Atmospheric electrode effect: Approximate theory and wintertime observations

Summary The steady-state equations of the atmospheric electrode effect, i.e. the depletion of negative ions near the ground, are solved analytically in an approximate way. The presence of monodisperse aerosol is included. The method is based on the assumption that the positive ion density remains nearly, although not strictly, constant with height. The results show explicitly the effect of various parameters on the electrode layer. In particular, the height is directly proportional to the current density, and it depends on aerosol density only through the influence of the aerosol on the current density. The results are used to give a tentative explanation, in terms of the electrode effect, to an observed wintertime difference of the two polar conductivities.     

The effect of the pollution of the ground layer of the atmosphere on the albedo

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.     

Numerical simulation of the influence of aerosol radiation effect on urban boundary layer

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.     

平流层O3、O动力系统的平衡性质及南极平流层O3季节变化规律的研究

本文首次利用常微分方程定性理论对平流层O₃、O动力系统的平衡性质进行了讨论.结果表明,如果在平流层O₃的主要分布高度内,大气扩散作用小于光化学作用,那么平流层的O₃层处于稳定状态;反之,平流层的O₃层将遭到破坏.利用这一机制,我们可以解释南极平流层O₃的季度变化规律和每年9-10月份出现的南极O₃洞.     

地基热红外亮温遥感云底高度可行性的模拟研究

本文利用Modtran40模式比较系统地研究了不同强度（以地面能见度表示）和不同类型气溶胶情况下,晴空和各种云所形成的天空红外亮温Tb (Infrared Brightness Temperature)随地面观测天顶角的变化,从中发现利用Tb观测来遥感云底高度CBH（Cloud Base Height）的可行性,以及定量分析气溶胶层的影响.并且根据模拟计算结果,推出了由地面温度和湿度来计算晴天和不同CBH的中低云天天顶Tb的统计算式,以及由观测Tb和地表温、湿值反演CBH的方法.从模式计算和试验的初步结果可以看出：对于低云和中云,地基观测的Tb对CBH的变化有相当的敏感性,因此可以用于CBH的反演.地面气溶胶（能见度和气溶胶类型）对天空背景Tb有明显的影响,必须加以订正.但由于其影响对不同天顶角的贡献有一定的规律性,因此有可能得到较好的订正.     

Persistent, Widespread, and Strongly Absorbing Haze Over the Himalayan Foothills and the Indo-Gangetic Plains

We examine the impact of the Atmospheric Brown Clouds on the direct radiative forcing of the Himalayan foothills and the Indo-Gangetic Plains (IGP) regions, home for over 500 million S. Asians. The NASA-Terra MODIS satellite data reveal an extensive layer of aerosols covering the entire IGP and Himalayan foothills region with seasonal mean AODs of about 0.4 to 0.5 in the visible wavelengths (0.55 micron), which fall among the largest seasonal mean dry season AODs for the tropics. We show new surface data which reveal the presence of strongly absorbing aerosols that lead to a large reduction in solar radiation fluxes at the surface during the October to May period. The three-year mean (2001 to 2003) October to May seasonal and diurnal average reduction in surface solar radiation for the IGP region is about 32 (±5) W m⁻² (about 10% of TOA insolation or 20% of surface insolation). The forcing efficiency (forcing per unit optical depth) is as large as −27% (note that the forcing is negative) of top-of-atmosphere (TOA) solar insolation, and exceeds the forcing efficiency that has been observed for other polluted regions in America, Africa, East Asia, and Europe. General circulation model sensitivity studies suggest that both the local and remote influence of the aerosol induced radiative forcing is to strengthen the lower atmosphere inversion, stabilize the boundary layer, amplify the climatological tendency for a drier troposphere, and decrease evaporation. These aerosol-induced changes could potentially increase the life times of aerosols, make them more persistent, and decrease their single scattering albedos, thus potentially leading to a detrimental positive feedback between aerosol concentrations, aerosol forcing, and aerosol persistence. In addition, both the model studies and observations of pan evaporation suggest that the reduction in surface solar radiation may have led to a reduction in surface evaporation of moisture. These results suggest the vulnerability of this vital region to air pollution related direct and indirect (through climate changes) impacts on agricultural productivity of the region.     

An analytical model for the altitude variation of aerosol number densities in the coastal atmospheric boundary layer

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.     

Interactions among waves,current, and mud: Numerical and laboratory studies

Interactions between waves, current, mud and turbulence are very complicated in the coastal and estuarine turbid waters. It is still necessary to improve our understanding of the fundamental physical processes governing the cohesive sediment transport in the coastal and estuarine waters. A numerical model is developed to study the interactions among waves, current, and mud. An eddy viscosity model for wave and current is proposed in order to close the equations of wave motion or of current motion in a combined flow, respectively. The equations of mud transport are derived based on the visco-elastic properties of mud. Coupling the equations of wave motion or of current motion for water layer with those of mud layer can give (1) wave height; (2) distributions of current velocities in the water layer; (3) distributions of transport velocities at the water–mud interface; and (4) distributions of mass transport velocities within the mud layer. These modeled results are in a reasonable agreement with experimental results. Results suggest that (1) the rate of wave attenuation increases in the opposing currents (currents against in the direction in which the waves propagate) and decreases in the following currents (currents in the same direction as that in which the waves propagate); (2) the opposing currents would have more significant effects on the rate of wave height attenuation than the following currents; (3) the effect of current on the rate of wave attenuation on the muddy bottom is larger than that on the rigid bottom; (4) mud transport rate increased in the following currents but decreased in the opposing currents; and (5) the rate of wave height attenuation on the mud bottom is one order of magnitude larger than that on the rigid bottom.     

The heterogeneous oxidation of SO2 on aerosol surface

A heterogeneous chemical model is developed by coupling aerosol, gas-phase and liquid-phase chemical model. SO₂ oxidation rates on the aerosol surface are calculated and the influence of some factors is discussed. Model simulations indicate that SO₂ heterogeneous oxidation rates are sensitive to the mass concentration and chemical composition of aerosols, relative humidity, initial values of SO₂ and H₂O₂. The heterogeneous chemical model is coupled with a Eulerian deposition model. Model results show that oxidation of SO₂ on the aerosol surface is found to reduce SO₂ levels by 5%–33%, to increase SO ₄ ^2- - concentrations by 8%–50% in the surface layer. Project supported by the National “85-912” Key Science and Technology Project.     

Internal gravity waves in a slowly varying,dissipative medium

Nonlinear internal gravity waves in a slightly dissipative, slightly compressible fluid are discussed for the case when the properties of the medium vary slowly on a scale determined by the local wave structure. A two‐timing technique is used to obtain transport equations which describe the changes in amplitude, phase and mean flow of a wave packet. Various solutions of these transport equations are discussed, with relevance to critical layer absorption.     

The effect of aerosols on the temperatures of a zonal average climate model

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.     

Simulation of secondary aerosols over North China in summer

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.     

东亚地区春季黑碳气溶胶源排放及其浓度分布

本研究收集整理了东亚地区一个黑碳气溶胶的排放源,并利用一个三维化学输送模式系统模拟研究了东亚地区春季黑碳气溶胶的输送和演变过程.黑碳气溶胶浓度的模拟值与地面观测站和观测船获取的监测值相比,模拟值与监测值具有良好的一致性,这表明本研究收集整理的黑碳气溶胶的排放量及其分布是基本合理的,模式系统较好地反映了黑碳气溶浓度的时空分布和变化趋势,再现了许多观测到的重要特征.模拟结果表明,东亚地区春季间隙性的长距离输送对于西北太平洋海域的黑碳气溶胶浓度分布具有非常重要的影响.     

ESF小尺度湍动谱簇射和非线性稳定性理论（Ⅰ）

本文从等离子体二流体方程出发,推导了适于描述赤道扩展F（ESF）层小尺度湍流的二维静电模型方程.对模型方程进行了线性分析,并且导出了描述波波相互作用的三波非线性耦合方程,以此为基础详细讨论了若干情况下的非线性稳定性和能谱簇射过程.结果表明,赤道F层不仅可以存在正能波,而且可能存在负能波;正能波和负能波的相互作用可以导致爆炸型不稳定性;各种可能的三个波（如三个正能波,二个正能波和一个负能波,等等）之间的相互作用可以产生不同类型的非线性不稳定性,导致不同形式的能量簇射,例如能量可以向大波数方向簇射,也可相反,还可能同时向大和小波数方向簇射等。     

A two-layer model for studying 2D dissolved pollutant runoff over impermeable surfaces

Dissolved pollutants in stormwater are a main contributor to water pollution in urban environments. However, many existing transport models are semi-empirical and only consider one-dimensional flows, which limit their predictive capacity. Combining the shallow water and the advection–diffusion equations, a two-dimensional physically based model is developed for dissolved pollutant transport by adopting the concept of a ‘control layer’. A series of laboratory experiments has been conducted to validate the proposed model, taking into account the effects of buildings and intermittent rainfalls. The predictions are found to be in good agreement with experimental observations, which supports the assumption that the depth of the control layer is constant. Based on the validated model, a parametric study is conducted, focusing on the characteristics of the pollutant distribution and transport rate over the depth. The hyetograph, including the intensity, duration and intermittency, of rainfall event has a significant influence on the pollutant transport rates. The depth of the control layer, rainfall intensity, surface roughness and area length are dominant factors that affect the dissolved pollutant transport. Finally, several perspectives of the new pollutant transport model are discussed. This study contributes to an in-depth understanding of the dissolved pollutant transport processes on impermeable surfaces and urban stormwater management.     

Aerosol extinction and ozone measurements

The effect of aerosol extinction on Dobson measurements of total ozone is investigated, and several recent attempts to resolve this problem are reviewed. It is pointed out that the balloon measurements of Paetzold and his colleagues circumvent this problem: Solar-cycle and quasi-biennial effects can be clearly discerned in the balloon data. It is suggested that Paetzold's data would be ideal for testing stratospheric models and searching for man's effect on the stratospheric ozone layer.     

Effects of polarization calibration on aerosol optical depth retrieval: An ocean case sensitivity analysis

Reflectance measurements of both the visible and infrared bands of passive remote sensing sensors are widely used to retrieve aerosol optical depth(AOD) information. This is performed commonly for data obtained over both ocean and land, and these measurements allow for the off line development of a lookup table using radiative transfer models. Owing to molecular and aerosol effects, the reflected light received by the sensor is usually highly polarized. The linear polarization effect may be up to 100%, and the polarization factor of a sensor optical system will change the total intensity as well as the polarization status of the signal reaching the detector. The detector response will be different when the incident light polarization status changes, even if the total intensity remains constant. However, if the polarization calibration is neglected, it will cause obvious errors in the aerosol data retrieval. This is especially true for aerosol optical depth retrieval over an ocean. This measurement relies directly on the reflectance output of the sensor. Cases involving land surfaces are not discussed herein because the inhomogeneous properties conceal the error due to polarization. Taking the 550 and 860 nm bands as examples, the difference between the real top-of-atmosphere(TOA) reflectance and the reflectance reaching the detector is calculated using three different sensor polarization standards according to the Sea-viewing Wide Field-of-view Sensor(Sea Wi FS) and Moderate Resolution Imaging Spectroradiometer(MODIS) standards. The differences in AOD retrieval are also demonstrated using the lookup table developed previously from a vector radiative transfer code. The results reveal that under a normal situation in which the AOD is 0.15, the maximum AOD retrieval error could reach 0.04 in 550 nm but only 0.02 in 860 nm for the dust aerosol model. For the soot aerosol model, the maximum AOD retrieval error is 0.1 in 550 nm and 0.12 in 860 nm, indicating that the lack of polarization calibration will lead to large errors in aerosol retrieval over an ocean.     

Simultaneous measurement of humidity and temperature in the lower troposphere over Chung-Li,Taiwan

A combined Raman–Rayleigh lidar has been designed at Chung-Li, Taiwan for the simultaneous measurement of water-vapor mixing ratio, temperature and extinction-to-backscatter ratio of aerosol in the lower troposphere. The technique of Raman–Rayleigh lidar can retrieve correct temperature profile in the lower troposphere where the measurements are underestimated due to the aerosol loading. Two typical cases are discussed under different humidity (dry/wet) conditions. The water vapor and temperature profile have shown a good agreement with radiosonde. Simultaneous measurement of Raman–Rayleigh lidar also illustrates the physical nature of the aerosol and is useful in understanding the effects of humidity on aerosol swelling.     

Application of a perfectly matched layer in seismic wavefield simulation with an irregular free surface

Recently, an effective and powerful approach for simulating seismic wave propagation in elastic media with an irregular free surface was proposed. However, in previous studies, researchers used the periodic condition and/or sponge boundary condition to attenuate artificial reflections at boundaries of a computational domain. As demonstrated in many literatures, either the periodic condition or sponge boundary condition is simple but much less effective than the well‐known perfectly matched layer boundary condition. In view of this, we intend to introduce a perfectly matched layer to simulate seismic wavefields in unbounded models with an irregular free surface. We first incorporate a perfectly matched layer into wave equations formulated in a frequency domain in Cartesian coordinates. We then transform them back into a time domain through inverse Fourier transformation. Afterwards, we use a boundary‐conforming grid and map a rectangular grid onto a curved one, which allows us to transform the equations and free surface boundary conditions from Cartesian coordinates to curvilinear coordinates. As numerical examples show, if free surface boundary conditions are imposed at the top border of a model, then it should also be incorporated into the perfectly matched layer imposed at the top‐left and top‐ right corners of a 2D model where the free surface boundary conditions and perfectly matched layer encounter; otherwise, reflections will occur at the intersections of the free surface and the perfectly matched layer, which is confirmed in this paper. So, by replacing normal second derivatives in wave equations in curvilinear coordinates with free surface boundary conditions, we successfully implement the free surface boundary conditions into the perfectly matched layer at the top‐left and top‐right corners of a 2D model at the surface. A number of numerical examples show that the perfectly matched layer constructed in this study is effective in simulating wave propagation in unbounded media and the algorithm for implementation of the perfectly matched layer and free surface boundary conditions is stable for long‐time wavefield simulation on models with an irregular free surface.     

描述激电效应的非线性扩散方程

从岩矿石激电效应的电化学机理出发,通过研究矿物-溶液界面离子的运动规律,给出了描述离子浓度的暂态变化和空间变化的有关偏微分方程．根据界面双电层结构理论以及方程组的稳态解,导出了描述激电效应的非线性扩散方程,给出相应的初始与边界条件,提出了一种激电理论模型．用有限差分法对方程分别在时间域和频率域进行了数值计算,显示了岩矿石的激发极化特性．数值计算结果表明,这一激电理论模型不论是在时间域、频率域还是在小电流激励下的线性区及大电流激励下的非线性区都能很好地描述激电现象．