Anomalous winter temperature and precipitation events in southern China

This paper analyzed the anomalous low-temperature events and the anomalous rain-abundant events in January since 1951 and winter since 1880 for southern China. The anomalous events are defined using +/- 1 sigma thresholds. Twelve cold Januaries are identified where temperature anomaly below -1 sigma, and ten wet Januaries are identified where precipitation anomaly above +1 sigma. Among these events there are three patterns of cold-wet Januaries, namely 1969, 1993 and 2008. The NCEP/NCAR reanalysis data are used to check the atmospheric circulation changes in association with the anomalous temperature and precipitation events. The results show that the strong Siberian High (SBH), East Asian trough (EAT) and East Asian jet stream (EAJS) are favorable conditions for low-temperature in southern China. While the anomalous southerly flow at 850 hPa, the weak EAT at 500 hPa, the strong Middle East jet stream (MEJS) and the weaker EAJS are found to accompany a wetter southern China. The cold-wet winters in southern China, such as January of 2008, are mainly related to a stronger SBH, and the circulation in the middle to upper troposphere is precipitation-favorable. In wet winters, the water vapor below 500 hPa is mainly transported by the anomalous southwesterly flow and the anomalous southern flow over the Indo-China Peninsula and the South China Sea area. The correlation coefficients of MEJS, EAMW (East Asian meridional wind) and EU (Eurasian pattern) to southern China precipitation in January are +0.65, -0.59 and -0.48 respectively, and the correlations for high-pass filtered data are +0.63, -0.55 and -0.44 respectively, the significant level is all at 99%. MEJS, EAMW and EU together can explain 49.4% variance in January precipitation. Explained variance for January and winter temperature by SBH, EU, WP (west Pacific pattern) and AO (Arctic Oscillation) are 47.2% and 51.5%, respectively. There is more precipitation in southern China during El Nino winters, and less precipitation during La Nina winters. And there is no clear evidence that the occurrence of anomalous temperature events in winter over southern China is closely linked to ENSO events.