Energy exchange between the atmosphere and a subalpine meadow in the Qilian Mountains, northwest China

Abstract

Understanding energy exchange between the atmosphere and the Earth’s surface is crucial. We observed the patterns of energy exchange between the atmosphere and a subalpine meadow in the Qilian Mountains, northwest China over the period of 2014 to 2016. Annual variations in energy exchange in study area exhibited drastic differences during time periods of frozen soil and non-frozen soil. Specifically, more than 80% and 28% of net radiation (Rn) were converted to sensible heat (H) during the frozen and non-frozen soil periods, respectively, whereas approximately 17% and 35% of Rn were converted to latent heat (LE) during the frozen and non-frozen soil periods, respectively. The non-frozen soil period was divided into the pre-growth period, the growth period, and the post-growth period. The high Bowe ratio (β) values of the pre-growth period were 4.34, 3.60, and 8.39 in 2014, 2015 and 2016, respectively. In general, rapid increases in Rn during this period increased the values of H, LE, and soil heat flux (G). The growth period was defined by a low β value that fluctuated between 0.3 and 0.4. The average β values for the post-growth period during 2014, 2015, and 2016 were 1.49, 3.12, and 2.37, respectively. The high decoupling coefficient (Ω) for the growth period indicated that the contribution of Rn to LE was greater than that of vapor pressure deficit (VPD). The small value of Ω during the other periods indicated that the effect of VPD on LE dominated that of other factors. The seasonal patterns of energy exchange showed that vegetation phenology is the major factor that affects energy partitioning significantly in the alpine meadow ecosystem in the Qilian Mountains. The annual energy partitioning in the same ecosystem over 3 years was not constant, and climate may be the main factor that influences interannual variations in energy exchange.