Sammendrag
Snow depth and sea ice thickness were observed applying an ice mass balance buoy (IMB) in the drifting ice station
Tara during the International Polar Year in 2007. Detailed in situ observations on meteorological variables and surface fluxes were
taken during May to August. For this study, the operational an alyses and short-term forecasts from two numerical weather
prediction (NWP) models (ECMWF and HIRLAM) were extracted for the Tara drift trajectory. We compared the IMB,
meteorological and surface flux observations against the NWP products, also applying a one-dimensional thermodynamic sea ice
model (HIGHTSI) to calculate the snow and ice mass balance and its sensitivity to atmospheric forcing. The modelled snow depth
time series, controlled by NWP-based precipitation, was in line with the observed one. HIGHTSI reproduced well the snowmelt
onset, the progress of the melt, and the first date of snow-free conditions. HIGHTSI performed well also in the late August freezing
season. Challenges remain to model the “false bottom” observed during the melting season. The evolution of the vertical
temperature profiles in snow and ice was better simulated when the model was forced by in situ observations instead of NWP
results. During the melting period, the nonlinear ice temperatur e profile was successfully modelled with both forcing options.
During spring and the melting season, tota l sea ice mass balance was mo st sensitive to uncertaintie s in NWP results for the
downward longwave radiation, followed by the downward shortwave radiation, air temperature, and wind speed.
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