Climatic characters of northeast cold vortex and its effect on air temperature in Liaoning province from May to September during 1961-2010

Based on the daily air temperature data in Liaoning province and the NCEP reanalysis data(2.5 ° × 2.5 °) from May to September during 1961-2010,the climatic characters of the northeast cold vortex and its effect on air temperature were analyzed.The results indicated that the variation tendency of the numbers of northeast cold vortex is not significant in recent 50 years.The mean number of annual northeast cold vortex processes is 8.3,and the mean duration of each process is 3.97 d.The northeast cold vortex often appears in May and seldom in September,and the annual mean length influenced by the northeast cold vortex in May,June and July is 7.3 d,7.5 d and 7.4 d respectively.According to a Morlet wavelet analysis method,there are 13-year,9-year and 5-year cycles for the numbers of northeast cold vortex processes.The northeast cold vortex could be divided into two types in terms of its structure,namely,deep cold vortex and shallow cold vortex.Air temperature anomalies in Liaoning province are negative when it is influenced by the deep cold vortex process,especially by the deep middle cold vortex process.The longer the duration of deep cold vortex is,the more significant the negative anomaly of air temperature is in Liaoning province.Air temperature anomalies in Liaoning province are positive when it is influenced by the north shallow cold vortex process,while anomalies are weakly negative when influenced by the central and south shallow vortexes.Furthermore,the effects of shallow cold vortex duration on air temperature are not significant.