Interactions Between East Asian Summer Monsoon Circulation And Aerosol

Based on MODIS-TERRA aerosol data, TOMS/OMI Al data and NCEP/NCAR reanalysis, the interactions between East Asian summer monsoon(EASM)circulation and aerosol are investigated by using RegCM4regional climate model, coupled manifold technique and some other mathematical statistics methods from the following four aspects: spatial distribution of aerosol and it’s shortwave aerosol radiative forcing (SWARF) in East Asian; impacts of EASM circulation on aerosol distribution; effects of aerosol on EASM circulation; evaluations of the interactions between EASM circulation and aerosol. The main conclusions are as follows:(1)Characteristics of spatial distribution of aerosol in East Asian show distinct differences in the main influence period of EASM. Sichuan Basin and the areas including the middle and lower reaches of the Yangtze River, North China and its adjacent seas display high value of AOD. However, AOD in Sichuan Basin performances less variation while AOD in the middle and lower reaches of the Yangtze River and North China shows significant seasonal variation from May to August. AOD in East Asian also have a clear time-latitude variation especially in areas near30。N where have high aerosol concentrations, the magnitude of AOD and scope of this areas experiences gradually northward increase and push, then southward decrease and retreat from May to August. The results of Fu-Liou radiation transfer model show that the aerosol direct radiation effect is usually high in the above-mentioned high-AOD areas and the clear-sky SWARF at the surface level and top-of-atmosphere are-80Wm2--50Wm2and-18Wm-2--lOWm-2respectively.(2) Aerosol advected by monsoon circulation illustrates the impacts of EASM on the distribution of aerosol. Due to the transport role of monsoon circulation, AOD decreases in the South China but increases in the North and Northeast China, the resulting changes in AOD can reach±0.35. Variance of aerosol’s local changes explained by the role of EASM circulation transport ranges from10%to20%during the evolution of EASM. Under the background of the two years with extreme strong and weak EASM, the differences of measured AOD can approach±0.5while the corresponding differences of the role of monsoon circulation transport are about±0.2in July. Moreover, spatial distributions of these two kinds’differences have a significant similarity. The leading four modes of EASM circulation anomalies can be obtained by adopting EOF method on horizontal wind fields at850hPa level. Total variance explained by these four modes is63.5%. AOD appears different degrees of anomalies in East Asian due to the influence of these four leading modes.(3) The magnitude of the influence of sulfphate aerosol on EASM circulation has significant differences in the two years with extreme strong and weak EASM. In generally, an anticyclonic circulation anomaly emerges in East Asian due to the existence of sulfphate aerosol, futhermore the position and intensity of this anomaly is largely determined by the actual atmospheric circulation and has less connection with the distribution of sulphate aerosol. Moreover, Absorbing aerosol concentration is high in May over the IGP and a wide range of significant warming exists in the lower troposphere owing to the absorption of solar radiation by absorbing aerosol. The response of East Asian atmosphere is a significant warming in the middle troposphere and forming a "warm core" high pressure anomaly in middle and high troposphere. Under the background of these anomalies, southwest airflow in lower troposphere over South Chine enhanced significantly with the presence of an anticyclonic circulation anomaly in the middle and upper troposphere, so EASM circulation has been enhanced in May.(5) The evaluation of the degree of influence of each part during the interactions of EASM circulation and aerosol which is achieved by using the coupled manifold technique demonstrate aerosol variation affected by monsoon circulation is large in oceans where have low aerosol concentrations and the variance of AOD explained by winds can reach38%, among them18%of the AOD variance is purely forced by winds and20%of variance is explained by the manifolds of AOD and winds that are fully coupled with each other. However, the areas where EASM circulation influenced largely by aerosol are located in high-AOD districts and the variance of winds explained by AOD reaches40%, among them18%-26%of the winds variance is purely forced by AOD and18%-22%of variance is explained by the manifolds of AOD and winds that are fully coupled with each other.