An isentropic vertical coordinate model: Design and application to atmospheric frontogenesis studies

Summary The isentropic vertical coordinate model developed at UCLA is briefly reviewed. The review includes an outline of the approach used to overcome technical difficulties in handling model layers with small mass.The model's performance is demonstrated by simulating the evolution of a middle-latitude baroclinic disturbance. During the evolution of the disturbance, sharp frontal zones are generated in the upper and middle troposphere with realistic tropopause folding. The extent to which different dynamical processes contribute to frontogenesis is analyzed.While the model successfully simulates frontogenesis in the upper and middle troposphere, it has a difficulty in simulating surface fronts. The difficulty arises due to the lack of degrees of freedom in surface temperatures since an isentropic vertical coordinate model requires a large number ofvertical layers to obtain a highhorizontal resolution at the lower boundary. This suggests the potential of a hybrid vertical coordinate, which approaches at upper levels and at lower levels.With 12 Figures     

Turbulent dispersion in coastal atmospheric boundary layers: An application of a Lagrangian model

A Lagrangian model is applied to simulate the dispersion of passive tracers (in particular, water vapour) in coastal atmospheric boundary layers under onshore wind conditions. When applied to convective boundary layers over uniform surfaces, the model gives results in agreement with those of similar studies. Numerical simulation of turbulent dispersion in coastal areas also reproduces the basic features known from experimental studies. Under onshore wind conditions, the humidity field is plume-shaped with the maximum vertical transport being over land downstream of the coast line. The model shows that the surface sensible heat flux over land, the static stability of the onshore air flow and the onshore wind speed are the most important factors determining the basic features of turbulent dispersion in coastal areas.     

三维大气扩散粒子分裂(ADPS)模式

本文描述了基于PIC方法的三维大气扩散粒子分裂(ADPS)模式,并用解析解和1988年的广州地区现场观测资料验证了本模式.模式根据局地均匀和定常假设引入大粒子概念、烟团扩散原理和大粒子分裂技术,并运用了嵌套网格.ADPS模式用于模拟气态污染物在大气中的散布,同时也具备模拟TSP扩散的效能.     

A multi-scale urban atmospheric dispersion model for emergency management

To assist emergency management planning and prevention in case of hazardous chemical release into the atmosphere,especially in densely built-up regions with large populations,a multi-scale urban atmospheric dispersion model was established.Three numerical dispersion experiments,at horizontal resolutions of 10 m,50 m and 3000 m,were performed to estimate the adverse effects of toxic chemical release in densely built-up areas.The multi-scale atmospheric dispersion model is composed of the Weather Forecasting and Research （WRF） model,the Open Source Field Operation and Manipulation software package,and a Lagrangian dispersion model.Quantification of the adverse health effects of these chemical release events are given by referring to the U.S.Environmental Protection Agency＇s Acute Exposure Guideline Levels.The wind fields of the urban-scale case,with 3 km horizontal resolution,were simulated by the Beijing Rapid Update Cycle system,which were utilized by the WRF model.The sub-domain-scale cases took advantage of the computational fluid dynamics method to explicitly consider the effects of buildings.It was found that the multi-scale atmospheric dispersion model is capable of simulating the flow pattern and concentration distribution on different scales,ranging from several meters to kilometers,and can therefore be used to improve the planning of prevention and response programs.     

Estimation of atmospheric parameters for determining dispersion ellipses of space rocket fragments

A new approach to the estimation of atmospheric parameters affecting the movement of space rocket fragments in case of accident launches is proposed by the example of the Plesetsk Cosmodrome. Due to the absence of operational information on the vertical distribution of atmospheric parameters above 30 km, the method is considered which allows using available archival aerological data and the statistical characteristics of air density and wind speed components computed from the rocket sounding of the atmosphere for ballistic calculations.     

Verification of a shore-line dispersion model for continuous fumigation

This paper describes the verification of a dispersion model for a shoreline environment developed by the author in an earlier paper. It is shown that the observed concentration field reported in a case study agrees well with model predictions. Emphasis has been given to verification of the location of the maximum ground-level concentration and the downwind trend of the concentration field. This is because time-averaged concentrations are dependent on averaging time. Since a model generally predicts ensemble average concentrations which may not be achieved within half-hour periods within a convective boundary layer, numerical comparisons may not be very meaningful. Nevertheless, good agreement is found for the case study under consideration.     

An experimental study of two-dimensional atmospheric gas dispersion near two objects

Two-dimensional gas dispersion in the atmosphere was investigated experimentally using an atmospheric boundary-layer wind tunnel. Argon gas, which is one and one half times heavier than air, was injected two-dimensionally and uniformly near two square objects at the rates of 3.55 and 4.93 m³/min per lateral meter from the bottom of the wind tunnel floor through a porous metal plate. The gas injection source was located at one object distance upstream of the first square object. Gas concentrations and velocities of the flow field were measured using an aspirating hot-film probe and a low velocity flow analyzer, respectively. The gas was dispersed no higher than approximately 2.0 object heights near the objects, and dispersed no higher than 3.5 object heights at the location of downwind distances of nine object lengths for the injection rates tested. The gas concentrations between the injection source and the first object were about 4 to 5 times higher than the gas concentrations of the other locations. The gas concentrations were 2 to 3% in the recirculation zone between the two objects, and were less than 2% behind the second object. The air-gas mixtures in the recirculation zone between the two objects and within the wake recirculation bubble behind the second object were well mixed and no gravitational settlement was detected in those regions. However, as the mixture moved down-stream, the gravitational settlement occurred beyond the wake recirculation bubble. This paper demonstrates that it is possible to model a two-dimensional heavy gas release in the atmosphere using wind-tunnel simulation with properly matched similitude parameters.     

10公里范围垂直扩散参数的一个估算方法

根据Monin-Batchelor相似理论和有效粗糙度长度的概念,本文提出了一个10公里范围的经验垂直扩散型,它既可在平坦均匀又可在复杂地形条件下应用。     

The variation of ENSO characteristics associated with atmospheric parameter perturbations in a coupled model

We analyse the differences in the properties of the El Niño Southern Oscillation (ENSO) in a set of 17 coupled integrations with the flux-adjusted, 19-level HadCM3 model with perturbed atmospheric parameters. Within this ensemble, the standard deviation of the NINO3.4 deseasonalised SSTs ranges from 0.6 to 1.3 K. The systematic changes in the properties of the ENSO with increasing amplitude confirm that ENSO in HadCM3 is prevalently a surface (or SST) mode. The tropical-Pacific SST variability in the ensemble of coupled integrations correlates positively with the SST variability in the corresponding ensemble of atmosphere models coupled with a static mixed-layer ocean (“slab” models) perturbed with the same changes in atmospheric parameters. Comparison with the respective coupled ENSO-neutral climatologies and with the slab-model climatologies indicates low-cloud cover to be an important controlling factor of the strength of the ENSO within the ensemble. Our analysis suggests that, in the HadCM3 model, increased SST variability localised in the south-east tropical Pacific, not originating from ENSO and associated with increased amounts of tropical stratocumulus cloud, causes increased ENSO variability via an atmospheric bridge mechanism. The relationship with cloud cover also results in a negative correlation between the ENSO activity and the model’s climate sensitivity to doubling CO₂.     

Long-term estimates of parameters of the vertical distribution of cloud layers from atmospheric radiosounding data

Based on the global aerological dataset and on the method for determination of the boundaries and amount of cloudiness using the profiles of temperature and humidity obtained from the atmospheric radiosounding data [23], the estimates are computed for the parameters of atmospheric temperature- humidity separation into cloud and intercloud layers from the surface to the height of 10 km. The base and top of cloud layers and their total thickness and frequency are selected as layering parameters. The computations are based on the data for the observational period of 1964-1998. To specify the spatiotemporal features of atmospheric layering, long-term geographic distributions of mean values and standard deviations of the mentioned parameters are constructed for January and July, and the amplitude of their variations is determined.     

On the dispersion effects of atmospheric motion

In this paper a set of new Reynolds averaged equations which contain both the dissipation and dispersion effects are derived by using Prandtl's mixing length theory. The dispersion effects. (b) The dispersion effects alone could result in the inverse energy cascade dispersion effects. (b) The dispersion effects alone could result in the inverse energy cascade which represents the eddies giving up kinetic energy to the mean flow in large-scale motion. The dispersion effects are also necessary for the eddies to gain kinetic energy from available potential energy. The necessary and sufficient conditions of an inverse energy cascade are given. (c) The dispersion effects are used to analyse atmospheric balance motions of the planetary boundary layer and produce a more satisfactory Ekman spiral fit to the observed wind hodograph.     

The pitfalls of thresholding atmospheric dispersion data

Atmospheric dispersion data are invariably corrupted by random noise and perhaps baseline drift giving rise to unreal negative values. This paper shows that the indiscriminate use of thresholding can give rise to large errors in estimates of some key statistical parameters.     

On the vertical extent of atmospheric feedbacks

This study addresses the question: what vertical regions contribute the most to water vapor, surface temperature, lapse rate and cloud fraction feedback strengths in a general circulation model? Multi-level offline radiation perturbation calculations are used to diagnose the feedback contribution from each model level. As a first step, to locate regions of maximum radiative sensitivity to climate changes, the top of atmosphere radiative impact for each feedback is explored for each process by means of idealized parameter perturbations on top of a control (1?×?CO₂) model climate. As a second step, the actual feedbacks themselves are calculated using the changes modelled from a 2?×?CO₂ experiment. The impact of clouds on water vapor and lapse rate feedbacks is also isolated using `clear sky' calculations. Considering the idealized changes, it is found that the radiative sensitivity to water vapor changes is a maximum in the tropical lower troposphere. The sensitivity to temperature changes has both upper and lower tropospheric maxima. The sensitivity to idealized cloud changes is positive (warming) for upper level cloud increases but negative (cooling) for lower level increases, due to competing long and shortwave effects. Considering the actual feedbacks, it is found that water vapor feedback is a maximum in the tropical upper troposphere, due to the large relative increases in specific humidity which occur there. The actual lapse rate feedback changes sign with latitude and is a maximum (negative) again in the tropical upper troposphere. Cloud feedbacks reflect the general decrease in low- to mid-level low-latitude cloud, with an increase in the very highest cloud. This produces a net positive (negative) shortwave (longwave) cloud feedback. The role of clouds in the strength of the water vapor and lapse rate feedbacks is also discussed.     

Mathematical model for hermitized atmospheric dispersion in low winds with eddy diffusivities as linear functions of down wind distance

Summary In the present paper, an attempt is made for generalized the atmospheric diffusion operator. This can be accomplished by employing the realizability procedure, to identify a surface operator, that ensures self-adjointness’ of the atmospheric diffusion operator. The dispersion modeling in low wind speeds assumes importance because of the high frequency of occurrence and episodic nature of these poor diffusion conditions. A steady-state mathematical model for hermitized model has been calculated for the dispersion of air pollutants in low winds by taking into account the diffusion in the three coordinate directions and advection along the mean wind. The eddy diffusivities have been parameterized in terms of downwind distance for near source dispersion (Arya, 1995). The constants involved in this parameterization are the squares of intensities of turbulence. An analytical solution for resulting advection-diffusion equation with the physically relevant boundary conditions has been obtained. The solution has been used to simulate the field tracer data collected at IIT Delhi in low wind convective conditions.     

A comparison of the BALTIMOS coupled climate model with atmospheric and sea surface parameters derived from AMSR-E

The BALTEX Integrated Model System (BALTIMOS) coupled atmosphere ocean model was compared to passive microwave observations of the Advanced Microwave Scanning Radiometer (AMSR-E). Emphasis was put on quantifying the uncertainties associated with the different variables based on data screening both in the model and observations. Monthly means of three atmospheric parameters, as well as sea surface temperature, were compared for a period of 1 year. Sea ice extent was also derived from AMSR-E and compared to the model data on a daily basis. It is shown that the accuracy of the comparisons on a monthly mean basis is limited by precipitation screening. Out of the three atmospheric parameters, surface wind speed and water vapor column amount agree with the model data to within the accuracy of the comparison. The vertically integrated cloud liquid water content diagnosed from BALTIMOS is systematically higher than the liquid water content derived from satellite, even if potential systematic errors are accounted for. In terms of coupling, the two most relevant variables discussed are sea surface temperature and sea ice extent. The temporal extent of sea ice in the investigation area is well represented, as are the periods of the main growing and decay periods. The total sea ice cover appears to be underestimated by BALTIMOS, especially in the peak season between January and the beginning of March. The amplitude of the annual cycle of sea surface temperature in BALTIMOS appears to be too weak compared to the observations, leading to too cold sea surface temperatures in summer and too warm sea surface temperatures in winter. This might also partially explain the underestimation of sea ice cover by BALTIMOS.     

大气气溶胶的粒度谱分布函数及其随高度的变化

本文对用光学粒子计数器在飞机上测量的大气气溶胶数密度-粒度谱分布进行了分析研究.根据对气溶胶谱形成过程的分析,指出大气气溶胶是四种气溶胶体系的混合物,需要用四个正态分布函数的和来描述大气气溶胶的体积-粒度谱分布.用非线性最小二乘法计算了谱分布函数的经验参数;研究了粒子浓度、体积、及粒度谱分布函数随高度的变化.观测资料表明,在大气温度和湿度水平均匀、层结稳定的情况下,气溶胶粒子浓度水平分布不均匀,而且垂直方向上也并不随高度单调递减.     

声雷达探测在大气扩散研究中的应用(三)——对流边界层中垂直扩散系数的计算

本文用多普勒声雷达探测的垂直风速连续观测资料,计算了垂直速度谱和垂直扩散系数.结果表明:在低频部分,n<3×10~(-2)赫,用声雷达资料计算的垂直速度谱密度和超声风速仪计算的能量峰值和变化趋势基本一致,数值略有差异,在高频部分有偏离.在混合层中,由于逆温层盖子对垂直方向的扩散过程有抑制作用,在逆温层底部计算得出的垂直扩散系数最小,在逆温层中次之.在充分发展的对流边界层中,垂直扩散系数随高度的增加而加大.用声雷达测量的垂直扩散系数能够较好地反映对流边界层中的扩散过程.     

Interannual variation of atmospheric CO2 concentration

A method is described for the analysis of the interannual variability of background atmospheric carbon dioxide concentration. The analysis is carried out on the data from 6 observatories for which records of >8 years were available.A global-scale interannual variation of CO₂ concentration in the troposphere with a characteristic time-scale of 2–3 years has been confirmed throughout the period of the records. These variations are estimated to be associated with carbon cycle imbalances of 2–3 Gt or annual net exchanges between the atmosphere and another carbon reservoir(s) at a rate of about 1.2 Gt of carbon per year. Lag correlations and amplitude comparisons between the records suggests a low latitude southern hemisphere origin to this phenomenon.The interannual variations of CO₂ increase are found to be correlated with those observed in data for Pacific sea surface temperatures and Pacific witd stress, the Southern Oscillation Index and the Quasi-Biennial Oscillation. However multiple regression studies found that once the Southern Oscillation index is used as an explanatory variable for CO₂ variations, the inclusion of additional geophysical variables does not give any significant improvement in the regression.     

Seasonal variation of the molecular hydrogen uptake by soils inferred from continuous atmospheric observations in Heidelberg, southwest Germany

The dominant sink of atmospheric molecular hydrogen (H₂) is its enzymatic destruction in soils. Quantitative estimates of the global sink strength, as derived from bottom-up process studies, are, however, still associated to large uncertainties. Here we present an alternative way to estimate atmosphere-to-soil flux densities, respectively deposition velocities of H₂, based on atmospheric H₂ and ²²²Rn observations in the boundary layer. Two and a half years of continuous measurements from a polluted site in the Rhine-Neckar area have been evaluated and night-time flux densities were calculated for situations of strong nocturnal boundary layer inversions using the Radon-Tracer Method. The influences from local anthropogenic combustion sources could be detected and successfully separated by parallel measurements of carbon monoxide. Inferred daily uptake fluxes in the Heidelberg catchment area range from 0.5 to 3 × 10⁻⁸ g H₂ m⁻² s⁻¹ with a mean value of (1.28 ± 0.31) × 10⁻⁸ g H₂ m⁻² s⁻¹. Uptake rates are about 25% larger during summer than during winter, when soil moisture is high, and diffusive transport of H₂ into the soil is inhibited. The mean deposition velocity is 3.0 ± 0.7 × 10⁻² cm s⁻¹_, which is very well in line with direct measurements on similar soil types in Europe and elsewhere.     

An overwater stability criterion for the offshore and coastal dispersion model

The Offshore and Coastal Dispersion (OCD) model proposed and evaluated by Hanna et al. (1985) requires the Monin-Obukhov length to compute the stability class. Both wind shear and heat flux are needed for this computation; since these parameters are not normally observed, the stability length has been converted into a nomogram which consists of routinely measured wind speed and air-sea temperature difference. An analysis of the vertical turbulence intensity as a function of the stability length demonstrates that under neutral conditions, the stability scheme used in the OCD model is reasonable.