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本文利用地球辐射平衡试验（ERBE）和国际卫星云气候计划（ISCCP）提供的地气系统行星反射率，长波射出辐射（OLR）和云量资料，计算出中国地区年、月总云量对地气系统净辐射的强迫，分别讨论了其与总云量及地气系统晴天净辐射的关系。结果表明：地气系统净辐射云强迫与总云量有较好的抛线物关系，各月净辐射云强迫与地气系统晴天净辐射的曲线相关也很明显，如以曲线上净辐射云强迫为零时的晴天净辐射值代表各月曲线位置，则该值随天文辐射作规律性季节变化。地气系统净辐射云强迫的地理分布与总云量及地气晴天净辐射分布有关，其在各地的年变化则主要由天文因素及雨季进行退决定。 相似文献
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红外高光谱资料模拟大气廓线反演对云的敏感性 总被引：3，自引：1，他引：2
用不同云顶高度和不同有效云量时的星载红外高光谱观测值,模拟大气温湿垂直廓线反演对云参数的敏感性。用特征向量统计反演法按照云顶高度和有效云量分类反演了大气温湿廓线,统计了不同云高（200,300,500,700和850hPa）及云高有50hPa误差时温度、水汽混合比反演的均方根误差随有效云量的变化。结果表明,随着有效云量的增大,云顶以下各高度层上的温度、水汽混合比反演误差都明显增大。云高有50hPa误差较准确已知而言,温度和水汽混合比的反演误差增大,但温度反演对云高误差的敏感性比水汽反演要高。 相似文献
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全天空成像仪（total sky imager 440,TSI-440）可以实现白天全天空云量的持续自动监测,时空分辨率较高,得到的云量计算结果更精确.首先介绍了TSI-440的基本原理和资料格式,并基于太湖地区2008年5-10月的TSI-440资料及无锡站地面观测资料,采用统计方法详细地分析了不同天气情况下图像的成像特征及云量的计算误差.结果发现：图像的成像特征与能见度密切相关,红蓝比值随着能见度的减小而增大.另外,仪器在处理阴天图像及复杂天空（多云）图像时,易造成一定的云量计算误差.针对上述问题,本文通过直方图分析,重新选定了红蓝比阈值（晴空点阈值0.62,云点阈值0.66）,基于新阈值计算的云量结果较仪器自带的处理结果更为准确,减小了因天气状况不同而产生的云量计算误差. 相似文献
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三维有云大气辐射变温率数值模拟研究——邻云辐射效应 总被引：1，自引：0，他引：1
大气数值模式普遍采用一维辐射传输模型,无法表征有云大气中的三维辐射传输过程,从而影响数值模拟乃至数值天气预报的准确性。为评估这种不确定性,研究了水平云体间的三维辐射相互作用及其改变云体热力结构的规律,力求为改进数值模式辐射计算方案提供理论依据。选取I3RC PhaseⅡ的典型积云场和层积云场作为试验对象,将云场中心区域云体视为目标云体,周围云体为邻近云体,采用宽带三维辐射传输模式SHDOM模拟长波和短波辐射变温率的空间分布,定量阐明邻近云体对目标云体热力结构的影响。结果表明,邻云在长波区域对目标云体主要起辐射保温的作用,目标云体增温区域集中于邻云一侧的云体表面层,增温强度与云覆盖率和云间距离倒数成正比,最高可达3.08K/h,云体增温的厚度与目标云体液态水含量成反比;在短波区域,邻云同时起散射增温和遮蔽降温的作用,太阳垂直入射时,散射增温效应较弱,变温率空间差异小;当太阳天顶角增大后,遮蔽降温效应逐步起主导作用,造成目标云体被邻云遮挡一侧的表面层明显降温,峰值可达-1.72K/h,数值上甚至超过邻云长波增温效应。总之,邻近云体可以明显改变目标云体的变温率空间分布,引入三维邻云辐射效应对改进大气数值模式辐射计算方案具有重要意义。 相似文献
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中国地区云对地气系统长波射出辐射（OLR）强迫的气候研究 总被引：1，自引：0，他引：1
本文利用地球辐射平衡试验（ERBE）和国际卫星去气候计划（ISCCP）提供的地气系统长波射出辐射（OLR）和云量资料，计算半讲座了我国各季和年平均去量对地气系统OLR的强迫及其所产生的温室效应，结果表明：我国各季的OLR云强迫与总云量，高云量都有较好的相关，且季节变化明显；OLR云强迫和云温室效应的地理分布受云量和云状的影响较大，它们的年变化一般呈弱双峰型，峰值在春，夏季出现。 相似文献
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在国家气候中心全球大气环流模式BCC_AGCM2.0中引入一组基于CloudSat/CALIPSO卫星观测的、能够体现真实时空变化特征的云垂直重叠参数（抗相关厚度,Lcf）数据,以减小由云的重叠描述造成的辐射场的不确定性。对比了采用时空变化的云重叠参数和采用恒定云重叠参数的气候模拟结果,发现无论在全球还是东亚区域,采用基于卫星观测的云重叠参数对模拟的总云量都有一定程度的改进。采用时空变化的云重叠参数后,冬、夏两季全球平均总云量与云和地球的辐射能量系统（CERES）卫星资料的误差都减少了1.6%,其中热带对流区域总云量的正偏差和副热带地区总云量的负偏差都明显减少,这些有助于正确模拟不同区域间的能量收支差异。在东亚区域,采用时空变化的云重叠参数后,冬、夏两季的东亚区域平均总云量与CERES卫星资料的误差分别减少了1.8%和1.4%。综上所述,基于CloudSat/CALIPSO卫星资料计算得到的Lcf有助于改进大气环流模式对总云量的模拟,从而提高模式对辐射场的模拟精度。 相似文献
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晴空与有云大气辐射分布的数值模拟及其对全天空图像云识别的应用 总被引：5，自引：0，他引：5
全天空图像自动云识别的研究相对来说是一项较新的研究领域。当前国际上较为通用的全天空图像云识别方法主要依靠图像蓝红灰度值对比的阈值方法进行判断。然而非洁净大气中气溶胶的增多给云识别增加了难度,同时太阳高度角不同天空色度分布情况也不同。文中利用Libradtran辐射传输模式,计算了不同能见度不同太阳高度角情况下3个典型波长(450,550,650nm;蓝/绿/红)无云及有云大气的天空辐亮度分布情况,并进行了比较分析。结果表明,相同太阳高度角情况下,无云及有云大气中蓝红比值随能见度的下降呈单调下降趋势。在特定的云光学厚度和能见度情况下,天空色度彼此呈现出类似的分布状况。全天空图像阈值判断云识别自适应算法的建立需要与太阳高度角、地面能见度联系起来。当前尚无法建立一个判断阈值随太阳高度角以及能见度变化的函数关系式。较为可行的办法是建立典型能见度、典型太阳高度角情况下的辐射信息库,在具体云识别时,首先确定太阳高度角,而后根据天空辐射比情况确定天空能见度,并利用辐射信息标准库做云或非云判别。该工作为全天空云识别算法提供判别依据,同时建立云识别随能见度和太阳高度角变化的判别信息库。 相似文献
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Dr. R. Vogelgesang 《Meteorology and Atmospheric Physics》1996,58(1-4):205-214
Summary An analytical method is developed for determining radiation transport in finite cylindrical clouds. The cylindrical form is taken as the idealized shape of cumulus clouds. In the shortwave part of the spectrum illumination by the direct solar beam is considered. In the infrared the cloud's emission as well as the radiation emitted by an underlying ground is taken into account. Numerical computations are carried out to illustrate the applicability of the technique developed in the present study. For a cloud in an absorbing midlatitude summer atmosphere results are shown for the shortwave region including spectral integration. Cloud transmission and albedo are presented as a function of solar zenith angle and as a function of the cloud's dimensions. The results are in agreement with published results from Monte Carlo calculations as far as a comparison is possible. Vertical profiles of the solar heating rate in the cylindrical cloud indicate the effect of the cloud's finite dimensions. Similarity as well as differences are found from comparison with results obtained for a cuboidal cloud from a finite analytical model that was tested successfully against Monte Carlo calculations.With 5 Figures 相似文献
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The influence of various cloud parameters and the interactions with the ground albedo and the solar zenith angle have been studied by means of model simulations. The radiative transfer model suitable for a cloudy atmosphere as well as for a clear atmosphere has been developed on the basis of the Discrete Ordinate Method. This study leads to a general understanding for cloudy atmospheres: in the presence of a uniform cloud, the cloud scattering is dominant to molecular and aerosol scattering, and it is also wavelength-independent; the ratio of transmitted irradiance in a cloudy atmosphere to that in the background clear atmosphere is independent of cloud height and solar zenith angle. That’s to say, the radiation downwelling out of a cloud is quite isotropic; it decreases approximately exponentially with the cloud optical depth at a rate related to the ground albedo; the reflected irradiance at the top of the atmosphere is dependent on cloud optical depth as well as on solar zenith angle, but not on ground albedo for clouds of not very thin optical depth. 相似文献
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针对地基测云系统中云在可见光波段与红外波段中表现出的不同特性,用双站数字式云高仪所测云高进行标校,结合地面实时观测天顶红外辐射亮温及地面环境参数,分析地面到云层底大气对红外辐射亮温的影响,从中发现利用天空红外辐射亮温来遥感云底高度的可行性,研发地基双波段测云系统。该系统以对流层大气的垂直温度递减率为理论基础,建立云层底到地面的温度递减梯度参数K,根据递减梯度参数反演天顶方向的云高。该算法不依赖于探空数据,通过实时定标形式得出符合仪器所在地的云底高反演公式。通过与维萨拉激光云高仪CL31进行数据对比分析得出,地基双波段测云系统反演结果具有较高的准确性。 相似文献
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We have designed a cloud generation scheme for use in the LMD GCM. It predicts the mixing ratio of the cloud's condensed water as a new prognostic variable. At present it does not fully interact with the radiation schemes, but the aim is to predict the cloud optical properties. We have used the Meteosat/ISCCP data to evaluate this scheme. Such a comparison allows us to place some constraints on the coefficients which are used in the parameterizations, such as the precipitation thresholds for the cloud's liquid water content and the relative variability of water vapour within a grid box. There is generally a good agreement between observed and simulated results, although there appear some discrepancies in the cloud's apparent temperatures. 相似文献
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Summary The diffuse sky radiation component in the ultraviolet wavelengths is often at least 50% of the global irradiance under clear skies, and is the dominant component of ultraviolet global radiation under translucent overcast skies. The distribution of sky radiance was measured in a rural area and modeled for wavelength bands of ultraviolet-B (UVB, 280–320 nm) and ultraviolet-A (UVA, 320–400 nm). Sky radiance measurements were made during the summer of 1993 over a wide range of solar zenith angles using radiance sensors mounted on a hand-operated hemispherical rotation mount. UVB irradiance measurements were also made during each scan. Since the ratio of measured irradiance under overcast skies and that predicted for clear skies was not correlated with cloud base height, opaque cloud fraction, or solar zenith angle, it was concluded that the scattering from the clouds dominated the global irradiance, and this scattering was relatively unaffected by the scattering off opaque clouds in the translucent atmosphere.Analysis of the translucent overcast sky UVA and UVB radiance measurements using a semi-empirical distribution model showed that the spectral influences on multiple scattering, single scattering, and horizon brightening components of the distributions agreed with basic atmospheric radiation theory. The best model used solar zenith, the sky zenith, and the scattering angle with resultant coefficient of determination values of 0.62 and 0.25 for the UVA and UVB respectively. The developed equations can be applied directly to the diffuse sky irradiance on the horizontal to provide radiance distributions for the sky.With 6 Figures 相似文献
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An analysis of heavy precipitation caused by a retracing plateau vortex based on TRMM data 总被引：1，自引：0，他引：1
In this paper, we study a persistent heavy precipitation process caused by a special retracing plateau vortex in the eastern Tibetan Plateau during 21–26 July 2010 using tropical rainfall measuring mission (TRMM) data. Results show that during the whole heavy rainfall process, the precipitation rate of convective cloud is steady for all four phases of the plateau vortex movement. Compared with the convective precipitation clouds, the stratiform precipitation clouds have a higher fraction of area, a comparable ratio of contribution to the total precipitation, and a much lower precipitation rate. Precipitation increases substantially after the vortex moves out of the Tibetan Plateau, and Sichuan Province has the most extensive precipitation, which occurs when the vortex turns back westward. A number of strong convective precipitation cloud centers appear at 3–5 km. With strong upward motion, the highest rain top can reach up to 15 km. In various phases of the vortex evolution, there is always more precipitable ice than precipitable water, cloud ice water and cloud liquid water. The precipitating cloud particles increase significantly in the middle and lower troposphere when the vortex moves eastward, and cloud ice particles increase quickly at 6–8 km when the vortex retraces westward. The center of the latent heat release is always prior to the center of the vortex, and the vortex moves along the latent heat release areas. Moreover, high latent heat is released at 5–8 km with maximum at 7 km. Also, the latent heat release is more significant when the vortex moves out of the Tibetan Plateau than over the Tibetan Plateau. 相似文献
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为了对全天空红外测云系统获得的红外图像进行云类自动识别, 提出了基于模糊纹理光谱结合云物理属性的全天空云类识别方法。首先根据不同滤波窗口的模糊纹理光谱图像特征, 确定了滤波窗口大小, 然后通过分析不同天空类型下的FUTS谱 (fuzzy uncertainty texture spectrum) 以及同一种天空类型下的FUTS谱, 考察了FUTS进行云类识别的适用性, 最后利用最小距离分类法和云基本物理属性对全天空红外图像进行了分类测试。在200个测试样本中, 层状云、积云、高积云、卷云和晴空的识别率分别为100%, 100%, 90%, 100%, 100%, 平均识别率达到98%。基于模糊纹理光谱的云分类算法对单一云空具有很好的分类效果, 可进一步应用于全天空红外图像的云分类识别。 相似文献
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Desert targets for solar channel calibration of geostationary satellites in the East Asia — Australian region were selected and their qualities were assessed with aid of Moderate Resolution Imaging Spectroradiometer data (i.e., white-sky surface albedo, aerosol optical thickness, and cloud fraction) from 2002 to 2008. The magnitude, spatial uniformity, and temporal stability of the white-sky surface albedo are examined in order to select bright and stable targets. Subsequently those selected targets over China, India, and Australia are further checked for their qualities in terms of data yielding ratio, aerosol optical thickness, cloud fraction, satellite viewing angle, and solar zenith angle. Results indicate that Chinese targets are found to be not adequate as calibration targets in spite of excellent surface conditions because of high percentage of cloud, possibly heavy aerosol loading, and lower solar elevation angle in particular during winter time. Indian site should be take care about relatively high temporal variation of surface condition and heavy aerosol loading. On the other hand, Australian desert targets are considered to be best when surface brightness, spatial and temporal stability, data yielding ratio, aerosol, and cloud are counted. 相似文献
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对2011—2016年部分夏季时段分别在西藏那曲、拉萨、林芝和阿里观测的大气向下长波辐射（L↓）进行分析,结果显示:L↓具有明显的日变化,最大值出现在北京时间15:00前后,而最低值出现在凌晨至10:00,日平均值林芝最高（368 W·m-2）,其次是拉萨（319 W·m-2）、阿里（305 W·m-2）和那曲（299 W·m-2）。晴天L↓ ?ngstr?m（1915）的经验公式最适合林芝,而Konzelmann（1994）的公式则适合那曲、拉萨和阿里;随着人工观测总云量的增加,L↓增强趋势明显,满云（云量7~10成）情形4个站点云增强效应均从20 W·m-2上升至50 W·m-2以上,低云量对L↓的增强效应明显高于总云量。云份额数（CF）上升所对应天顶方向平均云底高度下降,但云增强效应上升。在晴天（CF为-5%~5%、平均云底高度大于4 km）时,云增强效应仅为5 W·m-2左右（林芝接近20 W·m-2）,但当CF为90%以上（云底高度小于3.5 km）时,云增强效应则上升到60 W·m-2（林芝接近50 W·m-2）。固定云底高度,CF与L↓云增强效应呈显著相关（r2为0.91~0.97）,远高于云底高度与L↓云增强效应的相关（r2为0.32~0.58）。 相似文献