Numerical Simulation of Aerosol Direct Radiation Forcing over the Tibetan Plateau

The EMAC (ECHAM/MESSy Atmospheric Chemistry) general circulation model had been used to compare with satellites observation, EMAC was proven to be reliable from 2010 to 2012. Therefore, the results of EMAC simulation for the years 2010–2012 were used to analyze the seasonal changes in the optical properties of different aerosols and quantitatively evaluate aerosol direct radiative forcing. The results showed that mineral dust, water-soluble species, and aerosol liquid water were the main extinction substances in the aerosols over the Tibetan Plateau. Their annual extinction ratios are 0.27, 0.49, and 0.20, respectively. In June 2011, the eruption of Nabro Volcano considerably enhanced the upper aerosol extinction over 14 km. The distribution of direct radiative forcing of aerosols at the top of the atmosphere and surface decreased from the north to south of the Tibetan Plateau. Mineral dust caused positive radiative forcing at the top of the atmosphere over the Tibetan Plateau’s northern edge from March to September. Aerosols over the Tibetan Plateau caused positive radiative forcing to the atmosphere, mainly in areas with high mineral dust concentrations. In addition, the stratospheric aerosol generated considerably stronger negative radiation forcing in the second half of 2011 due to the impact of the eruption of Nabro Volcano. Compared with the year without volcanic eruption, the negative radiation forcing of aerosols in the stratospheric atmosphere in 2011 increased by 55.50% and 52.38%, in autumn and winter, respectively, over the Tibetan Plateau.