Seasonal Differences in the Trend Turning Characteristics of Surface Sensible Heat over the Central and Eastern Tibetan Plateau

This paper employed the piecewise linear fitting model (PLFIM) to analyze the seasonal differences of Surface Sensible Heat (SSH) trend evolution characteristics at 70 meteorological stations on the central and eastern part of Tibetan Plateau (TP) during 1982–2018. The key meteorological factors influencing the changes of SSH in different seasons were quantitatively evaluated using the linear tendency estimation and variance method analysis. Results show that: (1) the seasonal average SSH fluxes on the central and eastern TP have a trend turning feature in all four seasons. As a whole, the trend turning time of autumn and winter is earlier (1999) and that of spring and summer is later (2000). In terms of region, the turning time is earliest in Zone II (Eastern part of TP) and then expands to Zone IV (Southeastern part of TP) and Zone I (Northern part of TP), while the turning time is latest in Zone III (Southwestern part of TP). Before the trend turning time, the weakening of the SSH is most prominent in summer, followed by spring and autumn, and weakest in winter. After the trend turning time, the enhancement of SSH is strongest in winter and the enhancement trend is similar in other seasons. In winter and spring, the key areas for the trend turning of SSH are in the eastern and southern part of TP, respectively, while the key areas are mainly in Zone II and III in summer and autumn. (2) Before the trend turning time, the decrease in the surface wind speed has an important contribution to the decreasing trend of the SSH in four seasons; however, after the trend turning time, the key meteorological factors affecting the trend of SSH have significant differences in the four seasons, i.e., the change of surface wind speed is still dominant in summer, whereas winter and autumn are affected by both the variations of the ground-air temperature difference and surface wind speed. The increase of ground-air temperature difference in spring is the main reason for the trend strengthening of SSH. Additionally, in the interannual variability of SSH, the effect of the ground-air temperature difference is more prominent than that of the surface wind speed, particularly in autumn and winter. The ground-air temperature difference is always the dominant factor affecting its interannual variation. The eastern part of TP is primarily affected by the ground-air temperature difference in spring. Before the trend turning time, the interannual variability of the SSH in summer is affected by both the variations of ground-air temperature difference and surface wind speed. After the trend turning time, the influence of ground-air temperature difference on the SSH is more prominent.