Abstract
Abstract. Surface melting over the Antarctic Peninsula (AP) may impact the stability of ice shelves and thus the rate at which grounded ice is discharged into the ocean. Energy and mass balance models are needed to understand how climatic change and atmospheric circulation variability drive current and future melting. In this study, we evaluate the regional climate model MAR over the AP at a 10 km spatial resolution between 1999 and 2009, a period when active microwave data from the QuikSCAT mission is available. This model has been validated extensively over Greenland, has is applied here to the AP at a high resolution and for a relatively long time period (full outputs are available to 2014). We find that melting in the northeastern AP, the focus area of this study, can be initiated both by sporadic westerly föhn flow over the AP mountains and by northerly winds advecting warm air from lower latitudes. A comparison of MAR with satellite and automatic weather station (AWS) data reveals that satellite estimates show greater melt frequency, a larger melt extent, and a quicker expansion to peak melt extent than MAR in the centre and east of the Larsen C ice shelf. These differences are reduced in the north and west of the ice shelf, where the comparison with satellite data suggests that MAR is accurately capturing melt produced by warm westerly winds. MAR shows an overall warm bias and a cool bias at temperatures above 0 ∘C as well as fewer warm, strong westerly winds than reported by AWS stations located on the eastern edge of the Larsen C ice shelf, suggesting that the underestimation of melt in this region may be the product of limited eastward flow. At higher resolutions (5 km), MAR shows a further increase in wind biases and a decrease in meltwater production. We conclude that non-hydrostatic models at spatial resolutions better than 5 km are needed to better-resolve the effects of föhn winds on the eastern edges of the Larsen C ice shelf.
Highlights
Increased meltwater production over the Antarctic Peninsula (AP) in the latter half of the 20th century has been linked to a warming atmosphere, with potential implications for future sea-level rise (Barrand et al, 2013; Turner et al, 2005; Vaughan, 2006)
We conclude that Modèle Atmosphérique Régionale (MAR) captures melt that occurs just east of the AP with acceptable accuracy according to satellite estimates, but that melt is underestimated with respect to both automatic weather station (AWS) and satellite estimates in the eastern part of the Larsen C Ice Shelf
MAR shows lower melt occurrence than satellite estimates in the centre and east of the Larsen C Ice Shelf, while in the north and west of the NE basin, MAR reports melt occurrence largely concurrent with satellite estimates
Summary
Increased meltwater production over the Antarctic Peninsula (AP) in the latter half of the 20th century has been linked to a warming atmosphere, with potential implications for future sea-level rise (Barrand et al, 2013; Turner et al, 2005; Vaughan, 2006). Where the hydrostatic assumption is preserved (such as with MAR), higher resolutions may inhibit flow in the model, resulting in limited eastward föhn flow in the eastern AP (Hubert Gallée, personal communication, December 2017) Despite these drawbacks, the current class of hydrostatic RCMs, which include relatively complete representations of the snow physics are useful tools to simulate the effect of surface melt on the snowpack over long timescales. As melt on the Larsen C Ice Shelf can potentially be initiated by northwesterly föhn flow sourced from over the AP or southwesterly flow through gaps in the mountain range (even at sub-zero temperatures), we compare melt occurrence reported by satellite estimates vs MAR (coinciding with the 2000–2009 QuikSCAT period) partitioned by temperature differences and wind direction at the location of the Larsen Ice Shelf AWS.
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