4/3/2024 0 Comments Water vapor densityTo monitor the water vapor isotopic abundance in the Tibetan Plateau, a portable laser heterodyne radiometer was operated in Golmud in August 2019. HDO is the stable isotope of water vapor, which acts as an ideal tracer for studying the water cycle, and which is commonly used for atmospheric circulation and climatic studies. The Tibet Plateau is known as the “third pole” of the world, and its environmental change profoundly impacts East Asia and even the global climate. Diurnal patterns observed in both evaporation zones and DSL could potentially be determined by quantifying changes in the near-surface profile’s soil water content, relative humidity, pressure head, and vapor density. ![]() The occurrence of condensation zones was limited to the daytime when there was a downward surface temperature gradient present. As soil drying progressed, both the position of the evaporation zone within the profile and the DSL width exhibited an overall increasing trend, reaching about 4.9 mm by the end of the study period. The DSL and condensation zone, located immediately above and below the evaporation zone, respectively, also presented diurnal patterns following those of the evaporation zone. The evaporation zone presented a distinctly diurnal pattern, moving toward the deeper soil layer during the daytime and back toward the soil surface during the nighttime. Surface evaporation predominantly occurred during the early period each day, while subsurface evaporation dominated during the remaining part of the day. Simulated water contents and soil temperatures matched well with the measured data in the lysimeter. ![]() To better understand processes involved in the evaporative drying of the soil, simulations on the dynamics of the evaporation zone, condensation zone, and dry surface layer (DSL) were conducted during a 10-day drying event under diurnal atmospheric conditions.
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