共查询到20条相似文献，搜索用时 31 毫秒
1.
Z.N. Begum 《Journal of Atmospheric and Solar》1998,60(18):1751-1754
A theoretical model based on some physical assumptions has been integrated to study the scattering of solar radiation by aerosol particulates of any size present in the atmosphere. Using this model, which incorporates multiple scattering, scattered fluxes of radiation with varying optical depths and also the optical depth versus wavelengths are computed. The present results are found to be in close agreement with the observations of the Pre-Indian Ocean Experiment (INDOEX) 1996. This provides evidence of the direct effect of aerosol particulates on the radiative forcing of the atmosphere. 相似文献
2.
The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation
The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations. 相似文献
3.
George Ohring 《Pure and Applied Geophysics》1979,117(5):851-864
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
4.
Although the calculation of radiative transfer in the middle-shortwave infrared band is important in the field of optical remote sensing, studies in this area of research are rare in China. Both solar reflection and atmospheric emission should be considered when calculating radiative transfer in the middle-shortwave infrared band. This paper presents a new radiative transfer model based on the doubling and adding method. The new model uses approximate calculations of direct solar reflection,multiple scattering, and thermal emissions for a finitely thin atmospheric layer and considers both the solar and thermal sources of radiation. To verify its accuracy, the calculation results produced by the model for four typical scenarios(single layer at night,multi-layer aerosols, double-layer with ice and water clouds, and multi-layer with clouds and aerosols) were compared with those of the DISORT model. With the exception of a few channels, the absolute deviation between the two models was less than2×10~(-6) K. For the same calculation, the computation speed of the new model was approximately two to three times faster than that of the DISORT model. Sensitivity studies were performed to evaluate the error resulting from using simplified calculation methods in the new model. The results obtained in this study indicated that atmospheric thermal emission made a significant contribution to the measured radiance in the strong-absorption band(2230–2400 cm~(-1)), whereas solar radiation could be neglected in this region. However, neglecting solar radiation in the window region(2400–2580 cm~(-1)) introduced error on the order of dozens of K. Employing the average-layer temperature method simplified the calculation of thermal radiation but caused a larger error in the strong-absorption band than in the window region. In the doubling and adding method, the calculation error decreased as the value used for minimum optical thickness decreased. Under the condition of satisfying the requirement of calculation precision, we can consider using the layer-average temperature radiation method and selecting a relative larger minimum optical thickness value to improve the calculation efficiency. The new radiative calculation model proposed herein can be used in the simulation, inversion, and assimilation of middle-shortwave infrared measurements by hyper-spectral satellite instruments. 相似文献
5.
Summary The paper focuses on the applicability of simple optimizing methods to determining the aerosol structure based on the measured
values of the spectral optical thickness of aerosol δ(λ). The necessary conditions leading to a stable solution are assessed.
By applying the particle distribution function in the form of summations of modified gamma functions we obtain the simple
form of δ(λ). It is not suitable for proving Gaussian functions. The application of approximate methods to determine the aerosol
structure from spectral optical thickness of atmospheric aerosol is based on measurements of the direct spectral solar radiation
flux density which formed a part of the radiation experiment conducted in Zingst (Germany) on the coast of the Baltic Sea
in 1987.
on leave from the Astronomical Institute, Slovak Academy of Sciences 相似文献
6.
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. 相似文献
7.
8.
Erythemal ultraviolet (UVER; 280–400 nm) and total shortwave (SW; 305–2800 nm) solar irradiances were recorded from 2000 to 2009 in Valladolid, Spain. UVER and SW values under cloudless conditions are simulated by radiative transfer (TUV 4.6) and empirical models. These model estimations are tested with experimental measurements showing a great agreement (root mean square error around 7%). The aerosol effect on UVER irradiance is determined through a model study. UVER radiation and total ozone column (TOC) temporal evolutions show a negative relationship. TOC accounts for 80% of UVER variance and its radiation amplification factor is 1.1 at zenith of 65°. Cloud effects on solar radiation are shown and quantified by the cloud modification factor. Moreover the enhancement effect cases are analysed. SW radiation proves more sensitive to clouds than UVER. Clouds are seen to attenuate and enhance solar radiation by up to 93% and 22% in the UVER range, respectively. 相似文献
9.
Numerical simulation of the influence of aerosol radiation effect on urban boundary layer 总被引：2，自引：0，他引：2
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
10.
针对天文、大气、宏观地理与局地地形等因子对起伏地形下太阳散射辐射的复杂作用,将影响起伏地形下太阳散射辐射的天空因素与地面因素分开处理.通过基于数字高程模型（DEM）数据的起伏地形下天文辐射模型和地形开阔度模型,综合考虑地面因素对散射辐射的影响;基于常规地面气象站观测资料建立的水平面散射辐射模型考虑天空因素对散射辐射的影响;依据各向异性散射机理,建立了起伏地形下太阳散射辐射分布式计算模型,探索出一条利用DEM数据和常规气象观测资料实现山区太阳散射辐射定量模拟的技术路线.以1 km×1 km分辨率的DEM数据作为地形的综合反映,实现了起伏地形下黄河流域1 km×1 km分辨率的太阳散射辐射分布式模拟. 相似文献
11.
Miroslav Kocifaj 《Studia Geophysica et Geodaetica》1992,36(4):376-391
Summary The vertical profile of the aerosol attenuation coefficient can be calculated from the measurements of the spectral flux density of direct solar radiation and spectral radiance in a clear sky in a certain sun aureola by using the theory applied in this article. The process of solar radiation scattering is solved up to third order. 相似文献
12.
13.
Error analysis of multi-wavelength sun photometry 总被引：6，自引：0，他引：6
Glenn E. Shaw 《Pure and Applied Geophysics》1976,114(1):1-14
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. 相似文献
14.
A. A. Cheremisin P. V. Novikov I. S. Shnipov V. V. Bychkov B. M. Shevtsov 《Geomagnetism and Aeronomy》2012,52(5):653-663
Lidar observations during 2007–2008 in Kamchatka revealed aerosol layers in the upper stratosphere at heights of 35–50 km and in the mesosphere at heights of 60–75 km. It is well known that forces of gas-kinetic nature, i.e., photophoretic forces, act on aerosol particles that absorb solar radiation and terrestrial IR radiation; these forces can counteract the gravitational force and even lead to the levitation of these particles at particular heights. The accumulation of particles at these heights may lead to the formation of aerosol layers. We calculated these forces for the conditions of lidar observations in Kamchatka. Aerosol layers were observed at heights where particle levitation can occur. Thus, the stratospheric and mesospheric aerosol layers, detected at heights of 30–50 and 60–75 km, respectively, may be due to the effect of the photophoretic force on aerosol particles. 相似文献
15.
Photosynthetically active radiation (PAR) is essential for plant photosynthesis and carbon cycle, and is also important for meteorological and environmental monitoring. To advance China’s disaster and environmental monitoring capabilities, the HJ-1A/B satellites have been placed in Earth orbit. One of their environmental monitoring objectives is the study of PAR. We simulated direct solar, scattered and environment radiation between 400 and 700 nm under different atmospheric parameters (solar zenith angle, atmospheric water vapor, atmospheric ozone, aerosol optical thickness, surface elevation and surface albedo), and then established a look-up table between these input parameters and PAR. Based on the look-up table, we used HJ-1A/B aerosol and surface albedo outputs to derive the corresponding PAR. Validation of inversed instantaneous and observed PAR values using HJ-1 Heihe experimental data had a root mean square error of 25.2 W m?2, with a relative error of 5.9%. The root mean square error for accumulated daily PAR and observed values was 0.49 MJ m?2, with a relative error of 3.5%. Our approach improved significantly the computational efficiency, compared with using directly radiation transfer equations. We also studied the sensitivity of various input parameters to photosynthetically active radiation, and found that solar zenith angle and atmospheric aerosols were sensitive PAR parameters. Surface albedo had some effect on PAR, but water vapor and ozone had minimal impact on PAR. 相似文献
16.
Summary The paper deals with the effect of aerosol on the transmission of solar radiation in a metropolitan atmosphere. The work is based on field measurements of the intensity of direct solar radiation, carried out by the Institute of Meteorology and Climatology, Slovak Acad. Sci., at four points in Bratislava. 相似文献
17.
Photosynthetically active radiation (PAR) is essential for plant photosynthesis and carbon cycle, and is also important for meteorological and environmental monitoring. To advance China’s disaster and environmental monitoring capabilities, the HJ-1A/B satellites have been placed in Earth orbit. One of their environmental monitoring objectives is the study of PAR. We simulated direct solar, scattered and environment radiation between 400 and 700 nm under different atmospheric parameters (solar zenith angle, atmospheric water vapor, atmospheric ozone, aerosol optical thickness, surface elevation and surface albedo), and then established a look-up table between these input parameters and PAR. Based on the look-up table, we used HJ-1A/B aerosol and surface albedo outputs to derive the corresponding PAR. Validation of inversed instantaneous and observed PAR values using HJ-1 Heihe experimental data had a root mean square error of 25.2 W m−2, with a relative error of 5.9%. The root mean square error for accumulated daily PAR and observed values was 0.49 MJ m−2, with a relative error of 3.5%. Our approach improved significantly the computational efficiency, compared with using directly radiation transfer equations. We also studied the sensitivity of various input parameters to photosynthetically active radiation, and found that solar zenith angle and atmospheric aerosols were sensitive PAR parameters. Surface albedo had some effect on PAR, but water vapor and ozone had minimal impact on PAR.
相似文献18.
Karen L. Aplin 《Surveys in Geophysics》2006,27(1):63-108
Atmospheric electrification is not a purely terrestrial phenomenon: all Solar System planetary atmospheres become slightly
electrified by cosmic ray ionisation. There is evidence for lightning on Jupiter, Saturn, Uranus and Neptune, and it is possible
on Mars, Venus and Titan. Controversy surrounds the role of atmospheric electricity in physical climate processes on Earth;
here, a comparative approach is employed to review the role of electrification in the atmospheres of other planets and their
moons. This paper reviews the theory, and, where available, measurements, of planetary atmospheric electricity which is taken
to include ion production and ion–aerosol interactions. The conditions necessary for a planetary atmospheric electric circuit
similar to Earth’s, and the likelihood of meeting these conditions in other planetary atmospheres, are briefly discussed.
Atmospheric electrification could be important throughout the solar system, particularly at the outer planets which receive
little solar radiation, increasing the relative significance of electrical forces. Nucleation onto atmospheric ions has been
predicted to affect the evolution and lifetime of haze layers on Titan, Neptune and Triton. Atmospheric electrical processes
on Titan, before the arrival of the Huygens probe, are summarised. For planets closer to Earth, heating from solar radiation
dominates atmospheric circulations. However, Mars may have a global circuit analogous to the terrestrial model, but based
on electrical discharges from dust storms. There is an increasing need for direct measurements of planetary atmospheric electrification,
in particular on Mars, to assess the risk for future unmanned and manned missions. Theoretical understanding could be increased
by cross-disciplinary work to modify and update models and parameterisations initially developed for a specific atmosphere,
to make them more broadly applicable to other planetary atmospheres. 相似文献
19.
The challenges of ‘standard’ model of solar flares motivated by new observations with the spacecrafts and ground-based telescopes are presented. The most important problems are in situ heating of photospheric and chromospheric loop footpoints up to the coronal temperatures without precipitating particle beams accelerated in the corona, and the sunquakes which are unlikely to be explained by the impact of highenergy particles producing hard X-ray emission. There is also the long-standing ‘number problem’ in the physics of solar flares. It is shown that modern observations favored an important role of the electric currents in the energy release processes in the low solar atmosphere. Particle acceleration mechanism in the electric fields driven by the magnetic Rayleigh-Taylor instability in the chromosphere is proposed. The electric current value I ≥ 1010 A, needed for the excitation of super-Dreicer electric fields in the chromosphere is determined. It is shown that both Joule dissipation of the electric currents and the particles accelerated in the chromosphere can be responsible for in situ heating of the low solar atmosphere. Alternative model of the solar flare based on the analogy between the flaring loop and an equivalent electric circuit which is good tool for the electric current diagnostics is presented. Interaction of a current-carrying loop with the partially-ionized plasma of prominence in the context of particle acceleration is considered. The role of plasma radiation mechanism in the sub-THz emission from the chromosphere is discussed. 相似文献
20.
Continuous measurements of solar spectral radiation using the Multi-filter Rotating Shadow Band Radiometer (MFRSR) are performed at the Actinometric Station of the National Observatory of Athens (ASNOA). The present study utilizes three clear-sky days of continuous observations, from local sunrise to local sunset, in order to investigate the daily variation of the radiation components (diffuse, global and direct-beam) as well as their ratios (diffuse-to-global, DGR, and diffuse-to-direct-beam, DDR) under different atmospheric conditions. Both ratios have received great scientific interest, especially for investigating solar irradiance modifications under various atmospheric conditions, aerosol load and optical properties. Apart from this, the present study shows that the DDR can constitute a measure of atmospheric turbidity when it is determined at longer wavelengths, while the DGR cannot. The effect of the solar zenith angle (SZA) on both ratios is significant at the shorter wavelengths with varying sensitivities depending on the aerosol field and sun elevation. The present study confirms the results obtained by previous solar irradiance measurements in Athens and also those computed via radiative transfer codes and sheds light on the scientific knowledge of the use of spectral DDR as an atmospheric turbidity index. 相似文献