The diurnal variation of the difference between surface skin temperature and in-situ 2 m air temperature of forests in China

Forests play an important role in regulating land-atmosphere interactions, e.g., the temperature difference (δT) between land surface and air. However, previous studies have primarily focused on analyzing spatial characteristics of δT at global or regional scales, with limited research on its diurnal variations especially using observational data. In this research, we investigated the diurnal changes of δT, using air temperature from large numbers of meteorological stations and surface temperature data from ERA5-Land, for forested areas in China. Results revealed that the diurnal variations in δT (2.18°C) were greater than the observation across seasons (0.8°C), highlighting the importance of considering diurnal scale in understanding δT dynamics. The hourly δT exhibited strong positive correlations with Bowen ratio albeit with a 2-3 hour time lag. Obvious relations also detected between δT and precipitation at daytime, while nighttime relationships remained uncertain when considering the influence of elevation. Simulations from Community Earth System Model (CESM) agree well with the δT-precipitation relations during the daytime, but it overemphasizes the role of elevation in controlling hydrothermal process. We remain hopeful for further enhancement of relevant physical processes in CESM can improve its ability in simulating such interactions.