we show to have driven the recent trend in summer Greenland blocking. We show that this delayed response to anomalous spring snow cover follows from the snow-hydrological effect, whereby low spring snow cover causes early depletion of soil moisture and anomalously warm surface temperature over eastern North America. The consequent stationary Rossby wave response enforces an anomalous anticyclone, centered over Baffin Bay, that resembles that of high-amplitude Omega blocks and the atmospheric conditions which have promoted melt of the northern GrIS. Together, these results provide evidence that Arctic amplification, and thus anthropogenic climate change, has contributed to recent atmospheric dynamical forcing of GrIS surface mass loss. However, regardless of how strong this link between climate change and atmospheric circulation over Greenland may be, the change in the local thermodynamic environment under Arctic amplification represents a far more robust climate change signal. We also examine the thermodynamic contribution to GrIS surface mass loss using the regional climate model, Modèle Atmosphérique Régional (MAR) associated with blocking circulation. MAR output of surface temperature, meltwater production, and runoff are used to assess the differential impact of blocking events across the ice sheet.