Expanded application of the exhaustion method in diffusional decay measurements

Summary It is shown that the exhaustion method by which the components of a polydisperse aerosol are found or a continuous particle size distribution is split into a few, more or less arbitrary components, is applicable not only to the diffusional decay measurements in connection with diffusion batteries but also to cylindrical diffusers and to the modified dynamic method proposed by the Author [1].     

On deducing the magnetization of the lunar surface from orbital surveys

A combination of orbital photographic, selenochemical and magnetic surveys may elucidate the mechanism by which the lunar surface became magnetized and possibly yield an estimate of the intensity of the ancient magnetizing field and its time variation. The determination of the size and shape of the magnetized regions requires the measurement of the altitude dependence of field, especially at low altitudes (< 100 km) and with a high enough sampling rate to resolve the profile at the edges of magnetized bodies. The planned Lunar Polar Orbiter may well provide the necessary data.     

合肥地区沙尘暴降尘过程的大气细粒子谱观测研究

2010年3月20日至3月28日,利用大气细粒子谱分析仪对合肥地区大气细粒子谱进行连续在线观测.观测过程涵盖整个沙尘暴降尘期、间歇性降雨期及晴好天气粒子浓度增长期.颗粒物数浓度分析表明,沙尘暴降尘期内核模态(Nucleation mode, 5~20 nm)、爱根核模态(Aitken mode, 20~100 nm)和积聚模态(Accumulation mode, 100~1000 nm)粒子浓度分别为898 cm-3、3424 cm-3、1587 cm-3,并未明显高于间歇性降雨期(粒子浓度分别为255 cm-3、1509 cm-3、1213 cm-3)和晴好天气粒子浓度增长期(粒子浓度分别为706 cm-3、4891 cm-3、2468 cm-3);沙尘暴降尘期粗粒子模态(Coarse mode, 1~10 μm) 粒子值达到 48 cm-3,浓度远高于其他观测期.粒谱分析表明:合肥地区大气细粒子谱呈典型双峰结构,第一峰值出现在10~20 nm之间,第二峰值出现在100 nm左右,而且不同天气条件下细粒子谱峰值位置略有不同;沙尘暴降尘期,粒径10 nm以下和400 nm以上粒子浓度值高于间歇性降雨期和晴好天气粒子浓度增长期,而并非只有粗粒子模态粒子浓度高于其他时段.     

Some results of aerosol measurements

Summary In brief a newly developed freezing nuclei meter is described. Results of measurements made with this instrument in New Jersey, California and in the Thule area, Greenland, are shown. These data are compared with measurements of condensation nuclei, simultaneously made with the General Electric and the Aitkennuclei counters. Also the results obtained from some measurements of the lightscattering function of the aerosol in industrial areas near New York City are presented.     

A comparison of material damping measurements in resonant column using the steady-state and free-vibration decay methods

The study reports results associated with the small to medium strain range material damping of quartz sand. The experiments were conducted in a fixed-free type resonant column and the samples were subjected to torsional mode of vibration at their first natural frequency. A comparison between the derived damping values using two different methods is presented: the steady-state vibration method (SSV) and the free-vibration decay method (FVD). Within the scatter of the data the two different methods in measuring material damping provided comparable results with a scatter, in most cases, of less than ±15% for the working strain range of the resonant column method. The damping values derived from the FVD and SSV methods were also compared with proposed models in the literature by means of stiffness degradation–damping increase correlation.     

On the stationary charge distribution on aerosol particles in a bipolar ionic atmosphere

Summary By the «limiting sphere» method the combination coefficients for gaseous ions and aerosol particles were calculated, allowing for the jump in ion concentration at the surface of the particles. Hence the stationary charge distribution on aerosol particles in a symmetrical bipolar ionic atmosphere was determined. The use of the Boltzmann equation for this purpose proposed by some authors is theoretically wrong asthis equation applies to equilibrium rather than to stationary states. In practice, the Boltzmann equation can be used for particles with radius 3·10^–5 cm (under atmospheric pressure). Within this range the image forces and the jump in ion concentration may be neglected. The conditions of the applicability of the steady diffusion equations to the theory of the stationary charge distribution in aerosols are discussed.     

Urban aerosol particulates on Hong Kong roadsides: size distribution and concentration levels with time

A detailed study on particulate matter from vehicle emission was carried out at roadsides in Hong Kong downtown area. The study aims to explore the variations of particulate matter at roadsides in morning and afternoon. Data of concentrations of different size groups of particulate matter were collected and analyzed. It was found that the particulate levels generally vary periodically with traffic signal changes. During the green traffic light period, concentrations of the particulate matter increase to peak point and then diffuse to a relatively stable level in the red traffic light period. Such stable level is regarded as background level, to which pedestrians are exposed when they walk-by and cross the zebra zones. To analyze and further explore the collected data, a statistical distribution model, i.e., goodness-of-fit test, was employed. It was noticed that the lognormal distribution best fits the particulate matter data in both morning and afternoon. In addition, the non-parametric test was also used to assess the differences between morning and afternoon data. The results show that both data sets statistically differ from each other at 5% significance level. It can be deduced that the change of traffic volume, humidity and wind speed between morning and afternoon may cause this difference.     

Small-strain constrained elastic modulus of clean quartz sand with various grain size distribution

Approx. 120 resonant column (RC) tests with additional P-wave velocity measurements using piezoelectric elements have been performed on 19 clean quartz sands with piecewise linear, gap-graded, S-shaped or other smoothly shaped grain size distribution curves. For each material different pressures and densities were tested. It is demonstrated that the extended empirical equations for the small-strain constrained elastic modulus proposed by the authors in an earlier paper work well also for most of the more complex grain size distribution curves tested in the present study. These equations considering the influence of the uniformity coefficient of the grain size distribution curve were developed based on the data from tests on linear gradations. A further improvement of the prediction for the more complex grain size distributions can be achieved if the correlation equations are applied with a specially defined average inclination of the grain size distribution curve. Such an improvement is demonstrated not only for the small-strain constrained elastic modulus, but also for small-strain shear modulus, modulus degradation and Poisson's ratio.     

A minimum sample size required from Schmidt hammer measurements

The Schmidt hammer is a useful tool applied by geomorphologists to measure rock strength in field conditions. The essence of field application is to obtain a sufficiently large dataset of individual rebound values, which yields a meaningful numerical value of mean strength. Although there is general agreement that a certain minimum sample size is required to proceed with the statistics, the choice of size (i.e. number of individual impacts) was usually intuitive and arbitrary. In this paper we show a simple statistical method, based on the two‐sample Student's t‐test, to objectively estimate the minimum number of rebound measurements. We present the results as (1) the ‘mean’ and ‘median’ solutions, each providing a single estimate value, and (2) the empirical probability distribution of such estimates based on many field samples. Schmidt hammer data for 14 lithologies, 13–81 samples for each, with each sample consisting of 40 individual readings, have been evaluated, assuming different significance levels. The principal recommendations are: (1) the recommended minimum sample size for weak and moderately strong rock is 25; (2) a sample size of 15 is sufficient for sandstones and shales; (3) strong and coarse rocks require 30 readings at a site; (4) the minimum sample size may be reduced by one‐third if the context of research allows for higher significance level for test statistics. Interpretations based on less than 10 readings from a site should definitely be avoided. Copyright © 2009 John Wiley & Sons, Ltd.     

On the validity of Boltzmann's distribution law for the charges of aerosol particles in electrical equilibrium

Summary The validity ofBoltzmann's energy distribution law as applied to the charge distribution of monodisperse aerosols, i.e. aerosols which contain particles of one size only, was studied with improved equipment now available.Since monodisperse aerosols with particle size of about 10^–6 cm cannot yet be produced and because aerosols in general contain particles of different sizes, polydisperse aerosols stored in a large gasometer were used for the investigation. The composition and the average radius of these aerosols heterogeneous in particle size were determined by the Exhaustion Method employing a diffusion battery without end-pieces or connecting tubing.The experimental curve found for the ratio of the uncharged (N ₀) to the charged (N) nuclei versus radius (r) of the particles deviates for all investigated radii between 0.5 and 4.0·10^–6 cm from the theoretical curve of a monodisperse aerosol computed according to the Boltzmann law. For radii smaller than about 1.4·10^–6 cmN ₀/N is smaller than that given by Boltzmann's law, for radii greater than 1.4·10^–6 cm larger, or, in other words, forr<1.4·10^–6 cm the number of charged nuclei found in the aerosols investigated is greater than that predicted byBoltzmann's law, and forr>1.4·10^–6 cm smaller.The deviations from the theoretical curve forr>1.4·10^–6 cm can be fully explained by the polydispersity of the aerosols used; forr<1.4·10^–6 cm the deviations are too big to be attributed to polydispersity. From this it must be concluded thatBoltzmann's distribution law is not valid for the charge distribution of homogenous aerosols containing nuclei with radii smaller than about 1.4·10^–6 cm.The equivalent radius as deduced from a substitute monodisperse aerosol in charge equilibrium for which theBoltzmann law is assumed valid, deviates in the range of 1.0·10^–6<r<3.0·10^–6 cm (or 90%>100N ₀/Z>55%) on the average by up to 35% from the actual mean radius of the investigated polydisperse aerosols computed from the radii of their singly sized components.

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Zusammenfassung Die Gültigkeit desBoltzmannschen Gesetzes der Energieverteilung für die Ladungsverteilung von monodispersen Aerosolen, das heisst Aerosolen, welche Teilchen von nur einer Grösse enthalten, wurde mit den jetzt zur Verfügung stehenden verbesserten Mitteln studiert.Da monodisperse Aerosole mit Teilchengrössen von ungefähr 10^–6 cm noch nicht erzeugt werden können und Aerosole im allgemeinen Teilchen von verschiedenen Grössen enthalten, wurden für die jetzige Untersuchung polydisperse Aerosole, welche in einem grossen Gasometer gespeichert waren, benützt. Die Zusammensetzung und der mittlere Radius dieser Aerosole mit heterogener Teilchengrösse wurden nach der Exhaustions-Methode unter Benützung einer Diffusionsbatterie ohne Endstücke oder Verbindungsröhren bestimmt.Die experimentell gefundene Kurve, welche das Verhältnis der ungeladenen (N ₀) und geladenen (N) Kerne als Funktion des Radius (r) darstellt, weicht für alle untersuchten Radien zwischen 0.5 und 4.0·10^–6 cm von der theoretischen Kurve eines monodispersen Aerosols, wie sie nachBoltzmann's Gesetz berechnet wird, ab. Für Radien kleiner als ungefähr 1.4·10^–6 cm ist das VerhältnisN ₀/N kleiner als es durchBoltzmann's Gesetz gegeben wird, für Radien grössen als 1.4·10^–6 cm grösser oder, mit anderen Worten, fürr<1.4·10^–6 cm ist die Zahl der geladenen Teilchen, die in den untersuchten Aerosolen gefunden wurde, grösser als die vonBoltzmann's Gesetz vorausgesagte, und fürr>1.4·10^–6 cm kleiner.Die Abweichungen von der theoretischen Kurve fürr>1.4·10^–6cm können vollkommen durch die Polydispersität der benützten Aerosole erklärt werden; fürr<1.4·10^–6 cm sind die Abweichungen zu gross, als dass sie der Polydispersität zugeschrieben werden könnten. Daraus muss geschlossen werden, dassBoltzmann's Verteilungsgesetz für die Ladungsverteilung eines homogenen Aerosols, welches Kerne mit Radien kleiner als ungefähr 1.4·10^–6 cm enthält, nicht gültig ist.Der äquivalente Radius, wie er von einem im Ladungsgleichgewicht befindlichen, monodispersen Ersatz-Aerosol, für welchesBoltzmann's Gesetz als gültig angenommen wird, abgeleitet werden kann, weicht im Bereich von 1.0·10^–6<r<3.0·10^–6 cm (oder 90%>N ₀/Z>55%) durchschnittlich bis zu 35% vom tatsächlichen mittleren Radius des untersuchten polydispersen Aerosols ab.

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The research reported in this article has been supported in part by the Geophysics Research Directorate of the Air Force Cambridge Research Laboratories, through the European Office of the Air Force Research Division, United States Air Force under Contract AF 61(052)-26, by the United States Department of Army, through its European Research Office, Contract DA-91-591-EUC-1282 & 1657 and by the Instrumentation Engineering Physics & Analysis Laboratory of the General Electric Co., Schenectady, New York under Retainer Agreement.     

On the size distribution of ice-supersaturated regions in the upper troposphere and lowermost stratosphere

In order to determine typical sizes of ice-supersaturated regions (ISSRs) in the upper troposphere and lowermost stratosphere we set up the frequency distribution of path lengths flown by MOZAIC aircraft within ISSRs. The mean path length is about 150 km with a standard deviation of 250 km. We analyse the influence of a selection bias (viz. that large ISSRs are more often crossed by aircraft than small ones) on the obtained path length statistics and derive a mathematical equation that relates the path length distribution to the underlying size distribution of ISSRs, assuming that they have circular shape. We solve the equation (by trial and error) and test the result using numerical simulations. Surprisingly, we find that there may be many more very small ISSRs than apparent from the data such that the true mean diameter of the ISSRs may be of the order a few kilometres only. The relevance of the result is discussed and dedicated research flights to measure the true extension of ISSRs are recommended.     

Meridional distribution of tropospheric ozone from measurements aboard commercial airliners

Aboard commercial airliners twenty registrations of the ozone concentration of the upper troposphere were carried out within a period of 14 months between Europe and South Africa. Nearly each of these meridional ozone profiles shows an approximately constant ozone content between 25°S and 25°N with a pronounced seasonal variation. Most of these profiles show two marked peaks of the ozone concentration at about 30°N and between 40° and 45°N. Though the number of these registrations is not sufficient for statistical computations, the first results confirm the meridional ozone distribution, which was expected from studies with ozone-radiosonde soundings. Moreover a strong asymmetry of the northern and southern hemisphere is confirmed by these ozone measurements.     

Towards the production of a reproducible aerosol by radiolytic methods

Summary A convenient constant reproducible aerosol has been a long-felt need for satisfactory research and development purposes in the field of Aitken nucleus studies. An account is given of a recent attempt to produce such an aerosol by radiolytic methods. It consists of the introduction of -particle sources of different activities into nucleus-free air in aerosol containers. Condensation nuclei in the Aitken size-range are produced by radiolytic reactions in the air. The concentration, size and size-distribution of the particles have been measured for sources of various activities and the results are sufficiently consistent to allow us to state that radiolytic production seems a promising approach to the problem of providing aerosols of particles lying in the lower Aitken nucleus size range.     

ENSO对平流层气溶胶分布的影响

本文采用ONI(Oceanic Nino Index)和HALOE(Halogen Occultation Experiment)气溶胶面积密度资料,从其滞后相关性入手分析了ENSO循环对平流层气溶胶的影响,通过对滞后于El Nino和La Nina时气溶胶含量的比较探讨了ENSO强迫的影响程度,并用剩余环流及其输送量解释了平流层气溶胶变化的动力机制.结果表明:ENSO对平流层气溶胶的分布有明显影响,在赤道和低纬度上空尤为显著,El Nino发生后半年内热带平流层低层的气溶胶面积密度较平均值偏大,平流层中层的面积密度则偏小,而La Nina反之.El Nino和La Nina影响的差异显著,在分别滞后于El Nino和La Nina事件2~8个月间的60 hPa气溶胶含量差异甚至高达45%,海表温度变化1 K则在滞后半年内气溶胶面积密度的变化可达到16%.ENSO的强烈影响能够维持大约半年,两年后基本消退.热带的变化幅度明显强于中高纬度,南北半球的变化特征也有所不同.ENSO通过影响剩余环流导致气溶胶输送量发生变化,进而引起气溶胶分布出现上述差异.     

On the behavior of mud floc size distribution: model calibration and model behavior

In this paper, we study a population balance equation (PBE) where flocs are distributed into classes according to their mass. Each class i contains i primary particles with mass m _p and size L _p. All differently sized flocs can aggregate, binary breakup into two equally sized flocs is used, and the floc??s fractal dimension is d ₀?=?2, independently of their size. The collision efficiency is kept constant, and the collision frequency derived by Saffman and Turner (J Fluid Mech 1:16?C30, 1956) is used. For the breakup rate, the formulation by Winterwerp (J Hydraul Eng Res 36(3):309?C326, 1998), which accounts for the porosity of flocs, is used. We show that the mean floc size computed with the PBE varies with the shear rate as the Kolmogorov microscale, as observed both in laboratory and in situ. Moreover, the equilibrium mean floc size varies linearly with a global parameter P which is proportional to the ratio between the rates of aggregation and breakup. The ratio between the parameters of aggregation and breakup can therefore be estimated analytically from the observed equilibrium floc size. The parameter for aggregation can be calibrated from the temporal evolution of the mean floc size. We calibrate the PBE model using mixing jar flocculation experiments, see Mietta et al. (J Colloid Interface Sci 336(1):134?C141, 2009a, Ocean Dyn 59:751?C763, 2009b) for details. We show that this model can reproduce the experimental data fairly accurately. The collision efficiency ?? and the ratio between parameters for aggregation and breakup ?? and E are shown to decrease linearly with increasing absolute value of the ??-potential, both for mud and kaolinite suspensions. Suspensions at high pH and different dissolved salt type and concentration have been used. We show that the temporal evolution of the floc size distribution computed with this PBE is very similar to that computed with the PBE developed by Verney et al. (Cont Shelf Res, 2010) where classes are distributed following a geometrical series and mass conservation is statistically ensured. The same terms for aggregation and breakup are used in the two PBEs. Moreover, we argue, using both PBEs, that bimodal distributions become monomodal in a closed system with homogeneous sediment, even when a variable shear rate is applied.     

Comparison of methods for estimating earth resistivity from airborne electromagnetic measurements

Earth resistivity estimates from frequency domain airborne electromagnetic data can vary over more than two orders of magnitude depending on the half-space estimation method used. Lookup tables are fast methods for estimating half-space resistivities, and can be based on in-phase and quadrature measurements for a specified frequency, or on quadrature and sensor height. Inverse methods are slower, but allow sensor height to be incorporated more directly. Extreme topographic relief can affect estimates from each of the methods, particularly if the portion of the line over the topographic feature is not at a constant height above ground level. Quadrature–sensor height lookup table estimates are generally too low over narrow valleys. The other methods are also affected, but behave less predictably. Over very good conductors, quadrature–sensor height tables can yield resistivity estimates that are too high. In-phase–quadrature tables and inverse methods yield resistivity estimates that are too high when the earth has high magnetic susceptibility, whereas quadrature–sensor height methods are unaffected. However, it is possible to incorporate magnetic susceptibility into the in-phase–quadrature lookup table. In-phase–quadrature lookup tables can give different results according to whether the tables are ordered according to the in-phase component or the quadrature component. The rules for handling negative in-phase measurements are particularly critical. Although resistivity maps produced from the different methods tend to be similar, details can vary considerably, calling into question the ability to make detailed interpretations based on half-space models.     

A comparison of methods for low streamflow estimation from spot measurements

Low streamflow statistic estimators at ungauged river sites generally have large errors and uncertainties. This can be due to many reasons, including lack of data, complex hydrologic processes, and the inadequate or improper characterization of watershed hydrogeology. One potential solution is to take a small number of streamflow measurements at an ungauged site to either estimate hydrogeologic indices or transfer information from a nearby site using concurrent streamflow measurements. An analysis of four low streamflow estimation techniques, regional regression, regional plus hydrogeologic indices, baseflow correlation, and scaling, was performed within the Apalachicola–Chattahoochee–Flint watershed, a U.S. Geological Survey WaterSMART region in the south‐eastern United States. The latter three methods employ a nominal number of spot measurements at the ungauged site to improve low streamflow estimation. Results indicate that baseflow correlation and scaling methods, which transfer information from a donor site, can produce improved low streamflow estimators when spot measurements are available. Estimation of hydrogeologic indices from spot measurements improves regional regression models, with the baseflow recession constant having more explanatory power than the aquifer time constant, but these models are generally outperformed by baseflow correlation and scaling.     

Meridional tropospheric ozone distribution north of 50° from airplane measurements

Ozone measurements aboard commercial airliners over Scandinavia and on transpolar flights were analyzed for tropospheric ozone concentration. The results confirm a region of enhanced stratospheric-tropospheric exchange around 60° latitude which was expected from Sr-90 fallout measurements.     

On the sampling errors from raingauges and microwave attenuation measurements

The sampling error formalism by North and Nakamoto (1989) has been widely referenced in research papers on sampling using space-borne sensors or ground-borne sensors. However, their formalism is found to not only underestimate the sampling error, especially for the raingauge network case, but also not be applicable for the cases of using a line of raingauges or microwave attenuation measurements. In this paper, the sampling error formalism has been revised and applied to the same sampling design and the same rainrate model as in North and Nakamoto (1989) for the comparison. The sampling error estimated using the revised formula was found to be more than 50% higher than that by North and Nakamoto (1989). For the case of using a line of raingauges we found that the sampling error converges to a certain value, not zero as in North and Nakamoto formalism, as the number of gauges increases. The microwave attenuation measurements case, which is the same as the case of using a line of infinite raingauges, also gives non-zero sampling errors. Finally, the combined sampling using both satellite and ground-borne sensors (e.g., raingauge network, a line of raingauges, or microwave attenuation measurements) was reviewed to check their design orthogonality and estimated the sampling errors for the combination of satellite and raingauge network case to see its behavior depending on various settings of these two different measurements.     

On methods to select solutions in Euler deconvolution of gravitation and gradient measurements

Euler deconvolution is a standard technique in geophysical exploration to determine the depth of a subsurface mass density or magnetic anomaly from surface measurements of the corresponding field. Because the solution is unstable, some selection criterion must be employed to eliminate probably wrong depth estimates. An ad hoc decision criterion often used by geophysicists is compared here to a probabilistically founded test of the estimates using the Fisher F-distribution. It is shown that this test performs quite badly compared to the ad hoc criterion. However, a probabilistic foundation for the ad hoc criterion is also developed here using the coefficient of variation. Simulations are used to verify that it offers a methodological approach to selecting estimates based on a probabilistic relationship to their true values. That is, the depth estimate is selected based on a tolerance chosen to reflect the desired probability that the estimate should deviate not more than a given percentage from the true value.