Study On The Heat Wave And Sultry Weather In Summer Of Eastern China Area For Past 30 Years

Based on selecting and calculating the daily temperature data of nine cities in eastern China during summer (June till September) for 30 years, the current hot sultry weather is analyzed from several aspects, such as the days of the annual high temperature, high temperature process, extreme daily temperature, maximum and minimum temperature, average temperature, relative humidity, etc. Comparing the hot data of nine major cities on region and time scale, differences and consistency of heat wave and sultry weather of those cities in past 30 years is therefore summarized. Also, the changing characteristics of summer heat wave in eastern China are revealed.In the late 1990s, the average temperature differences between cities in eastern China was gradually reduced. After 2003, the temperature kept increasing slightly and the overall difference was not obvious, the heat wave phenomenon spread to higher latitudes cities in China. Eastern region in China, especially northern areas, had been significantly affected. Changes in different area show the same tendency and the gap narrowed. Heat wave phenomenon was intensified in the eastern region.The whole heat wave days in southern cities were dramatically up and down. Among these cities, Fuzhou is of strongest change:once the amount of hot days was over 40 days, it must drop to about 20 days immediately. The total days of heat wave in Shanghai and Guangzhou remained at the same level with it before 90s, since 2000 the number was significant upward. The heat wave days of Nanjing, Fuzhou, Wuhan, Nanchang is the wave-type slowly rising. There were no hot days in northern cities, now occurred, gradually from the stationary phase tend to turbulent period. Hot days in several cities were on the rise in general, heat wave weather not only affected the southern region but also northern region, and fluctuation extent was large.The extreme maximum temperatures of southern cities fluctuated between 35～40℃, with huge variation. Northern cities fluctuated between 36-39℃, a smaller fluctuation extent, but all historical extreme temperatures occurred in northern cities. Overall, extreme maximum temperatures of eastern region will continue rising in the future, and there might appear a new record again the northern cities.Sultry weather mainly appeared in three cities, Nanchang, Fuzhou and Guangzhou. From late 80s to mid 90s, it is the most serious sultry period in Guangzhou. It seemed there would be a recovering trend in recent 10 years. The fluctuation extent of the daily average minimum temperature in Fuzhou and Nanchang was of similar less, it was gradually increased in the past 10 years. Daily minimum temperatures in Nanjing, Shanghai and Wuhan were slowly rising. It is most likely that the daily minimum temperature will exceed 25℃in few years, and hot sultry weather in southward will spread to other higher latitude citiesAccording to the figure of daily maximum temperature in summer, there was a wide gap between North and South. Daily maximum temperature in northern cities generally maintained at 28-32℃, wave-type forward, and in southern cities was up and down more frequently in time scale. The temperature on day time and night time was very different, nights are relatively cool. In Shanghai, the difference between day and night was reduced from 7℃to 5℃.Heat wave during day cannot dissipate and was lasting till night, therefore, causing longtime heat accumulation.According to the change of subtropical high ridge line during 1977 to 2008, it showed that the position changes is along of time, and affected cities climates. In late 90s, the summer subtropical high ridge line position was comparatively northerly, North China was under the control of western Pacific subtropical high pressure, thus, more strong heat wave processes occurred in cities as Nanjing (32.03°N,118.46°E), Jinan (36.40°N,117.00°E), Shijiazhuang (38.02°N,114.30°E) and other cities. Because of being controlled by the strong and sustained subtropical high pressure, more hot days and more heat wave processes than normal appeared in eastern China.