Abstract
Abstract. We compare the performance of five different regional climate models (RCMs) (COSMO-CLM2, HIRHAM5, MAR3.10, MetUM, and RACMO2.3p2), forced by ERA-Interim reanalysis, in simulating the near-surface climate and surface mass balance (SMB) of Antarctica. All models simulate Antarctic climate well when compared with daily observed temperature and pressure, with nudged models matching daily observations slightly better than free-running models. The ensemble mean annual SMB over the Antarctic ice sheet (AIS) including ice shelves is 2329±94 Gt yr−1 over the common 1987–2015 period covered by all models. There is large interannual variability, consistent between models due to variability in the driving ERA-Interim reanalysis. Mean annual SMB is sensitive to the chosen period; over our 30-year climatological mean period (1980 to 2010), the ensemble mean is 2483 Gt yr−1. However, individual model estimates vary from 1961±70 to 2519±118 Gt yr−1. The largest spatial differences between model SMB estimates are in West Antarctica, the Antarctic Peninsula, and around the Transantarctic Mountains. We find no significant trend in Antarctic SMB over either period. Antarctic ice sheet (AIS) mass loss is currently equivalent to around 0.5 mm yr−1 of global mean sea level rise (Shepherd et al., 2020), but our results indicate some uncertainty in the SMB contribution based on RCMs. We compare modelled SMB with a large dataset of observations, which, though biased by undersampling, indicates that many of the biases in SMB are common between models. A drifting-snow scheme improves modelled SMB on ice sheet surface slopes with an elevation between 1000 and 2000 m, where strong katabatic winds form. Different ice masks have a substantial impact on the integrated total SMB and along with model resolution are factored into our analysis. Targeting undersampled regions with high precipitation for observational campaigns will be key to improving future estimates of SMB in Antarctica.
Highlights
The Antarctic ice sheet (AIS) is the largest body of freshwater on the planet and an important contributor to global sea level rise
Antarctic ice sheet (AIS) mass loss is currently equivalent to around 0.5 mm yr−1 of global mean sea level rise (Shepherd et al, 2020), but our results indicate some uncertainty in the surface mass balance (SMB) contribution based on regional climate models (RCMs)
centred root mean square error (CRMSE) is equivalent to the root mean square error, but systematic biases are removed by subtracting the mean observation and mean modelled values from each value as shown in Eq (4): CRMSE =
Summary
The Antarctic ice sheet (AIS) is the largest body of freshwater on the planet and an important contributor to global sea level rise. It is a significant part of the climate system, contributing freshwater to the ocean and with high relief that influences atmospheric circulation. Recent ice dynamics studies (DeConto and Pollard, 2016; Edwards et al, 2019; Sutter et al, 2016; Shepherd et al, 2018) have shown that there is potential for rapid ice sheet loss owing to ice sheet dynamics that are currently poorly understood, especially in West Antarctica. There has been disagreement between studies focused on the SMB contribution to the total mass budget of Antarctica and the contribution to sea level rise (Scambos and Shuman, 2016; Zwally et al, 2015) that makes it essential to understand potential biases and uncertainties
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