Possible Causes of Persistent Drought Event in North China during the Cold Season of 2010

Anomalies in the sea surface temperature (SST) and atmospheric circulation that are linked to the drought event in North China during the cold season spanning 2010-2011 are discussed. The possible impacts of the Arctic Oscillation (AO) and La Niña are also addressed in the framework of historical analog analysis based on daily station-observed and NCEP/NCAR reanalyzed data sets. The results suggest that the precipitation in North China exhibits a downward trend over the past decades, however, the extreme drought event occurred during the cold season of 2010 has been mainly affected by the negative phase of the AO and the stronger La Niña event. Statistical analysis suggests that during the negative phase of the AO, the geopotential height at 500 hPa decreases around Lake Baikal, the Ural blocking high develops, and meridional circulation anomalies prevail over East Asia. Such high-latitude circulation may enhance the cold surge around Lake Baikal and cause it to shift southward, indirectly causing a cold, dry climate in North China. During La Niña years, however, the cooling of the SST in the Niño3.4 region weakens the western North Pacific subtropical high and directly blocks the southward moisture flux supply. In contrast to historical drought cases, the stronger and persistent negative phases of the AO and the La Niña event pushed the cold front much further south, and the two together caused the persistent drought event in North China during the cold season of 2010.