Abstract: In this study, the meteorological data observed at Maqu Station for Climate and Environment Integrated Research, Chinese Academy of Sciences during the period from December 2011 to March 2012 were used. The purposes of the study were to compare and analyze the surface radiation and energy balance in three snow cover processes under the different conditions of soil freezing and thawing as well meteorological conditions in the headwaters of the Yellow River. The results showed that the net radiation was decreased significantly after snowfall, and the net radiations before and after snowfall were 154, 200 and 210 W·m^-2 and 93, 129 and 130 W·m^-2 respectively. After three times of snowfall and snowmelt, the ground-air energy exchange was strongly affected by weather conditions and soil freezing and thawing: after the first snowfall, the low temperature and land surface temperature did not affect the weak evaporation capacity of frozen soil, the latent heat flux and its difference before and after snowfall and snowmelt were low. On February 18 after second snowfall, the high wind speed (≥ 4 m·s-1) and strong solar radiation accelerated the sublimation of snow cover, the latent heat flux was high with a daily average of 118 W·m^-2, the wind speed and latent heat flux changed synchronously, and their peak values of 15m·s^-1 and 300 W·m^-2 occurred simultaneously. The sublimation energy consumption of snow cover reduced the surface temperature and was lower than the air temperature, and a negative sensible heat flux occurred with a daily average of -8 W·m^-2 and a peak value of -40 W·m^-2. After snowmelt, the latent heat flux and sensible heat flux reached their levels before snowfall. During the period from February 29 to March 3 after the third time of snowfall, the shallow soil temperature was gradually increased from -1 ℃ and maintained at -0.18 ℃, the frozen soil absorbed heat, the increase of latent heat flux was not significant compared with that before snowfall. March 4 was the last day of snowmelt, latent heat was released from damp soil and snowmelt water evaporation, the latent heat flux was increased significantly compared with that on March 3. After snowmelt, the effect of shallow soil evaporation capacity on the latent heat flux was increased significantly compared with that before snowfall.

Key words: snow cover, radiation, sensible heat, latent heat, energy balance, Maqu, headwaters, the Yellow River