Variation Characteristics and Cause Analysis of High-temperature Days from 1960 to 2013 in Nanyang
Based on the monthly surface meteorological observation data of Nanyang city,which provided by National Meteorological Information Center (NMIC),using linear regression,simple correlation coefficient,Mann-Kendall mutation test and Morlet wavelet analysis,the variation characteristics of high-temperature (HT) days from 1960 to 2013 in Nanyang city were analyzed.The results showed that there were 788 HT days appeared from 1960 to 2013,the most days was 2013 with 37 HT days,while there was no HT day in 1987.The HT days occurred most in June,and least in September,which account is 36.7% and 2.2%.The HT days showed a decline trend during 1960-2013 with the rate of-1.59 day/10a.There was a mutation when days reduced in 1970s,which was beginning in 1971.The real part figure of wavelet coefficient of Nanyang HT days showed there was multi-time scales characters of HT days number.The variation of Nanyang HT days had three significant periodic oscillation in 10-12 a,26-28 a and 50-51 a time scale.From the wavelet variance figure,there were peaks of 12 a,28 a,50 a;the 50 a peak was highest and with the maximum energy,the 12 a peak followed.The western end of the ridge of Western Pacific Subtropical High (WPSH) in more HT days years was at west side of that in less HT days years,which was in 500 hPa mean circulation field during June to August.In more HT days years,the mean circulation field was more straightly,with zonal circulation mainly,and made it hard for the cold air southward,so the sunny hot weather days were more.In less HT days years,the volatility of circulation field in North China was bigger,and cold air and precipitation weather days were more.From May to September during 1960-2013 in Nanyang,the precipitation increased,and the sunshine duration decreased,both of those led to HT days decreased.
high temperature characteristicslinear trendmutation testwavelet analysiscause of high temperatureNanyang city