Pentad Average Temperature Changes of Inner Mongolia During Recent 40 Years

In order to understand characteristics of the pentad average temperature changes from 1964 to 2003 in Inner Mongolia, daily temperature records of 47 meteorological stations are analyzed. According to the results of the jump point tests, this 40 years are divided into two 20-year periods, the first 20-year period is from 1964 to 1983, and the second is from 1984 to 2003. From these daily temperature data, the pentad (5 days) average temperature is calculated, and then the pentad average temperature of the second 20-year period is compared with that of the first 20-year period at 5-day interval (pentad). Then the cluster analysis is done. First, the stations are classified into 5 clusters using 4 optimal determining indices. Based on kmeans method and the pentad average temperature differences between the two periods, clustering analysis is conducted, so the spatial pattern of the pentad average temperature differences clusters are obtained. By analyzing the polar plots of the pentad average temperatures, it is clear that the patterns of the pentad average tem perature changes are different in different regions and seasons. The warming in north is more obvious than in south, and it happens more frequent in winter, late summer to early fall than in other seasons. The pentad average temperature in most of the stations rises most of the time, and the spatial distribution of the pentad temperature changes clusters shows that there is a zonation along the latitude. Significant warming most frequently appears in winter. Meanwhile, there are a few pentads that show cooling, but not quite significant. Both the maximum and minimum pentad temperature rise, but the differences betw een them decrease. The timings of the minim um temperature pentads are earlier in the second 20-year period, and the timings of the maximum temperature pentads are earlier or later, while the timings of the minim um and maximum temperature pentads are more synchronic, so the temporal and spatial evenness of the minimum and maximum temperature pentads enhances. In addition, most of the stations show that the durations between the maximum and minimum temperature pentads are longer in the second 20-year period than that in the first 20-year period. From these results, it can be concluded that the global warming may reduce the seasonal and regional temperature differences. The medians of the annual average temperatures of the first 20-year period and the second 20-year period are compared, indicating that the annual average temperatures rise all over Inner Mongolia, and no temperature decrease is found.