Abstract
Abstract. To improve surface mass balance (SMB) estimates for the Greenland Ice Sheet (GrIS), we developed a 5 km resolution regional climate model combining the Japan Meteorological Agency Non-Hydrostatic atmospheric Model and the Snow Metamorphism and Albedo Process model (NHM–SMAP) with an output interval of 1 h, forced by the Japanese 55-year reanalysis (JRA-55). We used in situ data to evaluate NHM–SMAP in the GrIS during the 2011–2014 mass balance years. We investigated two options for the lower boundary conditions of the atmosphere: an offline configuration using snow, firn, and ice albedo, surface temperature data from JRA-55, and an online configuration using values from SMAP. The online configuration improved model performance in simulating 2 m air temperature, suggesting that the surface analysis provided by JRA-55 is inadequate for the GrIS and that SMAP results can better simulate physical conditions of snow/firn/ice. It also reproduced the measured features of the GrIS climate, diurnal variations, and even a strong mesoscale wind event. In particular, it successfully reproduced the temporal evolution of the GrIS surface melt area extent as well as the record melt event around 12 July 2012, at which time the simulated melt area extent reached 92.4 %. Sensitivity tests showed that the choice of calculation schemes for vertical water movement in snow and firn has an effect as great as 200 Gt year−1 in the GrIS-wide accumulated SMB estimates; a scheme based on the Richards equation provided the best performance.
Highlights
In the Greenland Ice Sheet (GrIS), the second largest terrestrial ice sheet, a significant loss of ice mass has been occurring since the early 1990s (e.g., Rignot et al, 2008; van den Broeke et al, 2009, 2016; Hanna et al, 2013)
The surface mass balance (SMB) of the GrIS calculated by NHM–SMAP for the study period was evaluated by using data provided by PROMICE (Machguth et al, 2016) as well as ice core data from the SIGMA-D (Matoba et al, 2015) and SE Dome (Iizuka et al, 2015) drilling sites (Table 2 and Fig. 2b)
Notable overestimates by the model (ME reached 6.6 ◦C at Summit, for example) were corrected in the online configuration (ME was within 2.3 ◦C at all sites). These results suggest that the surface analysis provided by JRA-55 is of inadequate quality in the GrIS and that SMAP improves the results through the use of more realistic snow/firn/ice physical conditions
Summary
In the Greenland Ice Sheet (GrIS), the second largest terrestrial ice sheet, a significant loss of ice mass has been occurring since the early 1990s (e.g., Rignot et al, 2008; van den Broeke et al, 2009, 2016; Hanna et al, 2013). Once the validity of these models is confirmed on the basis of the in situ data, output from the models can be used for analysis of ongoing environmental changes around the entire GrIS These models enable us to perform present and future climate simulations for the GrIS, including the effects of ice mass loss on global sea level rise (e.g., Rignot et al, 2011). The purpose of this study was to assess the performance of the NHM–SMAP polar RCM in reproducing current GrIS atmospheric and snow/firn/ice conditions by utilizing in situ measurements. The success of our attempt may make model output data from NHM–SMAP valuable for assessing long-term climate change in the GrIS and detailed diurnal variations of the meteorological, snow, firn, and ice conditions in the GrIS.
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