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1.
The paper focuses on the redistribution of aerosol particles (APs) during the artificial nucleation and subsequent growth of ice crystals in a supercooled cloud. A significant number of the supercooled cloud droplets during icing periods (seeding agents: C3H8, CO2) did not freeze as was presumed prior to the experiment but instead evaporated. The net mass flux of water vapour from the evaporating droplets to the nucleating ice crystals (Bergeron–Findeisen mechanism) led to the release of residual particles that simultaneously appeared in the interstitial phase. The strong decrease of the droplet residuals confirms the nucleation of ice particles on seeding germs without natural aerosol particles serving as ice nuclei. As the number of residual particles during the seedings did not drop to zero, other processes such as heterogeneous ice nucleation, spontaneous freezing, entrainment of supercooled droplets and diffusion to the created particle-free ice germs must have contributed to the experimental findings. During the icing periods, residual mass concentrations in the condensed phase dropped by a factor of 1.1–6.7, as compared to the unperturbed supercooled cloud. As the Bergeron–Findeisen process also occurs without artificial seeding in the atmosphere, this study demonstrated that the hydrometeors in mixed-phase clouds might be much cleaner than anticipated for the simple freezing process of supercooled droplets in tropospheric mid latitude clouds.  相似文献   

2.
One of the purposes of the Fourth Cloud Modeling Workshop was to compare different microphysical treatments. In this paper, the results of a widely used bulk treatment and five versions of a detailed microphysical model are presented. Sensitivity analysis was made to investigate the effect of bulk parametrization, ice initiation technique, CCN concentration and collision efficiency of rimed ice crystal–drop collision. The results show that: (i) The mixing ratios of different species of hydrometeors calculated by bulk and one of the detailed models show some similarity. However, the processes of hail/graupel formation are different in the bulk and the detailed models. (ii) Using different ice initiation in the detailed models' different processes became important in the hail and graupel formation. (iii) In the case of higher CCN concentration, the mixing ratio of liquid water, hail and graupel were more sensitive to the value of collision efficiency of rimed ice crystal–drop collision. (iv) The Bergeron–Findeisen process does not work in the updraft core of a convective cloud. The vapor content was always over water saturation; moreover, the supersaturation gradually increased after the appearance of precipitation ice particles.  相似文献   

3.
In this paper, a 1-D time dependent cold cumulus chemistry model is presented. In the coldcumulus model, 4 categories of hydrometeors: cloud drops, raindrops, cloud ice crystals, graupelparticles, and 18 microphysical interactions are considered, In the chemical model, the source andsink terms for pollutants include: the complicated interactions between pollutants (gases andaerosol particles) and the hydrometeors (especially ice crystals and graupel particles), the ex-changes of chemical compounds between two hydrometeors accompanying microphysical processesand the aqueous oxidations of S (IV) to S (VI). The two models are combined to study the acidifi-cation processes in cold cumulus clouds.  相似文献   

4.
Reliable cloud microphysical measurements can lead to a better understanding of the development of precipitation and cloud radiation. However, imaging of cloud particles with sizes < 200 μm has been limited to small (collected) samples of high-quality photographs or large quantities of poor-quality digital images. Here we introduce two new instruments with demonstrated abilities for improved measurements of cloud drop spectra, liquid water content and digital imaging of the size and shape of small ice crystals. The first instrument uses digital holography to increase the sample volume over that possible with in-focus imaging of small particles. The digital holograms can be processed automatically and are expected to reveal the size and shape of small ice crystals, and the three-dimensional concentration, spacing and liquid water content of cloud drops. The second instrument measures cloud drop spectra and liquid water content from high-resolution measurements of forward-scattered light from an ensemble of drops. This eliminates inherent problems of coincidence and the small sample volume associated with single-drop measurements of drops. The theory of measurement and results from tests of both instruments are presented.  相似文献   

5.
在中国科学院大气物理研究所的三维全弹性对流风暴云催化数值模式(简称为IAP-CSM3D)的基础上,对模式中催化部分的参数化方案进行了改进,推导出人工冰晶与其它粒子之间相互作用的微物理过程的参数化方程。改进后的模式将催化产生的人工冰晶单独作为预报量进行处理,把人工冰晶与自然冰晶区分开,且考虑的人工冰晶谱型为双参数粒子谱,使模式更符合实际。利用改进后的模式模拟了2005年7月8日发生在辽宁省朝阳市的一次冰雹云天气过程,着重分析了催化云人工冰晶的微物理过程、空间分布和谱型,以及对冰相降水粒子的贡献。数值试验表明,自然雹云模拟结果与观测事实相吻合,说明改进后的模式对冰雹云具有较可靠的模拟能力。模拟分析表明,冻滴是该例自然雹云冰雹胚胎的主要来源,对该冰雹云进行AgI催化可明显地减少降雹量,特别是在云中冰雹形成初期进行催化防雹效果最好,既可产生最大的防雹作业效果又不至于过度减少降雨量。催化减雹的主要原因是催化显著地减少了云中冻滴向冰雹胚胎的转化总量。进一步研究发现,人工冰晶在云的不同阶段对各种冰相降水粒子的贡献是不同的。人工冰晶对雪花总质量的贡献较小,对霰总质量的贡献有所增大,而对冻滴总质量的贡献较大。模拟的冰晶粒子谱可较好地反映出人工冰晶谱型较窄,浓度较大,尺度较小的特征。  相似文献   

6.
The scavenging efficiency, E, of small hexagonal plate ice crystals for aerosol particles has been measured in a series of laboratory cloud experiments. The ice crystal diameters, D μm ranged from 35 to 150 μm with aerosol particles in the range 4 to 6 μm. An ice crystal replication technique made possible the individual examination of more than 43m500 individual crystals from which the relation: log10 E = 1.554 − 1.047 log10D was established with values of E in the range 0.2–0.9 corresponding to the range of crystal sizes investigated. For some crystal collectors, values of E extended above unity and this was attributed to wake capture, oscillations and the extended sweep out path of the ice crystals associated with their spiral fall pattern.  相似文献   

7.
陈宝君  肖辉 《大气科学》2007,31(2):273-290
利用中国科学院大气物理研究所开发的三维全弹性冰雹云模式，对美国对流降水协作试验（CCOPE）期间观测的1981年8月1日雹云进行模拟，讨论在过冷雨水低含量条件下冰雹形成和增长机制及其碘化银催化效果。结果表明:(1) 自然云的模拟与观测事实一致，如最大上升气流速度、云顶高度、流场结构以及雹胚组成等。(2) 雹胚以霰为主，霰主要来自冰雪晶与过冷小水滴的碰冻，其次来自雪的积聚转化；霰、冻滴和冰雹在形成后主要靠碰并过冷云水增长。(3)人工催化试验表明，碘化银主要以凝华核（包括凝结－冻结）的作用产生大量的人工冰晶，加速了过冷水向冰晶的转化，过冷云水因而大量减少；催化后霰和冻滴的数浓度增大，对过冷云水的竞争增强，其平均尺度减小导致转化成雹的数量减少；冰雹碰冻过冷云水的增长在催化后也被削弱，导致冰雹总质量进一步减少。此外，催化后降雨量也显著减少。  相似文献   

8.
利用2013年10月13日机载粒子测量系统（PMS）在张家口涞源地区对积层混合云中上部进行的增雨探测数据,分析了云的垂直微物理结构、云区的可播性和作业前后液态云粒子、冰晶及降水粒子的微物理变化。结果表明,此次降水性积层混合云的垂直结构由冷、暖两层云配置,云层发展厚实,冷云区云粒子浓度平均为62 cm-3,液态水含量最大0.05 g/m3;2DC和2DP探测的冰晶及降水粒子平均浓度分别为1.9和2.2 L-1;暖云内云粒子数浓度集中在300 cm-3左右,液态水含量约0.1 g/m3。探测区域云粒子数浓度的水平分布不均匀。利用云内过冷水含量和冰晶浓度等参数判断,该降水性积层混合云的播撒作业层具有强可播性。对比作业前后云中粒子浓度及平均直径发现,云粒子在作业前时段内的平均浓度为31 cm-3,远高于作业后平均浓度（17.6 cm-3）;但平均直径变化不大。作业后冰晶粒子通过贝吉龙过程消耗过冷水长大,浓度由之前的0.86 L-1增至4.27 L-1,平均直径也增至550 μm。冰晶粒子逐渐长大形成降水,降水粒子浓度也相应有所升高,谱明显变宽。   相似文献   

9.
回流天气系统层状云的非均匀性   总被引：5，自引：1，他引：4  
利用一次回流天气过程的PMS资料,从微物理结构上对回流天气系统层状云的不均匀性进行了分析,发现飞机在进入较强降水云带时,云物理量(液水含量、云滴浓度、云滴平均直径,温度)等会产生剧烈变化,表现为液水含量跃增、云滴浓度快速增大、云滴谱谱宽拓宽、温度下降等,在同一较强云带中,温度变化不大并且比周围低,较强降水云带冰晶含量丰富,自然催化较好。  相似文献   

10.
A ground-based seeding experiment using carbon dioxide and propane sprayed from pressurized bottles was carried out under supercooled cloud conditions on a small spatial and short time scale. Water vapor deposition on the artificially generated dry ice and propane ice germs as the main ice formation process (nucleation and growth) is consistent with the experimental results. After nucleation, diffusional growth of the ice particles, partly at the expense of evaporating small droplets, was identified during the mixing of the seeding line with the ambient supercooled cloud. Within the seeding plume, ice water contents up to 80% of the total condensed water are observed, although the size of the formed ice particles did not exceed 25 μm. From the changes of the ice and supercooled liquid phase with time under mixed-phase conditions, liquid water content (LWC) evaporation, ice water content (IWC) formation, and ice crystal growth rates are estimated, which are not affected by the artificial nucleation process. Thus, these rates are assessed to be applicable for a growing ice phase of small ice particles in a young mixed-phase cloud, where other growth mechanisms, like riming or aggregation, are negligible.  相似文献   

11.
青海省秋季一次对流云人工增雨的数值模拟   总被引：10，自引：3，他引：10  
利用中国气象科学研究院的三维对流云数值模式，模拟了青海省2002年秋季一次对流云过程，分析了青海省秋季对流云云体发展的动力学特点和微物理特征。数值模拟结果表明，青海省秋季的对流云降水几乎全部是由霰的融化形成的，而自然云中冰晶含量少、冰霰自动转化形成霰胚的过程非常微弱。但采用合适的方法催化以后，冰晶的核化、繁生量增加，通过冰霰自动转化过程形成大量霰胚，霰胚再通过其他冷云微物理过程迅速增长，融化成降水。催化后各种微物理机制都比催化前活跃，同时催化改变了云体的动力场分布，在动力过程和微物理过程的相互促进下，使增雨取得了很好的效果。  相似文献   

12.
This paper outlines a one-dimensional,heightdependent bin model with detailed microphysical processes in which ice splinters are produced by a riming process.The model is then applied to simulate the shift of particle size distribution effected by the secondary ice production process within clouds with different generating cells and cloud top temperatures.The result of model simulations reveals the general effects of cloud updrafts on increasing ice particle concentration by extending the residence time of ice particles in clouds and providing sufficiently large supercooled water droplets.The rimesplintering mechanism is more effective in clouds with lower ice seeding rates than those with higher rates.Evolutions of hydrometeor size distribution triggered by the rime-splintering mechanism indicate that the interaction between large ice particles and supercooled water drops adds a "second maximum" to the primary ice spectra.  相似文献   

13.
利用GRAPES模式研究气溶胶对云和降水过程的影响   总被引：5，自引：3，他引：2  
石荣光  刘奇俊  马占山 《气象》2015,41(3):272-285
在GRAPES中尺度模式的双参数微物理方案中加入了气溶胶活化参数化过程,实现了对云滴数浓度的预报。选取不同季节两个降水过程进行模拟,并分别开展了不同气溶胶背景下的两个试验进行对比分析,研究气溶胶对云和降水可能的影响。结果表明:气溶胶浓度增加后,因为活化产生了更多尺度较小的云滴,抑制了云雨的自动转化,使大气中滞留了更多的云水,暖云降水减小;另一方面,云水的增加会使冰相粒子,尤其是雪和霰通过碰并云水等过程而增大,最后融化成雨增加冷云降水,同时冰相粒子增加会释放更多的潜热,促进上升气流的发展,进一步增加冷云降水。气溶胶对降水的影响存在空间不一致性,暖云较厚的地方暖雨过程受到的抑制明显,使地面降水减小,冷云厚度相对较厚时,冷云降水的增加会大于暖云降水的抑制,使地面降水增加。同时由于在云降水发展的不同阶段冷暖云的变化,气溶胶对降水的影响也存在着时间不一致性。  相似文献   

14.
利用耦合Morrison 2-mon(MOR)双参数微物理方案的中尺度天气研究与预报模式(WRF)中的单气柱模式,对热带暖池国际云试验(TWP-ICE)期间的个例进行数值模拟。通过与观测资料和云分辨率模式的模拟结果进行对比,检验MOR方案对热带对流云系的微物理特征的模拟能力。模拟结果显示:MOR方案能够较好地模拟出热带云系中液相和冰相水凝物的垂直分布以及随时间的演变特征。地表向下长波辐射和大气顶向外长波辐射的量级和时间演变趋势同观测也非常接近。对与冰晶和雪有关的云微物理特征分析之后发现:季风活跃期,冰晶主要的源汇项有凝华增长过程、沉降过程、冰晶向雪的自动转化以及冰晶被雪碰并的过程。由于冰晶主体位于温度低于―20℃的高空,因而它对雨水的形成主要是间接贡献。同时期雪的主要源汇项中,凝华增长和沉降过程占据着主导地位。雪的凝华过程消耗了大量的水汽,可能抑制了冰晶的增长。另外雪的融化过程非常强盛,是产生降水的重要因子。季风抑制期,冰相的微物理过程变得相对简单且整体削弱,以凝华升华和沉降过程为主。凝华凝冻核的数浓度(Ndep)的气溶胶敏感性试验表明:季风抑制期,高空的冰晶云的宏观和微观性质对凝华凝冻核数浓度的响应情况呈现显著的线性特征。冰晶的含量随着Ndep的增加而增加,反之降低。该时期微物理过程主要同冰晶有关,水分的分配较为简单,Ndep增加时,高空冰云中小冰晶粒子数目增多且云顶升高,使得大气顶部向外长波辐射(OLR)值减小,反之冰云主体中冰晶有效半径增加,高空的冰云更加透明,云顶更低,对 OLR值增加起促进作用。而季风活跃期,微物理过程复杂,冰晶云的宏微观特征对Ndep的响应表现出一定的不规律特征。  相似文献   

15.
《Atmospheric Research》2008,87(3-4):225-240
During June and July 2003 the Sources and Origins of Atmospheric Cloud Droplets experiment (SOACED) was carried out on a mountain-top site in central Sweden. The main objective of the experiment was to characterise the microphysical and chemical properties of cloud droplet residuals and interstitial aerosol particles in continental clouds and to understand the processes controlling cloud properties at this location.Interstitial and residual aerosol size distributions, cloud liquid water content and species- and size-resolved aerosol mass concentrations are the main variables employed to address questions pertaining to the cloud droplet number concentration and scavenging efficiency during a stratocumulus cloud event observed on July 28, 2003. In this cloud event, about 56% of the aerosol mass was associated with organic species, whilst SO4 accounted for 23% and NH4 for 14%. NO3 and Cl made up about 7% of the total mass.The partitioning of the aerosol particles between cloud droplets and interstitial air has been studied in terms of their microphysical properties. The scavenging efficiency, defined as the fraction of particles activated into cloud elements compared to the total amount of particles, was investigated as a function of size. The scavenging efficiency curves displayed different shapes during the cloud event, from an S-shaped curve, with low scavenging efficiency in the Aitken mode and larger scavenging efficiency in the accumulation mode, to more unusual shapes where Aitken-mode particles were either solely activated or activated in addition to accumulation-mode particles.This study suggests that alterations of the aerosol chemical composition occurred during the measurement period, changing the hygroscopic nature of the CCN and decreasing their activation diameter. It is also hypothesized that entrainment of drier air aloft may have introduced inhomogeneities in the supersaturation field and modified the S-shaped scavenging curves.  相似文献   

16.
During June and July 2003 the Sources and Origins of Atmospheric Cloud Droplets experiment (SOACED) was carried out on a mountain-top site in central Sweden. The main objective of the experiment was to characterise the microphysical and chemical properties of cloud droplet residuals and interstitial aerosol particles in continental clouds and to understand the processes controlling cloud properties at this location.Interstitial and residual aerosol size distributions, cloud liquid water content and species- and size-resolved aerosol mass concentrations are the main variables employed to address questions pertaining to the cloud droplet number concentration and scavenging efficiency during a stratocumulus cloud event observed on July 28, 2003. In this cloud event, about 56% of the aerosol mass was associated with organic species, whilst SO4 accounted for 23% and NH4 for 14%. NO3 and Cl made up about 7% of the total mass.The partitioning of the aerosol particles between cloud droplets and interstitial air has been studied in terms of their microphysical properties. The scavenging efficiency, defined as the fraction of particles activated into cloud elements compared to the total amount of particles, was investigated as a function of size. The scavenging efficiency curves displayed different shapes during the cloud event, from an S-shaped curve, with low scavenging efficiency in the Aitken mode and larger scavenging efficiency in the accumulation mode, to more unusual shapes where Aitken-mode particles were either solely activated or activated in addition to accumulation-mode particles.This study suggests that alterations of the aerosol chemical composition occurred during the measurement period, changing the hygroscopic nature of the CCN and decreasing their activation diameter. It is also hypothesized that entrainment of drier air aloft may have introduced inhomogeneities in the supersaturation field and modified the S-shaped scavenging curves.  相似文献   

17.
The interpretation of the physico-chemical processes in clouds is facilitated by segregating in situ cloud elements from their carrier gas and small particles (interstitial aerosol). Thus, the present study focuses on the quantitative phase segregation of interstitial air from cloud phase by two complementary samplers with microphysical on-line analysis of the separated phases. An improved counterflow virtual impactor (CVI) was developed for the collection and subsequent evaporation of the condensed phase, releasing dissolved gaseous material and residual particles. This sampler operates in the size range of few micrometers up to 50 μm in cloud element diameter and is matched by an interstitial Round Jet Impactor sampling the gas phase with interstitial particles. Calibrations of both samplers verified the calculated cut sizes D50 of 4, 5, and 6 μm and quantified the slope of the collection efficiency curves. Until this study no direct CVI measurements of the residual particle sizes far below the diameter of 0.1 μm were available. For the first time a CVI was connected to a Differential Mobility Particle Sizer (DMPS) scanning between 25 nm and 850 nm, thus, including the entire Aitken mode in the residual size analysis. Cloud studies on the Puy de Dôme, France, revealed residual particle sizes including Aitken mode (diameter D<100 nm) and accumulation mode (D>100 nm). A major feature of the CVI data is expressed by the fact that despite incomplete incorporation of accumulation mode particles in cloud elements there are contributions of particles with diameters smaller than 0.1 μm to the number of residual particles. Cloud entrainment from height levels above the maximum supersaturation as wells as the size-dependent chemical composition of the aerosol population most likely produced the S-shaped size-dependent partitioning of residual particles. Compared to earlier studies the 50% partitioning diameters dropped significantly below 100 nm to roughly 70 nm.  相似文献   

18.
为了探讨对流强度大小对雷暴云内微物理发展和起电过程的影响,基于已有的二维积云起、放电模式,改变其扰动温度进行敏感性试验。试验结果表明:对流强度对雷暴云内微物理过程、起电率及后续电荷结构的产生均有一定程度的影响:1）对流强度较小时,冰晶粒子极大值在高温区（高于-13.8℃）出现,对流强度较大时,上升风明显增强,将更多的水汽带入高空,气溶胶活化过程明显增强,使得云滴粒子明显增多,冰晶粒子较早产生,冰晶粒子极大值在低温区（低于-13.8℃）出现,发展过程更为剧烈;同时,较高的对流强度也使得降雨量增多,霰粒子数目也在对流发展旺盛时期显著增多。2）非感应起电率主要和冰晶-霰的碰并分离过程有关,对流强度较大时,非感应起电率较大,电荷结构持续时间较长,过程明显,感应起电率也较强。3）对流强度较大时,电荷结构更为复杂,雷暴云发展初期基本呈现为三极性,发展旺盛时期底部正电荷区域嵌入一个较小的负电荷区,呈现四极性电荷结构,雷暴云发展末期基本呈现偶极性电荷结构;对流强度较小时,发展初期、旺盛时期均呈现三极性电荷结构,发展末期呈现偶极性电荷结构。  相似文献   

19.
A comprehensive parameterized model of microphysical processes in cumulonimbus clouds is presented.The transformation rates of the water contents and number concentrations of the cloud droplets,rain drops,ice crystals,graupels and hails are deduced on theoretical and experimental results for 26 kinds of micro-physical processes,which include condensation,deposition,evaporation,collection,ice nucleation,ice mul-tiplication,melting,freezing,and autoconversions of cloud to rain,ice to graupel and graupel to hail.  相似文献   

20.
徐戈  孙继明  牛生杰  周碧  王永庆 《大气科学》2016,40(6):1297-1319
霰和冻滴是深对流降水的主要来源。由于二者密度差异造成的不同下落末速度必然会导致云微物理过程的变化以及降水时空分布的改变。我们在以色列特拉维夫大学二维轴对称对流云全分档模式的基础上,将水成物粒子从34档增加到40档,修改了霰和雪的密度,加入冻滴分档处理的微物理过程,发展了一个包括液滴、冰晶、雪、霰和冻滴更为详细的云微物理分档模式。利用改进后的模式模拟了一次理想的强对流天气过程,分析了改进模式与原模式模拟的云微物理量场以及水成物粒子的时空分布特征,模拟结果表明:（1）由于冻滴的产生,较大的下落末速度导致在云内-3℃至-8℃较早地出现了冻滴,并造成了大量的冰晶繁生。（2）冻滴形成前期,液态水中心区域位于垂直上升速度大值中心上方,形成液态水累积区;冻滴形成期,液态水累积区位于0℃层以上,雨滴冻结生成冻滴,霰与半径大于100 μm的液滴碰并生成冻滴;冻滴增长期,在垂直上升气流的支撑下,冻滴碰并过冷水增长,导致冻滴含量增大,液态水含量减小。因此,改进模式能较好的模拟冻滴的形成过程,可以将该分档处理的微物理方案耦合到三维WRF（Weather Research and Forecasting model）模式中,更深入地研究强雷暴风切变在冰雹生成过程中的作用。  相似文献   

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