Upper-air temperature change trends above arid region of Northwest China during 1960-2009

This study summarized upper-air temperature change trends based on the monthly datasets of 14 sounding stations in the arid region of Northwest China during 1960-2009. Over the investigated period, the change in upper-air temperature measured at eight standard pressure levels shows that an obvious warming at 850-400 hPa, which decreases with altitude, changes to an apparent cooling at 300-50 hPa. There is a positive correlation between the surface and 850-300-hPa temperatures, but a negative correlation between the surface and 200-50-hPa temperatures. Over the full 1960-2009 record, patterns of statistically significant mid-lower tropospheric warming and upper tropospheric and mid-lower stratospheric cooling are clearly evident. Also, the annual temperature cycle indicates that the peak temperature shifts from July in the troposphere to February in the mid-lower stratosphere, suggesting the importance of seasonal trend analysis. We found that the warming in the mid-lower troposphere is more pronounced during the summer, autumn, and winter, whereas the cooling in the upper troposphere and mid-lower stratosphere is larger during the summer and autumn. Furthermore, there are also many regional differences in the upper-air temperature change, regardless of both season and layer.