Validation of ECMWF (re)analysis surface climate data, 1979–1998, for Greenland and implications for mass balance modelling of the ice sheet

Abstract

Climate (re)analysis products are potentially valuable tools, when properly verified, for helping to constrain the surface mass balance of the Greenland Ice Sheet (GIS). Monthly surface fields from European Centre for Medium-Range Weather Forecasts (ECMWF) operational-and re-analyses spanning 1979-1998 were validated using in situ data (surface air pressure and temperature, precipitation, cloud cover, short-/all-wave radiation, and wind speed/direction). These validation data are from coastal or near-coastal Danish Meteorological Institute (DMI) synoptic stations, inland Greenland Climate Network (GC-Net) and University of Wisconsin Automatic Weather Stations (AWSs), and two energy balance stations near the southern ice margin. The ECMWF analyses closely reproduce the seasonal patterns and interannual variations of much of the in situ data. Differences in the mean values of surface air pressure and temperature can mainly be ascribed to orography errors in the analyses' schemes, compared with the latest available accurate digital elevation model. Much of the GIS margin as modelled by ECMWF was too cold, on average by 4°C, and ECMWF precipitation averaged some 136% of the DMI station values. The misrepresentation of the (relatively) steep ice-sheet margin, which tends to be broadened and systematically over-elevated by several hundred metres, orographically reduced temperature and enhanced precipitation there in the ECMWF models. The cloud-cover comparison revealed not dissimilar annual mean cloud covers (ECMWF −8%) but the ECMWF analyses had too little cloud and were too 'sunny' during the critical summer melt-season. ECMWF-modelled surface albedo in summer was 11% lower than GC-Net values, which was mainly responsible for the disagreement of modelled surface short-wave radiation fluxes with observations. Model albedo and cloud errors need to be rectified if the analyses are to be used effectively to drive energy balance models of Greenland snowmelt. ECMWF wind speed averaged 66% (62%) of the DMI station (AWS) values. The validation results provide useful insights into how one can best improve the ECMWF Greenland climate data for use in glaciological and climatological studies.

Empirical modeling of summer lake surface temperatures in southwest Greenland

“…Although this region is not mountainous, there are altitude differences that must be taken into account when interpolating air temperatures between the surrounding WMO stations. Hanna and Valdes (2001) suggest a lapse rate correction of Ϫ5ЊC km Ϫ1 for this region, which in the absence of further data, was applied to all sites. Following this, it became apparent that the air temperature recorded at the AWS was much higher than expected from spatial interpolation of the WMO station temperatures because of the unfortunate siting of the WMO stations.…”

“…This region is presently cooling (average decrease in annual temperature of 1.29ЊC from , presumably as a result of the current positive tendency of the North Atlantic Oscillation (Hanna and Cappelen 2003). In an attempt to develop predictive models from chironomids preserved in lake sediments to address Holocene climate variability, we measured lake surface temperature (LST) with miniature thermistors with integrated automatic dataloggers (cf.…”

The Northeast Asia mountain glaciers in the near future by AOGCM scenarios

“…Among glacier regime characteristics related to high altitudes, A is considered more reliable than C because it is relatively easy to calculate it basing on air temperature, since temperature lapse rates are easier to define and therefore better known than precipitation lapse rates (e.g. Hanna and Valdes, 2001). Accumulation is then set equal to the ablation at the mean ELA.…”

Testing hypotheses of the cause of peripheral thinning of the Greenland Ice Sheet: is land-terminating ice thinning at anomalously high rates?

“…2.4. Although it is possible that data from these coastal stations are not representative of prevailing conditions on the ice sheet, coastal meteorological stations have been used in many previous PDD analyses (Abdalati et al, 2001;Hanna et al, 2005Hanna et al, , 2006Hanna and Valdes, 2001;Thomas et al, 2003). Hanna et al (2008:332), suggest that coastal "DMI data reflect changing meteorological conditions on the adjacent low-lying marginal ablation zone of the ice sheet, where much of the seasonal melt and subsequent runoff occurs".…”