A 5 year record of surface energy and mass balance from the ablation zone of Storbreen, Norway

A 5 year record of data from an automatic weather station (AWS) operating in the ablation zone of Storbreen, Norway, has been used to calculate the local surface energy and mass balance. The AWS observations cover five mass-balance years with an unusually strong mass deficit on Storbreen. The average energy flux (Q) contributing to melt for the period 2001-06 is 113 W m(-2). Of this, the net shortwave radiation flux is the dominant contributor (92 W m(-2)), followed by the sensible heat flux (20 W m(-2)) and the latent heat flux (9 W m(-2)). The net longwave radiation (-6 W m(-2)) and the subsurface heat flux (-2 W m(-2)) contribute negatively to the budget. Net radiation thus produces 76% of the melt, while the turbulent fluxes and the subsurface heat flux produce 24% of the total melt. The seasonal mean incoming shortwave radiation is remarkably constant between the years, whereas variations in temperature and reflected shortwave radiation (albedo) explain most of the interannual variation in melt. The modelled ablation compares well with the measured ablation from stake readings. The sensitivity of the energy-balance model was examined by varying the surface roughness length of momentum and the sensitivity of the calculated melt by perturbations of temperature, wind speed and relative humidity.