Upper-air Temperature Change Trends above Arid Region of Northwest China during 1960–2009

The rise in global mean surface temperatures is considered as the best-known indicator of climate change, so surface temperature change has become a topic that is increasingly popular over the recent years and receives broad media coverage. However, temperature changes are not limited to the Earth’s surface, but are extending to the troposphere and the stratosphere which are important components of the Earth’s climate system. As an indispensable foundation for climate-change research, the determination of the change trend of the upper-air temperature has quickly become one of the most important directions of climate-change research in recent years.

Due to an apparent mechanism of glaciers and snow cover melt water acceleration in response to recent climate warming in the arid region of Northwest China, the glaciers and snow cover on the high mountains have been losing mass in recent years. Obviously, it is critical to understand the climate change of the study area. The impact of upper-air warming on glaciers and snow cover on the high mountains is more important than that of surface warming. However, to date, there is still a lack of research to detect the long-term change trends of upper-air temperatures in this area.

To present the radiosonde time-series data from 1960 to 2009 in the arid region of Northwest China, researchers checked data temporal homogeneity and then measured temporal and spatial variation of the upper-air temperatures in the troposphere and mid-lower stratosphere using the Mann-Kendall nonparametric trend test and GIS technique. Moreover, they also ascertained the extent that surface air temperature variability was linked with upper-air temperature variation and preliminarily discussed possible causes of the upper-air temperature variability.

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 midlower 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.

The result was published in Theoretical and Applied Climatology in April 2015.