A review of the spatial differentiation of ground surface temperature in alpine permafrost regions

Permafrost is one of the most important components of the cryosphere, profoundly affecting the biogeochemical cycles and ecological environment stability as a result of its thermal state and heat-water exchange, which are affected by the freezing and thawing cycles. The processes of energy exchange between the atmosphere and the ground in the permafrost region plays a decisive role in the stability and dynamic changes of climate change and permafrost eco-hydrology in the cryosphere. The ground surface temperature (GST) is an important indicator of the energy balance on the ground surface, and is essential for both the empirical modelling and numerical simulation of permafrost. In this paper, we review the permafrost-climate relationship and summarize advances on the spatial differentiation of GST and its impact factor. We also outline the global monitoring of GST, in particular across the northern hemisphere, as well as the modeling of permafrost using GST as input data. Additionally, this paper forecasts the difference of air temperature and GST by taking into consideration the thermal effects of local factors, such as the vegetation layer and snow cover, as well as the preprocessing of GST before its application in permafrost modeling for mountainous permafrost. Based on these findings, a monitoring network of GST for mountainous permafrost based on international cooperation was built herein. This paper also argues that GST is likely to be a more efficient indicator of the existence of mountainous permafrost than air temperature and land surface temperature, wherein the monitoring of GST is a more economical method to determine the thermal state of mountainous permafrost than the measurement of temperature via borehole drilling. Furthermore, we highlight the fact that the quantitative thermal reduction of air temperature and land surface temperature should be taken into account before being used in empirical models and numerical simulations, as well as the precision mapping of mountainous permafrost, which could otherwise result in large bias errors when simulating the spatiotemporal variations of active layer and permafrost in mountainous regions. Moreover, the thermal effects of snow cover, which are prone to being neglected in mountainous regions, will need to be evaluated in the future, although snow cover typically does not form stably due to strong solar radiation in mountainous regions at middle latitudes, especially on the Tibetan Plateau. The extremely frequent solid precipitation (snowfall or hailstone) in this region may result in a relatively high snow water equivalent. The continuous processes of falling and melting of snow on the ground surface and the occurrence of latent heat exchanges are likely to influence both the thermal regimes and the freezing and thawing of the underlying active layer and permafrost.