共查询到20条相似文献，搜索用时 46 毫秒
1.
Prof. K. N. Liou J. L. Lee S. C. Ou Q. Fu Y. Takano 《Meteorology and Atmospheric Physics》1991,46(1-2):41-50
Summary Parameterization programs for cloud microphyscs and radiative transfer involving ice clouds have been developed in terms of the mean effective size and ice water path. The mean effective size appears to be adequate in representing the ice crystal size distribution for radiative parameterizations. For a given ice water path, smaller mean effective sizes reflect more solar radiation, emit more IR radiation and enhance net radiative heating/cooling at the cloud top and bottom than larger sizes. The presence of small ice crystals may generate steeper lapse rates in clouds. A 3-D global cloud model that prescribes the horizontal wind fields in a 24 hour period is used to investigate the sensitivity of the mean effective size of ice crystals on the simulation of radiative heating, temperature, cloud cover and ice water content. A variation in the mean effective size from 75 to 50 m in a 24 hour prediction on simulation generates more cooling above the high cloud top and a decrease of temperature. These results lead to an increase of high cloud cover in some latitudes by as much as 4% and, at the same time, a decrease of middle cloud cover by 3–4% in latitudes between 60°S and 60°N.With 7 Figures 相似文献
2.
3.
图割模型在卫星云图云检测中的应用 总被引：2，自引：0，他引：2
提出一种基于图割模型的卫星云图云检测方法。利用FY-2C卫星云图的长波红外通道和可见光通道的云图提取了10个灰度特征和80个Gabor纹理特征,再用主成分分析方法（principal component analysis,PCA）降维到9个主成分。将这9个主成分构成的特征作为每个像素的特征,建立相似度矩阵,再利用改进的NormalizedCuts模型进行分割,将云图分成了晴空区域和有云区域。与地面观测结果相比,平均一致率达到86．51％,表明将Gabor纹理特征和灰度特征相结合并利用改进的Normalized Cuts模型对卫星云图云检测有比较好的效果。 相似文献
4.
ATHANASIOS NENES STEVEN GHAN HAYDER ABDUL&#;RAZZAK PATRICK Y. CHUANG JOHN H. SEINFELD 《Tellus. Series B, Chemical and physical meteorology》2001,53(2):133-149
Under certain conditions mass transfer limitations on the growth of cloud condensation nuclei (CCN) may have a significant impact on the number of droplets that can form in a cloud. The assumption that particles remain in equilibrium until activated may therefore not always be appropriate for aerosol populations existing in the atmosphere. This work identifies three mechanisms that lead to kinetic limitations, the effect of which on activated cloud droplet number and cloud albedo is assessed using a one‐dimensional cloud parcel model with detailed microphysics for a variety of aerosol size distributions and updraft velocities. In assessing the effect of kinetic limitations, we have assumed as cloud droplets not only those that are strictly activated (as dictated by classical Köhler theory), but also unactivated drops large enough to have an impact on cloud optical properties. Aerosol number concentration is found to be the key parameter that controls the significance of kinetic effects. Simulations indicate that the equilibrium assumption leads to an overprediction of droplet number by less than 10% for marine aerosol; this overprediction can exceed 40% for urban type aerosol. Overall, the effect of kinetic limitations on cloud albedo can be considered important when equilibrium activation theory consistently overpredicts droplet number by more than 10%. The maximum change in cloud albedo as a result of kinetic limitations is less than 0.005 for cases such as marine aerosol; however albedo differences can exceed 0.1 under more polluted conditions. Kinetic limitations are thus not expected to be climatically significant on a global scale, but can regionally have a large impact on cloud albedo. 相似文献
5.
地面观测是大气探测中的一个重要组成部分。地面观测资料又是短期天气预报与短期气候预测的基础。资料的正确与否，直接影响到天气预报的准确程度。云的观测是地面目测项目的核心。云的发展变化是大气中各种物理量场的综合表征。因此，云状、云高的正确辨别判断是十分重要的。 相似文献
6.
Junghwa Lee Yign Noh Siegfried Raasch Theres Riechelmann Lian-Ping Wang 《Meteorology and Atmospheric Physics》2014,124(1-2):1-21
A precipitating convective cloud is simulated successfully using the Lagrangian cloud model, in which the flow field is simulated by large eddy simulation and the droplets are treated as Lagrangian particles, and the results are analyzed to investigate precipitation initiation and to examine the parameterization of cloud microphysics. It is found that raindrops appear initially near the cloud top, in which strong turbulence and broadened droplet spectrum are induced by the entrainment of dry air, but high liquid–water mixing ratio is maintained within cloud parts because of insufficient mixing. Statistical analysis of the downward vertical velocity of a droplet W reveals that the transition from cloud droplets to raindrops occurs in the range 20 μm < r < 100 μm, while the variation of W depends on turbulence as well as the droplet radius r. The general pattern of the raindrop size distribution is found to be consistent with the Marshall–Palmer distribution. The precipitation flux can be underestimated substantially, if the terminal velocity $w_{\text{s}}$ is used instead of W, but it is not sensitive to the choice of the critical droplet radius dividing cloud drops and raindrops. It is also found that precipitation starts earlier and becomes stronger if the effect of turbulence is included in the collection kernel. 相似文献
7.
A precipitation enhancement operation using an aircraft was conducted from 1415 to 1549 LST 14 March 2000 in Shaanxi Province. The NOAA-14 satellite data received at 1535 LST soon after the cloud seeding shows that a vivid cloud track appears on the satellite image. The length, average width and maximum width of the cloud track are 301 kin, 8.3 and 11 kin, respectively. Using a three-dimensional numerical model of transport and diffusion of seeding material within stratiform clouds, the spatial concentration distribution characteristics of seeding material at different times, especially at the satellite receiving time,are simulated. The model results at the satellite receiving time axe compared with the features of the cloud track. The transported position of the cloud seeding material coincides with the position of the track. The width, shape and extent of diffusion of the cloud seeding material are similar to that of the cloud track.The spatial variation of width is consistent with that of the track. The simulated length of each segment of the seeding line accords with the length of every segment of the track. Each segment of the cloud track corresponds to the transport and diffusion of each segment of the seeding line. These results suggest that the cloud track is the direct physical reflection of cloud seeding at the cloud top. The comparison demonstrates that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulated results are sound and trustworthy. The area, volume, width, depth, and lateral diffusive rate corresponding to concentrations 1, 4, and 10 L^-1 are simulated in order to understand the variations of influencing range. 相似文献
8.
河套低压降水性层状云的云雨特征 总被引：4，自引：0，他引：4
1963—1978年,使用飞机,对河套低压的降水性层状云作了21架次的云雾物理探测,结合天气分析与统计计算发现: 1.系统各部位层状云云状不一,对应云层的宏观特征及降水强度也有差别。 2.系统的平均冰质点浓度在 10~(-2)个/升—10~2个/升之间,其各部位浓度、浓度的垂直分布及晶形出现频数都不一样。液态含水量在 0—0.77克/米~3之间,平均为 0.122克/米~3,各部位液态含水量虽有差别,但都是正温层较大,负温层较小,到-10℃层以上已很少见液态水存在。 3.系统层状云的降水强度和系统部位、云厚、正温层厚度、云底温度以及平均液态水含量相关较好,而和云顶温度、冰云厚度及冰质点平均浓度相关不好,可用—多元迴归方程来拟合 相似文献
9.
毫米波雷达云回波的自动分类技术研究 总被引：1，自引：0，他引：1
毫米波雷达在云探测方面比厘米波天气雷达和激光雷达具有显著优势,可获得更多的云粒子信息,是研究云特性的主要遥感探测设备。为了开展对毫米波雷达探测的云回波进行自动分类的研究,利用161次云回波的个例数据,统计得到了卷云、高层云、高积云、层云、层积云和积云6类云型的特征量和其他参量的数值范围,利用分级的多参数阈值判别方法,达到了自动分类的目标,通过与人工分类的初步验证,两种分类结果的一致性达到84%,其中,层云和积云的识别一致较低的原因在于样本数据有限,仅有6次层云和8次积云的个例样本数据。通过更多样本的处理,提取的特征参量更可靠,自动分类的准确率会得到提高,以便将基于毫米波雷达的云分类技术应用于将来的云观测自动化业务。 相似文献
10.
星载双频云雷达的云微物理参数反演算法研究 总被引：2，自引：1，他引：1
使用星载雷达模拟器输出的模拟数据,为星载双频云雷达选择了最佳的频点组合,并开展了双频联合反演云微物理参数的算法研究。结果表明:（1）在位于大气窗口的6组频点组合中,94/220 GHz的组合对滴谱参数的微小变化较为敏感,有利于进行双频的联合反演。综合考虑不同频点的探测能力、衰减以及工业部门的制造水平后,认为94/220 GHz可以作为未来星载双频测云雷达的探测频点。（2）双频反演中最核心的双波长比（DWR）和体积中值直径（D0）的关系与冰晶粒子密度相关。当密度随着粒子直径变化时,DWR随着D0单调递增,当粒子密度固定不变时,DWR-D0曲线可能会出现非单调变化,从而使得固定密度时的反演比变密度时更加复杂。（3）后向迭代的双频反演算法同样适用于94/220 GHz进行云微物理参数的反演,并且对模拟数据的反演精度较高。此外,反演精度受到系统噪声以及定标精度的影响,为了满足反演精度的要求,系统噪声和定标误差应该控制在1 dBz以内。 相似文献
11.
Presented are the results of radar investigations of cloud merger during their natural cycle of development and after the seeding. The observations were carried out in the southwest of the Kingdom of Saudi Arabia in 2008. It is revealed that the merging was observed under conditions of very unstable atmosphere, when the convective available potential energy exceeded 3000 J/kg. The cloud merger impacts significantly their development. The most considerable changes due to the cloud merging were observed for the cloud mass and precipitation flow increased as a result of this process by two or three times. It is discovered that the impact of the merger of clouds on their characteristics exceeds significantly the effect of seeding carried out for the feeder clouds. 相似文献
12.
Environmental aspects of cloud seeding 总被引：1，自引：0，他引：1
The estimates are presented of the possible level of environmental pollution with reagents resulting from precipitation modification by cloud seeding. It is demonstrated that the amount of reagents (crystallizing reagents based on silver iodide (AgI), cooling reagents, and powder reagents) injected to the clouds does not exceed the level of inflow of these chemicals to the atmosphere from natural and anthropogenic sources. These data and the data on the pollution level in the areas where AgI is actively used, allow stating the extremely low impact of cloud seeding on the environmental pollution. No change in the precipitation regime was detected in the regions adjoining the areas where weather modification experiments on the meteorological protection of megalopolises were conducted. 相似文献
13.
F. H. Ludlam 《Meteorology and Atmospheric Physics》1955,8(3):283-292
Summary It is suggested that a theory of cloud seeding needs to be developed before seeding experiments can be properly planned and assessed. This theory will arise from improved knowledge of cloud processes gained by the study of natural clouds. Some techniques used in observing shower clouds in Sweden are described, and some preliminary results mentioned.
With 3 Figures. 相似文献
Zusammenfassung Es wird die Ansicht vertreten, daß eine Theorie des Cloud seeding entwickelt werden muß, bevor die diesbezüglichen Experimente in vorteilhafter Weise geplant und ihr Effekt abgeschätzt werden können. Diese Theorie hat sich aus einer Verbesserung unserer Kenntnisse über die Vorgänge in den Wolken durch die Ausführung entsprechender Beobachtungen in der Natur zu ergeben. Einige Verfahren, welche bei der Beobachtung von Schauerwolken in Schweden angewendet wurden, werden beschrieben und einige vorläufige Ergebnisse werden mitgeteilt.
Résumé La nécessité de développer une théorie de l'ensemencement des nuages avant que de pouvoir projeter et analyser de telles experiences est démontrée. Cette théorie se déduira d'une connaissance améliorée de la physique des nuages, acquise par l'observation directe. Quelques procédures employées, au Suède, pour l'observation des nuages d'averses sont décrites et quelques résultats préliminaires sont mentionnés.
With 3 Figures. 相似文献
14.
利用2008年4—7月、2009年5—8月和2011年5—9月黄山光明顶的云滴谱观测资料,对离散度和体积平均半径之间的关系进行了深入的分析和讨论。结果表明,随着体积平均半径的增大,离散度与体积平均半径之间的相关从正变成负,主要与活化、凝结、蒸发和去活化有关,与以往研究一致。在此基础上,进一步发现负相关比较弱,主要与碰并过程有关。当云雨自动转化阈值函数增大时,碰并增强,离散度与体积平均半径之间的相关性由负转正,且正相关性逐渐增强。碰并导致的正相关削弱了凝结和蒸发导致的负相关。此外,尽管云滴谱出现了双峰谱,但第一档强度(第一档浓度除以总的浓度)仍然可以很好地区分正负相关性。 相似文献
15.
Conventional power plants are prolific sources of cloudnucleating particles. Consequently clouds forming in air influenced by such emissions contain higher concentrations of cloud droplets than would prevail in clean conditions; optical properties of clouds are thereby modified, causing them to reflect more sunlight and transmit less. That has obvious consequences for climate physics, but it may also be relevant for mesoscale processes since quite substantial energy changes are involved. Ships constitute isolated sources in an environment that is often quite clean, and when low thin cloud layers are present, ships delineate their courses in satellite images by bright lines. These lines are caused by the above-mentioned increase in reflectance, providing, on a scale of tens to hundreds of kilometers, a realization of an effect which on a climatic scale cannot be directly observed (but which is likely to be comparable in magnitude to the CO2 effect, but oppositely directed). 相似文献
16.
Keith D. Williams Catherine A. Senior Anthony Slingo John F. B. Mitchell 《Climate Dynamics》2005,24(7-8):701-719
Most of the discrepancies in the climate sensitivity of general circulation models (GCMs) are believed to be due to differences in cloud radiative feedback. Analysis of cloud response to climate change in different ‘regimes’ may offer a more detailed understanding of how the cloud response differs between GCMs. In which case, evaluation of simulated cloud regimes against observations in terms of both their cloud properties and frequency of occurrence will assist in assessing confidence in the cloud response to climate change in a particular GCM. In this study, we use a clustering technique on International Satellite Cloud Climatology Project (ISCCP) data and on ISCCP-like diagnostics from two versions of the Hadley Centre GCM to identify cloud regimes over four different geographical regions. The two versions of the model are evaluated against observational data and their cloud response to climate change compared within the cloud regime framework. It is found that cloud clusters produced by the more recent GCM, HadSM4, compare more favourably with observations than HadSM3. In response to climate change, although the net cloud response over particular regions is often different in the two models, in several instances the same basic processes may be seen to be operating. Overall, both changes in the frequency of occurrence of cloud regimes and changes in the properties (optical depth and cloud top height) of the cloud regimes contribute to the cloud response to climate change. 相似文献
17.
毫米波雷达测云个例研究 总被引：9，自引：2，他引：7
云参数是影响降水和大气辐射过程的重要因子,但对云参数的遥感探测存在许多困难。利用35GHz的毫米波雷达进行云探测,并进行云参数反演研究,反演了云水含量、冰水含量和云滴有效直径的垂直廓线,得到了6类云况的垂直分布。结果表明：1）不同类型的云具有不同的云参数分布;2）在低于-15dBz的非降水云情况下,反演的云水含量及云滴有效直径较可靠;3）雷达探测的线性退偏振比因子,可以用于判别云中的过冷却水和冰晶,有助于更好了解云的宏微观特征。 相似文献
18.
Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements 
下载免费PDF全文
下载免费PDF全文 Lei Wei Mengyu Huang Rong Zhang Yuhuan Lü Tuanjie Hou Hengchi Lei Delong Zhao Wei Zhou Yuan Fu 《大气和海洋科学快报》2022,15(2):65-70
在积云中,大多数云粒子的直径在7到10微米之间,而在层云中,大多数云粒子的直径不超过2微米.云滴有效半径与云中行星边界层(PBL)及PBL上层的气溶胶数浓度(Na)呈负相关.在1500米以上的高液态水含量区域,云滴浓度(Nc)变化不大,Na含量降低.高雷达反射率对应于大的FCDP云粒子浓度和小的气溶胶粒子浓度.积云中的... 相似文献
19.
利用宁夏六盘山气象站2017年9月至2018年8月的Ka波段云雷达观测资料,统计分析了六盘山顶不同云的出现频率及宏观特征。结果表明：六盘山顶云出现频率最高值在7月,为61%,最低值在12月,为26%;按云层数划分,六盘山顶出现的云主要以1层云、2层云及3层云为主,相对总云的月平均出现频率分别为68%—86%、14%—27%及0.4%—4.8%;按云底高度及云层厚度划分,六盘山顶低云、中云、高云及直展云相对总云的月平均出现频率分别为29%—53%、14%—58%、6%—22%及2%—20%。云底高度在冬春季节高于夏秋季节,云顶高度在夏秋季节高于冬春季节,云层厚度为1.6—3.6 km,年变化特征与云顶高度类似。整体来看,春、夏、秋季云厚在白天大于夜间,冬季云厚在夜间大于白天,其中夏、秋季云厚日变化特征较为明显。 相似文献
20.
Vertical vorticity characteristics within individual cumulonimbus (Cb) cloud moving over complex terrain are investigated by cloud-resolving mesoscale model. Orography impact on vorticity is recognized by comparison of its characteristics within the storm moving over flat terrain under the same other conditions. In present study, two cases are considered: complex terrain case (referred to as CT case) and flat terrain case (referred to as FT case). A sensitivity study shows that orographical effects on vorticity are important. Main findings are:
- – For CT case vortices produced by convective tilting of horizontal vortices are closer to each other and more stretched in form owing to valley configuration. The vortex with positive vorticity is mainly stronger in magnitude compared to its negative counterpart.
- – Magnitudes of vorticities for CT case are greater at lowest levels and initial time intervals compared to those for FT case.
- – For CT case the vortices with opposite signs of vorticity produced by precipitation appear later than in FT case. Their duration is shorter and they are weaker in intensity compared to those formed within a cloud over flat terrain.
- – Complex terrain intensifies the splitting of simulated cloud.
Keywords: Mesoscale model; Vertical vorticity; Orography effects; Vortices 相似文献