Studies of modern and ancient solar energetic particles     

R. C. Reedy 《Journal of Earth System Science》1998,107(4):433-440

Modern solar energetic particles (SEPs) have been studied for about 50 years by satellites and groundbased observations. These measurements indicate much about the nature of SEPs but cover too short a period to quantify the probabilities of very large solar particle events. Many SEPs have high enough energies to make nuclides in material in which they interact. Radionuclides measured in lunar samples have been used to extend the record about SEPs back several million years. Some new measurements of modern SEPs during the last solar cycle and new results for nuclides made by SEPs in lunar samples are presented and their implications discussed. Both the modern and ancient records need to be improved, and methods to get a better understanding of solar energetic particles discussed. The fluxes of SEPs during the last million years show an increasing trend when averaged over shorter radionuclide half-lives.  相似文献   

Humidity effects on gravitational settling and Brownian diffusion of atmospheric aerosol particles     

Gottfried Hänel 《Pure and Applied Geophysics》1977,115(4):775-797

The dependency on relative humidity of the settling velocity of aerosol particles in stagnant air and of the diffusion coefficient due to Brownian motion of aerosol particles was computed for six aerosol types and different particles sizes in dry state. The computations are based (1) on mean bulk densities of dry aerosol particles obtained from measurements or from the knowledge of the chemical composition of the particles, (2) on micro-balance measurements of the water uptake per unit mass of dry aerosol substance versus water activity at thermodynamic equilibrium, and (3) on measurements of the equilibrium water activity of aqueous sea salt solutions. The results show a significant dependence of the settling velocity and Brownian diffusion of aerosol particles on relative humidity and on the particle's chemical composition.Nomenclature A surface parameter of a particle - B surface parameter of a particle - c _L velocity of sound in moist air - C 1+Kn[A+Qexp(–B/Kn]=slip correction - D diffusion coefficient of a particle - D ₁ D(=1)=diffusion coefficient of a spherical particle - f P _w /P _we (T,P)=relative humidity (f=0 dry air,f=1 saturated air) - g acceleration due to gravity - g |g| - k 1.3804×10^–16 erg/°K=Boltzmann constant - Kn _L /r=Knudsen number of a particle - Kn _{0 0L} /r ₀=Knudsen number of a dry particle - m 4r ³/3=mass of a particle - m _L 4r ³ _L /3=mass of the moist air displaced by a particle - M mobility of a particle - M ₀ molar mass of dry air - M _w molar mass of water - Ma |u–u _L |/c _L =Mach number of the particles motion relative to the ambient air - n particle number per unit volume of air - P P ₀+P _w =pressure of the moist air - P ₀ partial pressure of the dry air - P _w partial pressure of the water vapour - P _we P _we (T,P)=equilibrium partial water vapour pressure over a plane surface of water saturated with air - Q surface parameter of a particle - r equivalent radius of a particle (radius of a sphere with the particles volume) - r ₀ equivalent radius of a particle in dry state - R 1+0.13Re ^0.85=inertia correction - R ₀ specific gas constant of dry air - R _w specific gas constant of water - Re 2r _L u–u _L / _L =Reynolds number of the particles motion relative to the ambient air - t time - T absolute temperature - u velocity of a particle - u (amount of the) settling velocity of a particle in stagnant air - u ₁ u(=1)=(amount of the) settling velocity of a spherical particle in stagnant air - u _L velocity of the ambient moist air (far enough from the particle where the flow pattern remains undistorted) - W drag coefficient of a particles equivalent sphere - empirical parameter in equation (3.1) - dynamic viscosity of a particles liquid cover - _L dynamic viscosity of moist air - _0L dynamic viscosity of dry air (at the same pressure and temperature like the moist air) - celsius temperature - dynamic shape factor of a particle (=1 for a sphere) - ₀ dynamic shape factor of a dry particle - _L mean free path of the molecules in moist air - _0L mean free path of the molecules in dry air (at the same pressure and temperature like the moist air) - _Po mean free path of the molecules in dry air at the pressureP ₀ of the dry air and the temperature given - factor of solid to liquid change-over (=1 for a solid particle) - mean bulk density of a particle - _L density of the moist air - _0L density of the dry air at the same pressure and temperature like the moist air - ₀ mean bulk density of a dry particle - ₀ mean diameter of the molecules of dry air - _w diameter of water molecules - relaxation time of a particle - gradient operation - 3.141593  相似文献   

Study of background aerosols in the Antarctic troposphere     

T. Ito 《Journal of Atmospheric Chemistry》1985,3(1):69-91

Systematic year-round observations of submicron aerosols were carried out at Syowa Station (69°00'S, 39°35'E) in 1978. On the basis of the results of these observations, it is concluded that two types of aerosols originating from different sources are present in the Antarctic croposphere. With the intrusion of maritime air, mostly in the polar night months, sea salt particles and ammonium sulfate particles contained originally in the clean maritime air are dominant. The size distribution of such aerosols is monomodal, having a single mode at around 0.03 m in radii. On the other hand, in the sunlit months, sulfuric acid droplets are predominant and the size distribution is bimodal, having an additional mode at around 0.005 m in radii. Those sulfuric acid particles seem to be formed photochemically within a specific layer in the mid to lower troposphere over Antarctica. Most Antarctic submicron particles are of tropospheric origin, not of stratospheric nor anthropogenic origin.  相似文献   

广州夏季硫酸盐巨粒子的分布特征   总被引：10，自引：0，他引：10       下载免费PDF全文

吴兑  甘春铃  何应昌 《气象》1995,21(3):44-46

作者分析了１９８７年８－９月广州观的硫酸盐巨粒子资料，主要结果是：（１）干直径大于２μｍ的硫酸盐巨粒了平均浓度１．２个．Ｌ＾－１，平均含盐量３．０μｇ．ｍ＾－３，其中干直径大于４μｍ的特大粒子平均为０．６个．Ｌ＾－１，均低于南海西沙永兴岛的结果。（２）浓度谱是典型的准单调下降型幂函数递减谱，其谱型参数与永贪的结果甚为接近；质量谱在单对数坐标中为较为平直的分布，表明各谱段粒子对含盐量均有贡献。（２）  相似文献   

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

A. Schwarzenbck  S. Mertes  J. Heintzenberg  W. Wobrock  P. Laj 《Atmospheric Research》2001,58(4)

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   

Preparation and characterization of micron and submicron-sized vermiculite     

L. A. Pérez-Maqueda  O. B. Caneo  J. Poyato  J. L. Pérez-Rodríguez 《Physics and Chemistry of Minerals》2001,28(1):61-66

 The effect of ultrasounds on natural macroscopic vermiculite flakes has been studied. Conditions for the preparation of submicron vermiculite particles of narrow particle-size distribution by sonochemistry are described. The resulting material is crystalline, as assayed by X-ray diffraction. Effects of ultrasound treatment on the mean particle size, crystal structure, crystallite dimensions in different directions, and specific surface area of the resulting particles are investigated. Under the conditions used in this work, there is a practical limit at 40 h in the sonication time for the preparation of submicron particles; longer treatment times promoted aggregation. Received: 21 March 2000 / Accepted: 21 August 2000  相似文献   

计算雷达截面的积分方程法     

嵇驿民  王宝瑞 《南京气象学院学报》1991,14(1):61-72

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Phosphorus transport to the bottom of Lake Constance     

Joachim Kleiner  Hans-Henning Stabel 《Aquatic Sciences - Research Across Boundaries》1989,51(3):181-191

Despite decreasing nutrient loading of Lake Constance over the past few years, annual sedimentation rates of dry matter remained nearly constant at a level of about 1000 gm^–2y^–1. The phosphorus content in settling material varied between 0.13 and 0.22% of dry weight. Phosphorus was transported to the lake bottom mainly by POM and by coprecipitation with authigenically formed calcite (estimated from results of laboratory studies). Adsorption to sinking particles of allochthonous origin was of minor importance. The effect of a self-cleaning mechanism is discussed with regard to continuously declining contents of dissolved phosphorus in Lake Constance since 1981, due to external sanitation measures in the drainage area.  相似文献   

Trace elements in aerosol particles from Bermuda and Barbados: Concentrations,sources and relationships to aerosol sulfate   总被引：8，自引：0，他引：8  

R. Arimoto  R. A. Duce  D. L. Savoie  J. M. Prospero 《Journal of Atmospheric Chemistry》1992,14(1-4):439-457

The concentrations of selected trace elements and non-sea salt sulfate were determined for aerosol particle samples collected over the open North Atlantic Ocean as part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). The concentrations of atmospheric sea salt and mineral aerosol, which together dominate the mass of particulate material in the atmosphere, were higher at Barbados than at Bermuda. In contrast, the impact of pollution sources on trace element concentrations was more evident at Bermuda than at Barbados. At both sites Sb and Se were enriched significantly over the concentrations expected from mineral dust or from atmospheric sea salt. Moreover, the concentrations of Sb and Se were correlated, and the observed Sb/Se ratios often were similar to those resulting from anthropogenic emissions. At Bermuda, the concentrations of Sb and Se co-varied with non-sea salt sulfate, suggesting that a significant fraction of the non-sea salt sulfate is anthropogenic. In a broader context, the synthesis of results demonstrates that trace element data are useful for evaluating the relative contributions of anthropogenic vs. natural sources to the budgets of non-sea salt sulfate in acrosol particles.  相似文献   

极光区电离层扰动的两种类型          下载免费PDF全文

沈长寿  资民筠 《极地研究》1996,8(4):14-22

本文从ＥＩＳＣＡＴ探测资料分析确认，沉降粒子对极光区电离层的电离生成率有极重要的作用，但高能和低能粒子的有效电离高度范围完全不同，另一方面，磁层对流的增强却常使Ｆ层电子密度Ｎ下降，１９８５年１月２８～２９日期间出现Ｎ（Ｅ层）Ｎ（Ｆ层），且１４７ｋｍ以上Ｎ随高度增加而下降的典型扰动剖面。这是高能粒子和强磁层对流共同作用的结果。１９９３年２月１６～１７日期间，中午前后ＮｍＦ异常地增大，而Ｎ（Ｅ层）却无明显变化。这是与前者特征不同的另一类典型剖面。磁层内低能粒子（能量小于１ｋｅＶ）从极隙区沉降直抵电离层是使Ｆ层电子密度剧增的物理机制  相似文献