Spatiotemporal variation of heat and cold waves and their potential relation with the large-scale atmospheric circulation across Inner Mongolia, China

Global warming has exerted increasingly serious impacts on the society, economy, and environment across Inner Mongolia, China. In this context, Sen's slope method and Morlet wavelet transformation were employed to analyze the spatiotemporal variation characteristics of heat waves (HWs) and cold waves (CWs) based on excess factors (EFs) during 1961-2016. The Pearson correlation coefficient was applied to explore four climate indices' potential relation with the EFs. The results show that the intensity and frequency of excess heat factors (EHFs) were increasing, and the increasing rate in high-latitude regions was higher than that in low-latitude regions. Excess cold factors (ECFs) showed a decreasing trend in almost all meteorological stations; severity of ECFs was increasing in the northeastern region. The EFs had a periodic variation of 1-4 years and crossover on the interdecadal scale. Climatic indices had a greater relation with ECFs than EHFs, but the previous year remained stable with a greater link with EHFs in the same year for climatic indices. The Arctic Oscillation index (AOI) and the North Atlantic Oscillation (NAO) were negatively correlated with the duration and frequency of ECFs for most meteorological stations, but there was a significant positive correlation with their severity. Multivariate El Nino/Southern Oscillation (ENSO) index (MEI) and Pacific Decadal Oscillation (PDO) had higher link with ECFs in the midwest than that in other regions. MEI and AOI had a notable relation with the severity and frequency of EHFs compared with the other two climatic indices. In the warm and cold periods, the atmospheric circulation showed different airflow convergence and divergence around Inner Mongolia, which may affect the spatiotemporal characteristics of CWs and HWs.