47 research outputs found
2 m temperatures along melting mid-latitude glaciers, and implications for the sensitivity of the mass balance to variations in temperature
No full textAbstractIn calculations of the variation in the 2 m temperature along glaciers, the lapse rate is generally assumed to be constant. This implies that the ratio of changes in the 2 m temperature above a glacier to changes in the temperature outside the thermal regime of that glacier (“climate sensitivity”) is equal to 1. However, data collected during the ablation season on several mid-latitude glaciers show that this sensitivity is smaller than 1. The lowest measured value (0.3) was obtained on the tongue of the Pasterze, a glacier in Austria. The measured temperature distribution along the Pasterze cannot be described by a constant lapse rate either. However, there is almost a linear relationship between potential temperature and the distance along die glacier. This paper introduces a simple, analytical, thermodynamic glacier-wind model which can be applied to melting glaciers and which explains the observed “climate sensitivities” and temperature distributions much better than calculations based on a constant lapse rate.This way of modelling the 2 m temperatures has implications for the sensitivity of the surface mass balance to atmospheric warming outside the thermal regime of the glacier. The magnitude of this sensitivity is computed with a surface energy-balance model applied to the Pasterze. When a constant lapse rate is used instead of the proposed glacier-wind model to compute changes in the 2 m temperature along the glacier, the negative change in mass balance due to 1°C warming is overestimated by 22%.</jats:p
2 m temperatures along melting mid-latitude glaciers, and implications for the sensitivity of the mass balance to variations in temperature
No full textAbstractIn calculations of the variation in the 2 m temperature along glaciers, the lapse rate is generally assumed to be constant. This implies that the ratio of changes in the 2 m temperature above a glacier to changes in the temperature outside the thermal regime of that glacier (“climate sensitivity”) is equal to 1. However, data collected during the ablation season on several mid-latitude glaciers show that this sensitivity is smaller than 1. The lowest measured value (0.3) was obtained on the tongue of the Pasterze, a glacier in Austria. The measured temperature distribution along the Pasterze cannot be described by a constant lapse rate either. However, there is almost a linear relationship between potential temperature and the distance along die glacier. This paper introduces a simple, analytical, thermodynamic glacier-wind model which can be applied to melting glaciers and which explains the observed “climate sensitivities” and temperature distributions much better than calculations based on a constant lapse rate.This way of modelling the 2 m temperatures has implications for the sensitivity of the surface mass balance to atmospheric warming outside the thermal regime of the glacier. The magnitude of this sensitivity is computed with a surface energy-balance model applied to the Pasterze. When a constant lapse rate is used instead of the proposed glacier-wind model to compute changes in the 2 m temperature along the glacier, the negative change in mass balance due to 1°C warming is overestimated by 22%.</jats:p
The evolution of the englacial temperature distribution in the superimposed ice zone of a polar ice cap during a summer season
No full textThe aim of the present investigation was to provide more insight into
the processes affecting the evolution of the englacial temperature
distribution at a non-temperate location on a glacier. Measurements were
made in the top 10 m of the ice at the summit of Laika Ice Cap (Canadian
Arctic) during the summer 1975 (by Blatter et al.). This location is in
the superimposed ice zone. The model simulation includes calculation of
the surface energy fluxes, of radiation penetration, of the englacial
temperature and density distribution, and of the formation, penetration
and refreezing of melt water.
In the first kind of experiments the energy fluxes from the
atmosphere were tuned in such a way as to obtain the right amount of
ablation. With these energy fluxes as a boundary condition the
consequences of melt water penetration and refreezing for the englacial
temperature distribution were proofed to be considerable. In the second
kind of experiments the measured temperature at the interannual surface
was used as boundary condition, and to start with the temperature below
the interannual surface could only be affected by conduction. The
measured and the calculated temperatures match until melt water
penetrates to the interannual surface. Thereafter, calculations give too
low temperatures. Most of this energy deficiency will probably be due to
radiation penetration, whereas a minor part of it may be caused by melt
water penetration into open veins or an error in the assumed interface
temperature
Skill and sources of skill in seasonal streamflow hindcasts for South America made with ECMWF's SEAS5 and VIC
No full textThe first aim of the present paper is the determination of the magnitude, annual variation and spatial distribution of skill in seasonal hindcasts of runoff and discharge in the entire continent of South America. We evaluated 35 years of hindcasts generated with the Variable Infiltration Capacity (VIC) hydrological model forced with SEAS5 hindcasts. Initial conditions of terrestrial water and so-called pseudo-observations were computed with a reference (i.e. historic) simulation. Skill was determined with monthly temporal resolution for the entire annual cycle and mostly using the pseudo-observations for verification. The second aim of the paper is the explanation of skill in terms of its sources, namely meteorological forcing and the initial conditions. Therefore, two sets of restricted hindcasts, which isolate the sources of skill, were analysed. The SEAS5 precipitation hindcasts exhibit significant skill even at the longest lead times (7 months). Beyond the first lead month we found significant skill in 13–43 % of the grid cells, depending on target and lead month. Levels of skill are higher in the full hindcasts (significant skill in 31–89 % of the grid cells). At the continental scale more of the skill is caused by the forcing than by the initial conditions. The runoff hindcasts are skilful in large parts of the continent. In a 1000 km wide band along the north coast of the continent and in southeast South America, most of the skill is due to the forcing. A typical feature of these regions is an increase of skill with lead time during specific parts of the year, which is against the common tendency. In Argentina and north Chile most of the skill in the runoff hindcasts can be attributed to the initial conditions of soil moisture. Verification with real observations of discharge broadly confirmed the skill pattern obtained with pseudo-observations
Energy balance calculations on and near the Hintereisferner (Austria) and an estimate of the effect of greenhouse warming on ablation
No full textDuring some 10 days in July 1986, measurements of meteorological
variables and ablation were made at two sites on and near
Hintereisferner (Austria), namely at GLACSTAT (2500 m), located on the
glacier tongue, and at ROCKSTAT (2440 m), just in front of the tongue.
In this paper energy balance calculations for both stations are
presented. About 90% of the ablation energy at GLACSTAT came from
radiation. This large value is a consequence of the low albedo (0.16)
and the long periods of sunny, relatively cold weather. A detailed
comparison is made of the surface energy budget at the two sites. While
melting is important at GLACSTAT, the loss of energy by the turbulent
fluxes and the outgoing long wave radiation is larger at ROCKSTAT.
Finally, the consequences of the rising concentrations of
atmospheric trace gases on ablation are discussed. The data from
GLACSTAT will be adapted to estimated past and projected future
concentrations. If all relevant trace gases are considered and under the
specific conditions of the experiment total ablation for the 10-days
period will increase by 11% in the 50 years after 1986
Impacts of +2°C global warming on winter tourism demand in Europe
No full textAbstractIncreasing temperatures and snow scarce winter seasons challenge the winter tourism industry. In this study the impacts of +2°C global warming on winter tourism demand in Europe’s ski tourism related NUTS-3 regions are quantified. Using time series regression models, the relationship between natural snow conditions and monthly overnight stays is estimated. Based on these model results, we quantify the risk of tourism demand losses due to weather variability and assess the potential impacts of climate change. Hereby, the concept of Weather-Value at Risk (0.95) is applied. Snow data are provided by the hydrological model VIC, which is forced by E-OBS data to obtain historical snow values for tourism model calibration and forced by EURO-CORDEX climate simulations to obtain snow projections until 2100.Under +2°C warming, the weather-induced risk of losses in winter overnight stays related to skiing tourism in Europe amounts to up to 10.1 million nights per winter season, which is +7.3 million overnight stays additionally at risk compared to the reference period (1971–2000). Among the top four European skiing tourism nations – Austria, France, Italy and Switzerland – France and Switzerland show the lowest increase in risk of losses in winter overnight stays. The highest weather-induced risk of losses in winter overnight stays – in the reference period as well as in the +2°C scenarios – is found in Austria, followed by Italy. These two countries account for the largest fraction of winter overnight stays in skiing related NUTS-3 regions
