Recent variability and trends in Antarctic snowfall accumulation and near-surface air temperature

Approximately 6 mm of sea level equivalent falls as snow on Antarctica each year, comprising the dominant term in the surface mass balance---the net accumulation of moisture---over the continent. Therefore, short- or long-term fluctuations in the annual amount of snowfall may have a substantial impact on the surface mass balance and eustatic global sea level change. Due to the continent's inaccessibility and the inherent shortage of observational data, Antarctic snowfall accounts for substantial uncertainty in global sea level change estimates. Taken over the grounded ice sheet, even the sign of the snowfall trends---whether they are contributing to, or mitigating sea level rise---is a matter of intense debate. The work presented here uses a variety of methods to better understand how Antarctic snowfall, as well as near-surface air temperature (an important modulator of snowfall), have been changing in the later decades of the 20th century.; Polar MM5, a mesoscale atmospheric model optimized for use over polar ice sheets, is employed to simulate Antarctic snowfall over the past two decades. Two sets of simulations, each with different initial and boundary conditions, are evaluated for the 17-y period spanning 1985-2001. The initial and boundary conditions for the two sets of runs are provided by the (1) European Centre for Medium-Range Weather Forecasts 40-year Reanalysis, and (2) National Centers for Environmental Prediction - Department of Energy Atmospheric Model Intercomparison Project Reanalysis II, an approach used so that uncertainty can be assessed by comparing the resulting datasets.; The simulated snowfall changes are in general agreement with ice core and snow stake accumulation records at various locations across the continent, indicating broad areas of both positive and negative trends. Averaged over the continent, the annual snowfall trends in both Polar MM5 datasets are not statistically different from zero, suggesting that recent Antarctic snowfall changes do not mitigate currently observed sea level rise. However, the lack of a continent-averaged annual trend does not suggest that Antarctica is isolated from the recent climate changes occurring elsewhere on Earth. Rather, snowfall variability is expressed by strong seasonal and regional changes.; The Polar MM5 simulations are useful for assessing snowfall variability from the mid-1980s onward, but because the accuracy of the model initial conditions relies on the quality and volume of satellite data over the otherwise data sparse Antarctic, atmospheric models and reanalyses are known to be unreliable over Antarctica prior to the modern satellite era, which begins around 1980. However, by blending the spatial information provided by the model fields during the post-1980 era with scores of new ice core measurements in the pre-1980 era, it has been possible to reconstruct Antarctic snowfall with spatial and temporal continuity over 1955-2004. The resulting dataset is consistent with the results from the shorter, 1985-2001 Polar MM5 assessment, indicating that there has been no significant net change in Antarctic snowfall since the 1950s, and thus Antarctic snowfall is not mitigating observed global sea level rise as expected, despite recent warming of the overlying atmosphere.; The observational analysis technique devised to 'fill in the gaps' between the ice core records to reconstruct snowfall can be applied to other fields in Antarctica for which few observations exist. A new Antarctic near-surface temperature dataset spanning 1960-2005 is constructed using the same methodology used for snowfall. The new dataset is compared with other observationally-based Antarctic near-surface temperature datasets for the past ∼45 years and all are in good agreement at annual and seasonal timescales. The new snowfall and near-surface temperature records, which are representative of the entire continent, are useful for assessing global climate model (GCM) simulations of A...