Characteristics of stable flows over Southern Greenland

The main characteristic features of stable atmospheric flows over a large mountain plateau are summarised and then compared with mesoscale and synoptic scale numerical simulation, meteorological analysis, satellite imagery, and surface observations for the cases of flows over Southern Greenland for four wind directions. The detailed features are identified using the concepts and scaling of stably stratified flow over large mountains with variations in surface roughness, elevation, and heating. For westerly and easterly winds detached jets form at the southern tip, where coastal jets converge, which propagate large distances across the ocean. Near coasts katabatic winds can combine with barrier jets and wake flows generated by synoptic winds. Note how the approach flow rises/falls over southern Greenland for easterly/westerly winds, leading in both cases to more cloud on the western side. Some conclusions are drawn about the large-scale influences of these flows; detached jets in the atmosphere; air-sea interaction; formation of low pressure systems. For accurate simulations of these flows, mesoscale models are necessary with resolutions of order of 20 km or less. © Birkhäuser Verlag, Basel, 2005

High resolution (1 km) positive degree-day modelling of Greenland ice sheet surface mass balance, 1870–2012 using reanalysis data

We show results from a positive degree-day (PDD) model of Greenland ice sheet (GrIS) surface mass balance (SMB), 1870–2012, forced with reanalysis data. The model includes an improved daily temperature parameterization as compared with a previous version and is run at 1 km rather than 5 km resolution. The improvements lead overall to higher SMB with the same forcing data. We also compare our model with results from two regional climate models (RCMs). While there is good qualitative agreement between our PDD model and the RCMs, it usually results in lower precipitation and lower runoff but approximately equivalent SMB: mean 1979–2012 SMB (± standard deviation), in Gt a−1, is 382 ± 78 in the PDD model, compared with 379 ± 101 and 425 ± 90 for the RCMs. Comparison with in situ SMB observations suggests that the RCMs may be more accurate than PDD at local level, in some areas, although the latter generally compares well. Dividing the GrIS into seven drainage basins we show that SMB has decreased sharply in all regions since 2000. Finally we show correlation between runoff close to two calving glaciers and either calving front retreat or calving flux, this being most noticeable from the mid-1990s

A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change

Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources. © 2014 The Author(s) Published by the Royal Society. All rights reserved

Annual accumulation for Greenland updated using ice core data developed during 2000-2006 and analysis of daily coastal meteorological data

An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950-2000 is better represented by the data than are earlier periods. Ice-sheetwide accumulation was estimated based on kriging. The average accumulation (95 confidence interval, or ±2 times standard error) over the Greenland ice sheet is 30.0 ± 2.4 g cm -2 a-1, with the average accumulation above 2000-m elevation being essentially the same, 29.9 ± 2.2 g cm-2 a -1. At higher elevations the new accumulation map maintains the main features shown in previous maps. However, there are five coastal areas with obvious differences: southwest, northwest, and eastern regions, where the accumulation values are 20-50 lower than previously estimated, and southeast and northeast regions, where the accumulation values are 20-50 higher than previously estimated. These differences are almost entirely due to new coastal data. The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long-term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland. A significant and sustained precipitation measurement program will be needed to resolve this uncertainty. Copyright 2009 by the American Geophysical Union

Predicting Resource Management Benefits By Simulating Angler Demand and Supply Responses

The “product” travel cost model (PTC) improves supply and substitution specification in travel cost models (TCM), eliminating common biases in estimating welfare effects of qualitative changes at specific sites. Angling sites and participation are modeled as a system of product supplies and demands; changes in angling quality at specific sites are evaluated as changes in the supplies of relevant products. PTC assumes that each angler chooses from a selection of angling opportunities (i.e., products) based on access cost (i.e., travel cost) and the nature of each angling product. Key factors defining angling products (e.g., success rate, fish size) are derived from angler travel patterns: Anglers are assumed indifferent between sites providing identical angling products, so choose the lowest cost site. Therefore, the benefits of any management action not only differ from average welfare-change values, but are also site-specific. Changing angling attributes at a site changes its angling product: a unit of the existing product (potentially decreasing its supply) is lost while a unit of the newly created product is produced (potentially increasing its supply). Changes in supply at one site may alter angler participation patterns and the value of angling opportunities at the affected site plus at many other sites as well. Credit Valley Conservation contracted the application of the PTC examined here, namely angling in the Credit River watershed near Toronto, Canada. Average angler consumer surplus was estimated at $40 per angler day and varied according to angling product, location and season.Keywords: Fishery Management, Special Topics, Fisheries Economics, Valuing Recreational Fisheries and Modelling Human Responses to Changes in their Management Regime

Annual net snow accumulation over southern Greenland from 1975 to 1998

As part of NASA's Program for Arctic Regional Climate Assessment (PARCA), extensive ice core measurements of annual net water-equivalent accumulation have been made recently around the southern Greenland ice sheet. Analysis of these measurements demonstrates that annual and seasonal accumulation patterns are sometimes regional, with temporal variability in accumulation correlated over large areas. Using this unique, widely distributed set of contemporaneous accumulation measurements, as well as available previously published observations, we developed maps of annual net snow accumulation south of �73° N for each year from 1975 to 1998. Here net snow accumulation is defined as snow accumulation minus ablation. In order to achieve a more consistent spatial distibution of core measurements for each of the 24 years in the study period, some of the observed records were extrapolated up to 5 years using empirical relationships between monthly precipitation measured at coastal stations and the observed ice core net accumulation records. Initial comparisons between the maps of annual net snow accumulation and similar maps of net accumulation derived from meteorological model simulations show excellent agreement in the temporal variability of accumulation, although significant differences in the magnitude of accumulation remain. Both measurements and model simulations indicate that annual net accumulation, averaged over all higher-elevation regions (above 2000 m) of the southern ice sheet, varies significantly from one year to the next. The maximum year-to-year change during the 24-year study period occurred between calendar years 1995 and 1996, when the average annual net snow accumulation increased by 101 and 172 kg m-2 yr-1, or 37 and 57, for observations and model simulations, respectively. Taken alone, this 1-year change in average net snow accumulation corresponds to a drop in sea level of �0.16 and �0.28 mm yr-1. Copyright 2001 by the American Geophysical Union

Mass balance of the ice sheets and glaciers – progress since AR5 and challenges

Recent research shows increasing decadal ice mass losses from the Greenland and Antarctic Ice Sheets and more generally from glaciers worldwide in the light of continued global warming. Here, in an update of our previous ISMASS paper (Hanna et al., 2013), we review recent observational estimates of ice sheet and glacier mass balance, and their related uncertainties, first briefly considering relevant monitoring methods. Focusing on the response to climate change during 1992-2018, and especially the post-IPCC AR5 period, we discuss recent changes in the relative contributions of ice sheets and glaciers to sea-level change. We assess recent advances in understanding of the relative importance of surface mass balance and ice dynamics in overall ice-sheet mass change. We also consider recent improvements in ice-sheet modelling, highlighting data-model linkages and the use of updated observational datasets in ice-sheet models. Finally, by identifying key deficiencies in the observations and models that hamper current understanding and limit reliability of future ice-sheet projections, we make recommendations to the research community for reducing these knowledge gaps. Our synthesis aims to provide a critical and timely review of the current state of the science in advance of the next Intergovernmental Panel on Climate Change Assessment Report that is due in 2021