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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.
沙尘气溶胶对云和降水影响的模拟研究 总被引：9，自引：0，他引：9
采用二维分档云模式,对比背景大气气溶胶分布,讨论了扬沙和沙尘暴天气条件下矿物气溶胶对云微物理结构、光学特性以及降水形成的影响.结果表明:扬沙和沙尘暴天气增加大气中大核和巨核的浓度,促进云中水汽的活化,使降水提前出现,暖云和冷云降水量均大幅增加,但可忽略巨核增加对云光学厚度和反照率的作用;当矿物沙尘粒子同时作为有效的云凝结核和冰核参与云的发展时,冰核浓度增加使水成物有效半径减小,抑制了暖云和冷云降水,云内存留的大量冰晶增强云的光学厚度和反照率. 相似文献
3.
为全面了解水汽在气溶胶影响雷暴云电过程中的作用,本研究在已有的二维雷暴云起、放电模式基础上,通过改变相对湿度和气溶胶初始浓度（文中气溶胶浓度均指气溶胶数浓度）进行敏感性数值模拟试验。结果表明:（1）随着气溶胶浓度升高,雷暴云产生更多的小云滴,降水过程受到抑制。而当水汽含量升高时,云滴数浓度的增长速度更快,雨滴数浓度升高,缓解了降水变弱的趋势。（2）水汽含量较低时,随着气溶胶浓度升高,更多小云滴被带入冻结层形成大量小冰晶,霰粒含量升高,雷暴云起电过程增强。气溶胶浓度升高至一定的量级（3000 cm?3）时,冰晶尺度减小和雨滴浓度降低抑制霰粒生长,雷暴云起电过程受到削弱。感应起电和非感应起电过程随气溶胶浓度升高呈先增强后减弱的趋势。水汽含量的升高促进了冰相粒子的增长,起电过程呈现持续增强的趋势,气溶胶浓度为3000 cm?3时起电率达到极值,电荷密度的增幅扩大。（3）水汽含量较低时,雷暴云难以发展成深厚的系统,气溶胶浓度变化对其影响不明显,电荷结构由三极性发展,在消散期演变为偶极性电荷结构;水汽含量较高时,雷暴云迅速发展成深厚的系统,随着气溶胶浓度升高,在雷暴发展旺盛阶段电荷分布表现为多层复杂结构。研究显示水汽含量在气溶胶浓度变化对雷暴云微物理、起电过程及电荷结构的作用中扮演重要角色。 相似文献
4.
Aerosol particles can serve as cloud condensation nuclei(CCN)to influence orographic clouds.Autoconversion,which describes the initial formation of raindrops from the collision of cloud droplets,is an important process for aerosol-cloud-precipitation systems.In this study,seven autoconversion schemes are used to investigate the impact of CCN on orographic warm-phase clouds.As the initial cloud droplet concentration is increased from 100 cm-3to 1000 cm-3(to represent an increase in CCN),the cloud water increases and then the rainwater is suppressed due to a decrease in the autoconversion rate,leading to a spatial shift in surface precipitation.Intercomparison of the results from the autoconversion schemes show that the sensitivity of cloud water,rainwater,and surface precipitation to a change in the concentration of CCN is different from scheme to scheme.In particular,the decrease in orographic precipitation due to increasing CCN is found to range from-87%to-10%depending on the autoconversion scheme.Moreover,the surface precipitation distribution also changes significantly by scheme or CCN concentration,and the increase in the spillover(ratio of precipitation on the leeward side to total precipitation)induced by increased CCN ranges from 10%to 55%under different autoconversion schemes.The simulations suggest that autoconversion parameterization schemes should not be ignored in the interaction of aerosol and orographic cloud. 相似文献
5.
Simulation of the influence of aerosol particle characteristics on clouds and precipitation with LM-SPECS: Model description and first results 总被引：1，自引：0，他引：1
The novel model system LM-SPECS is presented combining a spectral bin microphysics scheme and the three-dimensional Lokalmodell (LM, today called COSMO) of the German Weather Service (“Deutscher Wetterdienst”). The model is designed to investigate in detail the interaction of atmospheric aerosol particles, clouds and precipitation. The microphysics scheme includes a combined spectrum of wetted aerosols, cloud droplets and rain drops. As a first application of the model, sensitivity studies on an artificial deep convective cloud were done. The results produced by LM-SPECS are satisfying. The studies show, e.g., that a diminished initial particle number leads to larger cloud droplets and thus to a higher efficiency of coalescence. This results in a larger amount of precipitation. Furthermore, studies on mixed phase clouds show the influence of varying ice nuclei, such as bacteria, kaolinite and soot, on cloud properties. Here, a more effective freezing leads to an increased number of ice particles with smaller radii. The results point to the importance of a detailed knowledge of the underlying microphysical processes in order to understand the formation of clouds and precipitation more accurately. Though to date the model was applied to artificial cases only, the use of the mesoscale weather model allows for more complex realistic cases which are subject to further studies. 相似文献
6.
Numerical Simulation of Macro- and Micro-structures of Intense Convective Clouds with a Spectral Bin Microphysics Model 总被引：1，自引：0，他引：1
By use of a three-dimensional compressible non-hydrostatic convective cloud
model with detailed microphysics featuring spectral bins of cloud
condensation nuclei (CCN), liquid droplets, ice crystals, snow and graupel
particles, the spatial and temporal distributions of hydrometeors in a
supercell observed by the (Severe Thunderstorm Electrification and
Precipitation Study) STEPS triple-radar network are simulated and analyzed.
The bin model is also employed to study the effect of CCN concentration on
the evolution characteristics of the supercell. It is found that the CCN
concentration not only affects the concentration and spectral distribution
of water droplets, but also influences the characteristics of ice crystals
and graupel particles. With a larger number of CCN, more water droplets and
ice crystals are produced and the growth of graupel is restrained. With a
small quantity of CCN the production of large size water droplets are
promoted by initially small concentrations of water droplets and ice
crystals, leading to earlier formation of small size graupel and restraining
the recycling growth of graupel, and thus inhibiting the formation of large
size graupel (or small size hail). It can be concluded that both the macroscopic
airflow and microphysical processes influence the formation and growth of large
size graupel (or small size hail). In regions with heavy pollution, a high
concentration of CCN may restrain the formation of graupel and hail, and in
extremely clean regions, excessively low concentrations of CCN may also limit
the formation of large size graupel (hail). 相似文献
7.
《Atmospheric Research》2009,91(2-4):233-242
The novel model system LM-SPECS is presented combining a spectral bin microphysics scheme and the three-dimensional Lokalmodell (LM, today called COSMO) of the German Weather Service (“Deutscher Wetterdienst”). The model is designed to investigate in detail the interaction of atmospheric aerosol particles, clouds and precipitation. The microphysics scheme includes a combined spectrum of wetted aerosols, cloud droplets and rain drops. As a first application of the model, sensitivity studies on an artificial deep convective cloud were done. The results produced by LM-SPECS are satisfying. The studies show, e.g., that a diminished initial particle number leads to larger cloud droplets and thus to a higher efficiency of coalescence. This results in a larger amount of precipitation. Furthermore, studies on mixed phase clouds show the influence of varying ice nuclei, such as bacteria, kaolinite and soot, on cloud properties. Here, a more effective freezing leads to an increased number of ice particles with smaller radii. The results point to the importance of a detailed knowledge of the underlying microphysical processes in order to understand the formation of clouds and precipitation more accurately. Though to date the model was applied to artificial cases only, the use of the mesoscale weather model allows for more complex realistic cases which are subject to further studies. 相似文献
8.
对流云对大气气溶胶和相对湿度变化响应的数值模拟 总被引：6，自引：3，他引：3
利用二维面对称分档云模式研究了气溶胶颗粒物浓度和尺度谱分布对混合相对流云微物理过程和降水的影响, 并重点讨论了气溶胶效应随环境相对湿度的变化。结果表明, 在初始热力和动力条件相同的情况下, 相对清洁的海洋性云在发展和成熟阶段能更有效地产生雨滴、 冰晶和霰粒, 形成更强的雷达反射率。随着气溶胶浓度增加, 比如在本文模拟的污染大陆性云中, 气溶胶粒子数浓度的增加限制云滴增长, 不利于降水粒子的形成。模拟结果也发现, 环境相对湿度对气溶胶效应有显著影响, 即当地面相对湿度从50%增大到70%时, 所模拟的云从浅对流泡发展为深对流云; 气溶胶对云微物理特性和降水的影响在干空气中较小, 但在湿空气中表现非常显著, 这与前人结果一致。随着相对湿度的增加, 冰相粒子出现的时间提前, 增长加快, 云砧范围扩大, 但相对来说, 降水起始时间对相对湿度的变化比气溶胶更敏感。 相似文献
9.
The effect of clouds on aerosol growth in the rural atmosphere 总被引：1，自引：0，他引：1
Measurements of accumulation mode aerosol in the atmospheric boundary layer under cloudy and cloud-free conditions, and in the lower free troposphere under cloud-free conditions, were conducted over the rural northwest of England. Normalised size distributions in the cloud-free boundary layer (CFBL) and the cloud-free free troposphere (CFFT) exhibited almost identical spectral similarities with both size distributions possessing a concentration peak mode-radius of ≈0.05 μm or less. By comparison, aerosol distributions observed in cloudy air exhibited a distinctive log-normal distribution with mode-radii occurring at ≈0.1 μm concomitant with a local minimum at ≈0.05 μm. The consistent and noticeable difference in spectral features observed between cloudy and cloud-free conditions suggest that a greater amount of gas-to-particle conversion occurs on cloudy days, presumably through in-cloud aqueous phase oxidation processes, leading to larger sized accumulation mode particles. Apart from the distinct difference between cloudy and cloud-free aerosol spectra on cloudy days, aerosol concentration and mass were observed to be significantly enhanced above that of the ambient background in the vicinity of clouds. Volatility analysis during one case of cloud processing indicated an increase in the relative contribution of aerosol mass volatile at temperatures characteristic of sulphuric acid, along with a smaller fraction of more volatile material (possibly nitric acid and/or organic aerosol). Growth-law analysis of possible growth mechanisms point to aqueous phase oxidation of aerosol precursors in cloud droplets as being the only feasible mechanism capable of producing the observed growth. The effect of cloud processing is to alter the cloud condensation nuclei (CCN) supersaturation spectrum in a manner which increases the availability of CCN at lower cloud supersaturations. 相似文献
10.
气溶胶影响云和降水的机理和观测研究进展 总被引：5，自引：3，他引：2
气溶胶对云和降水的影响,对于气候系统、大气环境以及水循环至关重要。气溶胶粒子作为云凝结核和大气冰核影响云的微物理过程,进而影响雨、雪、雹和其他形式的降水。近年来,在理解气溶胶的化学成分,气溶胶微物理特性以及气溶胶作为云凝结核和大气冰核影响云降水等方面已取得重大进展。本文对于气溶胶的概念、来源以及气溶胶的直接和间接效应进行了简要概述,重点总结了国内外在气溶胶影响云和降水的机理研究方面的成果,回顾了近年来利用卫星、地面观测设备、机载探测设备等对气溶胶和云进行遥感观测和直接观测所获得的观测事实并讨论了其可能的物理机制,在总结前人研究成果的基础上对未来的研究方向进行了讨论。 相似文献
11.
气溶胶对雷暴云起电以及闪电发生率影响的数值模拟 总被引：5，自引：1，他引：4
本文利用二维耦合气溶胶模块的雷暴云起电模式,结合一次南京雷暴个例,进行250 m分辨率雷暴云起电模拟实验,探讨了气溶胶浓度对雷暴云空间电荷分布以及闪电发生率的影响。在这个气溶胶模块中,假定一个三模态的气溶胶对数分布,考虑了气溶胶活化过程。结果显示:(1)随着气溶胶浓度增大,雷暴云电荷结构保持为三极型。(2)当气溶胶浓度从50 cm-3增加至1000 cm-3时,水成物粒子浓度上升,雷暴云电荷量和闪电发生率增加明显。(3)气溶胶浓度在1000~3000 cm-3范围时,云水竞争限制了冰晶的增长,导致雷暴云上部主正电荷堆电荷量降低。云滴和霰粒子浓度缓慢上升促进中部主负电荷堆和底部次正电荷堆电荷量继续增大。闪电发生率保持稳定。(4)当气溶胶浓度大于3000 cm-3时,水成物粒子浓度稳定,云内的电荷量以及闪电发生率保持为一定量级。 相似文献
12.
2014年8月15日,山西省人工降雨防雹办公室在山西忻州开展了气溶胶和浅积云的飞机观测,本文利用机载云物理资料,详细分析了华北地区气溶胶、云凝结核（CCN）和浅积云微物理特性及其相互影响。主要结论有:（1）此次过程的边界层高度约为3600 m,不同层结情况下,0.1～3 μm尺度范围内的气溶胶粒子浓度Na、有效直径Da和CCN数浓度的垂直廓线明显不同,近地面Na可达2500 cm?3。（2）CCN的主要来源为积聚模态、爱根模态或者核模态的气溶胶颗粒,0.2%过饱和度下,气溶胶活化率（AR）在各高度层的结果变化不大;0.4%过饱和度下,AR随着高度增加而降低。（3）后向轨迹模式分析表明,2 km以下的气溶胶主要来自于当地城市排放,由细颗粒污染物组成;2 km以上的气溶胶主要来源于中国西北和蒙古地区的沙漠,由亚微米沙尘组成,溶解度相对较低,可作为潜在的冰核。（4）本文细致分析了两块相邻浅积云（Cu-1和Cu-2）的云物理特性。Cu-1云底高度约4500 m,云厚约600 m,云体松散,夹卷较多;云中液态含水量（LWC）基本保持在0.5 g m?3,云粒子浓度Nc平均值为278.3 cm?3,云滴有效直径Dc整体在15 μm以内;毛毛雨滴粒子浓度最大值为0.002 cm?3,云中几乎无降水粒子;粒子谱宽随着高度增加而增大,主要集中在30 μm以内。Cu-2云底高度约3900 m,云厚约1200 m,云体密实;云中过冷水丰沛,LWC有多个超过1 g m?3的区域,云顶附近出现冰晶,云中粒子从凝结增长状态直接进入到混合相态;积云内部粒子水平分布不均,同一高度Nc相差较大,最大可达1240 cm?3。Dc随着高度增加而增大;粒子谱宽随着高度增加而拓展,最大可达1100 μm,谱型由单峰向多峰转变;降水粒子和冰晶图像大多为霰粒子、针状和板状。 相似文献
13.
The effects of the initial cloud condensation nuclei(CCN) concentrations(100–3000 mg~(-1)) on hail properties were investigated in an idealized non-severe hail storm experiment using the Weather Research and Forecasting(WRF) model, with the National Severe Storms Laboratory 2-moment microphysics scheme. The initial CCN concentration(CCNC) had obvious non-monotonic effects on the mixing ratio, number concentrations, and radius of hail, both in clouds and at the surface, with a CCNC threshold between 300 and 500 mg~(-1). An increasing CCNC is conducive(suppressive) to the amount of surface hail precipitation below(above) the CCNC threshold. The non-monotonic effects were due to both the thermodynamics and microphysics. Below the CCNC threshold, the mixing ratios of cloud droplets and ice crystals increased dramatically with the increasing CCNC, resulting in more latent heat released from condensation and frozen between 4 and 8 km and intensified updraft volume. The extent of the riming process, which is the primary process for hail production, increased dramatically. Above the CCNC threshold, the mixing ratio of cloud droplets and ice crystals increased continuously, but the maximum updraft volume was weakened because of reduced frozen latent heating at low level. The smaller ice crystals reduced the formation of hail and smaller clouds, with decreased rain water reducing riming efficiency so that graupel and hail also decreased with increasing CCNC, which is unfavorable for hail growth. 相似文献
14.
2016年11月13日在北京地区上空存在持续稳定的层状云天气背景下,利用飞机开展气溶胶粒径谱、化学组成、云滴谱等参量的垂直观测,研究该个例云底气溶胶的活化能力。结果表明:探测期间北京地区为轻度污染天气,地面气溶胶浓度(0.11~3 μm)达到4600 cm-3。云层高度为800~1200 m,云底气溶胶数浓度相对于近地面大幅度降低,有效粒径显著增大(0.3~0.6 μm)。同时,近地面气溶胶中疏水性的一次有机气溶胶贡献显著,而云底气溶胶中一次有机气溶胶的贡献大幅降低,无机组分和二次有机气溶胶的贡献明显增大,造成吸湿性参数κ由0.25(地面)增大至0.32(云底)。云中气溶胶和云滴的谱分布衔接较好,且两者的数浓度之和与云底气溶胶浓度一致,可分别代表未活化和已活化的粒子。基于云底气溶胶粒径谱和吸湿性参数计算得到不同过饱和比下云凝结核的活化率,通过与云中观测结果对比,反推得到云底过饱和度约为0.048%。 相似文献
15.
Wolfram Wobrock Andrea I. Flossmann Marie Monier Jean-Marc Pichon Laurent Cortez Jean-Franois Fournol Alfons Schwarzenbck Stephan Mertes Jost Heintzenberg Paolo Laj Giordano Orsi Loretta Ricci Sandro Fuzzi Harry Ten Brink Piet Jongejan Ren Otjes 《Atmospheric Research》2001,58(4):7907
The second field campaign of the Cloud Ice Mountain Experiment (CIME) project took place in February 1998 on the mountain Puy de Dôme in the centre of France. The content of residual aerosol particles, of H2O2 and NH3 in cloud droplets was evaluated by evaporating the drops larger than 5 μm in a Counterflow Virtual Impactor (CVI) and by measuring the residual particle concentration and the released gas content. The same trace species were studied behind a round jet impactor for the complementary interstitial aerosol particles smaller than 5 μm diameter. In a second step of experiments, the ambient supercooled cloud was converted to a mixed phase cloud by seeding the cloud with ice particles by the gas release from pressurised gas bottles. A comparison between the physical and chemical characteristics of liquid drops and ice particles allows a study of the fate of the trace constituents during the presence of ice crystals in the cloud.In the present paper, an overview is given of the CIME 98 experiment and the instrumentation deployed. The meteorological situation during the experiment was analysed with the help of a cloud scale model. The microphysics processes and the behaviour of the scavenged aerosol particles before and during seeding are analysed with the detailed microphysical model ExMix. The simulation results agreed well with the observations and confirmed the assumption that the Bergeron–Findeisen process was dominating during seeding and was influencing the partitioning of aerosol particles between drops and ice crystals. The results of the CIME 98 experiment give an insight on microphysical changes, redistribution of aerosol particles and cloud chemistry during the Bergeron–Findeisen process when acting also in natural clouds. 相似文献
16.
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
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
17.
Jefferson R. Snider Jean&#;Louis Brenguier 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):828-842
During the 2nd Aerosol Characterization Experiment (ACE‐2), relationships between stratocumulus cloud properties and aerosols were examined. Here, the relevant measurements including the cloud condensation nuclei (CCN) activation spectrum, updraft velocity, cloud microphysical and aerosol properties are presented. It is shown that calculations of droplet concentration based on updraft velocity and the CCN activation spectrum are consistent with direct observations. Also discussed is an apparent disparity among measurements of the CCN activation spectrum, the accumulation mode size distribution, and the composition of the submicrometric aerosol. The observed consistency between CCN, updraft and cloud droplets is a necessary refinement; however, extended analyses of the ACE‐2 data set are needed to guide improvements in model simulations of the interaction between aerosols and cloud microphysics. In particular, there is need for an examination of aerosol size spectra and chemical composition measurements with a view towards validating droplet activation schemes which relate the aerosol and cloud dynamical properties to cloud albedo. 相似文献
18.
飞机观测是云中粒子相态、分布和转化特征的重要探测技术。我国云降水物理飞机观测开始于20世纪60年代,经过60多年的发展,在飞机平台、机载测量技术、云微物理结构和降水形成机制认识等方面均取得了长足进步。发现积层混合云中对流泡区具有更高的过冷水含量,凇附增长起重要作用,符合“播撒-供给”降水形成机制,而在层云区,当云厚度较小时,过冷水含量很少,冰雪晶的凝华、聚并增长起主导作用,并不符合“播撒-供给”降水形成机制,而当云厚度较大时,过冷水含量较为丰富,凝华、聚并和凇附增长起主导作用,基本符合“播撒-供给”降水形成机制;我国北方冬季降雪过程的形成机制主要是凝华-聚并机制,只有在水汽非常充足、云较厚的情况下,凇附增长过程才具有重要作用。近年虽然在人工影响天气播撒效应、数值模式云物理过程验证、卫星及雷达遥感数据检验、对流云结构观测等方面也取得了一些进展,但仍较薄弱,亟待加强。 相似文献
19.
Role of organic acids (formic, acetic, pyruvic and oxalic) in the formation of cloud condensation nuclei (CCN): a review 总被引：2，自引：0，他引：2
Although it is believed that organic aerosols play a key role in cloud nucleation and make an important contribution to the cloud condensation nuclei (CCN) population, their specific species remain poorly characterized. This paper reviews the current knowledge of organic acids (mainly formic, acetic, pyruvic and oxalic acids). Without specification, organic acids in this paper refer to these four organic acids in the gas and aerosol phases. This paper analyzes the extent to which organic acids act as CCN and compares the physical and chemical properties of organic acids with those of CCN. The results show that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol m−3 and from 0.03 to 12.4 nmol m−3, respectively, and that between 34 to 77% of formate and between 21 to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98–99%) of these volatile organic acids are present in the gas phase, their concentrations in the aerosol particles are sufficient to make them a good candidate for CCN. The results also show that organic acids may make an important contribution to the formation of CCN in some special sources such as vegetation emissions and biomass-burning. Organic acids are expected to contribute significantly to the estimates of indirect (cloud-mediated) forcing due to aerosols. 相似文献
20.
E.K. Bigg 《Atmospheric Research》1990,25(6)
In a first attempt to assess a proposed climatic change feedback process involving cloud condensation nuclei (CCN) and cloud albedo, CCN concentrations N as a function of supersaturation S were measured on a voyage from latitude 43 to 65°S in October–November 1988. The usual relationship N=CSk, with k=0.5 and C a constant was a fair apprraximation for S in the range 0.3–0.7% implying that CCN concentrations should largely determine cloud drop concentrations and hence albedo for clouds with S in that range. South of latitude 50°S and at smaller S,k was 1 or larger on average, which would lead to reduced dependence of albedo on CCN for the relevant clouds. N varied very widely for separations of the order of 100 km or 6 hours in time, particularly when the sea was partly ice-covered, suggesting strong local influences. During a large increase in N 60°S, unaccompanied by an increase in condensation nuclei (CN), cloud drops grew more rapidly than usual. In a subsidiary experiment particles were collected and examined by transmission electron microscopy. For particles less than 0.2 μm diameter, 80–90% appeared to consist of ammonium sulfate, the remainder being sea salt or an unknown substance which was more liquid and heat-resistant. Dialysis showed that the sulfate particles contained a few percent of insoluble material. Particles which formed cloud drops in vapours other water, were also studied. Comparison of these and water CCN and the rates of droplet suggested that the water insoluble portion of the particles was ethanol-soluble and surface-active. CN concentrations decreased by a factor of about 2 between 43 and 65°S, a change closely paralleled by ethanol CCN concentrations. 相似文献