Soot on snow experiments: light-absorbing impurities effect on the natural snowpack (original) (raw)

2015, The Cryosphere Discussions

Light-absorbing impurities affect snow and ice via a decrease in albedo and a consequent disturbance to the radiative energy balance. Experimentally, these matters have only been examined in a few studies. Here we present results from a series of experiments in which we deposited different soot concentrations onto natural snow in different regions of Finland, and thereafter monitored the changes of the snowpack through the melting season. Measurements of the particulates in the snow indicated concentrations in the range of thousands of ppb to have clear effects on the snow properties, including the albedo, the physical snow characteristics, and an increased melt rate. For soot concentrations in the hundreds of ppb range, the effects were not as clearly visible, and it was more difficult to attribute the effects solely to the soot on the snow. Comparisons between our experimental data and the widely used Snow, Ice and Aerosol Radiation (SNICAR) model showed a general agreement when the model was specifically tuned to our measurements. This study highlights the importance of additional experimental studies, to further articulate and quantify the effects of light-absorbing impurities on snow. 1 Introduction Snow has a crucial role in the Earth's radiative energy budget due to its naturally high reflectivity (or albedo) for incoming solar light. The albedo of fresh snow is 0.7-0.9 (see, e.g. review by Gardner and Sharp, 2010), which is significantly higher compared to that of other natural surfaces (Peltoniemi et al., 2010a, 2015). Snow albedo depends on many parameters, including, e.g. the snow's physical properties (such as snow grain size and snow thickness) and the wavelength range of the incoming solar radiation (Peltoniemi et al., 2010b; Wiscombe and Warren, 1980). The presence of light-absorbing impurities in snow can also have an effect on its albedo (e.g. Clarke and Noone, 1985;