Sublimation over Seasonal Snowpack at the Southeastern Edge of the Gubantonggut Desert

Sublimation during snow accumulation season is an important component of the winter moisture budget, constituting a proportion of precipitation that does not contribute to melt. The dominant meteorological elements affecting sublimation are the wind speed and the air temperature, with the latter affecting sublimation indirectly through the vapor deficit.

Almost all previous studies of sublimation have been carried out in or adjacent to the Arctic or Antarctic or in alpine areas, which are characterized by extremely strong winds or rugged terrain. However, as vegetation cover increases, the interception of snow in the canopies reduces the amount of snow that accumulates on the ground, and vegetation cover also provides shelter and shading to the snow and thus reduces snow ablation rates compared to open areas. Thus, it is extremely important to select a suitable site when studying sublimation over snowpack. There ought to be no vegetation and no topographic complications at all, and the wind speed also ought not to be large enough to blow snow to the atmosphere from the snowpack.

The Gurbantonggut Desert, located in the northwest of China, is an ideal site to study sublimation over snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. So, Prof. ZHOU Hongfei et al. conducted observations at the southeastern edge of the Gubantonggut Desert. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert.

The results shown that on a daily scale, there was an extremely significant no-intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter.

It is also demonstrated that -10°C and 2m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2m above the ground averaged -17.2°C and 1.3m/s, respectively, and the percentages of the time when the air temperature was below -10°C and the wind speed was below 2m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi-static state until the melt stage started.

The research was supported by the 973 program of China (2009CB421301), the International Science & Technology Cooperation Program of China (2010DFA92720) and a grant from Natural Science Foundation of China (40671037). The result was published in Hydrological Processes on December 2012, 26(25): 3911-3920.