Abstract
Abstract. In this study, we use run-time bias correction to correct for the Action de Recherche Petite Echelle Grande Echelle (ARPEGE) atmospheric model systematic errors on large-scale atmospheric circulation. The bias-correction terms are built using the climatological mean of the adjustment terms on tendency errors in an ARPEGE simulation relaxed towards ERA-Interim reanalyses. The bias reduction with respect to the Atmospheric Model Intercomparison Project (AMIP)-style uncorrected control run for the general atmospheric circulation in the Southern Hemisphere is significant for mean state and daily variability. Comparisons for the Antarctic Ice Sheet with the polar-oriented regional atmospheric models MAR and RACMO2 and in situ observations also suggest substantial bias reduction for near-surface temperature and precipitation in coastal areas. Applying the method to climate projections for the late 21st century (2071–2100) leads to large differences in the projected changes of the atmospheric circulation in the southern high latitudes and of the Antarctic surface climate. The projected poleward shift and strengthening of the southern westerly winds are greatly reduced. These changes result in a significant 0.7 to 0.9 K additional warming and a 6 % to 9 % additional increase in precipitation over the grounded ice sheet. The sensitivity of precipitation increase to temperature increase (+7.7 % K−1 and +9 % K−1) found is also higher than previous estimates. The highest additional warming rates are found over East Antarctica in summer. In winter, there is a dipole of weaker warming and weaker precipitation increase over West Antarctica, contrasted by a stronger warming and a concomitant stronger precipitation increase from Victoria to Adélie Land, associated with a weaker intensification of the Amundsen Sea Low.
Highlights
The Antarctic Ice Sheet (AIS) contribution to sea-level rise (SLR) has increased substantially since the 1990s (Velicogna, 2009; Shepherd et al, 2018)
As already presented in Beaumet et al (2019a), the mean sealevel pressure (SLP) of the uncorrected ARP-Atmospheric Model Intercomparison Project (AMIP) control run is low biased in the southern mid-latitudes, especially in the Pacific sector, while the depth of the circum-Antarctic troughs is underestimated, the Amundsen Sea Low (ASL)
Bias correction can be turned off, and its impact on projected climate change can be identified. Applying these bias-correction methods allows us to assess remaining uncertainties on projected climate change in coupled and atmospheric climate models such as suggested by Dommenget and Rezny (2018) and could help in identifying which efforts one should focus on in order to reduce these uncertainties. Considering it removes most of the biases on large-scale atmospheric circulation, the bias-correction method implemented in this study offers the opportunity to test the tuning of the parametrizations of smaller-scale processes in a different context than nudged simulations often used in this purpose
Summary
The Antarctic Ice Sheet (AIS) contribution to sea-level rise (SLR) has increased substantially since the 1990s (Velicogna, 2009; Shepherd et al, 2018). The largely positive AIS surface mass balance (SMB), for which positive but generally not significant trends have been reported during the second part of the 20th century (Lenaerts et al, 2016; Palerme et al, 2017; King and Watson, 2020), is largely overtaken by the increasing ice losses of the West Antarctic Ice Sheet (WAIS, Velicogna, 2009; Pritchard et al, 2012; Shepherd et al, 2018). Main sources of uncertainties arise from poorly represented sea surface conditions and changes in atmospheric
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