Assessment of differences between near-surface air and soil temperatures for reliable detection of high-latitude freeze and thaw states

- Differences between near-surface air temperatures and upper layer soil temperatures were assessed.
- Notable differences between air and soil temperatures were observed over temporal scales.
- Ground-based soil temperatures should be considered as reference for freeze-thaw states detection.

Near-surface air temperature and the underlying soil temperature are among the key components of the Earth's surface energy budget, and they are important variables for the comprehensive assessment of global climate change. Better understanding of the difference in magnitude between these two variables over high-latitude regions is also crucial for accurate detections of freeze and thaw (FT) states. However, these differences are not usually considered and included in current remote sensing-based FT detection algorithms. In this study, the difference between near-surface air temperature at the 2-m height and soil temperature at the 5-cm depth is assessed using ground-based observations that span a three-year period from 2013 to 2015. Results show noticeable differences between air and soil temperatures over temporal scales that range from diurnal to seasonal. The study also suggests that the ground-based upper layer soil temperature may be a better surrogate than the near-surface air temperature for the reliable detection of FT states at high-latitudes. Furthermore, the results from this study are particularly useful for better understanding the surface energy budget that ultimately drives the land surface processes that are embedded within weather and climate models.