In recent winters, Northeast China has experienced more frequently persistent cold events with very low temperatures lasting for over three consecutive days. Such extreme weather events had devastating effects on agriculture, transportation, power infrastructure, and health.
For instance, the prolonged cold event of -30°C to -40°C observed in Northeast China and eastern Inner Mongolia Province from mid-January to mid-February, 2012, affected 41 thousand people, damaged 25 thousand houses, and led to $1.8 million in economic losses. Thus, understanding what drives the occurrence of such events is crucial for both scientists and the larger public.
While previously, scientists have argued that these persistent cold events are triggered by cold air from the polar regions, a recent study led by the Nanjing University of Information Science & Technology (NUIST) has identified another crucial factor driving the occurrence of such events: the tropical thunderstorms related to eastward-propagating low-frequency cloud clusters (known in the meteorological community as the Madden-Julian oscillation).
“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,” explained study lead author Yitian Qian, a postdoctoral fellow at NUIST. “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.”
According to the scientists, when the cloud clusters of Madden-Julian oscillation are located over the Indian Ocean, a cooling effect induced by ascending motion over Northeast China emerges, leading to the occurrence of persistent extreme cold events. However, when the tropical cloud clusters propagate toward the western Pacific region, extreme cold in Northeast China is caused by cold air transportation from northern regions.
“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,” concluded study corresponding author Pang-chi Hsu, an expert in Atmospheric Science at NUIST.
The study is published in the journal Atmospheric and Oceanic Science Letters.
By Andrei Ionescu, Earth.com Staff Writer