【作者】 马奋华；

【导师】 管兆勇；

【作者基本信息】 南京信息工程大学 ， 气象学， 2019， 博士

【摘要】 中国东部因城市化进程加快,导致排放到大气中的气溶胶粒子大量增多,造成气溶胶污染日趋严重。中国东部同时地处东亚季风区,东亚季风的强弱及其建立时间的早晚异常也将是影响降水分布和旱涝的主要原因。气溶胶与季风被认为是影响中国东部气候环境的两大重要影响因子,这两个因子不是独立的,而是相互联系与相互影响的。因此,弄清楚中国东部气溶胶与季风环流的联系具有重要的科学意义和现实意义。以往研究主要是采用数值模拟和资料诊断分析的手段,来研究气溶胶与季风的联系。数值模拟因气溶胶与云的相互作用过程复杂,难以真实反映气溶胶的影响,所以数值模拟结果仍有很大的不确定性,因此,有必要来用观测资料分析来揭示事实。但是,以往由于观测时间序列较短、气溶胶光学厚度反演精度不高等问题,这对分析受到局限。如今,MODIS气溶胶光学厚度,已有连续的观测数据,且其反演精度逐步提高,这为进一步研究气溶胶与季风的联系提供了可能。论文利用MODIS最新版本C06的大气三级产品中的逐月气溶胶光学厚度(AOD,aerosol optical depth)资料、大气再分析资料、CERES资料、CMAP降水资料等,首先分析了中国东部AOD的季节变化特征,通过与印度地区AOD特征对比,揭示AOD与东亚夏季风环流的联系;其次从AOD年际异常变化特征出发,对AOD进行分级后,分析不同气溶胶污染等级下AOD与东亚季风环流的联系。最后,利用REOF分析方法,分离出中国东部AOD的关键区域分布,进一步揭示AOD的局地成因。所得主要结论如下:(1)中国东部AOD远远大于印度地区,尤其是春季最明显,且AOD季节变化特征明显与印度地区不同,AOD春、夏季最大,秋、冬季次之,而印度地区为夏季最大,春季及秋、冬季较小。在季节变化尺度上,中国东部AOD与地面风速变化关系更为密切,而与降水没有明显的联系。边界层大气环流和层结稳定性对AOD分布有影响。中国东部与印度地区对流层高、低层环流配置特点明显不同,且对AOD产生不同影响。对流层低层大气环流对AOD的平流作用以及辐散辐合运动对AOD分布的影响对中国东部与印度地区气溶胶的维持起到了不同作用。(2)中国东部夏季区域平均AOD距平具有显著的年际变化特征。夏季中国东部AOD异常偏大与地面风速小、中高层季风环流系统不利于气溶胶扩散有关。气溶胶污染最重(最轻)时,气溶胶与到达地面的太阳短波辐射、地面气温、风速及降水存在密切联系;在其他污染等级下,除了与到达地面的短波辐射密切相关外,与其他量的联系并不明显。气溶胶污染严重时,到达地面的太阳短波辐射相对减小,地面气温异常偏低,低层大气冷却,地面风速减小,地面降水呈现南多北少的变化特征;反之,气溶胶污染较轻时,到达地面的太阳短波辐射相对增加,地面气温异常偏高,低层大气加热,地面风速增大,地面降水呈现南少北多的变化特征。(3)中国东部夏季AOD年际变化还具有显著的区域性。AOD年际异常变化主要集中在华北平原大部、长江中下游地区、陕蒙山区以及京津冀以北地区等4个关键区,基本覆盖了整个中国东部地区。各关键区AOD年际变化显著不同,且与东亚季风区气候变量场的关系显著不同。整体上,在关键区内AOD异常与环流变量场的相关关系不高,在关键区外相关关系相对偏高,这充分说明环流变量场对区域AOD分布年际异常变化的影响主要是外围影响。中国东部4个关键区AOD分布异常变化与东亚夏季风环流指数的相关关系总体偏弱。(4)中国东部冬季区域平均AOD距平具有显著的年际变化特征,且与夏季明显不同。冬季中国东部AOD区域平均值与气候要素场有很好的相关关系,即AOD异常偏高(低)时,入射到地面的太阳短波辐射通量减小(增加),地面气温降低(增加),地气系统冷却(加热)、地面降水呈现“华北与江淮内陆少、江淮东南多”(“华北与江淮西南部多、江淮地区东部少”)的分布特征。中国东部冬季AOD异常偏高与风速异常偏小有关,且这种负相关关系在华北表现最明显:即冬季AOD异常偏高(低)时,华北地面风速偏小(大),江淮地面风速偏大(小)。个例分析表明,纬向风速异常偏小、东风异常及阿留申低压偏弱是2013年冬季AOD异常偏高的主要原因。(5)中国东部冬季AOD年际异常变化同样具有显著的区域性,主要集中在(1)长江中下游以南;(2)京津冀以南及淮河流域一带;(3)晋陕及四川巴中、南充一带以及(4)京津冀北部锡林浩特及辽宁一带。各关键区AOD年际异常与风场异常的关系都比夏季联系紧密,风场对冬季AOD年际异常变化的区域性分布影响相对夏季更显著。冬季各关键区AOD异常与地面辐射异常的相关关系,并不能很好地揭示出气溶胶对辐射的影响。对比分析各关键区夏季AOD异常与地面辐射的关系发现,云的影响是不可忽略的重要因素,且AOD异常与地面长波辐射的联系及与地面气温联系相对短波辐射联系紧密。各关键区AOD异常与地面相对湿度及比湿的关系同AOD异常与地面降水的关系有联系,即AOD与地面相对湿度与比湿的相关关系强时,AOD与地面降水的联系也强;反之亦然。上述研究结果有助于深刻认识中国东部气溶胶的时空变化特征及其与东亚季风环流的联系及机理。更多还原

【Abstract】 Due to the accelerated urbanization process in East China,a large number of aerosol particles are discharged into the atmosphere,resulting in increasingly serious aerosol pollution.East China is located in the East Asian monsoon area at the same time.The strength of the East Asian monsoon and the abnormal monsoon setup will be the main factors affecting the distribution of precipitation,especially the and drought and flood events in China.Aerosol and monsoon are considered to be two important factors affecting the climate and environment in East China.These two factors are not independent of each other,they do interrelate and interact with each other.Therefore,it is of great scientific and practical significance to clarify the relationship between aerosols and monsoon circulation in East China.Previous studies mainly used numerical simulation and data diagnostic analysis to study the relationship between aerosols and East Asian monsoon.Because the interaction process between aerosol and cloud is complex,it is difficult to fully understand the impact of aerosol,so the results of numerical simulation are still uncertain.Therefore,data analysis is a supplement to numerical simulation.However,in previous data analysis,the aerosol optical thickness inversion accuracy is not high because of the short observation time series.MODIS aerosol optical thickness data have been continuously accumulated,and the inversion accuracy is gradually improved,which provides a possibility for further study of the relationship between aerosols and monsoon.Based on the monthly aerosol optical depth(AOD)of the latest version of MODIS C06,NCEP/NCAR reanalysis data,CERES data and CMAP precipitation data,the seasonal variation characteristics of AOD in East China are analyzed,and the relationship between AOD and East Asian summer monsoon circulation is revealed by comparing AOD characteristics with those in India.Secondly,the relationship between AOD and East Asian monsoon circulation under different pollution levels is analyzed after classifying AOD according to its interannual anomalous variation characteristics.Finally,using REOF analysis method,the key regional distribution of AOD in eastern China is separated,and the local causes of AOD are further revealed.The main conclusions are as follows:(1)AOD values in East China are much larger than those in India,especially in spring.The seasonal variation characteristics of AOD in East China are obviously different from those in India.AOD values are the largest in spring and summer,followed by autumn and winter,while those in India are the largest in summer and smaller in spring,autumn and winter.On the scale of seasonal variation,AOD in East China is more closely related to the variation of surface wind speed,while precipitation has no obvious relationship with AOD distribution.The atmospheric circulation and stratification stability in the boundary layer affect the aerosol distribution a lot.The distribution characteristics of the upper and lower tropospheric circulations in East China and India are obviously different,and have different effects on AOD.The advection effect of lower tropospheric circulation on AOD and the influence of divergence and convergence on AOD distribution play different roles in maintaining AOD in East China and India.(2)According the interannual variations of AOD averaged over the eastern part of China,the AOD is divided into five different levels,which corresponds to five pollution grades.The results show that the anomalies of AOD in East China are larger when the surface wind speed is weaker together with the unfavorable aerosol diffusion condition of the anomalous monsoon circulation in the middle and high troposphere.When the aerosol pollution is strongest(weakest),variations of AOD is strongly related to the variations of the solar radiation at the earth surface,surface temperature,wind speed,and precipitation.At other AOD levels,the air pollution is significantly related to the surface solar radiation rather than other variables.When the air pollution is severe,the solar radiation at the earth surface is relatively lower,along with the lower surface temperature.The atmosphere in lower troposphere is cooling,and the wind speed is weakening.Meanwhile,the more precipitation occurs in the southern and less in the northern part of the eastern China.On the other hand,when the air pollution is very light,the solar radiation that reaches the earth surface will increase,and the surface air temperature gets higher.At this time,the surface wind will get stronger,and less precipitation will be received in the southern and more in the northern part of East China.(3)The interannual variation of AOD in summer in East China is also significant.The interannual variation of AOD is mainly concentrated in four key areas: the North China Plain,the middle and lower reaches of the Yangtze River,the Shanxi-Mongolia Mountains and the north of Beijing,Tianjin and Hebei,covering the whole eastern part of China.The interannual variation of AOD in each key region is significantly different,and the relationship between AOD and the circulation variable field in East Asian monsoon region is significantly different.On the whole,the correlation between AOD anomaly and circulation variable field is not high in the key area,but relatively high outside the key area.This fully shows that the influence of circulation variable field on the interannual variation of regional AOD distribution is mainly peripheral.The correlation between the anomalous variation of AOD distribution in four key areas of Eastern China and the East Asian summer monsoon circulation index is generally weak.(4)The regional average AOD anomaly in winter in eastern China has significant interannual variation characteristics,and is significantly different from that in summer.In winter,the regional average of AOD in East China has a good correlation with the climatic factor field.When AOD is abnormally high(low),the solar shortwave radiation flux decreases(increases),the surface temperature decreases(increases),the cooling(heating)of the earthatmosphere system and the surface precipitation show "less inland in North China and Jianghuai,more southeast in Jianghuai"("more in North China and Southwest Jianghuai,more in Jianghuai).The high AOD anomaly in winter in eastern China is related to the low wind speed anomaly,and the negative correlation is most obvious in North China: when the AOD anomaly is high(low),the surface wind speed in North China is small(large),and the surface wind speed in Jianghuai is large(small).A case study shows that the main reasons for the high AOD anomaly in winter of 2013 are the small zonal wind speed anomaly,the east wind anomaly and the weak Aleutian low.(5)The interannual variation of AOD in winter in eastern China is also significant,mainly concentrated in the south of the middle and lower reaches of the Yangtze River,the south of Beijing,Tianjin and Hebei and the Huaihe River Basin,the middle of Shanxi,Sichuan,Bazhong and Nanchong,and the north of Beijing,Tianjin and Hebei,Xilinhot and Liaoning.The relationship between AOD interannual anomaly and wind anomaly in each key area is closer than that in summer.Wind field has more significant influence on the regional distribution of AOD interannual anomaly in winter than in summer.The correlation between AOD anomalies and surface radiation anomalies in key areas in winter can not reveal the influence of aerosols on radiation.By comparing and analyzing the relationship between AOD anomaly and surface radiation in each key area in summer,it is found that the influence of cloud is an important factor that can not be ignored,and the relationship between AOD anomaly and ground long-wave radiation and ground temperature is relatively close to that of short-wave radiation.The relationship between AOD anomaly and surface relative humidity and specific humidity in key areas is related to the relationship between AOD anomaly and surface precipitation,that is,when the correlation between AOD and surface relative humidity and specific humidity is strong,the relationship between AOD and surface precipitation is strong,and vice versa.The above results are helpful for us to understand the spatial-temporal characteristics of aerosols in East China and their relationship with East Asian monsoon circulation as well as the mechanisms behind.更多还原