Study On Formation Mechanism And Climate Effect Of Sea Salt Aerosol Over East-Asia

Sea salt aerosol(SSA)is one of the most important aerosol components in atmosphere.It could affect climate through different ways,resulting in global and regional climate changing.Hence,it is necessary and meaningful to investigate the climate effects of sea salt aerosol.Here we first present numerical simulations on accessing the temporal and spatial variations of sea salt aerosol concentrations,column burden,and optical depth(AOD)and then its direct and indirect climate responses using a regional climate model coupled with a troposphere atmospheric chemistry model(RegCCMS).Firstly,four parameterization schemes of sea salt(Mohna(1986)?Zhang(2005)?Zakey(2008)?Erickson(1986)were added to RegCCMS,and the parameterization scheme which matched the observation best was chosen for later study.The results show that the order of magnitude of simulated concentration of four schemes are consistent with the observed values.And the simulated values of scheme Mohna(1986),zakey(2008),Erickson(1986)were lower than observed value.The simulated value of Zhang(2005)is much higher than the observed value.The result indicates that the normalized average deviation of sea salt Concentration of Zakey's parameterization scheme is the smallest,and as a result it is the most suitable for the simulation of sea salt in East Asia with RegCCMS..Secondly,we present numerical simulations on sea salt aerosol concentrations and column burden as well as aerosol optical depth in January,April,July and October 2006,representing for four seasons.The annual mean concentration of SSA over ocean areas of East Asia reaches 14.69?g·m-3.The maximum concentration of 26.27 ??g·m-3 occurs in winter,while the minimum concentration of 7.59?g·m-3 occurs in summer.The results indicate that:The spatial and temporal distribution of SSA shows obvious seasonal variation.The high value center of SSA concentration appears in the South China Sea in winter and in the Yellow Sea in summer.Then,we simulate the direct climate responses of sea salt with RegCCMS.The annual aerosol column content of sea salt is 11.78 mg/m2.The sea salt aerosol optical thickness in winter and spring is significantly higher than that in summer and autumn,and there is little difference between autumn and winter.The optical thickness of sea salt in the South China Sea is the highest and declines from the south to the north.The annual direct radiative forcing at the top of atmosphere of SSA in this area is estimated to be-2.35 W-m-2.The direct climate effects of SSA lead to cooling over the coastal land and islands.For Taiwan,the cooling is-1.0940 K,-0.0083 K in July and January,respectively.For the coastal land,the coolings in July and January are-0.1330 K and-0.0142 K,respectively.At the same time,the indirect climate effect of sea salt in East Asia was simulated with RegCCMS.The maximum radiative forcing in spring,autumn and winter is about-3.5 W·m-2,and there is little difference between the three seasons,but significantly higher than that in summer.The annual indirect radiative forcing at the top of atmosphere of SSA is estimated to be-0.382 W·m-2 in the area of East Asia Sea,-0.872 W·m-2 in the South China Sea,and-0.063 W·m-2 in the East China Sea.The first indirect effect of SSA leads to cooling over parts of East Asia,and the cooling ranges from 0.2?1 K.The cooling for the second indirect effect is about 0.04K and up to 0.1K.The first indirect effect of sea salt aerosol leads to the reduction of precipitation in some areas,and the reduction ranges from 0?12mm.For the second indirect effect the reduction ranges from 5?20mm.For the total indirect effect the cooling in some areas ranges from 0.2?1 K and the precipitation reduction ranges from 5?25mm.The cooling for the second indirect effect is far Iess than the first indirect effect,as a result the cooling is mainly caused by the first indirect effect.The precipitation reduction for the second indirect effect is about twice as much as it for the first effect.