| The temporal and spatial variations of Sand and Dust Storm(SDS) over China during1958—2007and their relationships with meteorological elements have been studied by using the Time Series of China Strong Sand Dust Storm and its Supporting Datasets, and daily rainfall of China observation station provided by National Metrological Information Center(NMIC) of China Meteorological Administration (CMA), and daily Composite Drought Index (CI) of China station provided by National Climate Center (NCC) of CMA, and the wind velocity of reanalysis data provided by National Center of Environmental Prediction (NCEP) of the US National Ocean and Atmosphere Administration(NOAA), introducing the concept of "Station-hour", according to the time duration of SDS, comparing the number of days and frequencies of SDS, as well as utilizing statistical methods such as wavelet analysis. The results demonstrate that in China,66.56%of the SDS occurred in Spring (March, April, May), with the maximum in April, which shows the double-peak distribution. The peak values appeared in early and middle April, respectively. SDS generally reduced rapidly. The variation of its annual anomaly shows "doors hinge" pattern, that is, positive anomalies in the former and negative anomalies in the later, with the turning point in1986. If take1983as the boundary, the mean value of the later25years is58.4%less than that of the former25years. During the50years, SDS had experienced6processes with twice rapid decreases (1958—1964and1983—1991), twice oscillating decreases (1966—1973and2000—2007), and twice gentle decreases (1974—1982and1992—1999). The time period of each process is6～8years. Wavelet analysis indicated that SDS had periodic change characteristics with a verity of time-scales. The time period is6-8years mainly, with2～3years'and1year's oscillations. The spatial distribution isn't very uniform, which shows the overall feature of "two-more and two-less" and "two centers of frequent occurrence ", that is, more in north and less in south, more in west and less in east. There are two frequently occurred centers in the Alashan League of the Inner Mongolia and Minfeng and Qiemo of Tarim Basin of Xinjiang, respectively. It is shown that the region influenced by SDS moved northwards and retreated westwards. During the past50years, the southern boundary of SDS averagely moved northwards1.98°, and the eastern boundary of SDS averagely moved westwards3.95°, and the influence region reduced about91622km2. The number of stations where SDS was observed decreased60.78%in the past50years. The occurrence time of SDS varied in different regions. In term of solar time (the local time of station), most of SDS overall occurred at12～18o'clock. SDS occurred mostly at12～15O'clock in the east SDS region (for short east region) with Inner Mongolia as the representative, and they occurred mostly at15～18O'clock in the west SDS region (for short west region) with Xinjiang as the representative. SDS occurance months had the feature that, in general, they were earlier in south than in north, and they were earlier in east than in west. For example, SDS occurred one month earlier in the East Region than in the west region, while it was one month earlier in the Southern SDS region with Tibet as the representative than in the east region. Except that there is an increasing tendency in the small area with Zurihe station of Inner Mogolia and Qijiaojing station of Xinjiang as the representative, there is a decreasing tendency in other areas.In the past50years, the SDS wind speed generally reduced2.1m/s (13.6%). The correlation coefficient between wind speed and SDS is0.84. The annual rainfall amount slightly increased (0.96%). The correlation coefficient between annual rainfall amount and SDS is0.10. The rainfall amount in spring increased5.67%. The correlation coefficient between spring rainfall and SDS is0.08. After the original data were processed with7-year moving average, the correlation coefficient is-0.47. After6order polynomial fitting of spring rainfall and SDS, it was found that they had significantly reverse6-8-year periodic variability. The absolute value of CI of one day before SDS decreased generally, namely drought relief. The anomaly pattern of CI is same as that of SDS, appearing as "Doors hinge" pattern but in opposite directions. The correlation coefficient between CI and SDS is-0.60. There is not notable mathematical and statistical relationship between overall annual rainfall amount and SDS, but it seems that the spring rainfall and SDS has some relationship on6-8-year time scale. The above-statement shows that the major reason for SDS rapid reduction in general is the decrease of SDS wind speed. Secondly, it is influenced by the drought degree of one day before SDS...
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