Abstract
Weather and climate extremes often lead to dramatic losses in our society and warrant improvement of their understanding. In this study, the decadal variations in the first two dominant empirical orthogonal function (EOF) modes of winter extreme cold days (WECDs) in northern China (NC) have been investigated. Results show that both EOF modes show distinct decadal variations that together explain around 24% of total variances. At the decadal time scale, the EOF1 is closely related to the decadal Arctic Oscillation (AO); the negative AO can lead to spatially consistent increase of WECDs in NC. On the other hand, the decadal EOF2 can be influenced by the decadal El Niño-Southern Oscillation (ENSO). The decadal El Niño can result in the large-scale negative sea level pressure (SLP) anomalies in the Eurasian continent west of the western NC and the positive ones over western China. The anomalous southwesterlies between the contrasted SLP anomalies can advect the warmer air from the lower latitudes to the western NC, decrease the WECDs there, and contribute to the east-west asymmetric WECD anomalies in NC. The impacts of El Niño are confirmed by the numerical simulations in the Atmospheric Model 2.1 (AM2.1) when forced by the El Niño-related sea surface temperature (SST) anomalies in the tropical Pacific.
Highlights
Weather and climate extremes such as flooding, drought, extreme hot and cold events often lead to dramatic losses in our society
The decadal variations in the first two dominant empirical orthogonal function (EOF) modes of winter extreme cold days (WECDs) in northern China (NC) have been investigated. Results show that both EOF modes show distinct decadal variations that together explain around 24% of total variances
At the decadal time scale, the EOF1 is closely related to the decadal Arctic Oscillation (AO); the negative AO can lead to spatially consistent increase of WECDs in NC
Summary
Weather and climate extremes such as flooding, drought, extreme hot and cold events often lead to dramatic losses in our society. In the Yangtze River basin, both intensity and frequency of the extreme precipitation are increasing, and their tendencies will continue into the future as projected by the coupled models under different global warming scenarios. To improve simulation and prediction skills of the extreme events for the better adaptation and mediation, it is essential to detect, attribute and model the large-scale drivers of the extreme events (Sillmann et al, 2017). This has not been well resolved yet. Yuan et al (2019) investigated the major empirical orthogonal function (EOF) modes of the winter extreme cold days (WECDs) in NC and examined the large-scale circulation anomalies responsible for their interannual variations.
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