On F. Verzaŕ's photo-electric automatic nucleus counter

Summary A Verzár condensation nucleus counter with automatic recording was tested under constant and controlled conditions in the laboratory and compared with the standard photo-electric nucleus counter of high precision of the School of Cosmic Physics. The photographic records of the fog formation in the cylindrical cloud chamber of theVerzár automat made with galvanometers of 0.019 sec and 1.0 sec periods show that a galvanometer of 1 sec period cannot follow the rapid formation and disappearance of the fog, apparently due to the horizontal arrangement of the fog tube and the absence of an insulating wet lining.TheVerzár automat is an excellent apparatus for continuously recording concentration of condensation nuclei. Its calibration curve, however, would require adjustment if the photo-electric nucleus counter of the School of Cosmic Physics in Dublin were accepted as standard. A new calibration curve deduced from the Dublin comparisons made so far is given.

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Zusammenfassung Ein Kondensationskernzähler mit automatischer Registrierung nachF. Verzár wurde im Laboratorium unter konstanten und gesteuerten Bedingungen geprüft und mit einem photo-elektrischen Kernzähler hoher Präzision, dem Standard der School of Cosmic Physics, verglichen. Die photographischen Aufzeichnungen der Nebelbildung in der zylindrischen Nebelkammer desVerzárschen Automaten, welche mit Galvanometern von 0.019 sec und 1.0 sec gemacht wurden, zeigen, dass ein Galvanometer mit einer Periode von 1 sec der raschen Bildung und Auflösung des Nebels nicht folgen kann, offenkundig durch die horizontale Anordnung des Nebelrohres und das Fehlen jeglicher Auskeidung mit feuchtem Isolationsmaterial bedingt.DerVerzársche Automat ist ein ausgezeichnetes Gerät für die fortlaufende Registrierung der Kernzahl. Seine Eichkurve bedarf jedoch einer Abänderung, falls der photo-elektrische Kernzähler der School of Cosmic Physics in Dublin als Standard angenommen wird. Eine neue Eichkurve, welche sich auf die bisher in Dublin gemachten Vergleichungen stützt, wird reproduziert.

     

Variability of thermal structure off Georgia,winter 1978

Temperatures recorded over the Georgia shelf and at near-bottom locations on the slope are compared with records of thermocline elevation from inverted echo sounders on the slope and with shore wind observations, for the period January to April 1978.Both upwelling and downwelling events are observed. Upwelling events are associated with upwelling-favorable wind and/or Gulf stream frontal eddies. Strong upwellings are accompanied by risings of the thermocline over the slope, but some weaker eddies occur without noticeable thermocline disturbance. Downwelling events are associated with onshore meander crests of the Gulf Stream, and sometimes with downwelling-favorable wind. The influence of downwelling does not extend seaward of the upper slope.A long-term (1 month) variation of the thermal structure is observed at the shelf break and under the Gulf Stream. It is related to a filament of cold water on the slope, varying in path and size. This cold filament appears to be Antarctic Intermediate Water which is variably advected through the Straits of Florida. Theory suggest that the variability may be caused by changes in the thermocline depth and tilt across the Gulf Stream in response to transport fluctuations.     

Jet flow over foredunes

Jet flows, which are localized flows exhibiting a high speed maxima, are relatively common in nature, and in many devices. They have only been occasionally observed on dunes, and their dynamics are poorly known. This paper examines computational fluid dynamic (CFD) two‐dimensional (2D) modelling of jet flow over a foredune topography. Flow was simulated in 10° increments from onshore (0°) to highly oblique alongshore (70°) incident wind approach angles. CFD modelling reveals that the formation of a jet is not dependent on a critical wind speed, and an increase in incident wind velocity does not affect the magnitude of jet flow. A jet is first formed at ~1.0 m seawards of the foredune crest on the Prince Edward Island foredune morphology example examined here. A jet is not developed when the incident wind is from an oblique approach angle greater than ~50° because there is significantly less flow acceleration across a much lower slope at this incident angle. The presence of a scarp does influence the structure of the crest jet, in that the jet is more pronounced where a scarp is present. Surface roughness affects the magnitude of jet expansion and jets are better developed on bare surfaces compared to vegetated ones. Copyright © 2016 John Wiley & Sons, Ltd.     

Marine Layer Stratus Study

The intent of this study is to develop a better understanding of the behavior of late spring through early fall marine layer stratus and fog at Vandenberg Air Force Base, which accounts for a majority of aviation forecasting difficulties. The main objective was to use Leipper (1995) study as a starting point to evaluate synoptic and mesoscale processes involved, and identify specific meteorological parameters that affected the behavior of marine layer stratus and fog. After identifying those parameters, the study evaluates how well the various weather models forecast them. The main conclusion of this study is that weak upper-air dynamic features work with boundary layer motions to influence marine layer behavior. It highlights the importance of correctly forecasting the surface temperature by showing how it ties directly to the wind field. That wind field, modified by the local terrain, establishes the low-level convergence and divergence pattern and the resulting marine layer cloud thicknesses and visibilities.     

Sur les aérosols intéressants la Météorologie

Summary The lecture is a critical survey of the studies regarding the particles in suspension in atmospheric air and which interest in the phenomenon of water vapor condensation and generally in cloud formation and in the ensuing precipitation.A part of the lecture is devoted to the manifold technics of study introduced, above all, in the last decade, in addition to the method ofAitken counting gear. It dwells particularly on the use of Millipore filter used byLodge and his collaborators for the gathering of the condensation nuclei and of the successive chemical analysis with specific reagents to make evident the nature of the nuclei.The review ends underlining the necessity that the measures of the atmospheric aerosol may be systematically carried on by the synoptical meteorological observatories and the necessity that the experiments in this field may be made with a more and more increasing care and critical mind.     

The Impact of Canyon Geometry on Intra Urban and Urban: Suburban Night Temperature Differences Under Warm Weather Conditions

The present paper investigates the impact of canyon geometry on the temperature regime and nocturnal heat island development in the very dense urban area of Athens, Greece. Detailed measurements of air temperature have been carried out within three deep urban canyons of different aspect ratios (H/W = 3, 2.1 and 1.7) during the night period of the summer and autumn of 2007. An analysis was carried out to investigate the relative impact of the canyon geometry, the undisturbed wind velocity, ambient temperature, and cloud cover on the development of a nocturnal heat island. A clear increase of the median, maximum and minimum values of the cooling rates has been observed for decreasing aspect ratios. Under low ambient temperatures, high wind speeds correspond to a substantial rise of the cooling rate in the urban canyons mainly because of the increased convective losses. On the contrary, cooling rates decrease substantially under high-undisturbed wind speeds and ambient temperatures because of the important convective gains. The impact of cloud cover was found to be important as cloudy skies cause a substantial decrease of the cooling rates in the urban canyons. Comparisons were performed between the temperature data collected in the three studied urban canyons and temperatures recorded in an urban as well as a suburban open space station.     

Ergebnisse der Eineinhalbjährigen Registrierungen der Anzahl der Kondensationskerne in Basel

Zusammenfassung Anhand von eineinhalbjährigen Registrierungen der Kernzahlen (nachVerzár) in Basel wird der Jahresgang und Tagesgang der Kernzahlen besprochen. Die Abhängigkeit von der Windrichtung und Windgeschwindigkeit wird eingehend untersucht. Es wird ein Wochenrythmus der Kernzahlen nachgewiesen und die Häufigkeit der Kerne bei verschiedernartigen Luftmassen untersucht. Anschliessend wird über gleichzeitige Registrierungen im Stadtinnern und am Stadtrand kurzberichtet.

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Summary On recordings of nuclei-countings (accordingVerzár) over a period of one and a half year et Basle the yearly and daily variations of the number of nuclei are discussed. The influence of wind direction and wind velocity on the number of nuclei are studied. A weekly periodicity of nuclei numbers is shown and the abundance of nuclei in different air masses is studied. Finally the results of simultaneous recordings in the center and at the border of the city are communicated.

     

Numerical simulation of a mesolow over a Gulf Stream filament

A three-dimensional mesoscale numerical model is used to investigate mesoscale circulation over a Gulf Stream filament. Two numerical experiments are performed with different initial uniform ambient wind speeds (U=0.1 m s^–1, 3.5 m s^–1 and 7 m s^–1) for a typical winter day. It is found that for both low and moderate winds, a closed mesoscale circulation forms over the Gulf Stream filament. When the Gulf Stream filament was removed, the model did not predict a mesoscale circulation. The modeled circulation over the filament is in agreement with the observations, suggesting that the atmospheric circulations over the filaments may be an important mechanism in the U.S. East Coast cyclogenesis.     

Gravity anomaly and density structure of the San Andreas fault zone

A densely spaced gravity survey across the San andreas fault zone was conducted near Bear Valley, about 180 km south of San Francisco, along a cross-section where a detailed seismic reflection profile was previously made byMcEvilly (1981). WithFeng andMcEvilly's velocity structure (1983) of the fault zone at this cross-section as a constraint, the density structure of the fault zone is obtained through inversion of the gravity data by a method used byParker (1973) andOldenburg (1974). Although the resulting density picture cannot be unique, it is better constrained and contains more detailed information about the structure of the fault than was previously possible. The most striking feature of the resulting density structure is a deeply seated tongue of low-density material within the fault zone, probably representing a wedge of fault gouge between the two moving plates, which projects from the surface to the base of the seismogenic zone. From reasonable assumptions concerning the density of the solid grains and the state of saturation of the fault zone the average porosity of this low-density fault gouge is estimated as about 12%. Stress-induced cracks are not expected to create so much porosity under the pressures in the deep fault zone. Large-scaled removal of fault-zone material by hydrothermal alteration, dissolution, and subsequent fluid transport may have occurred to produce this pronounced density deficiency. In addition, a broad, funnel-shaped belt of low density appears about the upper part of the fault zone, which probably represents a belt of extensively shattered wall rocks.     

Semitransparent cirrus clouds in the tropical tropopause layer during two contrasting seasons

Association between semitransparent cirrus (STC) and tropospheric dynamics during the two contrasting seasons (Summer-monsoon and Winter) is studied using lidar and MST radar observations at Gadanki (13.5°N, 79.2°E) along with data from Geo-stationary satellite (KALPANA-1). The tropical tropopause layer (TTL) is found to be very conducive for the formation of STC. For those thicker STCs forming within TTL, the cloud top remains mostly steady with the top of the TTL, while the cloud base varies significantly in accordance with the altitude extent of tropospheric convective outflow. Based on depolarization characteristics of STCs (from lidar) along with regional distribution of tropospheric clouds derived from satellite data, altitude profile of horizontal wind, wind field at 150 hPa and air mass back trajectories, it can be reasonably inferred that, while the multi-layered and highly structured STCs during the monsoon period originate mostly from the deep convections, the sub-visual/ultra thin STCs during winter could mostly be of in situ origin.     

Observations of condensation growth determined by entity type mixing

It has been speculated for many years that the development of the droplet spectra in cloud is probably influenced by mixing processes. Various theoretical attempts to broaden the droplet spectra by mixing parcels with different velocity histories has shown that that particular effect is small. Similarly, very simpleuniform entrainment procedures did not lead to cloud drop size spectra which were broad enough, although by producing cloud drop size distributions with a double mode these models did substantially improve the drop size spectra of earlier adiabatic models which only exhibited a single mode.Recently a model based on entraining entities representing moving parcels of cloud air within the cloud was detailed byTelford andChai (1980). This study showed that the mixing in of dry air at cumulus turrets could lead to vertical cycling of diluted parcels, and that this cycling, with continual entrainment across the parcel boundaries, will produce much larger drops, as well as smaller drops of all sizes, in the droplet spectra. The entity entrainment concept studied there appears to apply to the observations of stratus cloud discussed in this paper.This paper presents data taken in marine stratus off the California coast which give a particularly clear example of how such droplet spectra modification occurs in practice. Both large drops, and the spread of the spectra to smaller sizes, occur in relation to other variables in such a way as to be consistent with an entity entrainment explanation, with no other obvious possibility.In a marine stratus cloud just over 200 m thick and many tens of miles in extent we find clear evidence that dry air is mixing in at cloud tops. Strong vertical motion is to be found in the cloud, large sized drops are found in cloud parcels where the mixing gives lower droplet concentrations, and there is evidence that newly formed cloud parcels are warmer and contain many more smaller droplets.The observations show that immediately following entrainment of dry air drop diameters are not reduced appreciably, but, in the same parcels, drop concentrations have been reduced by a factor of ten or more. Further down in the cloud big drops, able to start growth by coalescence, are found associated with low total droplet concentrations.Overall, it seems likely from the consideration of these observations that the formation of the large drops which lead to precipitation processes in clouds depends critically on the mixing in of dry air at cloud tops, and very little on the size of the small drops resulting from the condensation nucleus counts. As a conclusion it appears reasonable to state that if entrainment occurs at cloud tops, then big drops will be formed!     

Comparison of geostrophic and nonlinear balanced winds from LIMS data and implications for derived dynamical quantities

Nimbus 7 LIMS geopotential height data are utilized to infer the rotational wind distribution in the Northern Hemisphere stratosphere and lower mesosphere during a period of substantial wave-mean flow interaction in January, 1979. Rotational winds are derived from the application of a successive relaxation numerical procedure which incorporates the spherical polar coordinate iterative algorithm ofPaegle andTomlinson (1975) for the nondivergent nonlinear balance equation. Optimum convergence of the numerical solutions is found to occur when under-relaxation is utilized. The LIMS height analyses were also latitudinally smoothed and constrained to obey the ellipticity criterion for spherical coordinates. The balanced winds are compared with geostrophically derived values and within situ radiosonde reports for 100 mb to 10 mb over Berlin.From a localized perspective, the Berlin-LIMS comparison indicates that radiosonde and balanced wind vectors exhibit somewhat closer agreement in direction than is associated with the geostrophic estimates. However, substantial quantitative differences between radiosonde, balanced, and geostrophic wind speeds are also evident, suggesting that caution should be exercised in the local application of derived winds, as for example in the quantitative interpretation of trajectories derived from satellite height analyses during periods of enhanced stratospheric wave activity.On a longitudinally averaged basis, balanced zonal-mean wind speeds are typically 20% weaker than geostrophic values in polar latitudes, and as much as 50% weaker in tropical and midlatitude regions. Meridional balanced wind velocities, at a given longitude, are generally within ±10% of geostrophic values. Although these alterations in horizontal wind components result in only modest differences between balanced and geostrophic meridional eddy heat fluxes, a more substantial change appears in the meridional eddy momentum flux analysis. The corresponding patterns of Eliassen-Palm flux divergence are found to be somewhat more (less) intense for the balanced wind case in the stratosphere (lower mesosphere) in polar latitudes.     

The physics of precipitation in cumulus clouds

Summary Over the past several years, the University of Chicago has conducted a program of research into the physics and chemistry of cumulus cloud precipitation. From these measurements it has been possible to isolate the sublimation-coalescence mechanism (Bergeron process) from the condensation-coalescence mechanism and to estimate the relative role of each process in the formation of rain n cumulus clouds. It is found that size of cloud capable of raining is a strong function of geography, that the environment of the cloud is very important in determining the probability of rain and that liquid water content is one of the most important within-cloud parameters.An essential part of the research concerned cloud treatment. Definite, positive treatment effects were demonstrated for rain initiation through coalescence using water spray. No effects were detectable from dry ice seeding of subcooled clouds, although any such effects may have been obscured by sample size (27 cloud pairs).Text of paper presented before Physical Society and Royal Meteorological Society Joint Conference on Cloud Physics, London, England, Jan. 4–5, 1956. The research reported in this paper has been sponsored by the Geophysics Research. Directorate of the Air Force Cambridge Research Center, Air Research and Development Command under Contract Nos. AF 19 (604)-618 and AF 19 (604)-1388.     

Principal component analysis of global maps of the total electronic content

In this paper we present results of the spatial distribution analysis of the total electron content (TEC) performed by the Principal Component Analysis (PCA) with the use of global maps of TEC provided by the JPL laboratory (Jet Propulsion Laboratory, NASA, USA) for the period from 2004 to 2010. We show that the obtained components of the decomposition of TEC essentially depend on the representation of the initial data and the method of their preliminary processing. We propose a technique for data centering that allows us to take into account the influence of diurnal and seasonal factors. We establish a correlation between amplitudes of the first components of the decomposition of TEC (connected with the equatorial anomaly) and the solar activity index F10.7, as well as with the flow of high energy particles of the solar wind.     

Relazioni tra la velocità del vento e le caratteristiche del moto ondoso al largo e in costa

Summary The A. points out that the confirmation of the theory ofNeumann's significative waves, which differ from those ofSverdrup andMunk, would require observations of an accuracy not yet available. The existence of these waves would not change, anyhow,Sverdrup andMunk's conclusions out of the wind area.     

Free and forced shallow-water oscillations in a rotating channel of parabolic cross-section

Free and forced oscillations of shallow water in an infinitely long rotating channel of parabolic cross-section are analyzed. The pure cross-channel oscillations ofChrystal (1905) and solutions for zero rotation first discussed byProudman (1925) andHidaka (1932) are special asymptotic solutions for the free modes of this model. However, for increasingly large, along-shore wave number, our solutions donot uniformly approach those ofReid (1958) andBall (1967) for a single shore-line and semi-infinite ocean. A method of computing eigen frequencies and eigen functions for the general problem is described, and a sufficient number of these are exhibited graphically to permit visualization of the transitions between the asymptotic regions.The forced problem consists of an incoming wave-train or surge generated at the center of the channel. Amplitude and transports near the shore are computed for a wide range of dimensionless incoming-wave frequencies and rotational frequencies.     

A remarkable formation of helmholtz waves near tropopause level

Summary A unique and very impressive wave cloud formation near tropopause level could be observed on 22 February 1966 over Southwestern Germany. This phenomenon may have been induced in a limited layer of rapid increase of wind speed by the updraught over the Schwarzwald mountains (Feldberg).     

Some aspects of the advance in the knowledge of hurricanes

Several topics discussed byBergeron (1954) are reviewed and compared with present-day positions. They are: conditions for formation; maintenance of the hurricane circulation; modification; and cyclones with hurricane winds outside the tropics.On some of these subjects, notably hurricane formation, Bergeron's views in many respects approach those of the present day. A rarely-occurring event is needed in the tropics besides the climatically favorable circumstances for formation. He postulated baroclinity in the form of a surface tropical front. If the baroclinity is shifted from the low to the upper troposphere, his and present-day viewpoints agree that release of baroclinic instability is the main mechanism of initial kinetic energy generation, in contrast to the CISK theory.Major additions can be made especially on the subject of the role of air-sea interaction in hurricane maintenance through downward momentum transport and establishment thereby of a thermal cyclostrophic wind which keeps the warm core in place. Furthermore, many new data exist on extratropical hurricanes; here, a serious research effort has still to be carried out in the future.     

Estimating fog deposition at a Puerto Rican elfin cloud forest site: comparison of the water budget and eddy covariance methods

The deposition of fog to a wind‐exposed 3 m tall Puerto Rican cloud forest at 1010 m elevation was studied using the water budget and eddy covariance methods. Fog deposition was calculated from the water budget as throughfall plus stemflow plus interception loss minus rainfall corrected for wind‐induced loss and effect of slope. The eddy covariance method was used to calculate the turbulent liquid cloud water flux from instantaneous turbulent deviations of the surface‐normal wind component and cloud liquid water content as measured at 4 m above the forest canopy. Fog deposition rates according to the water budget under rain‐free conditions (0·11 ± 0·05 mm h^?1) and rainy conditions (0·24 ± 0·13 mm h^?1) were about three to six times the eddy‐covariance‐based estimate (0·04 ± 0·002 mm h^?1). Under rain‐free conditions, water‐budget‐based fog deposition rates were positively correlated with horizontal fluxes of liquid cloud water (as calculated from wind speed and liquid water content data). Under rainy conditions, the correlation became very poor, presumably because of errors in the corrected rainfall amounts and very high spatial variability in throughfall. It was demonstrated that the turbulent liquid cloud water fluxes as measured at 4 m above the forest could be only ～40% of the fluxes at the canopy level itself due to condensation of moisture in air moving upslope. Other factors, which may have contributed to the discrepancy in results obtained with the two methods, were related to effects of footprint mismatch and methodological problems with rainfall measurements under the prevailing windy conditions. Best estimates of annual fog deposition amounted to ～770 mm year^?1 for the summit cloud forest just below the ridge top (according to the water budget method) and ～785 mm year^?1 for the cloud forest on the lower windward slope (using the eddy‐covariance‐based deposition rate corrected for estimated vertical flux divergence). Copyright © 2006 John Wiley & Sons, Ltd.