Long-term change of extreme temperature and its relationship with average temperature in Nanjing

Based on the daily average temperature,the daily maximum and minimum temperatures in Nanjing from 1951 to 2009,the trends of the daily extreme temperatures and the relationship with average temperature were analyzed.The results indicate that the mean annual temperature,the mean annual maximum and minimum temperatures are all in the increasing trends,especially in 1990s.The daily maximum temperature is in a decreasing trend in summer,and in an increasing trend in the other seasons.The mean air temperature and the mean minimum air temperature in different seasons are in the increasing trends.The difference of the daily air temperature in summer decreases obviously,which reduces the difference of air temperature between daytime and nighttime.The numbers of extreme high temperature and low temperature days show decreasing trends.The extreme air temperatures are significantly correlated to the mean air temperature,especially the minimum air temperature.