Accumulation rate changes in central Greenland from passive microwave data

Numerical modeling based on radiative transfer theory and observations of grain growth with depth have indicated that passive microwave brightness temperatures over the polar ice sheets should be a function of accumulation rate. Using accumulationrate time series from nine shallow cores in the dry-snow facies in central Greenland, we find that multi-year averages of mean annual SMMR brightness temperatures and accumulation rates are highly correlated. The 18 GHz vertically polarized channel is found to be the best predictor of accumulation rate. If the 18V brightness temperatures and the measured annual accumulation rates are averaged over 1979-1986, a linear regression to these multi-year average values reproduces the corresponding measured accumulation rates to within about ±5%. This regression also was used to compute annual accumulation rates at the nine core sites from the corresponding average annual SMMR brightness temperature. Measured and predicted annual accumulation rates agree to within ±10% if the mean annual passive microwave data is lagged by one year. Finally, we find that the predicted total annual accumulation over the 150 × 150 km study area agrees well with the corresponding value computed from the measured accumulation rate; both for an eight-year average and for annual values.