Understanding the Soil Temperature Variability at Different Depths: Effects of Surface Air Temperature, Snow Cover, and the Soil Memory

Abstract

The soil temperature (ST) is closely related to the surface air temperature (AT), but their coupling may be affected by other factors. In this study, significant effects of the AT on the underlying ST were found, and the time taken to propagate downward to 320 cm can be up to 10 months. Besides the AT, the ST is also affected by memory effects—namely, its prior thermal conditions. At deeper depth (i.e., 320 cm), the effects of the AT from a particular season may be exceeded by the soil memory effects from the last season. At shallower layers (i.e., < 80 cm), the effects of the AT may be blocked by the snow cover, resulting in a poorly synchronous correlation between the AT and the ST. In northeastern China, this snow cover blockage mainly occurs in winter and then vanishes in the subsequent spring. Due to the thermal insulation effect of the snow cover, the winter ST at layers above 80 cm in northeastern China were found to continue to increase even during the recent global warming hiatus period. These findings may be instructive for better understanding ST variations, as well as land-atmosphere interactions.

摘 要

土壤温度与地表气温密切相关,但两者之间的耦合会受到多种因素的影响。本文基于中国地表气温、积雪及多层土壤温度资料,利用线性相关及非线性因果分析方法研究了不同因素对土壤温度的影响。研究发现,地表气温可以显著的影响多层土壤温度,但随土壤深度的增加,地表气温的影响逐渐变弱且向下传递其影响所需的时间变长。地表气温的影响最长需要10个月才能传递到320厘米深的土壤。除了受地表气温的影响,土壤温度本身的记忆性特征也可以对未来的土壤温度产生显著的影响。在深层土壤(如320厘米),前一季度土壤温度记忆性对当季的影响甚至可以超过同期来自地表气温的影响。在浅层土壤(如80厘米以上),地表气温与土壤温度的耦合可能会被积雪阻挡。这种阻挡作用在我国东北地区的冬季尤其显著。受积雪的保温作用影响,即便是在本世纪初以来的全球变暖停滞期,我国东北地区冬季浅层土壤(80厘米以上)温度依旧保持升温趋势。这些研究结果有助于更好的理解多层土壤温度变率以及开展地-气相互作用的研究。