Widespread Persistent Extreme Cold Events Over South-East China: Mechanisms, Trends, and Attribution

South-East China usually experiences mild winter temperatures but can also be impacted by large-scale and long-lasting cold events. Here, we investigate how this category of events has changed during the past 6 decades and why, using both observation and climate model ensembles. We first show that models can reproduce the observed largescale dynamics associated with cold events. A dynamical advection of cold air is mostly responsible not only to trigger cold surges but also we found strong feedback from shortwave radiation, decreasing due to enhanced cloud cover. Recent trends are more difficult to evaluate. Models show a large internal variability and intermodel spread, while observation also indicates large uncertainties in its trend due to high internal variability. Our analysis indicates that even if cold events are likely to have been reduced due to greenhouse gases, trends cannot be attributed with high confidence to any anthropogenic signal alone. However, in the next few decades, the frequency of long-lasting cold events are expected to quickly reduce due to the emerging greenhouse gases signal and possibly weakening aerosol effect over South-East China. We also found that most of the trends are due to the change in the mean temperature. Thus, indirectly, there is no clear evidence that the change in cold event frequency is due to a change in the circulation.