Glacio-meteorological investigations on Vatnajokull, Iceland, Summer 1996:An overview

We give an overview of a glacio-meteorological experiment carried out in th e summer (melt season) of 1996 on the largest European ice cap, Vatnajokull , Iceland (area 8000 km(2); altitude range: from sea level to about 2000 m) . The main goal was to understand how the energy used in the melting of sno w and ice is delivered to the surface. Many meteorological stations were op erated simultaneously on the ice cap, at almost all of which profile measur ements were made. Cable balloons and radiosondes were used to probe the ver tical structure of the boundary layer. It appears that the flow near the su rface is katabatic most of the time, with the height of the wind maximum va rying between a few metres and a few tens of metres. It is only during the passage of intense storms that the katabatic wind in the melt zone disappea rs. Global radiation increases significantly with altitude. Surface albedo varies enormously in space and time, with very low values (approximate to 0 .1) being found at many places because of the melt out of volcanic ash laye rs. If we consider the total melt in the period 22 May-31 August 1996, we c onclude that radiation typically provides two-thirds of the melt energy, an d turbulent exchange of heat one-third. At locations high on the glacier, t urbulent exchange becomes less significant.