Microphysical and chemical characteristics of cloud droplet residuals and interstitial particles in continental stratocumulus clouds

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.     

Microphysical and chemical characteristics of cloud droplet residuals and interstitial particles in continental stratocumulus clouds

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.     

NaCl Aerosol Particle Hygroscopicity Dependence on Mixing with Organic Compounds

Organic compounds in the atmosphere can influence the activation, growth and lifetimes of haze, fog and cloud droplets by changing the condensation and evaporation rates of liquid water by these aqueous aerosol particles. Depending on the nature and properties of the organic compounds, the change can be to enhance or reduce these rates. In this paper we used a tandem differential mobility analyzer (TDMA) to examine the effect of tetracosane, octanoic acid, and lauric acid on the hygroscopic properties of NaCl aerosol particles at relative humidities (RH) between 30 and 95%. These organic compounds have been identified in ambient aerosol particle samples. A slight lowering of the deliquescence relative humidity (DRH) and suppression of hygroscopic growth for the NaCl-organic compound mixtures were observed when compared to pure NaCl particles. The growth of pure NaCl particles was 2.25 in diameter at 85% RH while the growth of the mixed particles was 1.3 to 1.7 in particle diameter at 85% RH with organic mass fraction of 30–50%. This shows that these organic compounds have to be present in rather large mass fractions to effect the hygroscopic behavior to a similar degree observed for ambient aerosol during field measurements. Despite the mixing of the organic material with NaCl, hysteresis was observed for decreasing RH histories, suggesting the formation of metastable droplets. These laboratory results are strikingly similar to ambient field results. For example, if the total organic mass fraction of the particles is between 0.30 and 0.50, the particle growth at 85% RH is about a factor of 1.4 for the laboratory and field measurements. Such reduction in growth compared to the pure inorganic salt is in contradiction to speculations concerning significant effects by organic compounds on cloud condensation nuclei and thus formation on clouds.     

Impacts of aerosol chemical composition on microphysics and precipitation in deep convection

Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNC). Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The MCE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation (S_c) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Köhler curve are deactivated by the insoluble substance, S_c is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances.     

基于航测的云底气溶胶活化率与过饱和度估算

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%。     

Size Distributions of Aerosol Sulfates and Nitrates in Beijing during the 2008 Olympic Games: Impacts of Pollution Control Measures and Regional Transport

For the 2008 Olympic Games, drastic control measures were implemented on industrial and urban emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_x) and other pollutants to address the issues of poor air quality in Beijing. To investigate the effects of SO₂ and NO_x reductions on the particulate sulfate and nitrate concentrations as well as their size distributions, size-segregated aerosol samples were collected using micro-orifice uniform deposit impactors (MOUDIs) at urban and downwind rural sites in Beijing before and after full-scale controls. During the sampling period, the mass concentrations of fine particles (PM_1.8) at the urban and rural sites were 94.0 and 85.9 μg m^-3, respectively. More than 90% of the sulfates and ～60% of nitrates formed as fine particles. Benefiting from the advantageous meteorological conditions and the source controls, sulfates were observed in rather low concentrations and primarily in condensation mode during the Olympics. The effects of the control measures were separately analyzed for the northerly and the southerly air-mass-dominated days to account for any bias. After the control measures were implemented, PM, sulfates, and nitrates were significantly reduced when the northerly air masses prevailed, with a higher percentage of reduction in larger particles. The droplet mode particles, which dominated the sulfates and nitrates before the controls were implemented, were remarkably reduced in mass concentration after the control measures were implemented. Nevertheless, when the polluted southerly air masses prevailed, the local source control measures in Beijing did not effectively reduce the ambient sulfate concentration due to the enormous regional contribution from the North China Plain.     

利用GRAPES模式研究气溶胶对云和降水过程的影响

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。     

Microphysics of clouds at Kleiner Feldberg

During a field measuring campaign at Kleiner Feldberg (Taunus) in 1990, microphysical characteristics of clouds have been measured by Forward Scattering Spectrometer Probes (FSSP). The aim was to study the influence of aerosol and meteorological factors on droplet size and number. The results are: More mass in the accumulation size range of the aerosol leads to more droplets in stratocumulus clouds and to higher soluble masses in droplets of stratus clouds. However, the aerosol distribution was coarser in the stratus clouds compared to the stratocumulus clouds. Within the first 200 m from cloud base, the droplets grow while their number decreases. The growth results in a stable size of about 14 µm diameter over a large distance from cloud base in many stratocumulus clouds. Two types of mixing processes were observed: processes with reductions in the number of droplets (inhomogeneous mixing) and with reductions in the size of the droplets (homogeneous mixing).     

对流云对大气气溶胶和相对湿度变化响应的数值模拟

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。     

Impact of the Bergeron–Findeisen process on the release of aerosol particles during the evolution of cloud ice

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.     

The influence of aerosol particle composition on cloud droplet formation

A difference in partitioning between cloud droplets and interstitial air for two chemical species (elemental carbon and sulphur) with different expected behaviour in nucleation scavenging was observed in clouds at Mt. Kleiner Feldberg (825 m asl), near Frankfurt, Germany. The fraction of sulphur incorporated in cloud droplets was always higher than the fraction of elemental carbon. This difference in partitioning has also been observed in fog but under different pollution conditions in the Po Valley, Italy. Both these studies were based on bulk samples. In the present study at Kleiner Feldberg, impactor samples of the particles in the interstitial air and the cloud droplet residuals were taken and a single particle analysis was done on the samples. It was found that, for a given particle size, the majority of particles forming cloud droplets were soluble and that insoluble particles preferentially remained in the interstitial air.     

Hygroscopicity of pre-existing particle distribution and formation of cloud droplets: a model study

The effects of the hygroscopicity of a pre-existing particle distribution and condensation of nitric acid on cloud droplet formation were studied by using an air parcel and multicomponent condensation model. The pre-existing particle distribution used is a bimodal distribution in which the particles are assumed to be internally mixed, i.e. they are composed partly from ammonium nitrate salt and partly from some insoluble substance. The mean diameters of the distributions and the mass fraction of soluble salt were varied in the simulations. Generally, the number of activated cloud droplets was found to be increased, when the initial mass fraction of salt (i.e. the initial amount of salt) was increased. However, the effects of increased initial amount of salt on the cloud droplet formation were not straightforward in all cases studied. The effects of the condensing hygroscopic substance, with initial nitric acid concentrations of 0.1, 1.0 and 10.0 ppbv on the activation of cloud droplets were also studied. The number of activated droplets increased when the initial concentration of nitric acid was increased.     

Single Particle Characterisation of the Aerosol in the Marine Boundary Layer and Free Troposphere over Tenerife, NE Atlantic, during ACE-2

In the framework of the 2nd Aerosol Characterization Experiment (ACE-2), in June and July 1997, size segregated samples were collected for single particle analysis on the island of Tenerife, in both the marine boundary layer (MBL) and the free troposphere (FT), to study the characteristics of the North Atlantic aerosol. A systematic assessment was made of the aerosol under background conditions and when the environment was perturbed by European emissions and/or Saharan dust. The aerosol particles were analysed by automated and manual SEM-EDX, followed by cluster analysis to identify the different particle types and their abundance. Basing on back trajectory calculations, particle numbers and volume concentrations, different periods can be identified regarding the origin of the sampled air masses. In the FT, the air masses were classified as clean Atlantic, Saharan dust from Africa or pollution from Europe. In the MBL, air masses were classified as clean, polluted or perturbed by emissions from Europe. For both the FT and MBL samples, the main changes in chemical composition were observed between the fine and coarse mode aerosol. The FT fine mode aerosol is dominated by S-poor aluminosilicates (62%) in the event of the dust samples or sulphates, carbonaceous particles (20%) and S-rich aluminosilicates (46%) in the polluted samples. For the larger fractions, a strong decreasing trend was observed for the sulphates (less than 20%) and carbonaceous particles (10%) in the polluted samples. The MBL fine mode was completely dominated by S-rich particles (polluted 55% and perturbed 59%), and to a lesser extent, carbonaceous and aged sea salt particles. In the coarse mode, the polluted air mass is dominated by sea salt particles (62%). Contrary to the fine fraction, the polluted air mass in the coarse fraction contained 5.3% of S-rich particles. The combined interpretation of the data from the analysis of size-fractioned particles and the calculated backward trajectories for air masses coming from Europe, Africa and the Atlantic, results in better insights on aerosol chemistry, especially for the comparison of the particle composition in the FT and the MBL.     

Development of RAMS-CMAQ to Simulate Aerosol Optical Depth and Aerosol Direct Radiative Forcing and Its Application to East Asia

The air quality modeling system RAMS （Regional Atmospheric Modeling System）-CMAQ （Models-3 Community Multi-scale Air Quality） is developed to simulate the aerosol optical depth （AOD） and aerosol direct forcing （DF）. The aerosol-specific extinction, single scattering albedo, and asymmetry factor are parameterized based on Mie theory taking into account the aerosol size distribution, composition, refractive index, and water uptake of solution particles. A two-stream solar radiative model considers all gaseous molecular absorption, Rayleigh scattering, and aerosols and clouds. RAMSCMAQ is applied to simulate all major aerosol concentrations （e.g., sulfate, nitrate, ammonium, organic carbon, black carbon, fine soil, and sea salt） and AOD and DF over East Asia in 2005. To evaluate its performance, the simulated AOD values were compared with ground-based in situ measurements. The comparison shows that RAMSCMAQ performed well in most of the model domain and generally captured the observed variations. High AOD values （0.2-1.0） mainly appear in the Sichuan Basin as well as in central and southeastern China. The geographic distribution of DF generally follows the AOD distribution patterns, and the DF at the top-of-the-atmosphere is less than -25 and -20 W m^-2 in clear-sky and all-sky over the Sichuan Basin. Both AOD and DF exhibit seasonal variations with lower values in July and higher ones in January. The DF could obviously be impacted by high cloud fractions.     

Biogenic and anthropogenic organic matter in aerosol over continental Europe: source characterization in the east Baltic region

An Aerodyne quadruple aerosol mass spectrometer (Q-AMS) has been used to provide on-line measurements of size dependent chemical composition of fine aerosol particles (PM₁) at the Air Pollution Research Station in Preila, Lithuania, representing the east Baltic region. The size dependent chemical composition measurements by AMS have revealed that in marine air masses 118?nm mode organics-containing particles were fresher compared to sulfate-containing particles (295?nm), likely originated as secondary aerosol from forest emissions or produced by primary sea spray over the Baltic Sea. In polluted continental air masses sulfate and organics were highly internally mixed and aged. The mass spectral results indicated that the major components of organic compounds were oxygenated organic species with strong signals at m/z 18, 43, 44 with several specific features. Positive matrix factorization (PMF) of AMS organic mass spectral data has identified three factors: aged oxygenated low-volatility organic aerosol (LV-OOA), less oxygenated semi-volatile organic aerosol (SV-OOA), and biogenic organic aerosol (BGOA) of either terrestrial or marine origin. The measurements were compared with a real-time particulate matter Beta Absorption Monitor (Thermo ESM Andersen) and Micro Orifice Uniform Deposit Impactor (MOUDI) data. The intercomparison showed a good correlation and a stable ratio between PM₁ and PM_2.5 concentrations. A comparison of the on-line Q-AMS data and the off-line MOUDI fine particle (<1???m) data yielded a reasonable agreement in size distributions but not the absolute mass concentrations due to sampling conditions, evaporation of acidic species from sampling substrates and bounce of the particles in the MOUDI.     

The Microphysical Characteristics of Wintertime Cold Clouds in North China

The microphysical characteristics of wintertime cold clouds in North China were investigated from 22 aircraft observation flights from 2014 to 2017, 2020, and 2021. The clouds were generated by mesoscale weather systems with little orographic component. Over the mixed-phase temperature range (–40°C to 0°C), the average fraction of liquid, mixed-phase, and ice cloud was 4.9%, 23.3%, and 71.8%, respectively, and the probability distribution of ice mass fraction was a half-U-shape, suggesting that ice cloud was the primary cloud type. The wintertime mixed-phase clouds in North China were characterized by large cloud droplet number concentration, small liquid water content (LWC), and small effective diameter of cloud droplets. The main reason for larger cloud droplet number concentration and smaller effective diameter of cloud droplets was the heavy pollution in winter in North China, while for smaller LWC was the lower temperature during flights and the difference in air mass type. With the temperature increasing, cloud droplet number concentration, LWC, and the size of ice particles increased, but ice number concentration and effective diameter of cloud droplets decreased, similar to other mid-latitude regions, indicating the similarity in the temperature dependence of cloud properties of mixed-phase clouds. The variation of the cloud properties and ice habit at different temperatures indicated the operation of the aggregation and riming processes, which were commonly present in the wintertime mixed-phase clouds. This study fills a gap in the aircraft observation of wintertime cold clouds in North China.     

First Surface-based Estimation of the Aerosol Indirect Effect over a Site in Southeastern China

The deployment of the U.S. Atmospheric Radiation Measurement mobile facility in Shouxian from May to December2008 amassed the most comprehensive set of measurements of atmospheric, surface, aerosol, and cloud variables in China.This deployment provided a unique opportunity to investigate the aerosol–cloud interactions, which are most challenging and, to date, have not been examined to any great degree in China. The relationship between cloud droplet effective radius(CER) and aerosol index(AI) is very weak in summer because the cloud droplet growth is least affected by the competition for water vapor. Mean cloud liquid water path(LWP) and cloud optical depth(COD) significantly increase with increasing AI in fall. The sensitivities of CER and LWP to aerosol loading increases are not significantly different under different air mass conditions. There is a significant correlation between the changes in hourly mean AI and the changes in hourly mean CER,LWP, and COD. The aerosol first indirect effect(FIE) is estimated in terms of relative changes in both CER(FIECER) and COD(FIECOD) with changes in AI for different seasons and air masses. FIECODand FIECERare similar in magnitude and close to the typical FIE value of ~ 0.23, and do not change much between summer and fall or between the two different air mass conditions. Similar analyses were done using spaceborne Moderate Resolution Imaging Spectroradiometer data. The satellite-derived FIE is contrary to the FIE estimated from surface retrievals and may have large uncertainties due to some inherent limitations.     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。     

Simulation of rocket seeding of convective clouds with coarse-dispersion hygroscopic aerosol. 1. Condensational growth of the cloud droplets at the salt crystals

Patterns of propagation of aerosol particles generated in the hygroscopic seeding of convective clouds from antihail rockets is studied. Effects of the salt particle dispersity on condensational growth rate of separate cloud droplets on these particles are studied; analytical formulas are obtained as describing change of radius of the NaCl crystal and of the cloud droplet which grows on the crystal till the moment of full dissolving of the crystal in the droplet. Numerical computations are used for comparative analysis of the salt effect on intensification of condensational growth of the droplets in the cloud.     

Numerical quantification of sources and phase partitioning of chemical species in cloud: application to wintertime anthropogenic air masses at the Puy de Dôme station

The Model of Multiphase Cloud Chemistry M2C2 has recently been extended to account for nucleation scavenging of aerosol particles in the cloud water chemical composition. This extended version has been applied to multiphase measurements available at the Puy de Dôme station for typical wintertime anthropogenic air masses. The simulated ion concentrations in cloud water are in reasonable agreement with the experimental data. The analysis of the sources of the chemical species in cloud water shows an important contribution from nucleation scavenging of particles which prevails for nitrate, sulphate and ammonium. Moreover, the simulation shows that iron, which comes only from the dissolution of aerosol particles in cloud water, has a significant contribution in the hydroxyl radical production. Finally, the simulated phase partitioning of chemical species in cloud are compared with measurements. Numerical results show an underestimation of interstitial particulate phase fraction with respect to the measurements, which could be due to an overestimation of activated mass by the model. However, the simulated number scavenging efficiency of particles agrees well with the measured value of 40% of total number of aerosol particles activated in cloud droplets. Concerning the origin of chemical species in cloud water, the model reproduces quite well the contribution of gas and aerosol scavenging estimated from measurements. In addition, the simulation provides the contribution of in-cloud chemical reactivity to cloud water concentrations.