Abstract: Lots of studies have focused on characteristics of air temperature, however, few studies have been done on characteristics of ground temperature and its relationship with air temperature. As a case study, the characteristics of ground temperature and its relationship with air temperature in arid region including variation trend, abrupt change, anomalous years of annual and seasonal mean air temperature and mean ground temperature are analyzed, based on the data of monthly mean air temperature and monthly mean ground temperature at 0-80 cm soil depths in Alxa weather station from 1961 to 2010, together with modern statistical diagnostic methods including the linear trend analysis, accumulated variance and signal-noise ratio. The results showed that there were good correlations between ground temperature at different depths and air temperature. Compared with annual mean temperature, annual ground temperature at 5-80 cm depths was higher and had a rising trend with the increase of the soil depth. The annual and seasonal mean air temperature and mean ground temperature displayed a significant increasing trend in recent 50 years, but the rise of mean air temperature and mean ground temperature was asymmetric. The ascending rate and range of annual mean air temperature were higher than changes of annual mean ground temperature at 5-80 cm depths. The ascending rates of air temperature, ground temperature at 0 cm and 80 cm were most obvious in winter, and the most significant increase of 5-40 cm ground temperature happened in spring. The mean ground temperature had a decreasing trend with the increase of the soil depth in both spring and summer. The air temperature was lower than 0-40 cm ground temperature and higher than 80 cm ground temperature in spring, and the air temperature was lower than 0-20 cm ground temperature and higher than 40-80 cm ground temperature in summer. The mean ground temperature had a rising trend with the increase of the soil depth in autumn and winter. The air temperature was lower than ground temperature at different depths in autumn, and the air temperature was higher than 0 cm ground temperature while lower than ground temperature at other layers in winter. Under global warming, the responses of annual, summer, autumn and winter air temperature to climate change were more significant than ground temperatures at different depths, while the responses of ground temperature at different depths to climate change were more significant than air temperature in spring. The difference between annual ground temperature at 5-80 cm depths and annual air temperature was reduced by 0.3-0.8℃ in recent 50 years, and the reducing amplitude of difference between annual mean ground temperature at 5-80 cm depths and annual mean air temperature decreased with the increase of the soil depth. The abrupt changes of annual mean air and ground temperatures at different depths occurred mainly in the 1980s and the 1990s, but no abrupt change in four seasons. The anomalous years of air temperature and ground temperatures at different depths were relatively consistent in four seasons, but there were less consistent of anomalous years between annual air and ground temperatures at different depths.

Key words: air temperature and ground temperature, climate change, statistical analysis, Alxa Left Banner