耗散大气中的声波射线追踪

基于分层大气中声波的局地色散关系方程,建立一种计入真实大气衰减效应的有耗大气声波射线追踪模型.在色散方程的虚部中导出声波在运动大气中的耗散系数和竖直方向上的增长因子,并利用真实大气中的衰减理论对所得到的耗散系数进行修正.利用Hamilton方程组解出大气声波在考虑耗散效应下的射线微分方程组.该有耗射线追踪模型的数值模拟...     

Error analysis of multi-wavelength sun photometry

The error terms involved in precision multi-wavelength sun photometry, as used to study atmospheric aerosols, are analyzed. The error terms treated include instrumental errors, calibration errors, and errors imposed by the atmosphere. It is shown that in order to derive accurate aerosol parameters, one must exercise great care in the photometer calibration. A procedure for accurate calibration is described, based on an intercalibration between extrapolations of the extraterrestrial solar spectral irradiance and irradiance of a standard lamp. Methods are described to assess, and reduce, uncertainties brought about by diffuse radiation in the photometer's field of view, temporal variations in aerosol optical depth, and gaseous absorption features at the operating wavelength. It is shown that if care is taken sun photometry can be used to derive monochromatic aerosol optical depth to an accuracy of several thousandths.     

The subsurface–land surface–atmosphere connection under convective conditions

The dynamics of the free groundwater table influence land surface soil moisture and energy balance components, and are therefore also linked to atmospheric processes. In this study, the sensitivity of the atmosphere to groundwater table dynamics induced heterogeneity in land surface processes is examined under convective conditions. A fully coupled subsurface–land surface–atmosphere model is applied over a 150 km × 150 km study area located in Western Germany and ensemble simulations are performed over two convective precipitation events considering two separate model configurations based on groundwater table dynamics. Ensembles are generated by varying the model atmospheric initial conditions following the prescribed ensemble generation method by the German Weather Service in order to account for the intrinsic, internal atmospheric variability. The results demonstrate that especially under strong convective conditions, groundwater table dynamics affect atmospheric boundary layer height, convective available potential energy, and precipitation via the coupling with land surface soil moisture and energy fluxes. Thus, this study suggests that systematic uncertainties may be introduced to atmospheric simulations if groundwater table dynamics are neglected in the model.     

Existence of the solutions and the attractors for the large-scale atmospheric equations

The atmosphere is a kind of fluid surrounding therotating earth, and its state can be described by thevelocity vector v, the temperature T, the density ρ, andthe pressure p at each point. Its evolution process isessentially governed by the Navier-Stockes equationand the temperature equation. Due to the specialty andthe complexity of the atmospheric problem, althoughsome modified and simplified work have made onthese fluid mechanics and temperature equations, theyare still a very complex forc…     

Ionization of the earth’s atmosphere by solar and galactic cosmic rays

A brief review of the research of atmospheric effects of cosmic rays is presented. Numerical models are discussed, that are capable to compute the cosmic ray induced ionization at a given location and time. Intercomparison of the models, as well as comparison with fragmentary direct measurements of the atmospheric ionization, validates their applicability for the entire atmosphere and the whole range of the solar activity level variations. The effect of sporadic solar energetic particle events is shown to be limited on the global scale, even for the most severe event, but can be very strong locally in polar regions, affecting the physical-chemical properties of the upper atmosphere, especially at high altitudes. Thus, a new methodology is presented to study cosmic ray induced ionization of the atmosphere in full detail using realistic numerical models calibrated to direct observations.     

Difference between the spectra of acoustic gravity waves in daytime and nighttime hours due to nonequilibrium effects in the atmosphere

The singularities of the wave disturbance spectra of the nonequilibrium atmosphere in the range of acoustic gravity waves (AGWs) have been analyzed. Using the dispersion ratio for AGWs in the nonequilibrium atmosphere, it has been established that the spectra in the daytime and nighttime hours are different and this difference, caused by a nonequilibrium spectrum sensitivity to atmospheric temperature, can reach several percent in certain atmospheric regions. For the spectrum of the equilibrium model of the atmosphere, the difference between the daytime and nighttime spectra makes up several fractions of percent. As a result of the spectral treatment of variations in pressure and intensity of cosmic rays (CRs), it has been found out that the daytime AGW spectrum is higher-frequency than the nighttime spectrum. A comparison of the theoretical calculations of the AGW spectrum with observations has made it possible to distinguish the effect of nonequilibrium in the AGW spectral composition.     

The comparison of ensemble or deterministic dispersion modeling on global dispersion during Fukushima Dai-ichi nuclear accident

Ensemble forcasting,originally developed for weather prediction,is lately being extended to atmospheric dispersion applications,which is a new,effective methodology for improving the atmospheric dispersion numerical modeling.In March 2011,due to the massive 9.0 earthquakes and ensuing tsunami that struck off the northern coast of the island of Honshu,the Fukushima Nuclear Plant I had the substantial leak of radioactive materials into surrounding environment and atmosphere.To aim at the global dispersion modeling of atmospheric radionuclides from Fukushima Nuclear Accident,this paper presents two approaches of atmospheric dispersion forecasting:ensemble dispersion modeling(EDM) and deterministic dispersion modeling(DDM),conducts the globally dispersion modeling cases for Fukushima nuclear accident,and analyzes and evaluates the simulation results using observation data.In this paper,EDM includes three different perturbation methods:meteorological perturbation method,turbulence perturbation method,and physical parameterization ensemble forecasting method.The simulation results show that the trajectories from EDM have a better performance,which is in better agreement with the atmospheric circulation and observation data; the spread from DDM is slower and not as far as EDM.Additionally,the results from EDM display a better performance in the modeling of transport from Japan to China East Sea on April 4.The reasons for these results are:the techniques of MET and TUR are performed by adding perturbations on mean wind and turbulent velocity,respectively; the various different flow fields will result in far spreading in horizontal and the simulation results closer to observation; PHY is performed by using different diffusion physical parameterizations and produces the perturbations on vertical wind,which results the spreading in smaller range and discontinuous in horizontal.Finally,the comparative analysis between modeling results and observation data shows that all cases results are in good agreement with trends of observed radionuclides surface concentration; however,the modeling surface concentration is smaller than observation,especially in DDM and PHY.Furthermore,the EDM results show that MET and TUR are of more evolutionary advantage than PHY in modeling of average and maximum concentration.Therefore,this study can serve as a reference to atmospheric dispersion and environmental emergency response(EER).     

Global hydrological changes associated with a perturbation of the climate system: the role of atmospheric feedbacks,their uncertainty and their validation

The anthropogenic increase of the atmospheric greenhouse effect is expected to bring important perturbations of the climate system during the next century. The models which are used to compute scenarios of this future climate change nevertheless suffer from important uncertainties which make impossible the detailed prediction of regional impacts. Characterizing these uncertainties as precisely as possible constitutes a necessary step to assess a climate risk and realize local impact studies. We describe the manifestation of water vapour and cloud feedbacks in the present models, and show that satellite data, in particular, may constitute an important source of information to constrain more efficiently the models.     

Sea Ice Dynamics Induced by External Stochastic Fluctuations

The influence of stochastic fluctuations in the atmosphere and in the ocean caused by different occasional phenomena (noises) on dynamic processes of sea ice growth with a mushy layer is studied. It is shown that atmospheric temperature variances substantially increase the sea ice thickness, whereas dispersion variations of turbulent flows in the ocean to a great extent decrease the ice content produced by false bottom evolution.     

Nonequilibrium Effects in Atmospheric Perturbations Caused by Solar Radiation Flux

The effects of atmospheric nonequilibrium in the generation of wave perturbations due to the solar radiation flux are studied. Equations of nonequilibrium thermodynamics are used to perform an assessment of the channels of solar energy transformation into the atmosphere for different altitudes. As a result of calculations of the dispersion relation for a nonequilibrium atmosphere, we consider how the flux of solar radiation changes the spectrum of natural atmospheric oscillations at different altitudes and for different solar activities. A qualitative relation between the results of wave spectra calculations and the data of ionosphere dynamics observations for different intensities of the solar radiation flux has been established.     

Assessing the uncertainties of hydrologic model selection in climate change impact studies

The uncertainties associated with atmosphere‐ocean General Circulation Models (GCMs) and hydrologic models are assessed by means of multi‐modelling and using the statistically downscaled outputs from eight GCM simulations and two emission scenarios. The statistically downscaled atmospheric forcing is used to drive four hydrologic models, three lumped and one distributed, of differing complexity: the Sacramento Soil Moisture Accounting (SAC‐SMA) model, Conceptual HYdrologic MODel (HYMOD), Thornthwaite‐Mather model (TM) and the Precipitation Runoff Modelling System (PRMS). The models are calibrated based on three objective functions to create more plausible models for the study. The hydrologic model simulations are then combined using the Bayesian Model Averaging (BMA) method according to the performance of each models in the observed period, and the total variance of the models. The study is conducted over the rainfall‐dominated Tualatin River Basin (TRB) in Oregon, USA. This study shows that the hydrologic model uncertainty is considerably smaller than GCM uncertainty, except during the dry season, suggesting that the hydrologic model selection‐combination is critical when assessing the hydrologic climate change impact. The implementation of the BMA in analysing the ensemble results is found to be useful in integrating the projected runoff estimations from different models, while enabling to assess the model structural uncertainty. Copyright © 2011 John Wiley & Sons, Ltd.     

大气GPS掩星观测反演方法

大气GPS掩星观测可获得全球的大气气象参量剖面信息.本文阐述了地球大气GPS掩星观测反演原理,详细介绍了其几何光学近似反演方法和全谱反演方法,提出了将几何光学反演方法和全谱反演方法结合以形成可以处理多路径掩星数据的反演新方案.该方案和几何光学反演方法应用于GPS/MET和CHAMP大气掩星数据反演,成功地获得了大气参量剖面.结果表明,新反演方案是可行的、有效的GPS大气掩星反演方案.     

The effect of model assumptions on computations of cosmic ray induced ionization in the atmosphere

The longitudinal profile of atmospheric cascades is sensitive to the energy, mass of the primary particle and to atmospheric state. In this work are compared ionization yield functions Y for winter, summer and US standard profiles of Earth's atmosphere. The various profiles are obtained on the basis of CORSIKA 6.52 code simulations using FLUKA 2006 and QGSJET II hadronic interaction subroutines. The energy deposit of proton induced cascade processes in the atmosphere is calculated for different types of atmospheres. The ion pair production in the atmosphere and the contribution of the different shower components, precisely the electromagnetic, muon and hadronic is estimated according applied atmospheric types. In addition simulations with different hadronic interaction models GHEISHA 2002, FLUKA 2006 and QGSJET II are carried out. The ion pair production in the atmosphere and the contribution of different shower components is estimated according the assumed hadronic interaction models. The yield function Y for total ionization, respectively, for the different components is compared. The observed differences are widely discussed. General conclusion concerning the application of various atmospheric profiles and hadron interaction models is carried out.     

Effect of atmospheric gases,surface albedo and cloud overlap on the absorbed solar radiation

Recent studies have provided new evidence that models may systematically underestimate cloud solar absorption compared to observations. This study extends previous work on this “absorption anomaly” by using observational data together with solar radiative transfer parameterisations to calculate f_s (the ratio of surface and top of the atmosphere net cloud forcings) and its latitudinal variation for a range of cloud types. Principally, it is found that (a) the zonal mean behaviour of f_s varies substantially with cloud type, with the highest values obtained for low clouds; (b) gaseous absorption and scattering can radically alter the pattern of the variation of f_s with latitude, but gaseous effects cannot in general raise f_s to the level of around 1.5 as recently determined; (c) the importance of the gaseous contribution to the atmospheric ASR is such that whilst f_s rises with surface albedo, the net cloud contribution to the atmospheric ASR falls; (d) the assumed form of the degree of cloud overlap in the model can substantially affect the cloud contribution to the atmospheric ASR whilst leaving the parameter f_s largely unaffected; (e) even large uncertainties in the observed optical depths alone cannot account for discrepancies apparent between modelled and newly observed cloud solar absorption. It is concluded that the main source of the anomaly may derive from the considerable uncertainties regarding impure droplet microphysics rather than, or together with, uncertainties in macroscopic quantities. Further, variable surface albedos and gaseous effects may limit the use of contemporaneous satellite and ground-based measurements to infer the cloud solar absorption from the parameter f_s.     

Normal Point Algorithm For Reduction Of Two Colour Slr Observations

Two colour laser ranging to artificial satellites is an attractivetechnique, which is capable to provide refraction corrected ranges without the need of an atmospheric model by measuring the dispersive delay of laser pulses of different wavelength. Although the required accuracy of the detection scheme is stringent, the technique has matured so far, that routine two colour observationsbecame feasible.The present paper describes a normal point procedure reducing two colour laser range observations with respect to the dispersive delay,exploiting the knowledge of satellite response signatures in conjunction with detector characteristics and the appropriate center of mass correction models.Moreover the dispersion model of the atmosphere is briefly reviewed, paying attention to the wavelength domains provided by modern twocolour ranging lasers, e.g., the Ti:SAP laser.Preliminary data is presented and compared to both, normal point data reduced with a standard procedure and zenith path equivalent meteorological parameters.     

Earth's Rotation And High Frequency Equatorial Angular Momentum Budget Of The Atmosphere

The effect of the atmosphere on the Earth's rotation can be computed by twodifferent but fundamentally equivalent approaches. The more commonly used is the so-called angular momentum approach, and the second is the torque approach. Their physicalmeanings are recalled, and numerical results from the two are intercompared, concentrating on the lowest periods of a few days or shorter. The indirect effect of the atmosphereon the Earth rotation due to atmospheric forcing on the ocean is also described based on both static and dynamic oceanic models.Results are discussed for the equatorial components and for the highest frequencies.     

Atmospheric effects on satellite gravity gradiometry data

Atmospheric masses play an important role in precise downward continuation and validation of satellite gravity gradiometry data. In this paper we present two alternative ways to formulate the atmospheric potential. Two density models for the atmosphere are proposed and used to formulate the external and internal atmospheric potentials in spherical harmonics. Based on the derived harmonic coefficients, the direct atmospheric effects on the satellite gravity gradiometry data are investigated and presented in the orbital frame over Fennoscandia. The formulas of the indirect atmospheric effects on gravity anomaly and geoid (downward continued quantities) are also derived using the proposed density models. The numerical results show that the atmospheric effect can only be significant for precise validation or inversion of the GOCE gradiometric data at the mE level.     

A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations

In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion. The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without using explicit filtering for numerical stability.     

Error bars for the global seismic Q profile

The radial attenuation profile of the Earth is needed to account for dispersion effects when interpreting seismic velocities and can provide important constraints on composition. To date, most radial Q models have been produced using traditional damped inversions of free oscillation and surface wave data. Because such inversions can severely underestimate the model uncertainties that are needed to guide mineralogical and dynamic interpretation, and because the quality of data has continued to improve, we revisit this seismic inverse problem using a model space search approach already proven effective with similar data. We do, indeed, observe model uncertainties at least an order of magnitude greater than earlier estimates. At the same time, we find that Q is determined well enough to confirm that the data favor several important features previously disputed because of questions of consistency. These include shear attenuation that drops significantly in the lower third of the lower mantle and bulk attenuation that is negligible in the inner core but stronger in the outer core and lower mantle than suggested by most models.