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1.
In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 109 m?3 and mass loading is ~265±70 μg m?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence.  相似文献   

2.
Iran is a mountainous country with large lateral density variations of its crust. Constant density value is commonly used to determine the geoid models as well as topographic corrections. The effect of lateral density variation in the geoid can reach up to 14 cm in Iran which is not negligible in a precise geoid modelling. Also, the current height datum of Iran is based on the orthometric system but the effect of gravity variation was not applied in height parameter. Furthermore, the height systems of most neighbouring countries are defined as normal height. Connection of networks can be useful for the unification of height datum, geodynamics researches and optimal adjustment of levelling network. The new quasi-geoid model based on a recent EGM2008 global geo-potential model was created to solve the mentioned problem. The main purpose of the present study is to discuss the results of a research project in which a gravimetric quasi-geoid model for Iran was computed based on the least-squares modification of Stokes' formula. The evaluation is made using 475 GPS/levelling height anomalies covering the major parts of the country except the mountainous areas to the North and West. After a 7-parameter fit, the most promising attempt achieved a RMS value of 19 cm for the residuals based on the GPS/levelling data.  相似文献   

3.
三维坑道直流聚焦法超前探测的电极组合研究   总被引：6，自引：3，他引：3       下载免费PDF全文
在坑道超前探测方法中,直流电阻率法原理和操作简单,应用前景广阔,其中侧向聚焦电阻率法应用在测井中已经成为一种常用方法.本文研究了三维坑道直流聚焦法电极组合,首先计算分析了两个同性点电源的电流分布规律,指出由于电流的相互排斥作用,电流密度在这两个点电源的中垂线下一定深度处产生最大值,这个深度与这两个点源之间的距离成正比.基于上述原理,设计出三种电极组合：四点电源、五点电源和九点电源布极方式.其次,用三维有限单元数值模拟的方法计算了上述三种电极系的空间电位分布,得出九点电源方式对电流聚束效果较好,而且当主电极电流小于屏蔽电极电流时效果最好.  相似文献   

4.
A simplified one dimensional analytical model to describe the altitude variation of aerosol number densities in the atmospheric boundary layer during clear sky and calm/moderate wind conditions, over a plane terrain on the tropical seacoast, is developed. The analytical model is mainly defined by two parameters, the aerosol mixing height and the exponential rate of decrease above the mixing height. The effect of surface impaction is also taken into account in this model. It is seen that this parameter varies with season. By matching the analytical profile with the observed mean profile in each month, the surface source strength has been estimated. The seasonal and inter-annual variations of this parameter are studied.  相似文献   

5.
Fernald前向积分法能否用于机载大气探测激光雷达气溶胶后向散射系数的反演一直是一个有争议的课题.本文利用青岛机载大气探测激光雷达实测数据、国外机载大气探测激光雷达实测数据和机载大气探测激光雷达模拟数据,对Fernald前向积分法应用于不同高度的机载大气探测激光雷达气溶胶后向散射系数反演的误差进行了定量分析,分析结果表明:飞机的飞行高度在3.5 km左右,标定值存在20%的误差时,离地面2 km的高度范围内反演得到的气溶胶后向散射系数的相对误差在12%以内,但在标定点附近相对误差可达20%;飞机飞行高度在7 km左右,当标定值存在100%的误差时,反演得到的气溶胶后向散射系数的相对误差大都在10%~15%之间,标定值存在400%的误差时,反演得到的气溶胶后向散射系数的相对误差大部分在15%~50%之间.本文从理论上对Fernald前向积分法应用于机载大气探测激光雷达气溶胶后向散射系数反演出现负值的原因进行了探讨.研究表明:Fernald前向积分法能够较准确地反演出中高空探测(4.5 km以上)机载大气探测激光雷达气溶胶后向散射系数,但应用于低空探测(4.5 km以下)机载大气探测激光雷达气溶胶后向散射系数反演时,反演误差较大甚至反演结果会出现负值.  相似文献   

6.
The common occurrence of tree and pole blow-down from pyroclastic currents provides an opportunity to estimate properties of the currents. Blow-down may occur by uprooting (root zone rupture), or flexure or shear at some point on the object. If trees are delimbed before blow-down, each tree or pole can be simulated by a cylinder perpendicular to the current. The force acting on a cylinder is a function of flow dynamic pressure, cylinder geometry, and drag coefficient. Treated as a cantilever of circular cross-section, the strength for the appropriate failure mode (rupture, uprooting or flexure) can then be used to estimate the minimum necessary current dynamic pressure. In some cases, larger or stronger standing objects can provide upper bounds on the dynamic pressure. This analysis was treated in two ways: (1) assuming that the current properties are vertically constant; and (2) allowing current velocity and density to vary vertically according to established models for turbulent boundary layers and stratified flow. The two methods produced similar results for dynamic pressure. The second, along with a method to approximate average whole-current density, offers a means to estimate average velocity and density over the height of the failed objects. The method is applied to several example cases, including Unzen, Mount St. Helens, Lamington, and Merapi volcanoes. Our results compare reasonably well with independent estimates. For several cases, we found that it is possible to use the dynamic pressure equations developed for vertically uniform flow, along with the average cloud density multiplied by a factor of 2–5, to determine average velocity over the height of the failed object.  相似文献   

7.
The dynamics of aerosol layers in comparison with geomagnetic and ionospheric data has been studied based on the nighttime single-frequency lidar sounding of the atmosphere over Kamchatka at altitudes of 10 to 90 km. The relation of the aerosol density to solar, magnetic, and ionospheric activity has been studied, and the stratospheric aerosol formation mechanisms have been considered. It has been indicated that variations in the aerosol density correlate with radiowave absorption, perturbations of the ionospheric parameters, and geomagnetic characteristics. The spatial and time scales of aerosol layers have been estimated. The role of stratospheric aerosol as an indicator of geophysical processes is discussed.  相似文献   

8.
Summary A layer of a few hundred meters thickness with suspended matter (a nepheloid zone) was discovered byEwing andThorndike [4]3) near the bottom on the continental slope of the North Atlantic. A downward pressure gradient is produced in this layer due to increment of water density with suspensoid. When only the Coriolis force balances with this pressure gradient, a bottom nepheloid current flows southwestward parallel to the depth contours with a velocity of about 10 (cm/sec) for a slope of one degree. The pressure gradient for fluid with locally variable density above a sloping bottom is treated and an extra term due to density gradient along the slope is derived. The vertical profiles of the nepheloid current with an effect on the vertical eddy viscosity are computed. Two kinds of vertical distributions of eddy viscosity are determined from the observed nepheloid distributions and used in the calculations: constant but different values at two layers and those increasing with height. The effect of the change of density along the bottom is treated by introducing dimensionless variables. Rossby number of the nepheloid current becomes about 10–2 indicating inertia terms to be negligible. Rossby number of turbidity currents ranges from 2 (in a decaying area) to 5 (developing area), suggesting that inertia terms are more important than Coriolis terms. The trajectories of turbidity currents are computed from motion of a mass of mud under the Coriolis force and friction, and the results are applied to those inferred byHand andEmery [6] in the San Diego Through off California.LGO Contribution Number 925.  相似文献   

9.
基于华北典型污染地区的地基多轴差分吸收光谱仪（MAX-DOAS）近4年的观测数据,利用最优估计算法和LIDORT辐射传输模式反演了该区域气溶胶的消光系数垂直廓线和光学厚度（AOD）.MAX-DOAS观测反演的AOD与全球气溶胶观测网络同波段在华北地区的AOD间具有很好的一致性,相关系数都在0.9以上,证明MAX-DOAS具备对华北污染区域气溶胶光学厚度和消光系数垂直廓线的反演能力.AOD的反演误差表现为冬季最大,春夏最小,早晚大于正午,这是因为冬季以及早晚太阳天顶角较大导致信噪比偏小,所以AOD反演误差偏大.反演廓线表明该区域气溶胶主要集中在1 km以下的边界层,浓度随高度呈指数递减,部分情况下峰值出现在300 m处;气溶胶光学厚度夏季最大,冬季最小,正午较大,早晚较小.在东风条件下浓度最高,表明东边（即重工业城市唐山方向）的输送对香河和周边区域的气溶胶积聚有重要贡献.  相似文献   

10.
The effect of atmospheric aerosols on the temperatures of a zonal average climate model is investigated. This is done by introducing into the climate model the results of extensive calculations of the effect of aerosols on the partitioning of solar radiation. Calculations are performed for a non-absorbing and a sloghtly absorbing aerosol, for average and for heavy aerosol amounts. The results indicate that the presence of atmospheric aerosols causes a cooling of the earth's surface and atmosphere, at all latitudes, with aerosol amounts, especially for the absorbing aerosols. The results are compared with some of the previous estimates of aerosol effects on climate.  相似文献   

11.
X. Qie  S. Soula  S. Chauzy 《Annales Geophysicae》1994,12(12):1218-1228
A numerical model called PICASSO [Production d’Ions Corona Au Sol Sous Orage (French) and Production of Corona Ions at the Ground Beneath Thundercloud (English)], previously designed, is used to describe the evolution of the principal electrical parameters below a thunderstorm, taking into account the major part played by corona ions. In order to improve the model restitution of a real situation, various improvements are performed: an initial vertical distribution of aerosol particles is introduced instead of the previously used uniform concentration; time and space calculation steps are adjusted according to the electric field variation rate; the upper boundary condition is improved; and the coefficients of ion attachment are reconsidered with an exhaustive bibliographic study. The influence of the ion attachment on aerosol particles, on the electric field and charge density aloft, is studied by using three different initial aerosol particle concentrations at ground level and two types of initial vertical distributions: uniform and non-uniform. The comparison between field data and model results leads to adjust the initial aerosol particle concentration over the experimental site at the value of 5000 cm−3 which appears to be highly realistic. The evolutions of the electric field and of the charge density at altitude are greatly influenced by the aerosol concentration. On the contrary, the surface intrinsic field, defined as the electric field that would exist underneath a thundercloud if there were no local charges, is weakly affected when the model is forced by the surface field. A good correlation appears between the success in the triggered lightning attempts and this intrinsic field evaluation. Therefore, when only the surface field is available, the model can be used in a triggered lightning experiment.  相似文献   

12.
Simulation of secondary aerosols over North China in summer   总被引：2，自引：0，他引：2  
The comparisons of observed and simulated NOx, CO, O3, NH3, HNO3, SO2 and PM2.5 indicate that CMAQ model can simulate variations of pollutants over North China well.Moreover, the model results show that high NH3 is in Hebei, Henan and Shandong provinces,with average concentration of (30-35)×10-9. The results of the sensitive experiment indicate that high concentration of NH3 has the efficiency of the production of secondary sulfate aerosol increase by more than 30%, especially at the juncture of Handan, Anyang and Changzhi that increased by 50%. In addition, NH3 also produces secondary ammonia and nitrate aerosol, and the sum of them is approximately equal to sulfate aerosol. The height of planetary boundary layer (PBL) in Beijing is higher in daytime, with average height of 1500 m at noon. This makes SO2,NH3 and HNO3 transported into upper PBL of 850 hPa. The high secondary sulfate, and ammonia and nitrate aerosol happen in the upper and lower PBL, respectively. Because PM2.5 lifetime is relatively long, it can be transported into the middle troposphere to form a thick aerosol layer,which is the arched roof of aerosol. The model result suggests that if the aerosol concentration in North China would be controlled, the reduction of NH3 emission is one of efficient ways besides the reduction of primary SO2, NOx and aerosol emission.  相似文献   

13.
We introduce the path length probability density function (PPDF) method, which is based on an equivalence theorem and parameterizes the aerosol scattering effect by adding four factors to the atmospheric transmittance model. Using simulated observations in the O2-A band, we examined the utility of the PPDF-based method to account for the aerosol scattering effect. First, observations were simulated using a forward model under different aerosol conditions; PPDF factors were then retrieved using an optimal estimation method; PPDF factors were used to reconstruct the observations; and finally, simulated true observations and reconstructions were compared. Analysis of the difference between the true observations and reconstructions confirmed the utility of the PPDF-based method. Additionally, the O2 band was demonstrated to be an efficient observing band for assisting the remote sensing of atmospheric trace gases in the near-infrared band.  相似文献   

14.
The outdoor experiments, using a metallic grid above the ground surface, have yielded well-defined vertical profiles of the space-charge density. The profiles showed strong evidence for the existence of an electrode effect, which could be named the artificial electrode effect and can serve as a very useful and well-controlled model for the study of atmospheric electric processes in the atmospheric surface layer. The build-up or break-down of an electrode-effect layer occurred in a time of the order of 10 s under the experimental conditions realized. The artificially generated electrode effect is dependent on the electrical field strength supplied, wind speed, turbulent mixing and ion mobilities. Wind speed and ion mobility seem to be the dominant factors, defining space-charge density profiles. A theoretical model for the artificial electrode effect has been developed, taking into account turbulent mixing of charged particles in the air flow with the logarithmic profile of the wind velocity. The numerical analysis of the boundary value problem for the two-dimensional equations for the light ion concentrations has been performed. The model presented shows a qualitative agreement of calculated space-charge profiles with measured ones, and explains the dependence of the artificial electrode effect on the dominant control parameters. The limiting conditions for the developed theory are discussed.Permanent address: Institute of Appl. Physics, 46 Ulyanov St., 603600 Nizhny Novgorod, Russia  相似文献   

15.
The MAGIC sounding rocket, launched in January 2005 into the polar mesosphere, carried two detectors for charged aerosol particles. The detectors are graphite patch collectors mounted flush with the skin of the payload and are connected to sensitive electrometers. The measured signal is the net current deposited on the detectors by heavy aerosol particles. The collection of electrons and ions is prevented by magnetic shielding and a small positive bias, respectively. Both instruments detected a layer of heavy aerosol particles between 80 and 85 km with a number density approximately 103 cm−3. Aerodynamic flow simulations imply that the collected particles are larger than ∼1 nm in radius. The particles are detected as a net positive charge deposited on the graphite collectors. It is suggested that the measured positive polarity is due to the electrification of the smoke particles upon impact on the graphite collectors.  相似文献   

16.
Summary A simple model is proposed suitable for studying the effect of the ground layer of the atmosphere, polluted by aerosol, on the albedo. This model is founded on solving the equation of transfer of radiative energy. The numerical results are discussed, particular attention being paid to the analysis of errors due to neglecting the multiple reflection of solar radiation on the aerosol particles. A method which would also include the multiple reflection is proposed, and the conditions under which the presence of the aerosol is responsible for an increase or decrease of the solar radiation balance on the Earth's surface, are analysed.  相似文献   

17.
平流层气溶胶的准两年周期特征分析   总被引：1，自引：0，他引：1       下载免费PDF全文
本文采用HALOE和SAGE Ⅱ资料,分析了平流层气溶胶的准两年周期变化(简称QBO)特征及其与臭氧QBO的关系,结果表明:(1)北半球中高纬上空平流层气溶胶存在明显的QBO特征,其QBO信号自上向下传播,振荡幅度在平流层中下层可以达到20%;而在赤道和南半球上空的平流层气溶胶的QBO特征相对于北半球则不明显;(2)在...  相似文献   

18.
With the intensification of pollution and urbanization, the aerosol radiation effect continues to play an important role in the urban boundary layer. In this paper, a winter pollution process in Beijing has been taken as an example, and a new aerosol vertical profile in the radiative parameterization scheme within the Weather Forecast Research and Forecasting (WRF) model has been updated to study the effect of aerosols on radiation and the boundary layer. Furthermore, the interactions among aerosols, urbanization, and planetary boundary layer (PBL) meteorology were discussed through a series of numerical experiments. The results show the following: (1) The optimization improves the performance of the model in simulating the distribution features of air temperature, humidity, and wind in Beijing. (2) The aerosols reduce the surface temperature by reducing solar radiation and increasing the temperature in the upper layer by absorbing or backscattering solar radiation. The changes in the PBL temperature lead to more stable atmospheric stratification, reducing the energy transfer from the surface and the height of the boundary layer. (3) With the increase in the aerosol optical depth, the atmospheric stratification most likely becomes stable over rural areas, most likely becomes stable over suburb areas, and has great difficultly becoming stable over urban areas. Aerosol radiative forcing, underlying urban surfaces, and the interaction between them are the main factors that affect the changes in the meteorological elements in the PBL.  相似文献   

19.
A numerical method is proposed for solving the problem of steady current flow. The electrodynamic model is replaced by the equivalent stationary charge distribution obtained by Poisson's analysis, in which the surface integral equation for field intensity is reduced to a set of simultaneous linear algebraic equations by means of the method of sub-areas. The solution of the set allows the calculation of an approximation for the charge density distribution on the discontinuity surfaces of conductivity. The method is valid for complex conductivities, whereby the apparent phase shift of IP can be calculated from the complex potential or field intensity. The phase shift anomaly calculated as an application is very similar to the corresponding frequency effect anomaly. The method allows the calculation of the mise-à-la-masse effect as a solution to a potential problem, in which the primary current electrode is located within the body to be surveyed.  相似文献   

20.
Summary The solution of the ionization balance equation is found in the surface air layer at horizontal homogeneity assuming an exponential law for the turbulent diffusion coefficient. Expressions describing the vertical distribution of the small ion concentration are found estimating on their basis the layer height by an electrode effect. A relation is found among the small ion concentration, the electric conductivity and the electric field in the surface layer.  相似文献   

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