Under global climate change, the mid-latitude region of the northern hemisphere is one of the regions with relatively fast warming rate. Some studies have found that the winter in mid-latitude central Eurasia has cooled since the mid-1990s.  

This unexpected temperature change and its driving mechanism have attracted wide attention. Some studies suggest that this phenomenon may be related to the melting of Arctic sea ice, while others have linked it mainly to fluctuations in atmospheric circulation, such as the Arctic Oscillation. 

Researchers from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences conducted an in-depth exploration of the global seasonal temperature change process, and found that the cooling in autumn in central Eurasia has been greater than that in winter since 2004. 

The research team used three different types of data from around the world (reanalysis data, MODIS surface temperature data, and weather station observations) to verify the autumn cooling result in several ways.  

They explained the mechanism of autumn cooling from the perspective of global atmospheric dynamics, and analyzed possible effects of 23 major global atmospheric circulation and Arctic sea ice on autumn cooling in different spatial scales of the Eurasian continent.  

They found that the driving mechanism of cooling in autumn was obviously different from that in winter. The autumn cooling in central Eurasia was mainly related to the change of surface temperature in the North Pacific, i.e., Pacific Decadal Oscillation (PDO), and the enhancement of the Siberian high (SH). When PDO is in positive phase, the East Asian trough is enhanced, which leads to low temperature in East Asia.  

According to the global 500hPa circulation field, when PDO is strengthened, the westerly circulation is southward and further increases, resulting in the cooling of the Eurasian continent. As a cold, dry anticyclone, the intensification of the Siberian high also provides favorable cooling conditions for the study area.  

The study was published in Nature Communications on Oct. 15. It was supported by the National Natural Science Foundation of China and the Strategic Priority Research Program of Chinese Academy of Sciences.  

Spatial patterns of the wind field anomaly at 500 hPa and temperature anomaly with the PDO positive (negative) phase. The letters 'P' and 'N' represent positive and negative phase temperatures, respectively. (Image by XIEG)