Characteristics Of Aerosol In East Asia Based On Satellite Remote Sensing

The applicability of MODIS aerosol products in East Asia are verified, temporaland spatial distribution and the influencing factors of aerosol optical depth (AOD) andfine mode fraction (FMF) over East Asia are studied in detail, by using AOD andFMF data at550nm from MODIS, Angstrom index from six East Asian stations ofAERONET in2000-2011, AOD from Qingdao Baguanshan Moutain, and airtemperature, humidity, wind, and geopotential height in2000-2011fromNCEP/NCAR. The impact of AOD on West Pacific subtropical high in850hPa is alsoresearched. Results show that:(1) MODIS aerosol products over East Asia are accurate, and can be used forresearch on East Asian aerosol characteristics.(2) East Asia can be divided into five high value areas about AOD, according to0.5isoline of AOD, terrain, population and weather conditions. Variation trend of AOD infive high value areas in2000-2011is not obvious, but the tendens in different seasonsare distinct. In addition, area1and2have obvious annual variation; area3and4alsohave semiannual variation as well as annual variation; area5has semiannual variationin2005-2010.(3) Seasonal diversity of AOD in five AOD high value areas decreases from northto south, as well as the seasonal variation of air temperature, humidity and othermeteorological element. Besides for that air temperature and humidity play animportant part in variation of AOD, wind direction and topography have greatinfluence on AOD in area1and5, wind-force and precipitation affect AOD in area3much, precipitation plays a significant role to AOD in area1and5.(4) In five AOD high value areas, the maximum annual mean FMF appears in area5, with the minimum in area1. FMF in area5declines from2000to2011, whichindicates that the contribution of fine mode aerosol to AOD decreases. The rise ofFMF in other four areas shows the contribution of fine mode aerosol to AODincreases. Air temperature and humidity affect FMF greatly. The higher the airtemperature and humidity are, the greater the extinction ability of fine mode aerosolwill be, which then causes a higher FMF.(5) Temporal and spatial distribution of East Asian AOD is studied by using the method of empirical orthogonal function (EOF) decomposition, and there are twosignificant modes from EOF analysis. The first mode reflects that AOD changes in thesame phase in almost the whole East Asia. Amplitude is large in spring and small inautumn, with large value in north of20°N and small in south of20°N. Furtheranalysis expose the first mode is mainly caused by impact of dust aerosol. The secondmode reflects that AOD has a large difference between north and south of East Asia,and between continent and ocean. This mode represents the distribution characteristicof AOD without contribution of dust aerosol. It is mainly influenced by airtemperature and humidity.(6) The correlation analysis between AOD and west ridge point index (IW) ofsummer West Pacific subtropical high in850hPa indicates that there is a significantcorrelation between AOD over ocean in April and IW in June. The related coefficientis negative in north of22.5°N, and positive in south. Preliminary analysis shows that,negative coefficient in the north is because in April this area is affected by dust, whilethe negative radiative forcing makes a decline of Western Pacific surface temperatureand atmosphere temperature in lower layer, leading to pressure increasing. Positivecoefficient in the south is because in April this area is affected by black carbon, whilethe positive radiative forcing makes an incline of Western Pacific surface temperatureand atmosphere temperature in lower layer, leading to pressure decreasing. Since WestPacific subtropical high tends to move toward the area where pressure is increasing,the correlation is engendered.