Extreme cold and warm events over China in wintertime

The characteristics of extreme cold and warm events (ECE; EWE) over the whole China in December, January and February are investigated using the observed daily surface air temperature for 1961-2012. Among the 3months, both the EWE and ECE in February are most frequent and strongest and least frequent in December and weakest in January. More than 50% of the EWE and ECE in February and less than 40% of the EWE and ECE in January exhibit persistent feature (lasting at least 5days). Generally, the persistent ECE are more frequent than the persistent EWE. The EWE (ECE) in February exhibit intensive increasing (decreasing) tendency and show more (less) persistent feature in 1961-1986 than that in 1987-2012. The persistent feature of the EWE (ECE) in December and January is more (less) obvious in 1961-1986 than that in 1987-2012 although the EWE (ECE) in 1961-1986 is less (more) frequent than that in 1987-2012. The significant weakening (strengthening) Siberia high and East Asia trough are the two main key factors for the EWE (ECE) in January and February and they can be found up to 5days before the occurrence of the EWE (ECE). The ECE (EWE) in December are associated with the three-wave structure anomalies in troposphere, but these anomalies cannot be found before the occurrence of the ECE (EWE). The warm North Atlantic and tropical central-eastern Pacific in previous autumn (SON, September-October-November) trigger significant weakening of Siberia high and East Asia trough in February and thereby cause the occurrence of the EWE. On decadal time scale, the increasing EWE in February seem to be the consequence of the warming North Atlantic. The cold SON Indian Ocean corresponds to significant atmospheric circulation anomalies in December similar to those associated with the ECE in December, indicating its importance in the ECE in December.