Inconsistency and correction of manually observed ground surface temperatures over snow-covered regions

Ground surface temperature (Ts) was manually measured using mercury thermometers in the early stage, and the snow surface temperature was substituted for Ts in areas with thick seasonal snow covers due to measurement difficulty. However, this practice produced Ts data that were inconsistent with more recent automatic measurements that determine Ts in the soil beneath the snow cover using modern instrumentation. In this study, we used observations from northeastern China to explore and correct this Ts inconsistency. Our results showed that the inconsistency varies from a few degrees to tens of degrees depending on the snow conditions and time periods considered. This inconsistency between earlier and modern measurements can lead to the overestimation of soil temperature warming rates in recent decades. We remove the Ts inconsistency using a numerical model that considers the effect of snow insulation on ground surface temperatures. This approach provides a means to improve Ts records that have similarly switched from manual to automatic measurements, which is critical for soil and climate investigations.