Global three-dimensional simulation of aerosol optical thickness distribution of various origins

A global three-dimensional model that can treat transportation of various s pecies of aerosols in the atmosphere is developed using a framework of an a tmospheric general circulation model (AGCM). Main aerosols in the troposphe re, i.e., soil dust, carbonaceous (organic and black carbon), sulfate, and sea-salt aerosols, are introduced into this model. Prior to the model calcu lations the meteorological parameters are calculated by the AGCM with the n udging technique using reanalysis data. To evaluate aerosol effects on the climate system and to compare simulated results with observations, the opti cal thickness and Angstrom exponent are also calculated taking into account the size distribution and composition. The model results are validated by both measured surface aerosol concentrations and retrieved aerosol optical parameters from National Oceanic and Atmospheric Administration/Advanced Ve ry High Resolution Radiometer. A general agreement is found between the sim ulated result and the observation globally and seasonally. One of the signi ficant results is that the simulated relative contribution of anthropogenic carbonaceous aerosols to the total optical thickness is comparable to that of sulfate aerosols at midlatitudes of the Northern Hemisphere, which agre es with recent observations. This result leads to a conclusion that the rad iative effect evaluation of aerosols on the climate system is necessary to be modified because optical properties of carbonaceous aerosols are differe nt from those of sulfate aerosols. The other finding is that the seasonal s hift off the west coast of North Africa observed by satellites, i.e., the l atitude of the maximum optical thickness moves seasonally, is also reproduc ed in consideration of a mixed state of soil dust and carbonaceous aerosols .