Page 144 - 《高原气象》2022年第1期

高 原 气 象 41 卷
142

The Characteristics of Land‐Atmospheric Water and Heat Exchange during

Soil Freezing‐Thawing Process over the Underlying Surface of the Alpine
Grassland in the Source Region of the Yellow River

1
3
2
1
1
1
WU Yueyue ，WEN Jun ，WANG Zuoliang ，JIA Dongyu ，LIU Wenhui ，JIANG Yuqin ，LU Xuancheng 1
（1. Key Laboratory of Plateau Atmosphere and Environment，Sichuan Province，College of Atmospheric Sciences，
Chengdu University of Information Technology，Chengdu 610225，Sichuan，China；
2. Northwest Institute of Ecological Environment and Resources，Chinese Academy of Sciences，Key Laboratory
of Land Surface Process and Climate Change in the Cold and Arid Region of the Chinese Academy
of Sciences Room，Lanzhou 730000，Gansu，China；
3. College of Geography and Environmental Engineering，Lanzhou City University，Lanzhou 730070，Gansu，China）
Abstract：The seasonal characteristics of water and heat exchange in the alpine grasslands are significant，and
the freezing‐thawing process has an important impact on the land‐atmospheric water and heat exchange. Based on
the observation data of the land surface process in the Tangchama small watershed in the source area of the Yel‐
low River from May 2014 to May 2015，this research divides the soil freezing‐thawing process into thawed stage
（TT），frozen stage（FF），thawing to freezing（T-F）and freezing to thawing（F-T），and the changes in the dif‐
ferent states and period of the net radiation，sensible heat flux，latent heat flux and surface heat flux of the under‐
lying surface of the alpine grassland are analyzed to explore the characteristics of water and heat exchange be‐
tween the land‐atmosphere in the soil freezing‐thawing process. The results are as follows：（1）The average val‐
ue of the net radiation flux in the thawed stage is generally greater than that of the other three stages，and the
maximum value reaches 203. 7 W·m . The frozen soil melts in the freezing‐thawing stage，and the soil moisture
-2
content gradually increases. The radiation ratio increased significantly during the frozen stage，the net radiation
-2
diurnal variation was the largest in the thawed stage，reaching 717. 6 W·m ，and the frozen stage was the small‐
est，followed by the freezing‐thawing stage.（2）The proportion of sensible heat flux and latent heat flux is differ‐
ent in the thawed and frozen stages. When completely thawed，due to precipitation and soil moisture content，the
net radiation is mainly converted into latent heat flux. The maximum diurnal variation of latent heat flux is 193. 7
-2
W·m ，while the sensible heat flux is only about 80. 0 W·m . The diurnal average of sensible heat and latent
-2
heat in the thawing‐freezing phase，the freezing‐thawing period and the frozen period is not much different. The
mean latent heat in the three period is 21. 9 W·m ，and the sensible heat is 20. 3 W·m ；The diurnal variation is
-2
-2
greater than the latent heat in the three period，the soil suffers a freezing‐thawing cycle，the soil temperature dif‐
ference is small，and the water content changes，and the net radiation is mainly converted into sensible heat dur‐
ing this period；the diurnal variation of sensible heat was greater than that of latent heat in the three stages. The
freezing-thawing cycle occurred in the soil，the difference between ground and air temperature was small，and
the moisture content changed. During this period，the net radiation was mainly converted to sensible heat.（3）
The soil heat flux is positive（negative）in thawed（frozen）state，indicating that the surface soil absorbs（releas‐
es）heat from the atmosphere，and its daily variation range is large（small）. The above results show that the state
and process of soil freezing and thawing have different characteristics for the water and heat exchange process be‐
tween the land and atmosphere.
Key words：The alpine grassland；freezing‐thawing；water and heat exchange；energy flux