Persistent extreme cold events with very cold temperature for more than three days have occurred frequently in China in recent winters and had devastating effects on agriculture, transportation, power infrastructure and human health. Northeast China is one of the most important regions for food production and is vulnerable to cold damage. A prolonged and extremely cold event of −30℃ to −40℃ was observed in Northeast China and eastern Inner Mongolia Province from mid-January to mid-February, 2012, which was the coldest winter from 1991. There were more than 41 thousand people affected, 25 thousand houses damaged and 1.8 million economic losses. What drives the occurrence of persistent extreme cold events in Northeast China is an important issue for both the public and the scientific community.
One may easily expect that the persistent cold events were triggered by cold air from the pole regions. Yes, the high-latitude effects play a key role in the Northeast China’s cold events, as reported by several other studies. A recent paper published in Atmospheric and Oceanic Science Letters, however, provides another scenario that the tropical thunderstorms related to eastward-propagating low-frequency could clusters (referred to as Madden-Julian oscillation in the meteorological community) may influence on the occurrence of persistent cold extreme events in Northeast China.
“We found that occurrence probabilities of persistent extreme cold events over Northeast China are significantly increased when cloud clusters are located over the eastern Indian Ocean and the western Pacific. But the triggering mechanisms of tropical cloud clusters in the two basins (Indian Ocean vs. western Pacific) on the Northeast China’s cold events are distinct.” says Dr. Yitian Qian, the first author on the paper and a postdoctoral researcher from Prof. Huijun Wang’s research team in the Nanjing University of Information Science & Technology.
According to this study, when the cloud clusters of Madden-Julian oscillation are located over the eastern Indian Ocean, the cooling effect induced by ascending motion over Northeast China appears, favoring the occurrence of persistent extreme cold events. In contrast, the cold events in Northeast China were generated by the cold air transportation from northern areas when the tropical cloud clusters propagate toward the western Pacific.
“Understanding the influential factors of persistent extreme cold events in Northeast China may help us to better assess the model prediction skill and thus improve the models’accuracy in predicting the disastrous extreme cold events in Northeast China in a few weeks ahead.” says Prof. Pang-chi Hsu, the corresponding author on the paper.
Atmospheric and Oceanic Science Letters
Distinct influential mechanisms of the warm pool Madden–Julian Oscillation on persistent extreme cold events in Northeast China