Activity of cold vortex in northeastern China and its connection with the characteristics of precipitation and circulation during 1960-2012

Based on the daily reanalysis data released by NCEP/NCAR and the daily precipitation of 753 Chinese stations from May to August during the period of 1960 to 2012, the statistical characteristics of the cold vortex in northeastern China were analyzed. In addition, the strength index, which described the characteristics of the vortex consistently and frequently, and the geographical distribution were given by continuous anomalies of circulation. Based on this index, the activity routines of the cold vortex, characteristics of atmospheric circulation, and their effects on precipitation in northeastern China were analyzed. The results show that: the activities of the cold vortex exhibit remarkable features of annual and interdecadal oscillation, and the vortex high frequency and its characteristics of atmospheric circulation are described more accurately by the strength index of the cold vortex, which shows a high correspondence with the vortex precipitation during early summer and midsummer in the northeast. In strong (weak) vortex years, the general circulation in the middle and high latitudes of Eurasia is to the advantage (disadvantage) of the formation, development and maintenance of the cold vortex, thus it is easy (difficult) to form the circulation which is beneficial to transmit vapor from south to north during the period of July to August. Blocking over the Ural Mountains prevails (does not prevail) in early summer, and blocking over the Sea of Okhotsk prevails (does not prevail) in midsummer. Areas where the subtropical high is too small (large) and moves toward the north too late (early) are better (worse) for the maintenance of the cold vortex in northeastern China.