| At the present stage, AOD data sequence are scarce for a long time, the adaptability of E mode, which is used for AOD inversion is poor in China. The main goal of this article is to fix the inversion solutions for a long time of AOD data. The primary methods includes linear trend, cluster analysis, EEMD, MK mutation test, EOF, etc. This article consists of three elements of analysis:Analyzing the temporal and spatial variation of visibility, to assess and improve the method of using horizontal visibility to inverse aerosol optical depth, then using AOD data sequence to analyze the AOD.The maximum average value of visibility of regional appears in July, which is 27.021km and minimum in December, which is 26.716km. The maximum value of annual average appeared in the year of 1965, which is 30.273km, and the minimun is in 2008, whihc 21.574km. The distrubution of region of visibility obvious differences between the west and the east. The visibility of east is about 10-20km while the west is about 30km, which divided by the line of 105°E. On annual average, from 1960 to 2009, visibility showed a trend of decrease of -1.29km/10yr. The obvious seasonal difference appeared in 2000, the order is that summer> autumn> spring> winter, and each season has a continued decreasing trend. In ten years as a stage,only the third decade, that is from 1980-1989 shows a positive growth trend, and the remaining four years are all of negative trends, and the maximum negative value appears in 2000-2009, It is-1.42km/10yr.Mutation Test by Mann-Kenddall confirms our country’s dramatic reduced visibility in 2000 is not a mutation phenomenon. Visibility cycle of the seven-year quasi-oscillation is most evident in EEMD decomposition.(Every mode’s abbreviation will be introduced in the page 33)With MODIS as astandard, the result of E-mode and Q mode basically show the distribution of AOD in China. About the extreme value, E-mode inversion results are poor in the eastern region, and generally small about 0.1 to 0.2. The result about Q mode is generally large about 0.2, in the eastern region is large to 0.3. Compared with E mode, although W mode has a positive correction, the extent is very small. L mode and C mode, the magnitude of aspects of a larger correction, relative error from the original 30% reduced to about 10%, but the L mode’results of the spatial distribution agreement with MODIS are poor. Then C mode is determined as the best optimal inversion scheme.By using the C mode, the AOD of 1960-2009(summer and autumn) about the eastern region is inversed. The maximum average value of region of AOD occurs in November, which id 0.555, and minimum value appears in June, which id 0.491. The maximum average value of year of AOD occurs in 1993, which is 0.598, and minimum value appears in 1963, which is 0.401, the average value of these years is 0.523. From 1960 to 2009, a generally decarase appears in Sichuan basin area, and AOD changes about 0.02-0.06/10yr in the other areas. And the decarase occurs only between the year of 1990 and 2000, at the scale od decades, the minimun value apperas in 1970-1989, which is 0.06/10yr. AOD cycle of the two-month and twelve-month quasi-oscillation is most evident in EEMD decomposition. |
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