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1.
2014—2017年四川地区开展了大范围云系观测科学试验。观测对象以盆地层状云系和积层混合云系为主,积状云(对流云)为辅。本文围绕试验目标、区域、观测要素、观测布局设计、观测方案设计、设备技术参数和典型个例等7个方面进行介绍,根据不同类型云系和降水变化特征,设计有针对性的观测方案,获得了不同类型云系和降水的多尺度连续性观测数据,为四川地区开展云和降水关系研究提供详实的综合型外场观测数据。层状降水云典型个例云高可达8km,云强核心部位的云雷达反射率可达28dBz,径向速度可达-6m·s~(-1),在0℃附近,反射率和退偏振因子LDR上有一条明显的亮带,表现为极大值,液态水主要集中于4.5km以下,随着雨强增大,液水含量增加,降水滴谱分布较窄,随着雨强减小,雨滴谱和速度谱变窄,但小粒径数浓度增加,说明对层状云雨强起主导作用的是雨滴直径,而不是数浓度;无降水层状云典型个例云层厚度为3.2km,云顶约为4km,云雷达反射率不超过0dBz,径向速度不超过5m·s~(-1),层状云内整层水汽含量和液水含量较为稳定,云中主要为液态粒子且粒径偏小、小粒径数浓度较高。 相似文献
2.
Shortwave cloud radiative forcing on major stratus cloud regions in AMIP-type simulations of CMIP3 and CMIP5 models 总被引：1，自引：0，他引：1
Cloud and its radiative effects are major sources of uncertainty that lead to simulation discrepancies in climate models. In this study, shortwave cloud radiative forcing (SWCF) over major stratus regions is evaluated for Atmospheric Models Intercomparison Project (AMIP)-type simulations of models involved in the third and fifth phases of the Coupled Models Intercomparison Project (CMIP3 and CMIP5). Over stratus regions, large deviations in both climatological mean and seasonal cycle of SWCF are found among the models. An ambient field sorted by dynamic (vertical motion) and thermodynamic (inversion strength or stability) regimes is constructed and used to measure the response of SWCF to large-scale controls. In marine boundary layer regions, despite both CMIP3 and CMIP5 models being able to capture well the center and range of occurrence frequency for the ambient field, most of the models fail to simulate the dependence of SWCF on boundary layer inversion and the insensitivity of SWCF to vertical motion. For eastern China, there are large differences even in the simulated ambient fields. Moreover, almost no model can reproduce intense SWCF in rising motion and high stability regimes. It is also found that models with a finer grid resolution have no evident superiority than their lower resolution versions. The uncertainties relating to SWCF in state-of-the-art models may limit their performance in IPCC experiments. 相似文献
3.
Ismail Gultepe 《Pure and Applied Geophysics》1995,144(2):321-350
Observations taken by aircraft and conventional platforms are used to investigate dynamical, physical, and radiative processes within a marine stratus cloud during the Canadian Atlantic Storms Program (CASP) II field project which took place over the east coast of Canada. Stratus which formed over the ocean on February 6, 1992 during the nighttime, is studied to analyze cloud top and base processes. The cloud was supercooled during the study period. Fluctuations and fluxes are calculated along constant flight altitude legs approximately 100 km long in space. The scales of structures larger than 5 km are removed from the analysis using a running average technique. Droplet spectra obtained by a forward scattering spectrometer probe (FSSP) were used in a 1-D radiative transfer model to calculate infrared (IR) fluxes and radiative heating rates. A heat conservation equation was used to estimate vertical air velocity (w
a
) within the cloud. The results showed that, because of a warmer ocean surface, significant moisture and heat were transferred from the ocean surface to the boundary layer. The cloud base was at about 400 m height and the top was at about 1.4 km.w
a
at the cloud base was estimated about 5 cm s–1. Strong IR cooling rate at the cloud top was calculated to be 75°C day–1 for a 100 m thick layer. Negative skewness inw
a
, suggesting narrow downdrafts, was likely due to radiative cooling at the cloud top. The entrainment velocity was found to be about 1.5 cm s–1 at cloud top. Mean moisture and heat fluxes within the cloud were estimated to be comparable to those from the ocean surface. Vertical air velocity at the cloud top due to radiative cooling was found to be about –40 cm s–1. 相似文献
4.
Cloud droplet chemistry is modelled for the first 150 m of rise in a wintertime, mid-latitude, marine stratus cloud using observations made at and near the Cape Grim Baseline Station as a source of input parameters. The emphasis in this work was to study the variation in droplet chemistry as a function of both droplet size and nucleus composition, with a particular focus on the way in which oxidation of dissolved sulfur dioxide varied.At 150 m above the condensation level, solute concentration as a function of droplet size was found to increase by as much as 2 to 3 orders of magnitude for only a factor of 2 increase in droplet radius, primarily as a consequence of the 1/r dependence in the droplet growth equation. This type of size dependence exists at all levels in the model cloud, and has a significant influence on oxidation rate of sulfur dioxide in droplets growing on sulfate nuclei, oxidation by ozone being favoured in the smallest droplets, but oxidation by hydrogen peroxide being favoured in the larger droplets. Oxidation by ozone is favoured at all sizes in droplets formed on sea-salt nuclei as a result of the initially high alkalinity of these droplets, and in the cloud overall is calculated to be the more important oxidation pathway. Although based on a simplified chemical scheme, these results suggest that both size-dependent and nucleus-dependent chemistry of cloud droplets may need to be considered explicitly in cloud modelling work.Volume-weighted mean pH values in the range 5 to 6 were predicted from sensitivity studies in which input variables were varied over reasonable ranges, in agreement with two sets of bulk cloud-water pH data obtained by aircraft near Cape Grim. 相似文献
5.
一次春季黄海海雾和东海层云关系的研究 总被引：2，自引：1，他引：1
结合多种观测数据和数值模拟结果对2011年3月12—13日的一次黄海海雾过程进行分析。观测数据分析表明:此次黄海海雾过程与东海层云之间存在密切的联系。地面高低压位置为水汽从层云区向北输送提供了有利的环流条件;黄海上空天气尺度下沉运动,加强了海洋大气边界层(MABL)层结的稳定性,MABL顶自南向北高度降低,有利于水汽在向北输送过程中不断向海面聚集;下沉导致的干层以及逆温层对海雾的发生发展起重要作用。模式结果进一步证明天气尺度下沉运动与MABL内的下沉在29°—30°N附近同位相叠加,使得该海区上空的下沉运动明显增强,边界层高度迅速下降。下沉可能会导致气块温度升高,云滴蒸发,来自层云区的水汽随流场向北向下输送逐渐接近冷海面凝结成雾,近海面水汽的平流输送使海雾进一步向北发展。本研究为海雾预报提供新的参考思路。 相似文献
6.
冬季层状云实施人工增雨作业可行性探讨 总被引：1，自引：1，他引：0
通过对百色市2004年至2007年冬季8次天气过程的22次层状云或层积混合云增雨作业个例分析,推断冬季对层状云或层积混合云进行增雨作业的环流背景、增雨潜力、催化可播高度和作业时机,得出百色市冬季对层状云或层积混合云开展增雨作业,只要存在有利的天气条件和持续长的时间,在降水云系的发展旺盛时期通过火箭将A gI焰剂播撒在-5℃~-10℃可播高度区域内,可收到良好的增雨作业效果结论。 相似文献
7.
8.
A stratus-sea fog event that occurred over the Yellow and East China Seas on 3 June 2011 is investigated using observa-tions and a numerical model, with a focus on the effects of background circulation and Sea Surface Temperature Front (SSTF) on the transition of stratus into sea fog. Southerly winds of a synoptic high-pressure circulation transport water vapor to the Yellow Sea, creating conditions favorable for sea fog/stratus formation. The subsidence from the high-pressure contributes to the temperature inversion at the top of the stratus. The SSTF forces a secondary circulation within the ABL (Atmospheric Boundary Layer), the sink-ing branch of which on the cold flank of SSTF helps lower the stratus layer further to reach the sea surface. The cooling effect over the cold sea surface counteracts the adiabatic warming induced by subsidence. The secondary circulation becomes weak and the fog patches are shrunk heavily with the smoothed SSTF. A conceptual model is proposed for the transition of stratus into sea fog over the Yellow and East China Seas. Finally, the analyses suggest that sea fog frequency will probably decrease due to the weakened SSTF and the reduced subsidence of secondary circulation under global warming. 相似文献
9.
It is essential to learn the temporal and spatial concentration distributions and variations of seeding agents in cloud seeding
of precipitation enhancement. A three–dimensional puff trajectory model incorporating a mesoscale nonhydrostatic model has
been formulated, and is applied to simulating the transporting and diffusive characteristics of multiple line sources of seeding
agents within super–cooled stratus. Several important factors are taken into consideration that affect the diffusion of seeding
materials such as effects of topography and vertical wind shear, temporal and spatial variation of seeding parameters and
wet deposition. The particles of seeding agents are assumed to be almost inert, they have no interaction with the particles
of the cloud or precipitation except that they are washed out by precipitation. The model validity is demonstrated by the
analyses and comparisons of model results, and checked by the sensitivity experiments of diffusive coefficients and atmospheric
stratification. The advantage of this model includes not only its exact reflection of heterogeneity and unsteadiness of background
fields, but also its good simulation of transport and diffusion of multiple line sources.
The horizontal diffusion rate and the horizontal transport distance have been proposed that they usually were difficult to
obtain in other models. In this simulation the horizontal diffusion rate is 0.82 m s−1 for average of one hour, and the horizontal average transport distance reaches 65 km after 1 h, which are closely related
to the background fields. 相似文献
10.
Dynamical Nighttime Fog/Low Stratus Detection Based on Meteosat SEVIRI Data: A Feasibility Study 总被引：1，自引：0，他引：1
Automated detection of fog and low stratus in nighttime satellite data has been implemented on the basis of numerous satellite
systems in past decades. Commonly, differences in small-droplet emissivities at 11μm and 3.9μm are utilized. With Meteosat SEVIRI, however, this method cannot be applied with a fixed threshold due to instrument design:
The 3.9μm band is exceptionally wide and overlaps with the 4μm CO2 absorption band. Therefore, the emissivity difference varies with the length of the slant atmospheric column between sensor
and object. To account for this effect, the new technique presented in this paper is based on the dynamical extraction of
emissivity difference thresholds for different satellite viewing zenith angles. In this way, varying concentrations of CO2 and column depths are accounted for. The new scheme is exemplified in a plausibility study and shown to provide reliable
results. 相似文献