A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958–2015)

Brice Noël,Xavier Fettweis,Ian Howat,Michiel R Van Den Broeke,Horst Machguth,Willem Jan Van De Berg,Stef Lhermitte

doi:10.5194/tc-10-2361-2016

Abstract

Abstract. This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958–2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily output of the polar regional climate model RACMO2.3 at 11 km. The data set includes all individual SMB components projected to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital elevation model and ice mask. The 1 km mask better resolves narrow ablation zones, valley glaciers, fjords and disconnected ice caps. Relative to the 11 km product, the more detailed representation of isolated glaciated areas leads to increased precipitation over the southeastern GrIS. In addition, the downscaled product shows a significant increase in runoff owing to better resolved low-lying marginal glaciated regions. The combined corrections for elevation and bare ice albedo markedly improve model agreement with a newly compiled data set of ablation measurements.

Highlights

During the last 2 decades, the Greenland ice sheet (GrIS) has experienced significant mass loss as a result of increased meltwater runoff and sustained high solid ice discharge from marine-terminating outlet glaciers (Van den Broeke et al, 2009; Rignot et al, 2008, 2011; Sasgen et al, 2012; Shepherd et al, 2012; Enderlin et al, 2014)
The current spatial resolution of regional climate models (RCMs), typically 5–20 km, remains too coarse to accurately resolve glaciated areas in topographically complex regions such as small isolated ice caps and marginal outlet glaciers flowing into narrow fjords
The downscaled surface mass balance (SMB) v0.2 agrees better with observations compared to the RACMO2.3 output at 11 km (Fig. 6a, b): we find a significant decrease of the root mean square error (RMSE) (190 mmWE or −16 %) and a smaller bias (100 mmWE or −21 %)

Summary

Introduction

During the last 2 decades, the Greenland ice sheet (GrIS) has experienced significant mass loss as a result of increased meltwater runoff and sustained high solid ice discharge from marine-terminating outlet glaciers (Van den Broeke et al, 2009; Rignot et al, 2008, 2011; Sasgen et al, 2012; Shepherd et al, 2012; Enderlin et al, 2014). RCMs explicitly calculate the individual SMB components (Lenaerts et al, 2012), i.e. precipitation, runoff and sublimation, over the entire ice sheet (Fig. 1) at high spatial and temporal resolution and over extended periods. The current spatial resolution of RCMs, typically 5–20 km, remains too coarse to accurately resolve glaciated areas in topographically complex regions such as small isolated ice caps and marginal outlet glaciers flowing into narrow fjords. In these regions, the relatively coarse elevation and land ice masks used in RCMs might result in runoff underestimation (Franco et al, 2012; Noël et al, 2015), hampering realistic regional SMB estimates.

Objectives

Methods

Results

Conclusion