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1.
研究了数值天气预报模式中次阿格湍流垂直扩散过程的参数化问题。以Ｂｏｕｇｅａｕｌｔ和Ｌａｃａｒｒｅｒｅ（１９８９）的参数化方案为基础，改进了处理湍流混合长的方法，使湍流混合长和热力混合长分别依赖于基本气流的静力稳定度和风场切变。新方案的基本思路是把ＶｏｎＫａｒｍａｎ（１９３０）提出的动力（风场切变）湍流扰动假设与ＢＬ－８９方案提出的热力（静力稳定度）湍流扰动假设结合在一起，强调了大气的热力结构、动力结构和湍流动能对湍流混合过程的共同影响。新方案和ＢＬ－８９方案的二维对比数值试验结果表明，在大气处于静力较稳定而风场切变明显条件下的湍流扰动表现能力方面，新方案比原方案有明显的改进。 相似文献
2.
Heterogeneous nucleation and condensation of dibutylphthalate, octadecane, octadecanol, and octadecanoic acid vapors at various pressures on insoluble AgCl and Ag nanoparticles in a turbulent mixing condensation nuclei counter (TMCNC) have been studied theoretically. A method to interpret the particle size distributions measured with a DMA and estimate the parameters for nucleation on single particles is proposed. Based on this semi-empirical method, the Gibbs free energy is calculated and a rate of heterogeneous nucleation on single particles is estimated directly from the experimental “condensation spectra” of inactive and active CN using the DMA data. In some cases, the dependence of the Gibbs nucleation energy on the vapor supersaturation had two maximums and one minimum, instead of one maximum as described by Gibbs' classical thermodynamics of phase transitions. This phenomenon, called “double barrier nucleation” (DBN) is caused by the surface heterogeneity of nano-CN; this is first experimental verification of DBN that had been previously predicted theoretically. Two types of heterogeneity may be present: topographic or energetic. Focusing on energetic heterogeneity, a theoretical model of DBN for spherical geometry is developed. The surface heterogeneity for insoluble nano-sized CN is shown to be critical to explaining the unusual transformation of a monomodal size distribution of inactive CN into a bimodal distribution of activated CN when coagulation is excluded. Future studies will be directed toward more data for further refining the theory and developing a model that simultaneously accounts for both types of surface heterogeneity of nano-CN. 相似文献
3.
Three “standard” Nolan–Pollak (N–P) and a modified N–P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N–P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N–P counters, typically better than ±12% for a range of aerosol sizes and compositions from a minimum diameter of 4 nm. The independently calibrated GIV CNC-440 (modified N–P type counter) also agreed well with the N–P counters. The minimum size sensitivity of the N–P counter was examined showing a lower detection limit for insoluble (Ag) particles of around 2.6±0.3 nm diameter. 相似文献
4.
一次南海海雾微物理结构个例分析 总被引：13，自引：2，他引：11
本文利用2010年3月22～23日广东省湛江市一次海雾过程的雾滴谱和能见度资料,分析了海雾的微物理特征及微物理参量(数浓度、液态含水量和平均直径)之间的相关性,并讨论了影响海雾的主要物理过程。结果表明:湛江地区海雾的平均雾滴谱符合Junge分布;在海雾发展和成熟阶段,雾滴谱拓宽过程以及数浓度与平均直径的正相关关系表明本次海雾过程主要以雾滴活化和凝结增长过程为主;湍流过程的参与使得雾滴混合均匀,雾滴平均直径向3.5 μm附近集中,趋向平均化。同时湍流使雾体内部和外部空气交流,外部空气的凝结核核化,数浓度升高,凝结增长造成小雾滴变大。 相似文献
5.
Per B. Storebø 《Boundary-Layer Meteorology》1983,27(4):359-370
The inertial subrange of the atmospheric turbulence spectrum extends downward from some 25 m in linear size. Energy is supplied to large eddies and cascades down the size range. The physics implies a certain concentration pattern for material being dispersed. The concentration frequency distribution (for very many ‘equal’ samples) should be log-normal with invariant slope, independent even of sample size. Correlations should be invariant if time lag or distance is measured in units proportional to linear sample size. Even sources with different characteristics might produce similar features. Turbulent dispersion data with air ions as tracer provide a means for testing the theory. Digitized and statistically processed data from 4 instantaneous-source and 8 continuous-source experiments agree well with the theory. Two other experiments, where analog data only are available, also support the conclusions. 相似文献
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8.
Edwin Kessler 《Dynamics of Atmospheres and Oceans》1998,27(1-4)
Condensation oscillations in showers and thunderstorms are represented by variations in the vertical air currents that are induced by the accumulation and fallout of condensed water. A simple analytic theory of condensation oscillations and calculations on more complete numerical models indicate that their period is approximately proportional to the inverse square root of the condensation function, i.e. the amount of condensate produced per unit rise of saturated air, and that the period is independent of the magnitude of thermal buoyancy. 相似文献
9.
城市边界层动量和保守物通量的特征 总被引：2，自引：0，他引：2
利用2005年1-5月北京325 m气象塔47 m高度的湍流脉动资料(风速、温度、水汽和CO2),对城市边界层冠层内的湍流运动统计特征(相似关系、高阶矩、通量和谱等)进行了分析。其中,谱分析的结果表明,城市冠层内稳定度对湍流谱的影响比较小,而水平风速的影响比较大。因此,速度和温度的相似关系在夜间稳定条件下也成立。但是,由于水汽和CO2还受其他因素的影响,相似关系并不适用。更高阶矩的研究表明它们的陡峭度与偏斜度之间存在平方关系。而水汽和CO2之间也存在差异,它们的通量日变化特征明显不同,CO2通量的日变化更能体现人类活动的影响。同时,感热通量、潜热通量和CO2通量存在季节变化,尤其是潜热通量季节差异很大。 相似文献
10.
《Atmospheric Research》2009,91(2-4):132-150
In this paper we summarize recent experimental, theoretical and observational results on the formation and growth of atmospheric nanoparticles. During the last years significant progress has occurred to explain atmospheric nucleation and initial steps of the growth. Due to climatic and health effects of fine and ultrafine particles the formation and growth of new aerosol particles is of growing interest. The question “How and under which conditions does the formation of new atmospheric aerosol particles take place?” has exercised the minds of scientists since the time of John Aitken, who in the late 1880s built the first apparatus to measure the number of dust and fog particles. However, only during the last 15–20 years has the measurement technology developed to such a level that size distributions of nanometer-size particles and concentrations of gases participating in particle formation can be measured in the atmosphere. Also from a theoretical point of view atmospheric nucleation mechanisms have not been resolved: several mechanisms such as ion-induced (or ion mediated) nucleation, ternary and kinetic (barrier-less) nucleation have been suggested. In the most recent theory, the activation of existing neutral and/or ion clusters has been suggested. 相似文献
11.
《Atmospheric Research》2009,91(2-4):303-312
Nucleation phenomena have a great importance in many areas of science. However, the main theoretical tool to analyse these phenomena, the classical nucleation theory (CNT), has known weaknesses. A decade ago a nucleation theorem based correction to CNT was developed [McGraw, R., Laaksonen, A., 1996. Scaling properties of the critical nucleus in classical and molecular-based theories of vapor–liquid nucleation. Phys. Rev. Lett. 76, 2754–2757]. We have analysed experimental nucleation rate data of two homologous series of molecular fluids in terms of this scaling relation. Our first results suggest possible universal functional form for correction to the temperature dependence of CNT. 相似文献
12.
Jussi Malila Antti-Pekka Hyvrinen Yrj Viisanen Ari Laaksonen 《Atmospheric Research》2008,90(2-4):303-ICNAA07
Nucleation phenomena have a great importance in many areas of science. However, the main theoretical tool to analyse these phenomena, the classical nucleation theory (CNT), has known weaknesses. A decade ago a nucleation theorem based correction to CNT was developed [McGraw, R., Laaksonen, A., 1996. Scaling properties of the critical nucleus in classical and molecular-based theories of vapor–liquid nucleation. Phys. Rev. Lett. 76, 2754–2757]. We have analysed experimental nucleation rate data of two homologous series of molecular fluids in terms of this scaling relation. Our first results suggest possible universal functional form for correction to the temperature dependence of CNT. 相似文献
13.
On the formation and growth of atmospheric nanoparticles 总被引：2，自引：0，他引：2
In this paper we summarize recent experimental, theoretical and observational results on the formation and growth of atmospheric nanoparticles. During the last years significant progress has occurred to explain atmospheric nucleation and initial steps of the growth. Due to climatic and health effects of fine and ultrafine particles the formation and growth of new aerosol particles is of growing interest. The question “How and under which conditions does the formation of new atmospheric aerosol particles take place?” has exercised the minds of scientists since the time of John Aitken, who in the late 1880s built the first apparatus to measure the number of dust and fog particles. However, only during the last 15–20 years has the measurement technology developed to such a level that size distributions of nanometer-size particles and concentrations of gases participating in particle formation can be measured in the atmosphere. Also from a theoretical point of view atmospheric nucleation mechanisms have not been resolved: several mechanisms such as ion-induced (or ion mediated) nucleation, ternary and kinetic (barrier-less) nucleation have been suggested. In the most recent theory, the activation of existing neutral and/or ion clusters has been suggested. 相似文献
14.
Growth of homogeneously nucleated water droplets: a quantitative comparison of experiment and theory
The formation of aerosols proceeds through nucleation, growth and aging stages. The understanding of nucleation and droplet growth is essential for handling the more complex atmospheric condensation processes. To achieve this goal, measurements of the nucleation rate of various systems are performed in an expansion chamber. In this manner nucleation and growth are decoupled by applying a short nucleation pulse of about 1 ms during which the nuclei are formed. The subsequent droplet growth is quantitatively monitored by Mie-scattering. To this end, the Mie-maxima and -minima are detected as a function of time and compared to theoretical Mie-scattering calculations for increasing radii. In this fashion, a wealth of growth curves for pure water depending on supersaturations, number densities of droplets, and temperatures were obtained. Following the approach of Fuchs and Sutugin [Fuchs, N.A., Sutugin, A.G., 1970. Highly Dispersed Aerosols. Ann Arbor Science Publishers, Ann Arbor; Fuchs, N.A., Sutugin, A.G., 1971. In: Hidy, G.M., Brock, J.R. (Eds.), International Reviews in Aerosol Physics and Chemistry: Topics in Current Aerosol Research (Part 2), Pergamon, New York, p. 1], we calculated theoretical growth curves taking into account the depletion of water vapor, the increase of droplet- and system-temperature, temperature-dependent functions of the diffusion coefficient, surface tension, liquid density and latent heat of condensation. The calculated growth curves and experimental data for 230, 240 and 250 K with number densities of droplets between 5×102 and 2×106 droplets/cm3 yield quantitative agreement between theory and experiment. This is remarkable in so far as the theory contains no adjustable parameters and assumes the sticking probability of the vapor molecules to be unity. Using a sticking probability smaller than 0.8 in the calculation leads to growth functions already outside the experimental error. 相似文献
15.
Andrey A. Grachev P. Ola G. Persson Edgar L. Andreas Peter S. Guest 《Boundary-Layer Meteorology》2005,116(2):201-235
Turbulent and mean meteorological data collected at five levels on a 20-m tower over the Arctic pack ice during the Surface
Heat Budget of the Arctic Ocean experiment (SHEBA) are analyzed to examine different regimes of the stable boundary layer
(SBL). Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime
to very stable stratification. Scaling arguments and our analysis show that the SBL can be classified into four major regimes:
(i) surface-layer scaling regime (weakly stable case), (ii) transition regime, (iii) turbulent Ekman layer, and (iv) intermittently
turbulent Ekman layer (supercritical stable regime). These four regimes may be considered as the basic states of the traditional
SBL. Sometimes these regimes, especially the last two, can be markedly perturbed by gravity waves, detached elevated turbulence
(‘upside down SBL’), and inertial oscillations. Traditional Monin–Obukhov similarity theory works well in the weakly stable
regime. In the transition regime, Businger–Dyer formulations work if scaling variables are re-defined in terms of local fluxes,
although stability function estimates expressed in these terms include more scatter compared to the surface-layer scaling.
As stability increases, the near-surface turbulence is affected by the turning effects of the Coriolis force (the turbulent
Ekman layer). In this regime, the surface layer, where the turbulence is continuous, may be very shallow (< 5 m). Turbulent
transfer near the critical Richardson number is characterized by small but still significant heat flux and negligible stress.
The supercritical stable regime, where the Richardson number exceeds a critical value, is associated with collapsed turbulence
and the strong influence of the earth’s rotation even near the surface. In the limit of very strong stability, the stress
is no longer a primary scaling parameter. 相似文献
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17.
Boundary-Layer Meteorology - Turbulent data from three sites are utilized to analyze the characteristic features of the Eulerian autocorrelation function (EAF) of horizontal (longitudinal and... 相似文献
18.
Summary Numerous tethered balloon soundings which measured meteorological parameters and ozone concentration during the POLLUMET field experiments are investigated. They give indications of the influence of ozone conservation in the nocturnal residual layer (RL) on the development of the near surface ozone concentration of the next day. Mixing down from the RL to the surface is simulated by a simple model based on transilient turbulence theory, using measured profiles as initial values or model verification. The cases investigated show that the ozone mixed down from the RL contributes 50–70% to the maximum concentration near the surface on the following day, the rest coming from chemical production and possibly advection. Various features of exchange characteristics between the RL and the nocturnal boundary layer, (NBL) are described by the analysis of the soundings. It can be shown that the vertical exchange situation during the night can have a considerable influence on the ozone concentration of the following day. 相似文献
19.
Cirrus clouds related to transported dust layers were identified on 22 occasions with ground-based polarization lidar from December 2012 to February 2018 over Wuhan (30.5°N, 114.4°E), China. All the events occurred in spring and winter. Cirrus clouds were mostly located above 7.6 km on top of the aloft dust layers. In-cloud relative humidity with respect to ice (RHi) derived from water vapor Raman lidar as well as from ERA5 reanalysis data were used as criteria to determine the possible ice nucleation regimes. Corresponding to the two typical cases shown, the observed events can be classified into two categories: (1) category A (3 cases), in-cloud peak RHi ≥ 150%, indicating competition between heterogeneous nucleation and homogeneous nucleation; and (2) category B (19 cases), in-cloud peak RHi < 150%, revealing that only heterogeneous nucleation was involved. Heterogeneous nucleation generally took place during instances of cirrus cloud formation in the upper troposphere when advected dust particles were present. Although accompanying cloud-top temperatures ranged from –51.9°C to –30.4°C, dust-related heterogeneous nucleation contributed to primary ice nucleation in cirrus clouds by providing ice nucleating particle concentrations on the order of 10?3 L?1 to 102 L?1. Heterogeneous nucleation and subsequent crystal growth reduced the ambient RHi to be less than 150% by consuming water vapor and thus completely inhibited homogeneous nucleation. 相似文献
20.
EFFECTS OF CONDENSATION HEATING AND SURFACE FLUXES ON THE DEVELOPMENT OF A SOUTH CHINA MESOSCALE CONVECTIVE SYSTEM (MCS) 总被引：3，自引：2，他引：1
A sensitive numerical simulation study is carried out to investigate the effects of condensation
heating and surface fluxes on the development of a South China MCS that occurred during 23 – 24 May 1998.
The results reveal the following: (1) Condensation heating plays an important role in the development of MCS. In
every different stage, without condensation heating, MCS precipitation is significantly reduced, and quickly
dissipates. (2) Condensation heating demonstrates most importantly during the early development stages of MCS
vortex; as the vortex develops stronger, the condensation heating effects reduces. (3) By affecting the MCS
development processes, condensation heating also influences the formation of MCS mesoscale environment
structure features such as low-level jet (mLLJ), upper-level divergence. (4) By changing the antecedent
environmental circulation, the surface fluxes also play an important role in the development of MCS. Because of
the surface heating, pressure declines over the heavy rainfall and MCS happening regions, which results in the
intensification of southerly flows from the ocean along the South China coastline areas, and leads to the
enhancement of horizontal convergence and increase of vapor amount in the lower layer. All of these make the
atmosphere more unstable and more favorable for the convection. 相似文献