Abstract
The two leading modes of winter surface air temperature (SAT) over China during 1961–2017 are a spatially consistent pattern and a north-south dipole pattern. Based on the two leading modes, the characteristics of the extreme cold and warm days in the two patterns, defined by the standard deviation larger than 1.28 or smaller than −1.28 in the time series of the two leading modes, are analyzed. With the increase of winter SAT during 1961–2017, the number of spatially consistent extreme cold days decreased and their occurrence was restricted to late December to early January, whereas the number of spatially consistent extreme warm days increased significantly in January and February. Global warming is associated with an increase in the spatially consistent extreme warm days and a decrease in spatially consistent extreme cold days, but has little relation to the sum of extreme cold and warm days of either the spatially consistent or north-south dipole pattern. The Siberian High (SH) is the main factor controlling the sum of spatially consistent extreme warm and cold days. The strong (weak) SH before (after) the 1990s corresponds to an increase (decrease) in the sum of the spatially consistent extreme warm and cold days. The occurrences of extreme south-cold-north-warm and extreme south-warm-north-cold days are related to the north-south difference of the SH. When the center of the SH is in mid-high latitudes, the extreme south-warm-north-cold (south-cold-north-warm) days occur more (less) often. During the winters of 1961–2017, the total number of extreme cold and warm days of the north-south dipole pattern changes negligibly. The North Atlantic meridional overturning circulation (AMOC) may be the main factor affecting the sum of the extreme cold and warm days of the two types of SAT pattern in China.
Highlights
Under global warming, the winter surface air temperature (SAT) in China has shown an obvious upward trend in recent decades, corresponding to a significant decrease in the frequency of extreme low temperature events over the past 50 years (Wang et al, 2012, 2013; Shi et al, 2019)
The interdecadal variations of winter SAT and extreme cold and warm events in China are significantly correlated with the interdecadal variations of the East Asian winter monsoon (EAWM)
The corresponding time series of the leading two modes are used to define the spatially consistent extreme warm/cold days and the extreme north-south dipole warm/cold days using a threshold of 1.28 standard deviations
Summary
The winter surface air temperature (SAT) in China has shown an obvious upward trend in recent decades, corresponding to a significant decrease in the frequency of extreme low temperature events Snow cover in the middle-high latitudes of Eurasia, Arctic sea ice, and tropical Pacific sea surface temperature are the main drivers of EAWM variability These factors have an important impact on China’s winter SAT by changing the Siberian High (SH), the Ural blocking high, the westerly belt, and the East Asian Trough (Guo, 1994; Kang et al, 2006, 2009; Zhou et al, 2007; Ma et al, 2008; Xiao et al, 2016; Zuo et al, 2018). The rapid reduction of Arctic sea ice after the 1990s corresponds to the frequent occurrence of a blocking high in the Ural Mountains, the deepening of the East Asian Trough, and the enhancement of the SH, which allows polar cold air into mid-latitude Eurasia, leading to the increase of the frequency of persistent low temperature events in northern China after 2000 (Liu et al, 2012; Liang et al, 2014; Mori et al, 2014; Wang and Lu, 2017). The main scientific problems include: (1) what is the spatial configuration of the extreme warm and cold days in winter? (2) How do these extreme temperature events with a given spatial configuration change with time? (3) What are the factors that drive this spatial configuration change with time? (4) Will global warming increase the number and intensity of temperature extremes during winter in China? (5) What role does the interdecadal variation of the EAWM play?
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