Physical mechanisms of summer spatiotemporal precipitation variations over mid-latitude Eurasia

Variations in summer precipitation in the arid regions of central Asian could be affected by anomalous Indian summer monsoon and by sea surface temperatures in the Atlantic, climate researchers have learned.

Research conducted by Dr. Wei Huang and Prof. Fahu Chen in the Key Laboratory of Western China's Environmental Systems at Lanzhou University found that weaker Indian summer monsoon and higher Atlantic sea surface temperatures are the cause of dry/wet fluctuations in this arid region.

According to large-scale atmospheric circulation pattern, the mid-latitude Asian continent can be divided roughly into two distinct climatic regions: A humid eastern region controlled mainly by East Asian monsoon (monsoon-dominated Asia), and an arid western region dominated by the mid-latitude westerlies (westerly-dominated Asia). Chen's research team found opposite precipitation (moisture) variations between westerly-dominated Asia and monsoon-dominated Asia on decadal to multi-millennial time scales. "We named it the 'westerlies-dominated climatic regime,'" Chen said.

Understanding the physical mechanisms of the westerlies-dominated climatic regime will enable scientists to better predict moisture changes in China, particularly in arid regions, Huang said. "Since relevant high-resolution paleoclimatic proxy records are lacking and the available records have a heterogeneous spatial distribution, the previous studies did not address the climatic characteristics of the core zone of the 'westerlies-dominated climatic regime' and its controlling factors."

Huang, along with colleagues at Lanzhou University and the University of Arkansas in the United States, published their findings in the latest issue of the journal Science China: Earth Sciences. In their article, the researchers define the core zone of the "westerlies-dominated climatic regime" and catalog its controlling factors during the instrumental period.

The study examined spatiotemporal variations of precipitation over the mid-latitudes of the Eurasian continent and found an opposing pattern of summer-precipitation variations between the arid central Asia-Xinjiang region in China and the mid-latitude, monsoon-dominated region of Asia and the Mediterranean. "The results identify for the first time that the summer 'westerlies-dominated climatic regime' is significant on a decadal time scale," said Huang. They also analyzed the relationship between decadal variations of the "westerlies-dominated climatic regime" and air-sea interaction. They found a west-east atmospheric teleconnection pattern over 35°N-50°N, with positive pressure anomalies developing over the Mediterranean region and North Central China, and negative pressure anomalies developing over Central Asia. The findings resemble the regional expression of the circumglobal teleconnection (CGT) pattern. The CGT pattern has been weak since 1979 due to the reduced interannual variability of ISM rainfall, which caused increased precipitation in arid Central Asia, and decreased precipitation in the Mediterranean region and North Central China (Figure 1). In addition, the Atlantic Multidecadal Oscillation (AMO) may have an important effect on the "westerlies-dominated climatic regime."

Another research conducted by the same team was published online in the top journal Journal of Climate found that a weaker Indian summer monsoon and associated meridional and zonal atmospheric teleconnection patterns (Figure 1) could bring low-level moisture along the eastern periphery of the Tibetan Plateau and water vapor from the Arabian Sea passing over the Tibetan Plateau to fuel precipitation development in the Tarim Basin, Northwestern China.

"To the best of our knowledge, above works represent the first demonstration of physical mechanisms of summer spatiotemporal precipitation variations over mid-latitude Eurasia," said Huang. The works could lead to a better understanding of the "westerlies-dominated climatic regime" on different time scales, and show how precipitation patterns in the arid areas are affected by ongoing global warming.

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These researches were funded by the National Basic Research Program of China (No. 2010CB950202, No. 2012CB955301) and National Natural Science Foundation of China (No. 41130102).

See the article: Huang W, Chen J H, Zhang X J, Feng S, Chen F H. 2015. Definition of the core zone of the "westerlies-dominated climatic regime," and its controlling factors during the instrumental period. Science China: Earth Sciences, doi: 10.1007/s11430-015-5057-y.

Huang W, Feng S, Chen J H, Chen F H. 2015. Physical Mechanisms of Summer Precipitation Variations in the Tarim Basin in Northwestern China. Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-14-00395.1.

These articles were published online:

http://link.springer.com/article/10.1007%2Fs11430-015-5057-y

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00395.1

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