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利用2007年1月至2009年1月的气象、电离层及气候卫星探测系统(COSMIC)湿空气数据,基于相对湿度廓线出入云层时发生突变反演云边界高度进而获取云垂直结构参数的思想,对中国及周边八个不同地区云的垂直结构特征进行统计分析.结果表明:(1)不同地区掩星样本数随季节的变化较小,不同季节各地区间差异却较大,且多层云样本数日变化呈现明显的"双峰"结构;掩星最低探测高度集中在3.0km以下,各地区多层云受限制概率大于单层云,主要影响部分中低云参数的反演.(2)南方各地区云厚及晴空厚度都大于北方,双层云上层云厚大于下层,三层云从大到小依次为顶层、底层和中间层,且顶层与中间层晴空厚度大于中间层与底层;各地区不同季节内各层云云顶高具有相同的排列规律,云底高也基本遵循类似的排列顺序;多层云晴空厚度季节变化不显著,各季节内南方大于北方.(3)中国地区各类云云底高和云顶高二维频率季节变化不大,出现两个较大值区但分布高度各异;另外,南北方有不同的频率分布特点,其中西南和华南在16.0km以上出现"尾翼"分布,表明有深厚对流云产生. 相似文献
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基于2007—2010年的CloudSat卫星观测数据,以云层液态水路径为指标将层积云的发展过程划分为五个阶段,对比研究了中国东部降水与非降水层积云发展过程中云微物理特征和云微物理机制的演变,并分析了其海陆差异.研究表明:非降水层积云中,云滴增长主要通过凝结过程完成,但云滴的凝结增长有限,难以形成降水,在非降水层积云发展的旺盛阶段,云层中上部云滴发生较弱的碰并过程.降水层积云中云滴碰并增长活跃,当云层液态水路径小于500 g·m~(-2)时,云滴在从云顶下落至云底的过程中持续碰并,并在云底附近出现云水向雨水的转化;当降水层积云液态水路径超过500 g·m~(-2)时,云滴碰并增长主要发生在云层上部,在云层中部,云液态水含量、液态粒子数浓度和液态粒子有效半径达到最大,云水向雨水的转化最为活跃.层积云微物理特征的海陆差异主要是由海陆上空气溶胶浓度和云中上升气流强度不同导致的.在非降水层积云中下部,陆地丰富的气溶胶为云滴凝结增长提供了充足的云凝结核,因而云微物理量的量值在陆地上空更大,而在云层中上部,云滴凝结增长达到极限,海洋充足的水汽输送使云微物理量的量值在海洋上空更大.当降水层积云液态水路径大于500 g·m~(-2)时,陆地层积云中更强的上升气流使大量云滴在云层中上部累积滞留,云滴碰并增长活跃,云层中上部云微物理量的量值在陆地上空更大. 相似文献
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GNSS-LEO电离层无线电掩星技术是近年来发展的电离层探测新技术.为消除LEO轨道以上的电离层影响,改正TEC反演方法采用非掩星侧的观测数据进行电离层掩星反演.本文首次提出了一种新方法--基于历元差分的电离层反演方法;并将改正TEC与历元差分两种反演方法应用于模拟掩星观测数据反演,随后基于反演结果及误差分析得到一些有益的结论:历元差分反演精度较改正TEC反演精度均有所提高;不管是哪种方法,高轨(约800 km)反演结果要优于低轨(约500 km)的反演结果;随着剖面高度的降低,反演精度随之下降;反演误差主要集中在8至18时(当地时),主要分布在磁纬-30°至30°之间. 相似文献
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电离层水平不均匀结构是引起掩星资料反演的主要误差源.本文模拟不均匀结构对无线电掩星资料反演的影响.首先利用3-D全球射线追踪技术进行了模拟.结果指出:电离层电子密度20%的变化可能引起GPS的时延增加约12m.其次,将90%的掩星时延对应的路径长度,定义为电离层掩星测量的水平分辨率,其值为1200-2000 km.最后,计算了不同纬度电离层当地正午、子夜和日出时的电离层水平不对称指数.它表明:低纬夏季日出时,不对称指数达-78%,反演结果可能有较大误差. 相似文献
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本文利用2009年1月-2011年12月共3年的COSMIC大气掩星观测数据与SABER/TIMED探测数据开展15~60 km大气温度数据的比较分析研究,计算COSMIC与SABER/TIMED探测温度的绝对偏差(TSABER-TCOSMIC),并统计其平均温度偏差和标准偏差,分析温度偏差随高度、纬度和季节的分布特征,为COSMIC大气掩星与SABER/TIMED探测数据的应用提供更多的参考依据.结果表明:COSMIC与SABER/TIMED数据所反映的温度随高度的变化特征是一致的,数据的大体趋势吻合较好.全球范围的平均温度偏差在38 km左右接近于0 K,在38 km以上,平均温度偏差表现为负的系统性偏差,且随着高度逐渐增大,在38 km以下,平均温度偏差表现为正的系统性偏差,在23 km左右存在极大值,约为2.7 K.COSMIC与SABER/TIMED温度偏差的分布存在着随纬度和季节的变化特征,35 km以下,平均温度偏差在高纬地区和冬季较小,低纬地区和夏季较大,35 km以上,平均温度偏差在高纬地区和冬季较大,低纬地区和夏季较小.温度偏差的标准偏差在低纬地区和夏季较小,高纬地区和冬季较大.纬圈平均的温度偏差在南北半球的分布基本呈对称结构. 相似文献
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电离层掩星观测中，当低轨卫星（LEO）轨道高度较低时，轨道以上的电离层电子总含量（TEC）对掩星反演的影响不能忽略.目前，一般采用指数函数等外推方法来处理该问题，对反演结果可能引起较大误差.为提高电离层掩星反演精度，本文研究利用LEO处于非掩星一侧GPS观测数据的改正TEC新反演方法.用三维射线追踪程序计算出电离层掩星观测模拟数据，分别应用改正TEC方法和外推方法进行反演，将反演结果与所用模式值进行比较.结果表明：对于轨道高度约800km的GPS/MET掩星模拟数据，外推方法和改正TEC方法反演结果都与模式值基本一致；对于轨道高度约400km的CHAMP掩星模拟数据，外推方法误差较大，改正TEC方法反演结果与模式值相符得较好.将改正TEC方法应用于GPS/MET实测数据的反演，取得了合理的结果.这些说明，改正TEC算法是一种有效的电离层掩星反演方法，尤其是对于轨道较低的LEO的电离层掩星观测反演特别有用. 相似文献
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相对已经在轨运行的极轨卫星,搭载在静止卫星上的闪电成像仪能够提供全天候、无间断的闪电探测,是目前全球卫星闪电探测的方向.本文分析云不同特性对云顶闪电信号的影响,以及云高对静止卫星闪电定位的订正分析,将对静止卫星闪电成像仪的研发及其业务化运行提供技术支撑.研究中,通过建立云中闪电传输模型,模拟云中闪电传输.由于云粒子散射,云的体积、光学厚度和形状,以及闪电在云中发生的深度,都影响云中或云间闪电信号传输到云顶的能量衰减和持续时间,其持续时间可能超过已知静止卫星闪电成像仪假设的2 ms成像积分时间间隔,这样不能保证所有的闪电信号在一帧图像内探测到.但是,云粒子散射对云顶闪电的水平位置影响不大,闪电成像仪定位的云顶闪电可代表云中或云间的闪电位置.同时,在传统静止卫星图像定位模型的基础上,建立了闪电定位的云高订正模型.根据该模型,当云顶高度为10 km,云高所引起的闪电定位最大误差达到经向0.5379°、纬向0.2273°,超过已知静止卫星闪电成像仪假设的地面探测单元大小,有必要进行订正. 相似文献
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GPS大气掩星探测技术可以获得全球大气折射率、气压、密度、温度和水汽压等气象参数，该技术基本原理是基于几何光学近似的Abel积分反演.地球扁率、电离层传播时间延迟、大气大尺度水平梯度、多路径传播现象等因素在某些高度范围影响大气反演的精度.本文采用模拟的方法，分析其中地球扁率及电离层对反演结果的影响，并讨论局部圆弧修正及电离层修正的效果.利用CHAMP掩星实测轨道数据和有关电离层和大气经验模式、采用三维射线追踪方法模拟计算几种情形下的GPS掩星观测附加相位数据，对模拟数据进行反演，将反演气象参量剖面与模拟时给定模式剖面进行比较，得到了0～60 km高度范围内的反演误差.误差统计分析结果表明，局部圆弧中心的修正以及电离层修正，对于高精度的GPS掩星反演是非常重要的；电离层修正残差仍是制约30～60 km高度范围内反演精度的重要因素，进一步完善和优化大气掩星反演需要发展新的电离层修正算法. 相似文献
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The Clouds of the Middle Troposphere: Composition, Radiative Impact, and Global Distribution 总被引：1，自引：0，他引：1
The clouds of the middle troposphere span the temperature range where both ice and liquid water in a supercooled state can exist. However, because one phase tends to dominate, of the two midlevel cloud types, altostratus are deep ice-dominated, while altocumulus are shallow water-dominated, mixed-phase clouds with ice crystal virga typically trailing below. Multiple remote sensor examples of these cloud types are given to illustrate their main features, and the radiative consequences of the different cloud microphysical compositions are discussed. Spaceborne radar and lidar measurements using the CloudSat and CALIPSO satellites are analyzed to determine the global distributions of cloud frequencies and heights of these clouds. It is found that together these little-studied clouds cover ~25% of the Earth’s surface, which is about one-third of the total cloud cover, and thus represent a significant contribution to the planet’s energy balance. 相似文献
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Paul S. K. Pillai A. G. Selvam A. M. Murty A. S. R. 《Pure and Applied Geophysics》1985,123(6):930-940
Characteristics of cloud drop spectra were studied using 400 samples obtained from 120 warm cumulus clouds formed during the summer monsoon season.The total concentration of cloud drops (N
T) varied from 384 to 884 cm–3 and the maximum concentration was observed in the layer below the cloud-top. The width of the drop spectrum was broader in the cloud-base region and in the region below the cloud-top. The spectrum was multimodal at all levels except in the cloud-top region where it was unimodal. The concentration of drops with diameter greater than 50 m (N
L) varied from 0.0 to 0.674 cm–3.N
L was larger in the cloud-base region.N
L decreased with height up to the middle level and thereafter showed an increase. In the cloud-top region no large drops were present. The computed values of the liquid water varied between 0.132 and 0.536 g m–3 and the mean volume diameter (MVD) varied between 8.1 and 12.0 m. The LWC and MVD showed a decrease with height except in the middle region of the cloud where the values were higher than the adjacent levels. The dispersion of the cloud drops was lower (0.65) in the cloud-top region and higher (1.01) in the cloud-base region.The observed cloud microphysical characteristics were attributed to vertical mixing in clouds induced by the cloud-top gravity oscillations (buoyancy oscillations) generated by the intensification of turbulent eddies due to the buoyant production of energy by the microscale-fractional-condensation (MFC) in turbulent eddies. 相似文献
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LEO GPS观测已成为空间电离层研究重要手段之一,通过GPS双频观测值获取的TEC则是电离层探测的一个重要参量,为获取高精度TEC需估计和消除GPS接收机仪器偏差（DCB）.本文旨在探索一种全新的LEO GPS接收机仪器偏差的估计方法：基于电离层球对称的假设,利用CHAMP和COSMIC原始GPS观测数据,采用几何映射函数,通过最小二乘解算出GPS接收机仪器偏差.结果表明：(1)2008年1月份期间,通过上述方法解算的仪器偏差都较稳定,相比COSMIC网上发布结果,标准偏差都在0.6 ns以内;（2）COSMIC（轨道高度大约800 km）仪器偏差估计结果优于CHAMP（轨道高度大约400 km）的结果,原因为：对于不同轨道高度LEO GPS仪器偏差估计,其较高轨道高度的电离层球对称假设影响较小. 相似文献
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Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using observations and high-resolution modeling on large domains are discussed. 相似文献
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Biases in shortwave cloud radiative forcing (SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary layer processes are investigated in the atmospheric model GAMIL2, entrainment at the top of the boundary layer and longwave radiative cooling at the top of stratocumulus clouds, in order to reduce biases and reveal the mechanisms underlying these processes. Our results show that including the entrainment process in the model can reduce negative SWCF biases in most tropical regions but increases positive SWCF biases in subtropical marine stratocumulus regions. This occurs because entrainment reduces the low-level cloud fraction and its cloud liquid water content by suppressing the vertical turbulent diffusion in the boundary layer and decreasing the relative humidity when warm and dry free atmosphere is entrained in the boundary layer. Longwave radiative cooling at the top of stratocumulus clouds can enhance turbulent diffusion within the stratocumulus-topped boundary layer. When combined with the entrainment process, longwave radiative cooling reduces the positive SWCF biases in subtropical marine stratocumulus regions that are observed using the entrainment process alone. The incorporation of these two boundary layer processes improves the simulated SWCF in tropical and subtropical regions in GAMIL2. 相似文献
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Analysis of the Pampa, Texas, multicell storms showed prestorm environmental conditions of a strong horizontal convergence
of moisture, mixing ratio 12 g/kg at the 850 mb level in the Texas Panhandle areas and strong winds with shear veering with
height. Rapid-scan satellite imagery showed that the clouds penetrated above the tropopause and cloud-top temperatures were
at least 4 to 9° C colder than the temperature of the tropopause. This formation and collapsing of high-mass-density overshooting
cloud tops above the tropopause is characteristic of tornadoes in the middle portion of the United States. 相似文献
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Clouds affect local surface UV irradiance, even if the horizontal distance from the radiation observation site amounts to several kilometers. In order to investigate this effect, which we call remote clouds effect, a 3-dimensional radiative transfer model is applied. Assuming the atmosphere is subdivided into a quadratic based sector and its surrounding, we quantify the influence of changing cloud coverage within this surrounding from 0% to 100% on surface UV irradiance at the sector center. To work out this remote clouds influence as a function of sector base size, we made some calculations for different sizes between 10 km × 10 km and 100 km × 100 km. It appears that in the case of small sectors (base size 20 km × 20 km) the remote clouds effect is highly variable: Depending on cloud structure, solar zenith angle and wavelength, the surface UV irradiance may be enhanced up to 15% as well as reduced by more than 50%. In contrast, for larger sectors it is always the case that enhancements become smaller by 5% if sector base size exceeds 60 km × 60 km. However, these values are upper estimates of the remote cloud effects and they are found only for special cloud structures. Since these structures might occur but cannot be regarded as typical, different satellite observed cloud formations (horizontal resolution about 1 km × 1 km) have also been investigated. For these more common cloud distributions we find remote cloud effects to be distinctly smaller than the corresponding upper estimates, e.g., for a sector with base size of 25 km × 25 km the surface UV irradiance error due to ignoring the actual remote clouds and replacing their influence with periodic horizontal boundary conditions is less than 3%, whereas the upper estimate of remote clouds effect would suggest an error close to 10%. 相似文献