Diurnal freeze/thaw cycles of the ground surface on the Tibetan Plateau

Abstract

The exchange of energy and water between the lithosphere and atmosphere mainly takes place at the ground surface. Therefore, freeze/thaw condition at the ground surface is an important factor in examining the interactions between the land surface and atmosphere. Based on the observation data obtained by CEOP/CAMP-Tibet, the diurnal freeze/thaw cycles of the ground surface near Naqu, central Tibetan Plateau was preliminarily analyzed. The results show that the surface layer was completely frozen for approximately one month. However, the time that the ground surface experienced diurnal freeze/thaw cycles was about 6 months. The high frequency of freeze/thaw cycles at the ground surface significantly influences water and energy exchanges between ground and atmosphere over half a year. The interaction processes between the ground and atmosphere under different soil conditions (such as complete thaw, complete freeze and diurnal freeze/thaw cycles) are issues worthy of further examination.Tibetan Plateau, ground surface soil, freeze/thaw processes, diurnal freeze/thaw cycles Permafrost and seasonally frozen soil are nearly ubiquitous on the Tibetan Plateau because of its unique geophysical position. The seasonal freezing/thawing processes of the ground surface impact the soil thermal condition. The thermal conductivity and the thermal capacity are quite different when soil is in frozen or thawed state. Under frozen or thawed soil conditions, soil thermal conduction and the energy/water exchange between land surface and atmosphere are quite different [1] . The seasonal freezing/thawing cycles of the active layer significantly affect the water and energy balance by constant phase transitions of water in the soil. The existence of the thin frozen layer (mm to cm) on the ground surface essentially decouples the water exchange between atmosphere and deeper layer soil [2] . Owing to the fact that water and energy exchange between ground and atmosphere mainly occurs at the interface (i.e. ground surface), the freezing/thawing condition of the surface layer is very important when examining the land surface and atmosphere interactions. Traditionally, seasonal freeze/thaw processes were examined by using point observation data and limit scale numerical models [3] . Recently, microwave remote sensing techniques also have been employed to monitor the freezing/thawing conditions of the ground surface [4][5][6][7] .Due to the limitation of the data resolution (temporal

New discoveries on the effects of desertification on the ground temperature of permafrost and its significance to the Qinghai-Tibet Plateau

“…However, the whole permafrost layer below the surface remained in a frozen state. During the months of April and October, frequent positive and negative variations in the daily surface temperature occurred [19]. This coincides with the transition stages for the freeze-thaw transformation of the active permafrost layer.…”

Sensible and latent heat flux response to diurnal variation in soil surface temperature and moisture under different freeze/thaw soil conditions in the seasonal frozen soil region of the central Tibetan Plateau

“…The yellow band denotes the freezing stage, the green band denotes the thawing stage, the area between the two bands denotes the completely frozen stage, and the outside of them denotes the completely thawed stage. Yang et al (2007) examined the days of the four freeze/thaw stages and found that the time that the surface undergoes diurnal freeze/thaw cycles is approximately 6 months. In this study, an attempt was made to investigate the relationship between sensible and latent heat flux and diurnal variation in soil surface temperature and moisture under four soil freeze/thaw conditions.…”

“…The data collected during these projects have been used by many studies investigating the interaction between the land surface and atmosphere (Yang et al 1999a(Yang et al , b, 2003(Yang et al , 2007Ma et al 2004Ma et al 2005;Tanaka et al 2001;Gao et al 2004;Cheng et al 2008;Guo et al 2009a, b). Diurnal variation in sensible and latent heat flux, soil temperature, and soil moisture in different seasons has also been reported (Yu et al 2004;Ma et al 2005Yang et al 1999aYang et al , b, 2003Yang et al , 2007Zhao et al 2007). However, few studies have focused on the relationship between sensible and latent heat flux and diurnal variation in soil surface temperature and moisture over the Tibetan Plateau.…”

Climatology of the Timing and Duration of the Near-Surface Soil Freeze-Thaw Status Across China

“…They found an earlier onset date of soil thaw in spring, and determined that the number of frozen days decreased by ~16. Yang et al (2007) investigated the freeze-thaw processes in central Qinghai-Tibetan Plateau based on onestation high-frequency observation from 2003 through 2004. They found that the number of days at the station with a daily minimum temperature below 0 °C was ~230, and the freeze-thaw cycles were of high frequency at the ground surface.…”