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1.
西北太平洋是全球海雾最多的海域,但由于观测资料匮乏,对开阔大洋上海雾形成机理的个例研究很少。2019年9月12—14日,中国北极科考船“向阳红01号”在亲潮延伸体水域捕捉到一次海雾事件。主要利用船载观测数据,分析了海雾形成的物理过程。结果表明,这是一次温带气旋的暖锋和局地海洋锋(海面温度锋)共同影响下的海雾过程。伴随暖锋的偏南气流将暖湿空气向北输送,在亲潮延伸体区,海面空气增湿效应大于增温效应,导致相对湿度不断增加接近饱和。北上暖空气遇到较冷水域上空的冷空气团,向上爬升形成大范围锋面逆温;局地海洋锋强迫出大气边界层内的次级环流,其下沉支使该锋面逆温层底的高度进一步降低,有利于雾滴局限在近海面成雾,雾区出现于暖锋锋面过后局地海洋锋的冷水侧。这项研究明确了海雾形成过程中作为背景环流的大气暖锋与作为局地强迫项的海洋锋的贡献,可为海雾预报提供新的理论支撑。 相似文献
2.
2007年12月南京六次雨雾过程宏、微观结构演变特征 总被引：4，自引：1，他引：3
利用2007年冬季南京信息工程大学对雾的综合观测资料,包括能见度仪、雨滴谱仪、雾滴谱仪、宽范围颗粒粒径谱仪(WPS)观测资料,并结合地面常规气象观测资料和NCEP(National Centers for Environmental Prediction)再分析资料,分析2007年12月南京六次雨雾过程的宏、微观结构演变特征。结果显示:(1)南京2007年12月的六次雨雾过程主要是受天气系统的影响,以雨中雾为主,最低能见度均大于250 m。雨雾多出现在偏东气流的作用下,南京地区先发生弱降水,空气近饱和,随后受到来自北方的弱冷空气影响,水汽凝结,雾形成。(2)雨雾发生前贴地层多有逆温,雨雾过程中2 m高度与地表温度差由正转为负,逆温消失。但900 hPa以下,雨雾发生前和过程中,都少有逆温层,雨雾结束后均无逆温结构。雨雾前中低层有云,云状为高积云Ac或高层云As及层积云Sc或碎雨云Fn,低云高0.3～2.5 km,雨雾过程中,600 hPa以下都是饱和层,多伴有Fn,低云高度明显下降,雨雾过后,近饱和层仍然有可能存在。雨雾前900 hPa附近有明显的风切变。(3)雨雾形成初期,大粒子(粒子直径D≥10 μm)和小粒子(1 μm相似文献
3.
Simultaneous wind and droplet measurements have been made in three cloudy boundary layers using tethered balloon-borne instrumentation. The types of clouds studied ranged from small thin cumulus to medium cumulus (non precipitating) and stratocumulus formed by the spreading out (shelving) of cumulus. Available synoptic data have been analysed in order to investigate the relative importance of advection and subsidence over scales of order 100 km in the local boundary-layer development. The factors which influenced the extent of cloud cover are also discussed together with the effect of condensation on vertical air motions in the upper half of the boundary layer. Within individual clouds, horizontal variations in droplet spectra were observed to occur over distances of a few metres being related to both position within cloud and height above local cloud base. These results highlight difficulties which may arise in the interpretation of droplet data of horizontal resolution greater than a few metres. Different clouds sampled on the same day showed different amounts of variability in the droplet parameters but no systematic differences between the various case studies were detected. 相似文献
4.
714KaDP型云雾雷达具备30km内的低云和雾监测和预警能力,是专门针对影响机场运行的低云低能见度(两低)天气研制的国内首部毫米波脉冲多普勒雷达。昆明长水机场的试验验证表明,通过提供的云雾基本产品和二次产品,实现了机场两低天气生消演变的有效探测,显著提升了对严重影响空管正常运行的两低天气的监测预警能力。雷达探测发现,714KaDP型云雾雷达对机场及周边低云和雾的生消、演变、移动有着非常敏锐的捕捉能力,特别适合具有明显平流特征的低云和雾(锋面雾、低云平流、辐射雾平流等)的监测和预警,本文介绍了雷达特性、安装位置以及对锋面雾、平流低云和辐射平流混合雾过程的雷达产品分析方法,为提前预警、实时跟踪和云消雾散二次放行决策提供支撑提供了参考。 相似文献
5.
庐山云雾观测站2015年重新开始观测试验。利用2015年11月—2018年2月庐山云雾试验站观测的云物理资料和九江站的雷达资料,统计研究了庐山云雾及降水的日、季节变化和宏微观物理特征。结果表明,庐山强降水多发生在夏季,降水强度超过100 mm/h,而云雾天多发生在秋冬春季,最高云和雾天数达25 d/月,最低能见度仅20 m,东北风有利于水汽的冷却凝结。云雾辐射影响下的日最低温度出现在09时前后,即云雾消散前。利用雷达资料对降水分类,庐山秋冬季层状云、积层混合云和对流云降水分别占29%、44%和27%,春夏季的对流云和积层混合云降水分别占83%和17%。与城市降水和雾相比,庐山降水的中、小雨滴多,云雾滴谱的数浓度较低,双峰结构显著,且谱较宽。随着云内降水量级的增大,雨滴的数浓度和尺度不断增加,更易于启动碰并机制,使小于11 μm和大于30 μm云雾滴减少,导致11 μm的峰值更为显著。降雪期间的小云雾滴较为丰富,固态降水更容易通过凇附过程消耗大的过冷云滴。 相似文献
6.
In this study, a one-dimensional ensemble-average model is used to simulatethe Atlantic Stratocumulus Transition Experiment firstLagrangian, where the same airmass was followed from the subtropical high pressure region en route towards the trade wind region. The airmass experiences increasing sea-surface temperature and achange from subsidence to weak ascent on its way south. Thiscauses the marine boundary layer (MBL)to grow and the cloud deck to change from a solid stratocumulus deck tomore broken stratocumulus clouds with cumulus cloudsdeveloping beneath, and reaching up into the stratocumulus clouds.A control run is analyzed and compared in detail with theobservations. Both a statistical evaluation and a more subjective evaluation are performed, where both establish confidencein the model performance. The model captures the MBL growth and the cloudliquid water, as well as the drizzle flux, is well predicted by the model.A sensitivity study was performed with the objective of examining theMBL and the cloud response to external and internal 'forces'.The results show that, if drizzle formation is not allowed,unrealistically high cloud liquid water mixing ratios are predicted. Even though the drizzle flux is very small, it is still important for the water budget of the MBL and for the boundary-layer dynamics.We also found that the sea-surface temperature increase is more important for the increasing cloud top height than the synoptic-scale divergence fields. However, the synoptic-scale subsidence is crucial during the first day, when the sea-surface temperature was constant, in keepingthe cloud top at a constant height. Drizzle evaporation below the cloud base seems to be important for below-cloud condensation. The drizzle predictions are significantly altered when the prescribed cloud droplet and/or drizzle drop numbers are altered. 相似文献
7.
Michael Tjernström 《Boundary-Layer Meteorology》1988,44(3):207-230
A higher order closure mesoscale model is used to study the influence of different surface properties on stratiform boundary-layer clouds. The model is hydrostatic, has a terrain-following coordinate system and a sub-grid scale condensation scheme. It also has a radiation parameterisation for shortwave and longwave radiation in order to calculate radiative cooling/heating. The simulations show the effects on a cloud field when cool or cold air is advected over warm water, the possible influence of local circulation systems on cloud fields in situations with weak synoptic forcing and the influence on a cloud field by growing internal boundary layers. Some of the results are compared with simpler physical models, and limitations in those are demonstrated. 相似文献
8.
北京及周边地区2004年8、9月层积云结构及谱分析飞机探测研究 总被引：10，自引：4，他引：6
2004年8～9月利用机载粒子测量系统 (Particle Measuring System, 简称PMS) 对我国北京及周边地区的三次锋面云系进行了探测, 本文分析了三次降水性层积云中各种粒子的垂直、水平和谱分布。结果表明, 三次降水云系基本是冷锋或者暖锋系统下形成的层积混合云系。云内以直径5～9 μm、200 μm和400～1000 μm的云和降水粒子为主。9月14日暖锋层积云系的粒子浓度最大, FSSP-100 (前向散射粒子谱探头)、 GA2(二维灰度云粒子图像探头)、 GB2(二维灰度降水粒子探头)分别探测的最大粒子浓度为318.97 cm-3、0.03 cm-3、0.0065 cm-3。8月12日和8月15日的冷锋层积云系有多个干层。GA2探测的平均浓度谱基本为单峰分布, 并找出了合适的拟合函数。冷锋层积云系的负温云层中存在着相同浓度量级的过冷云水和雨水、霰粒、柱状和针状冰晶, 过冷水含量可达到0.26 g/m3, 暖锋云系中则以霰粒、结淞粒子和冰雪晶聚合体为主, 也存在少量柱状、针状冰晶和过冷水滴。与我国北方地区13架次飞行探测结果比较, 北京及周边地区2003年8月15日、2004年8月12日和9月14日层积云0 ℃层以上的冰雪晶粒子直径最大, 浓度居中, 过冷水含量因云系结构不同而变化较大。 相似文献
9.
10.
Frédéric Parol Jacques Descloitres Yves Fouquart 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):888-908
The POLDER instrument is devoted to global observations of the solar radiation reflected by the Earth–atmosphere system. The airborne version of the instrument was operated during the ACE‐2 experiment, more particularly as a component of the CLOUDYCOLUMN project of ACE‐2 that was conducted in summer 1997 over the subtropical northeastern Atlantic ocean. CLOUDYCOLUMN is a coordinated project specifically dedicated to the study of the indirect effect of aerosols. In this context, the airborne POLDER was assigned to remote measurements of the cloud optical and radiative properties, namely the cloud optical thickness and the cloud albedo. This paper presents the retrievals of those 2 cloud parameters for 2 golden days of the campaign 26 June and 9 July 1997. Coincident spaceborne ADEOS‐POLDER data from 2 orbits over the ACE‐2 area on 26 June are also analyzed. 26 June corresponds to a pure air marine case and 9 July is a polluted air case. The multidirectional viewing capability of airborne POLDER is here demonstrated to be very useful to estimate the effective radius of cloud droplet that characterizes the observed stratocumulus clouds. A 12 μm cloud droplet size distribution appears to be a suitable cloud droplet model in the pure marine cloud case study. For the polluted case the mean retrieved effective droplet radius is of the order of 6–10 μm. This only preliminary result can be interpreted as a confirmation of the indirect effect of aerosols. It is consistent with the significant increase in droplet concentration measured in polluted marine clouds compared to clean marine ones. Further investigations and comparisons to in‐situ microphysical measurements are now needed. 相似文献
11.
Formation,Evolution, and Dissipation of Coastal Sea Fog 总被引：5，自引：2，他引：3
Evolution of sea fog has been investigated using three-dimensional Mesoscale Model 5 (MM5) simulations. The study focused
on widespread fog-cloud layers advected along the California coastal waters during 14–16 April 1999. According to analysis
of the simulated trajectories, the intensity of air mass modification during this advection significantly depended on whether
there were clouds along the trajectories and whether the modification took place over the land or ocean. The air mass, with
its trajectory endpoint in the area where the fog was observed and simulated, gradually cooled despite the gradual increase
in sea-surface temperature along the trajectory. Modelling results identified cloud-top cooling as a major determinant of
marine-layer cooling and turbulence generation along the trajectories. Scale analysis showed that the radiative cooling term
in the thermodynamic equation overpowered surface sensible and latent heat fluxes, and entrainment terms in cases of the transformation
of marine clouds along the trajectories. Transformation of air masses along the trajectories without clouds and associated
cloud-top cooling led to fog-free conditions at the endpoints of the trajectories over the ocean. The final impact on cloud-fog
transition was determined by the interaction of synoptic and boundary-layer processes. Dissipation of sea fog was a consequence
of a complex interplay between advection, synoptic evolution, and development of local circulations. Movement of the high-pressure
system over land induced weakening of the along-shore advection and synoptic-pressure gradients, and allowed development of
offshore flows that facilitated fog dissipation. 相似文献
12.
13.
利用辽宁阜新国家站(121.7458°E,42.0672°N)的毫米波云雷达(8 mm)和微雨雷达(12.5 mm)对2020年8月12-13日东北冷涡影响下的一次降水过程进行了观测,分析了云降水的垂直结构特征并探讨了降水机制。结果表明：本次过程中,云水平方向发展不均匀,以层状云和层积混合云为主,云内有时还嵌有对流泡。云降水阶段性变化明显,先后出现了层状云降水、层积混合云降水和对流云降水。层状云降水和层积混合云降水均表现出明显的亮带特征,但层积混合云降水的雷达回波强度、回波顶高和降水强度明显大于层状云降水。对流云降水的雷达回波会因强降水而产生明显衰减,因此回波顶高不能表示出实际的云顶情况。层状云降水阶段,云雷达反射率随高度降低增长缓慢,雨滴在下落过程中受蒸发和碰并的共同作用,反射率降低。与层状云降水相比,层积混合云降水的碰并效应强,且由于前期降水对近地面的增湿作用,使云下蒸发弱。对流云降水阶段,反射率的增长主要发生在冰水混合层,有利于大滴的产生,拓宽了云滴谱,提高了碰并效率。 相似文献
14.
The radiative feedback from clouds remains the largest source of variation in climate sensitivity amongst general circulation
models (GCMs). A cloud clustering methodology is applied to six contemporary GCMs in order to provide a detailed intercomparison
and evaluation of the simulated cloud regimes. By analysing GCMs in the context of cloud regimes, processes related to particular
cloud types are more likely to be evaluated. In this paper, the mean properties of the global cloud regimes are evaluated,
and the cloud response to climate change is analysed in the cloud-regime framework. Most of the GCMs are able to simulate
the principal cloud regimes, however none of the models analysed have a good representation of trade cumulus in the tropics.
The models also share a difficulty in simulating those regimes with cloud tops at mid-levels, with only ECHAM5 producing a
regime of tropical cumulus congestus. Optically thick, high top cloud in the extra-tropics, typically associated with the
passage of frontal systems, is simulated considerably too frequently in the ECHAM5 model. This appears to be a result of the
cloud type persisting in the model after the meteorological conditions associated with frontal systems have ceased. The simulation
of stratocumulus in the MIROC GCMs is too extensive, resulting in the tropics being too reflective. Most of the global-mean
cloud response to doubled CO2 in the GCMs is found to be a result of changes in the cloud radiative properties of the regimes, rather than changes in the
relative frequency of occurrence (RFO) of the regimes. Most of the variance in the global cloud response between the GCMs
arises from differences in the radiative response of frontal cloud in the extra-tropics and from stratocumulus cloud in the
tropics. This variance is largely the result of excessively high RFOs of specific regimes in particular GCMs. It is shown
here that evaluation and subsequent improvement in the simulation of the present-day regime properties has the potential to
reduce the variance of the global cloud response, and hence climate sensitivity, amongst GCMs. For the ensemble of models
considered in this study, the use of observations of the mean present-day cloud regimes suggests a potential reduction in
the range of climate sensitivity of almost a third.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
对用液氮消过冷雾和冷云催化增雨作业的宏、微观条件进行比较，找出其异同点，并根据消冷雾作业所出现的物理响应推演冷云催化后应出现的结果，以弥补飞机云中催化后缺少直接观测资料的缺陷，进而对液氮（LN）增雨效果进行探讨。 相似文献
16.
The First Observed Cloud Echoes and Microphysical Parameter Retrievals by China's 94-GHz Cloud Radar 总被引：1，自引：0，他引：1 
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下载免费PDF全文 WU Juxiu WEI Ming HANG Xin ZHOU Jie ZHANG Peichang LI Nan 《Acta Meteorologica Sinica》2014,28(3):430-443
By using the cloud echoes first successfully observed by China's indigenous 94-GHz SKY cloud radar, the macrostructure and microphysical properties of drizzling stratocumulus clouds in Anhui Province on 8 June2013 are analyzed, and the detection capability of this cloud radar is discussed. The results are as follows.(1) The cloud radar is able to observe the time-varying macroscopic and microphysical parameters of clouds,and it can reveal the microscopic structure and small-scale changes of clouds.(2) The velocity spectral width of cloud droplets is small, but the spectral width of the cloud containing both cloud droplets and drizzle is large. When the spectral width is more than 0.4 m s-1, the radar reflectivity factor is larger(over –10 dBZ).(3) The radar's sensitivity is comparatively higher because the minimum radar reflectivity factor is about–35 dBZ in this experiment, which exceeds the threshold for detecting the linear depolarized ratio(LDR) of stratocumulus(commonly –11 to –14 dBZ; decreases with increasing turbulence).(4) After distinguishing of cloud droplets from drizzle, cloud liquid water content and particle effective radius are retrieved. The liquid water content of drizzle is lower than that of cloud droplets at the same radar reflectivity factor. 相似文献
17.
Yoo-Jun Kim Byung-Gon Kim Mark Miller Qilong Min Chang-Keun Song 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(3):283-293
Modification of cloud microphysics and cloud albedo by cloud-active aerosol is generally identified and accepted, but the nature and magnitude of aerosol-cloud interactions are vaguely understood and thought to include a myriad of processes that vary regionally and confound the application of simple physical models of cloud-aerosol sensitivity. This paper presents observations demonstrating that cloud top stability through its regulation of mixing and vertical development is one of the critical mechanisms that regulate cloud response to cloud-active aerosol in some cloud systems. Strong above-cloud inversions are shown to buffer marine stratocumulus from the effects of mixing with drier, warmer inversion air. This buffering reduces the variability of the cloud liquid water path (LWP) and enables the clouds to remain nearly adiabatic. While weaker above-cloud inversions in continental stratocumulus promote variability in the LWP and sub-adiabatic LWPs, stronger inversions in marine stratocumulus enables a relatively adiabatic existence that increases the relationship of cloud microphysical alteration to cloud-active aerosol. This study has important implications for Geoengineering in that it demonstrates that cloud systems overlain by strong thermal inversions are more likely to respond predictably to intentional manipulation of the in-cloud concentration of cloud-active aerosol. 相似文献
18.
由于缺乏海上现场观测,对天气尺度扰动下,海表面温度锋 (海洋锋) 对海洋大气边界层 (MABL) 垂直结构和MABL内海洋性低云 (marine stratus) 的影响研究较少。2014年4月12日,中国海洋大学东方红2号科学考察船在黑潮延伸体海区的海洋锋附近捕捉到一次层积云的迅速发展。在比较稳定的天气形势下,由暖水侧向北穿越海洋锋时,云底和云顶高度升高,云区范围迅速扩大。本文利用多种大气-海洋联合观测数据,结合卫星观测和再分析资料,对此次层积云迅速发展的机理进行了综合分析。结果表明,在海上低压后部西北风控制下,在海洋锋的暖水侧 (下风方) 形成热通量大值中心和低压槽,有助于高空西风动量下传,进而又使得海气界面热通量增加,这种正反馈效应为MABL内混合层厚度加大和云底/顶高度在海洋锋的下风方升高提供有利背景条件。4月12日09:00~12:00(协调世界时),来自日本本州岛陆地的低空暖平流到达该热通量中心上空,暖平流与热通量中心的共同作用,导致该时段近海面暖中心强度异常增加,MABL中静力不稳定层加深和低压槽发展,综合作用的结果使得混合层厚度明显加深,云底高度升高,云区迅速发展。本研究有助于理解在复杂大气背景扰动下MABL对海洋强迫的响应机理。 相似文献
19.
Summary During the field experiment FRONTEX 1989 a shallow cold front with a fog field behind its leading edge was observed over the North Sea. The fog field was about 70 km wide, 160 m deep at the front side and 400 m deep at the rear side and was capped by a strong frontal inversion. With increasing height of the inversion the fog broke up into cumulus clouds. The horizontal temperature gradient was largest at 500 m with 9 K/100 km. The observed segment of the front was situated near the col of a geostrophic deformation field with vanishing cross-front wind but non-vanishing cross-front confluence. The front moved at a rate of 5 m/s. It exhibits characteristics of a gravity current which propagates into a stably stratified environment.The physical processes leading to the observed frontal structure and motion are elucidated by experiments with a two-dimensional numerical model. The charateristics of the observed front can be reproduced if both, geostrophic forcing and boundary-layer processes, such as air-sea temperature difference, moisture content and cloud radiational cooling are taken into account. The development of the front under altered conditions is studied by the comparison of different simulations. The reason for the movement of the front is discussed refering to the mechanisms of geostrophic forcing and the forcing by surface friction. The analysis of the forces acting on the cold air mass shows that the Coriolis force is important at some distance behind the frontal head, but has little effect on the processes at the frontal head.With 13 Figures 相似文献
20.
Differences in the radiative feedback from clouds account for much of the variation in climate sensitivity amongst General
Circulation Models (GCMs). Therefore metrics of model performance which are demonstrated to be relevant to the cloud response
to climate change form an important contribution to the overall evaluation of GCMs. In this paper we demonstrate an alternative
method for assigning model data to observed cloud regimes obtained from clustering histograms of cloud amount in joint cloud
optical depth—cloud top pressure classes. The method removes some of the subjectivity that exists in previous GCM cloud clustering
studies. We apply the method to ten GCMs submitted to the Cloud Feedback Model Intercomparison Project (CFMIP), evaluate the
simulated cloud regimes and analyse the climate change response in the context of these regimes. We also propose two cloud
regime metrics, one of which is specifically targeted at assessing GCMs for the purpose of obtaining the global cloud radiative
response to climate change. Most of the global variance in the cloud radiative response between GCMs is due to low clouds,
with 47% arising from the stratocumulus regime and 18% due to the regime characterised by clouds undergoing transition from
stratocumulus to cumulus. This result is found to be dominated by two structurally similar GCMs. The shallow cumulus regime,
though widespread, has a smaller contribution and reduces the variance. For the stratocumulus and transition regimes, part
of the variance results from a large model spread in the radiative properties of the regime in the control simulation. Comparison
with observations reveals a systematic bias for both the stratocumulus and transition regimes to be overly reflective. If
this bias was corrected with all other aspects of the response unchanged, the variance in the low cloud response would reduce.
The response of some regimes with high cloud tops differ between the GCMs. These regimes are simulated too infrequently in
a few of the models. If the frequency in the control simulation were more realistic and changes within the regimes were unaltered,
the variance in the cloud radiative response from high-top clouds would increase. As a result, use of observations of the
mean present-day cloud regimes suggests that whilst improvements in the simulation of the cloud regimes would impact the climate
sensitivity, the inter-model variance may not reduce. When the cloud regime metric is calculated for the GCMs analysed here,
only one model is on average consistent with observations within their uncertainty (and even this model is not consistent
with the observations for all regimes), indicating scope for improvement in the simulation of cloud regimes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献