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Moore G.W.K.,University of Toronto | Renfrew I.A.,University of East Anglia | Harden B.E.,Woods Hole Oceanographic Institution | Mernild S.H.,Center for Scientific Studies
Geophysical Research Letters | Year: 2015

Southern Greenland is characterized by a number of low-level high wind speed weather systems that are the result of topographic flow distortion. These systems include barrier winds and katabatic flow that occur along its southeast coast. Global atmospheric reanalyses have proven to be important tools in furthering our understanding of these orographic winds and their role in the climate system. However, there is evidence that the mesoscale characteristics of these systems may be missed in these global products. Here we show that the Arctic System Reanalysis, a higher-resolution regional reanalysis, is able to capture mesoscale features of barrier winds and katabatic flow that are missed or underrepresented in ERA-I, a leading modern global reanalysis. This suggests that our understanding of the impact of these wind systems on the coupled-climate system can be enhanced through the use of higher-resolution regional reanalyses or model data. ©2015. American Geophysical Union. All Rights Reserved. Source


Mernild S.H.,Los Alamos National Laboratory | Mernild S.H.,Center for Scientific Studies | Liston G.E.,Colorado State University | Hiemstra C.A.,U.S. Army
Journal of Climate | Year: 2014

Mass changes and mass contribution to sea level rise from glaciers and ice caps (GIC) are key components of the earth's changing sea level. GIC surface mass balance (SMB) magnitudes and individual and regional mean conditions and trends (1979-2009) were simulated for all GIC having areas greater or equal to 0.5 km2 in the Northern Hemisphere north of 25°N latitude (excluding the Greenland Ice Sheet). Recent datasets, including the Randolph Glacier Inventory (RGI; v. 2.0), the NOAA Global Land One-km Base Elevation Project (GLOBE), and the NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) products, together with recent SnowModel developments, allowed relatively high-resolution (1-km horizontal grid; 3-h time step) simulations of GIC surface air temperature, precipitation, sublimation, evaporation, surface runoff, and SMB. Simulated SMB outputs were calibrated against 1422 direct glaciological annual SMB observations of 78 GIC. The overall GIC mean annual and mean summer air temperature, runoff, and SMB loss increased during the simulation period. The cumulative GIC SMB was negative for all regions. The SMB contribution to sea level rise was largest from Alaska and smallest from the Caucasus. On average, the contribution to sea level rise was 0.51 ± 0.16 mm sea level equivalent (SLE) yr-1 for 1979-2009 and ~40% higher 0.71 ± 0.15 mm SLE yr-1 for the last decade, 1999-2009. © 2014 American Meteorological Society. Source


Mernild S.H.,Los Alamos National Laboratory | Mernild S.H.,Center for Scientific Studies | Pelto M.,Nichols College | Malmros J.K.,Center for Scientific Studies | And 3 more authors.
Journal of Glaciology | Year: 2013

Identification of the transient snowline (TSL) from high spatial resolution Landsat imagery on Lemon Creek Glacier (LCG), southeast Alaska, USA, and Mittivakkat Gletscher (MG), southeast Greenland, is used to determine snow ablation rates, the equilibrium-line altitude (ELA) and the accumulation-area ratio (AAR). The rate of rise of the TSL during the ablation season on a glacier where the balance gradient is known provides a measure of the snow ablation rate. On both LCG and MG, snow pits were completed in regions that the TSL subsequently transects. This further provides a direct measure of the snow ablation rates for a particular year. TSL observations from multiple dates during the ablation season from 1998 to 2011 at LCG and 1999 to 2012 at MG were used to explore the consistency of the TSL rise and snow ablation rate. On LCG and MG the satellite-derived mean TSL migration rates were 3.8 ±0.6 and 9.4±9.1md-1, respectively. The snow ablation rates were 0.028 ± 0.004 m w.e. d-1 for LCG and 0.051 ±0.018 m w.e. d-1 for MG estimated by applying a TSL-mass-balance-gradient method, and 0.031 ± 0.004 and 0.047 ± 0.019 m w.e. d-1 by applying a snow-pitsatellite method, illustrating significant agreement between the two different approaches for both field sites. Also, satellite-derived ELA and AAR, and estimated net mass-balance (Ba) conditions were in agreement with observed ELA, AAR and Ba conditions for LCG and MG. Source


Sutherland D.A.,University of Oregon | Roth G.E.,University of Oregon | Hamilton G.S.,University of Maine, United States | Mernild S.H.,Center for Scientific Studies | And 3 more authors.
Geophysical Research Letters | Year: 2014

Large, deep-keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently track the glacier speed, with slightly faster speeds near terminus and episodic increases due to calving events. In the fjord, icebergs accurately capture synoptic circulation driven by both along-fjord and along-shelf winds. Recirculation and in-/out-fjord variations occur throughout the fjord more frequently than previously reported, suggesting that across-fjord velocity gradients cannot be ignored. Once on the shelf, icebergs move southeastward in the East Greenland Coastal Current, providing wintertime observations of this freshwater pathway. © 2014. American Geophysical Union. All Rights Reserved. Source


Mernild S.H.,Los Alamos National Laboratory | Mernild S.H.,Center for Scientific Studies | Knudsen N.T.,University of Aarhus | Hoffman M.J.,Los Alamos National Laboratory | And 5 more authors.
Journal of Glaciology | Year: 2013

We document changes for Mittivakkat Gletscher, the peripheral glacier in Greenland with the longest field-based observed mass-balance and surface velocity time series. Between 1986 and 2011, this glacier changed by -15% in mean ice thickness and -30% in volume. We attribute these changes to summer warming and lower winter snow accumulation. Vertical strain compensated for ∼60% of the elevation change due to surface mass balance (SMB) in the lower part, and ∼25% in the upper part. The annual mean ice surface velocity changed by -30%, which can be fully explained by the dynamic effect of ice thinning, within uncertainty. Mittivakkat Gletscher summer surface velocities were on average 50-60% above winter background values, and up to 160% higher during peak velocity events. Peak velocity events were accompanied by uplift of a few centimeters. Source

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