Abstract
Abstract. The ERA5 reanalysis, recently made available by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a new reanalysis product at a high resolution replacing ERA-Interim and is considered to provide the best climate reanalysis over Greenland to date. However, so far little is known about the performance of ERA5 over the Greenland Ice Sheet (GrIS). In this study, we compare the near-surface climate from the new ERA5 reanalysis to ERA-Interim, the Arctic System Reanalysis (ASR) as well as to a state-of-the-art polar regional climate model (MAR). The results show (1) that ERA5 does not outperform ERA-Interim significantly when compared with near-surface climate observations over GrIS, but ASR better models the near-surface temperature than both ERA reanalyses. (2) Polar regional climate models (e.g., MAR) are still a useful tool to downscale the GrIS climate compared to ERA5, as in particular the near-surface temperature in summer has a key role for representing snow and ice processes such as the surface melt. However, assimilating satellite data and using a more recent radiative scheme enable both ERA and ASR reanalyses to represent more satisfactorily than MAR the downward solar and infrared fluxes. (3) MAR near-surface climate is not affected when forced at its lateral boundaries by either ERA5 or ERA-Interim. Therefore, forcing polar regional climate models with ERA5 starting from 1950 will enable long and homogeneous surface mass balance reconstructions.
Highlights
Reanalyses are global datasets describing the recent history and current state of the atmosphere, land surface, and oceans
(2) Polar regional climate models (e.g., MAR) are still a useful tool to downscale the Greenland Ice Sheet (GrIS) climate compared to ERA5, as in particular the near-surface temperature in summer has a key role for representing snow and ice processes such as the surface melt
The main goals of this study are (1) to evaluate ERA5 against ERA-Interim and Arctic System Reanalysis (ASR) reanalyses by comparison with a set of near-surface climate observations covering the GrIS not assimilated in the reanalyses (Ahlstrom et al, 2008), (2) to highlight the added value of using the state-ofthe-art regional climate models (RCMs) MAR (Modèle Atmosphérique Régional, Fettweis et al, 2017) forced by both ERA-Interim and ERA5 to simulate the near-surface climate of the GrIS, and (3) to evaluate the sensitivity of MAR based near-surface climate to the forcing used (ERA-Interim and ERA5 reanalyses) at its lateral boundaries
Summary
Reanalyses are global datasets describing the recent history and current state of the atmosphere, land surface, and oceans They merge sparse observations into a space- and timecontinuous product over the whole Earth. In addition to the model improvements listed in Hersbach and Dick (2016), ERA5 is available at higher vertical and spatial resolution (0.3◦) than ERAInterim (0.75◦) This new generation of reanalysis products has been already evaluated over North America as forcing field for a land surface model (Albergel et al, 2018), over Europe (Urraca et al, 2018), and over the Arctic Ocean (Wang et al, 2019) but not yet over the Greenland Ice Sheet (GrIS)
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