Abstract
At the HEIFE desert station established in the northwest of China, the humidity inversion was often observed in the surface air layer in the daytime; that is, water vapor density increased with height. Furthermore, it was verified by intensive observation that water vapor moved upward under the ground surface even during the humidity inversion, which means that the countergradient flow of water vapor occurred near the surface. It was also confirmed that this humidity inversion had close relations with a phenomenon that the water vapor density within the dry surface soil layer (DSL) and the surface air layer suddenly decreased when the ground surface temperature increased and exceeded the air temperature immediately above it by some threshold value.
