Features of Two Warming Periods and their Causes in Shanghai for the Last 127 Years
XU Jia liang (Shanghai Meteorological Bureau, Shanghai 200030, China)
Based on the observational data of meteorology from 1873～1999 in Shanghai and its suburbs from 1961～1999, after minimizing the possible biases against climate change caused by urban heat island, this paper mainly discussed the different structure distribution of temperature in two warming periods in Shanghai during the last 127 years. Then the reasons for the different structure distribution are diagnosed. The results obtained are as follows: (1) The variation of annual mean temperature in Shanghai during the last 127 years has gone through two obvious warming periods. They took place from the mid 1930s to the early 1950s and the mid 1980s to nowadays. (2) The difference of temperature structure is obvious, but the warming rates are very close during two warming periods. During the first period, the warming mainly occurred in daytime and maximum temperature was higher than the average year markedly, but minimum temperature was not obvious. These changes were remarkable in summer. During the second period, the warming took place in nighttime, minimum temperature had the most significant warming trend and maximum temperature dropped. The phenomenon is also obvious in summer. Compared with the former, daily temperature range has a decreasing trend during the second warming period. (3) The correlation analysis showed that the difference of temperature structure in the two warming periods is mainly related to solar radiation and atmospheric water vapor content. During the last 41 years, the decrease of Shanghai's direct solar radiation and global radiation and increase of diffused solar radiation are strongly correlated with the atmospheric pollution and atmospheric opacity. The increase of atmospheric water vapor content is depended on climate warming which is resulted from enhancement of greenhouse effect. (4) The cloud amount and daily temperature range in Shanghai are anti correlated to a correlated extent. Further study of the relationship will depend on the observation quality of cloud amount.