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Climate variables that control the annual cycle of the surface energy and mass balance on Zhadang glacier in the central Tibetan Plateau were examined over a 2 year period using a physically based energy-balance model forced by routine meteorological data. The modelled results agree with measured values of albedo, incoming longwave radiation, surface temperature and surface level of the glacier. For the whole observation period, the radiation component dominated (82%) the total surface energy heat fluxes. This was followed by turbulent sensible (10%) and latent heat (6%) fluxes. Subsurface heat flux represented a very minor proportion (2%) of the total heat flux. The sensitivity of specific mass balance was examined by perturbations of temperature (±1 K), relative humidity (±20%) and precipitation (±20%). The results indicate that the specific mass balance is more sensitive to changes in precipitation than to other variables. The main seasonal variations in the energy balance were in the two radiation components (net shortwave radiation and net longwave radiation) and these controlled whether surface melting occurred. A dramatic difference in summer mass balance between 2010 and 2011 indicates that the glacier surface mass balance was closely related to precipitation seasonality and form (proportion of snowfall and rainfall).
Vestfonna ice cap, northeastern Svalbard, is one of the largest ice bodies in the European Arctic, but little is known about the evolution of its mass balance. This study presents a reconstruction of the climatic mass balance of the ice cap for the period 1979/80-2010/11. The reconstruction is based on calculations using a mass-balance model that combines a surface-elevation-dependent accumulation scheme with a spatially distributed temperature-index ablation model that includes net shortwave radiation. Refreezing is included, based on the basic Pmax approach. The model accounts for cloud-cover effects and surface albedo variations that are calculated by a statistical albedo model. ERA-Interim derived air temperature, precipitation and total cloud-cover data are used as input. Results reveal a mean climatic mass-balance rate of +0.09 ± 0.15 m w.e. a–1 for the study period. Annual balances show a slight, insignificant trend towards less positive values over the study period. Refreezing is estimated to contribute about one-third to annual accumulation, and a significant positive trend in refreezing is present over the study period. The modelling results reveal a significant steepening of the climatic mass-balance gradient and indicate a lengthening of the characteristic 3 month ablation period in recent years.
During the snowmelt period in 1998, air-temperature data were acquired at 1 min intervals using different measurement systems as part of a field campaign in the Kärkevagge, Swedish Lapland. A comparison reveals that temperatures from naturally ventilated sensors exceed temperatures from aspirated sensors by as much as 6.2 K. Errors in temperature are closely connected to high values of upwelling shortwave radiation and are larger in periods of low wind speed. Measurement errors result from the instantaneous radiation conditions and propagate over the next measurements due to slow response time of the naturally ventilated sensor. A physically based method is developed for correcting temperature data influenced by radiation errors, which requires additional measurements of wind speed and upwelling shortwave radiation. Coefficients of the correction formula are automatically determined from the erroneous temperature data, so the method is independent of accurate air-temperature measurements. The high quality of the correction method could be validated by accurate psychrometer measurements. One of the most important applications is the computation of sensible-heat fluxes from snow-covered surfaces during the snowmelt period using the bulk-aerodynamic method, which is greatly improved by the new correction method.
In many high-latitude areas, slushflows occur frequently during the snowmelt period but information on the initiation mechanism is rare. Field observations and measurements of slushflows in northwestern Spitsbergen and in northern Sweden demonstrate the role of meltwater accumulation and the hydraulic pressure gradient in the release process. Snow metamorphism is revealed to be of minor importance in the observed events. The monitoring of water-pressure development in a saturated snow cover demonstrates that preferred release areas are within low-gradient valley sections, where meltwater inflow is higher than outflow.
Slushflows consist of mudflow-like flowage of water-saturated snow along stream courses. They represent transitional processes between fluvial floods and avalanches. On the other hand, they possess unique characteristics concerning release and movement. The comparative evaluation of definition items for fluvial floods, slushflows and avalanches offers hasic data suitable for a risk assessment.
Slush-flows of a large variety of magnitudes were observed during three field campaigns to Liefdefjorden, northwestern Spitsbergen, and one campaign to Kärke-vagge, northern Sweden. In the latter campaign, the release and movement of a slush torrent was documented on video and in photographs. Meteorological and snow-hydrological measurements carried out during these campaigns were analysed with respect to slushflow initiation due to snow-melt.
Since slushflows are quite common in polar and sub-polar drainage basins (although they are not restricted to these regions), specific atmospheric and hydrological boundary condittons must be fulfilled for slushflow initiation due to snowmelt. Radiative fluxes, air temperatures and wind velocities are the most important atmospheric variables, while snow depth, depth of the water-saturated layer, hydraulic conductivity and snow structure are the primary snow variables of interest.
It has been shown that slushflows can be released due to energy input in the snow cover by net radiation and sensible heat within the ordinary range of the high-latitudinal snow melt period. Slush torrent initiation is intensified by a superpositton of both energy fluxes. Infiltration losses were not significant even when permafrost was not present. Crucial for slushflow initiation due to snowmelt is the timing of energy input and meltwater flow through the snowpack.
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