Energy Budget over Seasonal Snow Surface at an Open Site and Beneath Forest Canopy Openness during the Snowmelt Period in Western Tianshan Mountains, China

In this study, meteorological factors and snowmelt rate at an open site on sunny slope (OPS) and beneath forest canopy openness on shady slope (BFC) were measured using an automatic weather station and snow lysimeter during the snowmelt period in 2009, 2010 and 2013. The energy budget over snow surface was calculated according to these meteorological datasets. The analysis results indicated that the net shortwave radiation (K) and sensible heat flux (H) were energy sources, and the latent heat flux (L_VE) was energy sinks of snow surfaces at all sites. The net longwave radiation (L) was energy sink at OPS and 80% BFC, but energy source at 20% BFC. The gain of K, H, and the loss of L_VE at BFC were obviously lower than those at OPS. The L was the maximum difference of energy budget between snow surface at BFC and OPS. In warm and wet years, the most important factor of the energy budget variation at OPS was air humidity and the second most important factor was air temperature. However, the ground surface temperature on the sunny slope was the most important factor for L and energy budget at BFC. With the increases in forest canopy openness and the slope of adjacent terrains, the influences of ground surface temperature on the sunny slope on L and the energy budget over snow surface at BFC increased, especially when the snow cover on the sunny slope melts completely.