Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320–370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5–20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uvérsbreen, Midre Lovénbreen and Austre Brøggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50–160 m thick) was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1 % of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uvérsbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uvérsbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovénbreen w as frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50 m thick) was fed by temperate ice from two cirques. On Austre Brøggerbreen, a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320–370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5–20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uvérsbreen, Midre Lovénbreen and Austre Brøggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50–160 m thick) was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1 % of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uvérsbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uvérsbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovénbreen w as frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50 m thick) was fed by temperate ice from two cirques. On Austre Brøggerbreen, a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

[1] We present measurements of solar UV radiation performed with multichannel moderate-bandwidth NILU-UV filter instruments during winter and summer in 2003 in the altitude region from 3000 m to 5000 m at 29N in the Lhasa region in Tibet. During summer the UV index was found frequently to exceed 15 on clear days and occasionally to exceed 20 on partially cloudy days. High altitudes, low ozone column amounts, clean atmospheres, and relatively low latitudes are factors that contribute to the high UV levels on the Tibetan plateau. UV index values of 12 were measured in late winter for a solar zenith angle of 40 at a snow-covered 5000 m altitude site. This is a 35% increase compared to a corresponding snow-free surface. Our measurements show that the solar UV radiation increases with altitude. For clear-sky and snow-free conditions the altitude increase is 7-8% per km for erythemal UV dose rates and 3% per km at a wavelength of 340 nm. Results from clear-sky calculations using a multiple-scattering radiative transfer model were found to agree within 5% with clear-sky UV measurements. Radiative transfer calculations combined with measurements were used to estimate the influence of clouds on the UV radiation at the surface. On the average the variable cloud cover in Lhasa reduced the daily integrated erythemal UV dose by 25%. The NILU-UV instruments also provide total ozone column amounts. The mean difference between daily total ozone column amounts derived from NILU-UV measurements and from Earth Probe TOMS data was À1.4% ± 3.2% (1s).

In 1987 an ice core to the bedrock at a depth of 85.6 m was drilled at the top of H0ghetta ice dome in northern Spitsbergen. Chronology of the ice core was examined by tritium and HC methods showing time gap at about 50 m depth. The age of three bottom ice samples was dete rmined as 4150-5670 year B.P. by 14C method done for frozen bacteria colonies and a frozen petal. This chronology and negative bottom temperature of -9.4 °c suggest that glaciers in Spitsbergen shrank considerably during the hyps ithermal.

Wind and temperature profiles in the constant flux layer obtained by tethersonde were used to compute the total aerodynamic drag on an area of 60Y0 pack ice in the Fram Strait (79"20", I-3"W). The boundary layer appeared adiabatic to heights greater than 150 m, and there were only minor air/water temperature differences. Drag coefficients of 4.9 and 5.1. 10-3 referred to 10 m above ground level were found. Eddy correlation measurements in the local constant flux layers over ice floes were used to estimate the skin drag of an area of 1002, ice cover. This was less than 40% of the total drag on the actual area. The corresponding drag coefficient was 1.4.A drag partition model is proposed for computing the total drag over an area of pack ice as a function of ice concentration, mean freeboard and length of the ice floes, and typical roughness lengths of ice and sea surfaces. The model predicts maximum form drag at 73"/, ice concentration for floes of the type observed in the Fram Strait.