中国西北地区沙尘气溶胶及其对气象场的影响

发布时间：2019-03-24 14:57

【摘要】：利用地面观测资料,借助耦合了起沙模块的大气/化学全耦合模式(WRF/Chem),分析沙尘预报过程中的敏感因子,确定了适用于中国西北地区起沙参数化方案的敏感因子的取值,模拟了中国西北地区的强沙尘天气过程,分析了沙尘气溶胶的辐射强迫及其与边界层的相互作用。沙尘暴预报对防灾减灾非常重要,然而目前沙尘暴的模拟预报尚存在较大的不确定性,其中沙尘排放即起沙参数化方案是否适当是一个关键影响因素。本文将邵亚平2004年提出的起沙参数方案与WRF/Chem相结合,模拟了沙尘过程中沙尘粒子的排放、大气中PM10的沉降、输送和垂直分布特征,检验了模式在中国地区的适用性,表明模式能够很好的模拟中国西北地区的沙尘过程,PM10浓度模拟值和范围与观测结果符合很好。通过敏感性实验分析了沙尘模式起沙参数化方案中土壤塑性压力P和起沙因子cy对地表水平沙通量以及垂直沙通量的影响,结合发生在中国西北地区的沙尘天气过程,分析了两个参数对沙尘暴模拟的不确定性,选择确定了适用于中国西北地区的土壤塑性压力P和起沙因子cy的取值。模拟的强沙尘暴过程表明,沙尘排放区域集中在张掖-武威-民勤一线,排放最大值超过55000 mg/m2,PM10在沙尘排放源地迅速沉降到地面,其中民勤地区干沉降占沙尘排放的约5%,银川地区干沉降量占72%,敦煌地区沙尘排放仅为4.01 mg/m2,干沉降量为6.23 mg/m2,而民勤地区排放量达到5040.79 mg/m2,干沉降量为231.74 mg/m2,西安地区沙尘干沉降为63.62 mg/m2。此次沙尘天气的主要沙尘源地位于民勤,黑风暴过程中民勤PM10排放为5.04 t/km2;分析PM10不同地区的垂直浓度分布情况,发现PM10集中分布在3000 m以下的大气中,并能够扩散到更高被输送到几千公里外。模拟分析了沙尘气溶胶对边界层内气象场的影响,结果表明沙尘气溶胶对地面温度的影响与沙尘层的高度、浓度和时段有关。在夜间,高浓度的沙尘气溶胶能够加热低层大气,可以使得低层大气升高1℃以上,沙尘气溶胶的这种“保温”作用还与地表反照率相关,地表反照率越大加热越强;而在沙尘气溶胶所在的中上层具有降温的作用。在白天,沙尘气溶胶使低层降温,地面温度降低约3℃。沙尘气溶胶浓度随高度的变化导致不同高度其对大气的作用存在差异,夜间沙尘气溶胶浓度越高加热作用越强烈,随着高度的增加及沙尘气溶胶浓度的降低,这种加热大气的能力减弱。夜间,沙尘气溶胶的加热作用能够使得大气稳定度降低,边界层高度抬升,平均约400 m。白天,沙尘气溶胶的冷却作用能够使大气稳定度增强,导致边界层高度降低约700 m,风速出现相应改变,水平风速增大约1 m/s,垂直风速增大,最大可达0.22 m/s。通过模拟对比实验,分析沙尘气溶胶对地面向下的长波辐射通量(GLW)、地面向下的短波辐射通量(SWDOWN)和大气层顶向外的长波辐射通量(OLR)的影响。结果表明沙尘气溶胶对短波辐射通量的影响十分显著,可以导致地面向下的短波辐射通量减小42.51%;沙尘气溶胶高浓度地区,地面向下的短波辐射通量减小约300 W/m2,沙尘气溶胶浓度较低地区,地面向下的短波辐射通量减小约100 W/m2。沙尘气溶胶对地面向下的长波辐射通量的影响与沙尘气溶胶浓度和源地有关,由于输送的沙尘气溶胶能够增大地面向下的长波辐射通量,起到降低地面温度的作用,而当地风蚀排放到大气中的沙尘气溶胶,能够减小地面向下的长波辐射通量,具有“保温”大气的作用,使夜间大气温度升高。沙尘气溶胶通过散射作用增加大气层顶向上的长波辐射通量,从而降低大气温度。分析不同地点的辐射通量的变化,发现沙尘气溶胶对地面向下的长波辐射通量的影响,平均17.49~50.49 W/m2;地面向下的短波辐射通量的影响为-3.30~-49.46 W/m2;大气层顶向外的长波辐射通量的影响为-25.29~28.83 W/m2。
[Abstract]:Using the ground observation data, by means of the atmospheric/ chemical all-coupled mode (WRF/ Chem), which is coupled with the sand-forming module, the sensitive factor in the sand-dust prediction process is analyzed, and the value of the sensitive factor for the sand-sand parameterization scheme in the northwest of China is determined. The strong sand-dust weather in the northwest of China is simulated, and the radiative forcing of the dust aerosol and its interaction with the boundary layer are analyzed. The prediction of sandstorm is very important to the disaster prevention and reduction. However, there are still great uncertainties in the simulation and prediction of the dust storm. Combined with WRF/ Chem, the paper has simulated the emission of sand and dust in the process of dust and the settlement, transport and vertical distribution of PM10 in the atmosphere, and examined the applicability of the model in China. It is shown that the model can well simulate the sand-dust process in the northwest of China, and the simulation value and range of the PM10 concentration are in good agreement with the observation. The influence of the soil plastic pressure P and the sand-forming factor cy on the surface water level and the flux of the vertical sand in the sand-sand model of the sand-dust model was analyzed by the sensitivity experiment, and the sand-dust weather process in the northwest of China was combined. The uncertainty of the two parameters on the sandstorm simulation is analyzed, and the value of the soil plastic pressure P and the sand-starting factor cy for the northwest of China is selected. The simulated strong sandstorm process shows that the sand-dust emission area is concentrated in the first line of Zhangye-Wuwei-Minqin, the emission maximum of which is more than 55000mg/ m2, and the PM10 is rapidly settled to the ground in the dust emission area, where the dry settlement of the Minqin area accounts for about 5% of the dust emission, and the dry settlement in the Yinchuan area accounts for 72%. The dust emission in Dunhuang area is only 4.01 mg/ m2, the dry settlement amount is 6.23 mg/ m2, and the discharge of the Minqin area reaches 5040.79 mg/ m2, the dry settlement amount is 231.74 mg/ m2, and the dust dry settlement in Xi 'an area is 63.62 mg/ m2. The main dust source of the sand-dust weather is in Minqin, the PM10 of Minqin in the process of black storm is 5.04 t/ km2, and the vertical concentration distribution in different areas of PM10 is analyzed, and the concentration of PM10 is found to be distributed in the atmosphere below 3000m, and can be spread to a higher level to be delivered to several thousand kilometers. The effect of the dust aerosol on the weather field in the boundary layer is simulated and analyzed. The results show that the effect of the dust aerosol on the surface temperature is related to the height, concentration and time period of the dust layer. In the night, the high-concentration dust aerosol can be used to heat the lower atmosphere, so that the atmosphere of the lower layer can be increased by more than 1 DEG C, and the "heat preservation" effect of the dust aerosol is also related to the surface albedo, and the higher the surface albedo is, the stronger the heating is; And the middle upper layer of the dust aerosol is provided with a cooling effect. During the day, the dust aerosol cools the lower layer and the surface temperature is reduced by about 3 & deg; C. The influence of the concentration of the dust aerosol on the atmosphere is different. The higher the concentration of the dust aerosol at night, the stronger the heating effect, and the ability of the heated atmosphere to decrease with the increase of the height and the decrease of the concentration of the dust aerosol. during the day, the cooling effect of the dust aerosol can enhance the stability of the atmosphere, and the height of the boundary layer is reduced by about 700m, and the wind speed changes correspondingly, The horizontal wind speed is increased by about 1 m/ s, and the vertical wind speed is increased to a maximum of 0.22 m/ s. The influence of the dust aerosol on the long-wave radiation flux (GLW), the downward short-wave radiation flux (SWDOWN) and the long-wave radiation flux (OLR) on the top of the atmosphere is analyzed by means of simulation and contrast experiments. The results show that the effect of the dust aerosol on the short-wave radiation flux is very significant, which can lead to a reduction of the short-wave radiation flux of 42.51% in the ground, the short-wave radiation flux in the high-concentration area of the dust aerosol is reduced by about 300W/ m2 and the dust aerosol concentration is lower, The short-wave radiation flux down the ground is reduced by about 100 W/ m2. the effect of the dust aerosol on the downward long-wave radiation flux of the ground is related to the concentration and the source of the dust aerosol, The long-wave radiation flux of the downward surface of the ground can be reduced, the effect of the "heat preservation" atmosphere is provided, and the temperature of the atmospheric air is increased. The dust aerosol increases the long-wave radiation flux in the top of the atmosphere by means of scattering, thereby reducing the atmospheric temperature. The change of the radiation flux in different locations was analyzed, and the effect of the dust aerosol on the long-wave radiation flux of the surface was found to be 17.49-50.49 W/ m2. The effect of the surface-down short-wave radiation flux was-3.30--49.46W/ m2, and the influence of the atmospheric top-to-outer long-wave radiation flux was-25.29-28.83 W/ m2.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P425.55

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