Long Term Change of Diurnal Temperature Range in Taiwan and its Relationship with Atmospheric Hydrologic Processes

[[abstract]]In this report, we analyze and discuss the overall data based on the applied difference analysis method. We have obtained the monthly data from 21 Taiwan meteorology stations operated by Central Weather Bureau and have divided them into three sets time series: we show the short term trend using station data sets from the period of 1970 to 2008, and present the long term trend using station data sets from the period of 1896 to 2008 and from 1901 to 2008. We analyze the long term change of diurnal temperature range (DTR) in Taiwan and its relationship with atmospheric-hydrologic processes on the basis of three different methods: Mann-kendall (MK) test, Hurst exponent, and principal component analysis (STATIS: Structuration des Tableaux A Trios Indices de la Statistique). The results of current study show that: (1) a steady increase of the average temperature is found in Taiwan especially during the wintertime; (2) the reduction of diurnal temperature range is due to the asymmetric change between the daytime maximum and nighttime minimum; a faster increasing rate is associated with the nighttime minimum; (3) sunshine duration and cloud cover have a direct thermal effect on daytime maximum; however, a decreasing trend is found not only in the sunshine duration but also in the daytime cloud cover. Such a paradox is interpreted as the evidence of anthropogenic influences due to emissions and aerosols; (4) although the increased trend of cumulative precipitation is statistically insignificant, the duration of it is significantly decreasing in northern Taiwan. It thus suggests an increasing intensity of rainfall. The results of STATIS also reveal (5) a decreased trend of springtime precipitation in northern Taiwan, and (6) a decreased (an increased) trend of water vapor in northern (southern) Taiwan whereas an islandwide decreased trend is found in the field of relative humidity.