A comparative study of the climatic characteristics of the periods of frequent occurrence of the regional extreme low temperature events in China in the recent 50 years

The climatic characteristics of the typical low-temperature periods of frequent occurrence were compared and analyzed based on the database of the Regional Extreme Low Temperature Events (RELTEs) in winter of China from 1960 to 2011. 5 typical low temperature periods of frequent occurrence (the middle of 1960s, the middle of 1970s, the beginning of 1990s, the beginning of 2000s and 2008-2011) were selected in order to analyze their scale characters. In general, RELTEs in 1960s which are characterized by high intensity and frequency exhibit a persistent feature of decadal scale, while other three frequent periods (the middle of 1970s, the beginning of 1990s and the beginning of 2000s) mainly show the annual oscillation characteristics. Besides, the inner atmospheric circulation and sea surface temperature (SST) external forcing are also compared among these 5 different periods. The results indicate that the current period of frequent occurrence has a similar character to that of 1960s, i.e. the surface temperature is extremely lower than normal from Europe to South Asia, the anomalies of 500 hPa field in the mid-latitudinal Europe-Asia show a north-positive and south-negative pattern, the north and south gradient at the west wind jet area is quite obvious, the AO index has the obvious character of negative phase, and the PDO shows the typical cold phase character with SST of the North Pacific warmer than normal. These characters are obviously different from other periods especially from 1990s. So, in addition to some new features in the background of global warming, the frequent occurrences of RELTEs recently might have implied some anomalous signal with the characters of decadal variability.