Impact of Snow and Vegetation Activity on Surface Energy Balance in a Mongolian Grassland

Detailed yearlong energy flux measurements were conducted using an eddy correlation method in Mongolian steppe from June 2004 to September 2005. The observation area was enclosed by a fence for protecting from grazing. We focused on effects of snow cover in winter as well as of vegetation activity in summer on energy budget at the ground surface. In the cold season, although snow cover impact on energy budget through rapidly changing albedo was relatively small at the beginning of continuous snow cover around the winter solstice (24th December 2004), it was very large at the disappearance of snow cover around the spring equinox (18th March 2005). Before and after the snow disappearing, net radiation and sensible heat flux exhibited a drastic increase from 15 Wm^{- 2} to 70 Wm-2 and from -10 Wm-2 to 50 Wm-2, respectively. Snow melting was caused mainly by warm air advection. In the warm season, amplitudes of seasonal changes in albedo and maximum roughness height, resulted from the growth of perennial plants, were 0.06 and 0.017 m, respectively. These values were observed inside of the fenced area and thus the value for grazed area which is representative in the Mongolian Steppe would be likely rather smaller. Our results showed that the influence of the snow-derived albedo change on each radiation and heat fluxes depended highly on the amount of global solar radiation, and the timing of snow disappearance (and also the early appearance of snow cover) is most likely to play a crucial role in the atmosphere-land interaction over the Mongolian grasslands.