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Journal Publications

This section contains all refereed journal publications that have some connection either with the Mace Head Research Station or with members, both present and past, of the Atmospheric Physics Research Cluster at NUI, Galway.

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Documents

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Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter. Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter.

Date added: 08/31/1946
Date modified: 07/22/2009
Filesize: 4.32 MB
P.J Nolan, L.W. Pollack, Proceedings of the Royal Irish Academy The Calibration of a photo-electric nucleus counter., Volume L1, Section A, No. 2, 1946

Abstract

 

Models of nucleus counterm designed to measure photo-electrically the decrease in intensity of a beam of light which has passed one or more times through an artificially produced fog, are described by L.W. Pollak and W.A. Morgan in a paper.

A Photoelectric Condensation Nucleus Counter On High Precision A Photoelectric Condensation Nucleus Counter On High Precision

Date added: 08/07/1955
Date modified: 07/13/2009
Filesize: 4.73 MB
L.w Pollak & Tc O'Connor, A Photoelectric Condensation Nucleus Counter On High Precision, Geofisica Pura E Applicata Milano Vol. 32 pp 139-146

Abstract

 

A new model of the direct beam photo-electrix condensation nucleus counter and itsproperties are described. the main feature of the construction is the reduction of the fog tube diameter which resulted in the elimination of all uncertainties in the measurement of the light intensity after the fog is formed by adiabatic expansion.- Individual measurements with two identical of this design which incorporate all previous improvements, agree to better than 5% in 70% in all cases, their aver absolute difference being 2%. Deviations of more than one division of meter reading (or 10% of concentration) were not observed, This agreement is maintained over long periods. - A calibration curve of the latest model of the photo-electric nucleus counter is given

Measurements Of Global Radiation Using Black And White Atmometers Measurements Of Global Radiation Using Black And White Atmometers

Date added: 08/07/1955
Date modified: 07/03/2009
Filesize: 1.43 MB
TC O Connor ,Measurements Of Global Radiation Using Black And White Atmometers , Geofiscica Pura E Applicata -Milano Vol 30 p 130-136 (1955)

Abstract

 

The difference in the evaporation from black and white Livingston atmometers was compared with the global radiation as measured by a Bellani spherical pyranometer. Results show that one unit (cm^3) of difference in the evaporation corresponds to 20+/- 3 cal/cm^2 of global radiation. The total of 95 daily values of radiation measured by pairs of atmometers differed from the corresponding Bellani figure by 2.3%. The operation of the atmometers and the accuracy of the results are discussed. The method is considered sufficiently accurate for the general climatological purposes.

Size Mobility Charge of multi charged Ions Size Mobility Charge of multi charged Ions

Date added: 08/07/1955
Date modified: 07/23/2009
Filesize: 4.14 MB
PJ Nolan and TC O'Connor ,Size Mobility Charge of multi charged Ions,  14 Dec 1955
Abstract

 

The experiments of J.J Nolan and J.G O'Keefe (1933) on multiply charged ions produced in various ways indicated that the mobility of these ions was independent of the charge. they suggusted the following way out of the difficulty: "It is possible that a nucleus on receiving a large electric charge, may in a moist atmosphere rapidly grow and adapt its size to its charge in such a way as to have approximately a constant mobility". the present research was designed to elucidate the problem by measureing the size as well as the mobility and charge of multiply charged ions. One of the methods of producing multiply charged ions used by Nolan and O'Keefe was the spraying of water. We found that production by bubblling was more convenient than production by spraying. During the course of the work certain features of the ionisation produced by bubbling were investigated. These investigations were not exhaustive since they were only incidental to the main purpose of the research.

Some Characteristics of condensation Nuclei stored in a large vessel Some Characteristics of condensation Nuclei stored in a large vessel

Date added: 08/07/1955
Date modified: 07/07/2009
Filesize: 1.44 MB
TC OConnor, Some Characteristics of condensation Nuclei stored in a large vessel ,Geofisica Pura E Apllicata- Milano Vol 31 pp 107-114 (1955)

Abstract

 

THe Coagulation coefficent, size and charge distribution of condensation nuclei from room air when stored in a 4000 litre rubber balloon gasometer were studied. The results indicate that the acquisation of water vapour contributes to the growth of stored nuclei. A preliminary trial was made to see if Junge's Approximate rule that the number of particles in an aerosol varies inversely as the third power of their radius, also holds for Aitken nuclei. Further cnfirmation of the relationship between the percentage of stored nuclei electrically charged and their average radius were obtained.

The measurements were carried out by means of the Pollak-Murphy improved version of the photo-electric nucleus counter. A statistical analysis based on over a thousand comparisions of two identical models shows that the agreement of individual readings is better than 10% of nucleus concentrations in 80% of all cases. Excessive differences have now been eliminated.

The Photoelectric Nucleus Counter as Hygrometer The Photoelectric Nucleus Counter as Hygrometer

Date added: 08/07/1955
Date modified: 07/22/2009
Filesize: 895.22 kB
PJ Nolan & TC O Connor, The Photoelectric Nucleus Counter as Hygrometer, Geofisica Pura E Applicata - Milano Vol. 31 pp 32-36 (1955)

Abstract

 

Hygrometric measurements on room air were made with a Nolan-Pollak nucleus counter from which the lining of blotting paper had been removed. The dew point can be determined from the critical overpressure for condensation on nuclei. Satisfactory agreement with the values given by a ventilated wet and dry blub hygrometer was obtained. The correction required is small since condensation occurs on ordinary atmospheric nuclei when the temperature is brought to about 0.3C below the dew point.

Further Measurements Of Global Radiation Using Black And White Atmometers Further Measurements Of Global Radiation Using Black And White Atmometers

Date added: 08/07/1957
Date modified: 07/01/2009
Filesize: 522.76 kB
TC O Connor, Further Measurements Of Global Radiation Using Black And White Atmometers, Geofisica Pura E Apllicata- Milano Vol 38 pp 154-157 (1957)

Abstract

 

The feasibility of using the difference in the evaporation from a black and whiteatmometer for the continuous routine measurement of global radiation at a field station was examined. The atmometers were operated continously for 177 days and the results obtained were compared with measurements of the global radiation for the corresponding period as given by a Bellani pyranometer. Good agreement between the monthly totals of global radiation from both methods were obtained

On condensation nuclei produced at heated surfaces On condensation nuclei produced at heated surfaces

Date added: 08/31/1959
Date modified: 07/03/2009
Filesize: 1.59 MB

O'Connor, T.C, Sharkey, W.P.F., and O Brolchain, C. (1959)- On condensation nuclei produced at heated surfaces, Geofisia pura e applicata, 42, 109-116.


Abstract

 

An investigation of heated surfaces of glass, metal and oil as sources of condensation nuclei is reported. Below a certain transition temperature the nucleus production is of a temporary nature and decreases to zero with the continued heating of the surface. Above this temperature, however, the nucleus production does not change with time. The transition temperature varies with the material of the surface and is not always associated with the onset of incandescence. The nuclei produced at the lower temperatures have a radius of about 10–5 cm and, on production, are mainly uncharged. Electric light bulbs can produce appreciable numbers of these nuclei.

Ionization Equibrium of maritime Air Ionization Equibrium of maritime Air

Date added: 08/07/1960
Date modified: 07/24/2009
Filesize: 5.83 MB
O'Connor, T.C, Sharkey, W.P, Ionization Equilibrium In Maritime Air, Procedding of the Royal irish Academy, Volume 61, Section A, No. 3
Abstract

Observations on the Aitken nuclei in Atlantic air Observations on the Aitken nuclei in Atlantic air

Date added: 01/01/1961
Date modified: 07/23/2009
Filesize: 796.79 kB

O'Connor, T.C, Sharkey, W.P.F., and Flanagan, V.P. (1961)- Observations on the Aitken nuclei in Atlantic air, Quart. J. R. Met. Soc., 87, pp.105-108.


Abstract

 

The concentration, size and distribution of charges on Aitken nuclei in air from the Atlantic Ocean were measured at a station on the western coast of Ireland where man-made pollution was most unlikely. The results are examined in relation to the meteorological elements and human activities. Some sources of the nuclei observed in maritime air are discussed.

Ionization equilibrium in aerosols Ionization equilibrium in aerosols

Date added: 01/01/1961
Date modified: 07/24/2009
Filesize: 3.34 MB
O'Connor, T.C. , Flanagan, V.P., Ionization equilibrium in aerosols, Geofisica Pura E Applicata - Milano, Vol. 50 (1961), pp. 148-154.

Abstract


Theoretical and experimental investigations were made on the time taken to achieve equilibrium charge distribution on Aitken nuclei. Theory indicates that the fraction of nuclei uncharged approaches its equilibrium value exponentially, with an approximate half time value of 0.693Z/4q and experiment gave good agreement with theory. The efficiency of a polonium-210 alpha ray source in producing ionization equilibrium in aerosols was examined and confirmed. The application of the methods described to the determination of the size of nuclei and to other observations in the free atmosphere are discussed.

Mesure de l'evaporation et de la radiation globale a St. Mortiz Mesure de l'evaporation et de la radiation globale a St. Mortiz

Date added: 08/07/1962
Date modified: 07/23/2009
Filesize: 1.21 MB
T.C O Connor ,Mesure de l'evaporation et de la radiation globale a St. Mortiz , Geofisica e Meteorologia Vol X  1962

Abstract


On the production of Aitken nuclei by sunlight in st. Moritz  On the production of Aitken nuclei by sunlight in st. Moritz

Date added: 08/07/1962
Date modified: 07/15/2009
Filesize: 4.41 MB
C. Mc Greevy & TC O Connor, On the production of Aitken nuclei by sunlight in st. Moritz, (1962) Geofisica E Meteorologia

Abstract

 

It has been found by VERZAR & al. that the concentration of Aitken nuclei in atmospheric air increased from sunrise until  mid-day and decreased again in the afternoon. This effect occurred over the ordinary ground, in a city and also over snow. A similar effect had been reported by MCLAUGHLIN in Paris in 1926 '). It seemed likely that irradiation by the sun caused the increase in the numher of condensation nuclei. In order to study this ii suneffect ), V E R ~&~ RKU NZa nd VERZAR& EVANS  investigated nucleus-free atmospheric air stored in a polyethylene balloon and showed that the same effict took place when the air in the balloon was exposed to direct and scattered sunlight ("5). As a result of their researches and from the findings of other investigators (C.'.'") it was considered a reasonable hypothesis that trace gases in the air were partly responsible for nucleus prduction when irradiation by the sun took place. It was suggested that the production of nuclei by sunrays was due to a photochemical reaction of some impurity in the air. Suspected impurities were SO,, H,S, NH, and ozone. The amount of these contaminants in ordinary atmospheric air has
been discussed by JUNGE( 9.In support of the above hypothesis it was found that when traces of SO, or H,S or NH, were added to nucleus-free atmospheric air in such polyethylene hallons a striking increase in the number of nuclei
produced by sun irradiation occurred over the nnmher produced by irradiation when no traces were added (9. The sun-effect also took place when industrial oxygen or nitrogen replaced the nucleus-free air in the balloons. This also could he due to impurities present in the oxygen or nitrogen. In order to show quite definitely that traces of impurity
gases were partly the cause of nucleus-production in atmospheric air we decided to eliminate the suspected trace gases by filling the balloons with atmospheric air through chemicals which would absorb these trace gases or at least reduce their concentration. In this way it was hoped to he able to discover what trace gases were partly responsible for nucleus production in the sun-effect.


Production Of Cn by Gaseous Reactions Production Of Cn by Gaseous Reactions

Date added: 08/07/1963
Date modified: 07/23/2009
Filesize: 4.02 MB
Tom OConnor ,Production Of Cn by Gaseous Reactions, Journal de Recherches Atmospherique, pg 127 - 133 (1963)
Abstract

 

The production of condensation Nuclei as a result of gaseous reactions is discussed.  A Portable nucleus counter used to investigate sources of nuclei in the littoral zone is described. Laboratory experiments show that decaying seaweed emits a gas which forms condensation nuclei on irradiation with ultra violet or sunlight. It also emits H2S and the significance of this in the natural cycle of sulphur in the atmosphere is considered. Electrically heated wires produce very small condensation nuclei and also NO2.

Condensation Nuclei In maritime Air Condensation Nuclei In maritime Air

Date added: 08/07/1966
Date modified: 07/27/2009
Filesize: 858.97 kB
O'Connor, Condensation Nuclei in Maritime Air, Journal de Recherches Atmospheriques, Vol II, 2 annee (1966), no 2-3, pp 181-184
Abstract

 

Data is reported on the concentration of condensation nuclei, their size and the fraction uncharged, in maritime air at a station on the west coast of Ireland well away from sources of man-made pollution. These are correlated with some meteorological paratmeters and the state of the ocean. These observations were made mainly with on-shore winds and they supplement those of O'Connor, Sharkey and Flanagan, in Q.J..R.M.S., 87,1961,pp. 105-8.

The concentration of nuclei per cm3 varied from about 100 to 12,500 but was usually less than 1,000. The size of the nuclei decreased with increasing concentration with an average value of about 3.5 X 10^-6 cm for their radii. It did not depend markedly on the relative humidity.

The production of Condensation Nuclei By Heated Wires The production of Condensation Nuclei By Heated Wires

Date added: 08/07/1966
Date modified: 07/23/2009
Filesize: 4.73 MB
T.C. O'connor, AF Roddy, The production of Condensation Nuclei By Heated Wires, Journal de Recherches Atmospheriques Vol II 2e nos 2-3 pp 239-44
Abstract

 

Investigations of the condensation nuclei produced by heated wires, particularly platinum, are described. There is a 'transient' type due to surface containation and a 'permanent' type which contain the material of the wire and are about 4 x 10-7 cm in diameter. Nitrogen dioxide is also produced by the wires in the gaseous and not in the particulate form.

Deposition in ionic Diffussion Deposition in ionic Diffussion

Date added: 08/07/1968
Date modified: 07/27/2009
Filesize: 1.69 MB

TC OConnor, F Anderson, PJ Nolan, Electrostatic Deposition in ionic Diffussion ,Proceeding of the Royal Irish Academy 1968, Volume 66 Section A No. 5


Abstract

 

Errors in the determination of ionic diffusion coefficients caused by the neglect of electrostatic deposition are examined. Correction formulae applicable to low ionic concentrations are derived for cylindrical channels. These are similiar to the Fuchs formulae for rectangular channels. Formulae applicable in the case of high ionic concentration are also derived.

For singly charged particles the correction tot the diffusion coefficient under the usual experimental conditions is about two or three per cent. The error becomes large when the number electronic charges per ion aproaches 100. Previous Dublin experiments with multiply charged nuclei are examined in this connection and corrections applied. The Corrections do not invalidate the main conclusion of these experiments that the Einstein equation B=D/KT does not apply in the absence of charge equilibrium.

Electrostatic Deposition in ionic Diffussion Electrostatic Deposition in ionic Diffussion

Date added: 08/31/1968
Date modified: 07/21/2009
Filesize: 1.69 MB
F. Anderson, P.J Nolan and T.C. O'Connor, Electrostatic Deposition in ionic Diffussion, Volume 66, Section A, No. 5, 1968

Abstract

 

Errors in the determination of ionic diffusion coefficients caused by the neglect of electrostatic deposition are examined. Correction formulae applicable to low ionic concentrations are derived for cylindrical channels. These are similiar to the Fuchs formulae for rectangular channels. Formulae applicable in the case of high ionic concentration are also derived.

For singly charged particles the correction tot the diffusion coefficient under the usual experimental conditions is about two or three per cent. The error becomes large when the number electronic charges per ion aproaches 100. Previous Dublin experiments with multiply charged nuclei are examined in this connection and corrections applied. The Corrections do not invalidate the main conclusion of these experiments that the Einstein equation B=D/KT does not apply in the absence of charge equilibrium.

Atmospheric Sulphur Levels in Western Ireland Atmospheric Sulphur Levels in Western Ireland

Date added: 08/07/1969
Date modified: 07/27/2009
Filesize: 2.97 MB
O'Connor. TC., Atmospheric Sulphur Levels In Western Ireland, Sulphur in Agriculture, AN Foras Taluntais, Dublin, 1969

Abstract

 

Sulphur compounds can exist in the atmosphere in the solid, liquid or gaseous form, depending on their origin and subsequent history. They have deleterious effect on the health of humans, plants and animals and by their corrosive action on buildings and other materials. They have also been studied for their beneficial effects, for example, the nutrition of plants and other natural processes in soils and weathering. They can also be involved in processes of cloud formation and the geochemistry around the world. Although there have been many studies or atmospheric sulphur levels in polluted areas there is little data available on the natural background concentrations of sulphur dioxide in unpolluted areas in temperate latitudes.

This paper is concerned with some aspects of the atmospheric portion of the natural cycle of sulphur. it describes some investigations into the concentrations of sulphur dioxide at a variety of sites. in Galway city, Sine references to recent paper on specific aspects of the sulpur cycle are also given.

Accelerated Rates of Rainfall Accelerated Rates of Rainfall

Date added: 07/09/1971
Date modified: 06/30/2009
Filesize: 384.37 kB
P. R. BRAZIER-SMITH, S. G. JENNINGS & J. LATHAM, Accelerated Rates of Rainfall,  Nature 232, 112 - 113 (09 July 1971); doi:10.1038/232112b0

Abstract

 

RAINFALL intensity within clouds may be greatly increased by the production of satellite drops when raindrops collide, and this process could explain the extremely high rates of rainfall development reported in certain clouds1,2. We have set out to test this possibility by laboratory experiments.

Weather: Understanding rainfall Weather: Understanding rainfall

Date added: 08/01/1971
Date modified: 07/22/2009
Filesize: 336.23 kB
Weather: Understanding rainfall,1971
Abstract

Nature-times Weather Understanding rainfall Nature-times Weather Understanding rainfall

Date added: 08/01/1971
Date modified: 09/11/2009
Filesize: 336.23 kB

Nature-times Weather Understanding rainfall Nature-times Weather Understanding rainfall

Date added: 08/01/1971
Date modified: 08/01/2008
Filesize: 336.23 kB

An investigation of the behaviour of drops and drop-pairs subjected to strong electrical forces An investigation of the behaviour of drops and drop-pairs subjected to strong electrical forces

Date added: 09/12/1971
Date modified: 07/23/2009
Filesize: 703.62 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J.  (1971)- An investigation of the behaviour of drops and drop-pairs subjected to strong electrical forces. Proc. Roy. Soc., A325, 363-376.


Abstract


A numerical model is described which simulates irrotational, incompressible flow on a computer. It has been applied to the problems of the deformation of uncharged drop-pairs separated in an electric field of critical strength and isolated drops charged to the Rayleigh limit in the absence of an electric field. In the case of pairs of drops of radius R, separated by an initial distance X in an electric field equal to that predicted by Brazier-Smith (1971) to cause disruption two types of interaction were identified. For values of X/R less than about 1.2 the drops deform and their surfaces accelerate towards each other and make contact. For X/R greater than about 1.2 the drops deform, a concavity appears at the near poles and then the near surfaces assume a conical profile of angle equal to that predicted by Taylor (1964). The subsequent issuance of liquid from these jets could not be studied with the present model. The computations predict that an isolated drop carrying the critical charge calculated by Rayleigh (1882) will deform, while retaining an approximately spheroidal shape, until the axial ratio achieves a value of about 2.5, whereupon cones possessing the Taylor angle are formed at each end of the drop, from which liquid will issue in the form of a jet. Experiments were performed in which uncharged water drops of radius R and surface tension T were directed towards a highly polished, earthed electrode at a shallow angle in an electric field of strength E. Each drop experienced the same electric forces as would result if the earthed electrode were removed and replaced by an identical drop twice as far away. Stroboscopic photographs of drops and their optical image in the polished electrode illustrated their deformation and eventual disintegration. The experimentally determined relation between normalized disintegration field E(R/T)1/4 and both X/R and the elongation a/b agreed well with theory over a wide range of separations.

The charging of water drops falling and colliding in an electric field The charging of water drops falling and colliding in an electric field

Date added: 01/01/1972
Date modified: 07/07/2009
Filesize: 1.67 MB

O'Connor, T.C. and Sharkey, W.P.F. (1960)- Ionization equilibrium in maritime air, Proc. Roy. Ir. Acad., 61, p.15-27.


Abstract


Studies have been made of the charge transfer resulting from the collision and separation of water drops falling in an electric field. The charge transferq was measured for values of field strengthE, impact velocityV, drop radiiR, r, radius ratioR/r, and angle THgr ranging from 0.5 to 80 kV/m, 0.5 to 3 m·sec–1, 200 to 600 mgr, 1.0 to 3.0 and 0 to 90 degrees respectively, where THgr is the angle between the field and the line of centres of the drops at the moment of separation.

Two uniformly sized drop-streams were ejected from hypodermic needles by modulating the flow of water through them and then collided between a pair of electrodes across which a potential difference existed. The drops coalesced temporarily, swung around each other and separated, each resulting stream being collected in a vessel connected to an electrometer in order to measure the charge. The measured values ofq were generally in good agreement with theoretical values derived from the equationq = 1.1 · 10-10 gamma1 E r 2 Cos THgr, where gamma1 is a function ofR/r.
Calculations based on this equation, the Marshall-Palmer drop-size distribution and established values of separation probabilities of colliding drops showed that collisions between raindrops within electrified clouds will act powerfully to dissipate the existing fields.

Advance, 12 the growth of snowflakes and hail Advance, 12 the growth of snowflakes and hail

Date added: 06/01/1972
Date modified: 08/01/2008
Filesize: 330.33 kB

The Interaction of Falling Water drops:Coalescene The Interaction of Falling Water drops:Coalescene

Date added: 07/30/1972
Date modified: 07/08/2009
Filesize: 802.92 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J. (1972)- The interaction of falling water drops: coalescence. Proc. Roy. Soc.., A326, 393-408.


Abstract


Experimental studies have been conducted of the interaction of falling water drops of radii R and r (R > r), density p and surface tension or colliding in air with a relative velocity U and a perpendicular distance X between the centre of one drop and the undeflected trajec- tory of the other. R and r were varied from 150 to 750 /m, R/r from 1.0 to 2.5, U from 0.3 to 3.0 m s-1 and X from 0 (head-on collisions) to the maximum value for contact, R+r. Four types of interaction were observed: (1) bouncing; (2) permanent coalescence; (3) coalescence followed by separation; (4) coalescence followed by separation and the formation of satellite drops. The principal effort was devoted to a study of the critical conditions under which drops will separate after coalescence. It was found that there was a critical value of X, denoted by Xc, below which the coalesced drops remained united and above which there was sufficient angular momentum for the drops to separate after coalescence. For a wide range of values of r, R and U the coalescence efficiency e = Xc(R + r)2 was found to lie between 0.1 and 0.4 for drops of identical size and about 0.2 and 0.6 for drops with Rlr = 2.0. A theoretical analysis based on energy concepts predicted that the coalescence efficiency is given by the equation = 2.40(Up f (r) wheref (Rlr) is a function which varies from 1.3 for Rlr = 1 and 3.8 for R/r = 3. The predic- tions of this equation were in excellent agreement with the experimental results over the entire range of conditions studied. Investigations are also described of the critical conditions for the bouncing of colliding drops, the influence of electric charges upon the interactions and the elongation and splitting of a rotating drop.

How falling raindrops collide How falling raindrops collide

Date added: 08/01/1972
Date modified: 07/02/2009
Filesize: 470.45 kB

S.G Jennings, P.R. Brazier-Smith, J. Latham, ,How falling raindrops collide,Page 313, New Scientist, 10 February 1972


Abstract

The Photo-Electric Counter The Photo-Electric Counter

Date added: 08/31/1972
Date modified: 08/31/2008
Filesize: 3.79 MB

Raindrop interactions and rainfall rates within clouds Raindrop interactions and rainfall rates within clouds

Date added: 11/30/1972
Date modified: 07/06/2009
Filesize: 787.75 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J. (1973)- Raindrop interactions and rainfall rates within clouds. Quart. J. Roy. Met. Soc., 99, 260-272.


Abstract

 

Experiments showed that when a pair of water drops of raindrop dimensions collide and separate in air at their relative terminal velocities satellite drops are generally produced. Although the numbers and sizes of satellites resulting from individual interactions are highly variable a typical event produces about 3 satellites each having a volume of 0.04 ViVj/(Vi + Vj), where Vi and Vj are the volumes of the parent drops.

A full stochastic treatment is presented of the development of rainfall in a volume within a cloud where water is being released by condensation at a constant rate J. The production of satellites and an experimentally verified expression for the coalescence efficiency are incorporated into these calculations. Computations are made of the variation with time of the cloud water content, C, the rainwater content, L, the radar reflectivity, Z, the rainfall rate, P, and the drop-size distribution. The calculations show that the crucial parameter in governing the intensity and duration of rainfall is J, and that the microphysical processes are of secondary importance; C, L and P are all insensitive to and the production of satellite drops. The influence upon rainfall development of the break-up of large raindrops on attaining their maximum size within a cloud is found to be even less than that of the satellites.

The drop size distribution after several minutes of growth is insensitive to the initial spectrum but is markedly dependent upon and the production of satellites, which tend eventually to produce a bimodal spectrum. The radar reflectivity increases very rapidly with time (typically by about an order of magnitude every 2 1/2 minutes) and depends quite strongly on , but is unaffected by the production of satellites.


 

Increased rates of rainfall production in Electrified clouds Increased rates of rainfall production in Electrified clouds

Date added: 07/30/1973
Date modified: 07/22/2009
Filesize: 822.23 kB

Brazier-Smith, P.R., Jennings, S.G., and Latham, J. (1973)- Increasing rates of rainfall production in electrified clouds. Quart. J. Roy. Met. Soc., 99, 776-779


Abstract

The influence of evaporation and drop-interaction on a rainshaft The influence of evaporation and drop-interaction on a rainshaft

Date added: 07/30/1973
Date modified: 07/08/2009
Filesize: 1.13 MB

Brazier-Smith, P.R., and Jennings, S.G., and Latham, J. (1973)- The influence of evaporation and drop-interaction on a rainshaft. Quart. J. Roy. Met. Soc., 99, 704-722.


Abstract


Calculations have been made of the variations with fall-depth z of the liquid water content, L, rainfall rate, p, radar reflectivity, Z, drop concentration, NT, and raindrop size distribution n(r), within a steady-state rainshaft as a result of the evaporation and interaction of the drops. The interactions were described by a generalized stochastic equation which takes account, as described by Brazier-Smith, Jennings and Latham (1973), of the variation of coalescence efficiency s with drop radii R, r and the fact that satellite drops are produced when drops separate after collision. The relative humidity is assumed to fall linearly from 100 per cent at cloud base (z = 0, T = 8°C) with a gradient 8. The lapse rate within the rainshaft was taken to be 8°C krn- and the initial size distribution was generally given by the Marshall-Palmer equation. Calculations were made for 3 different situations in order to isolate the physical processes which most affect the rainfall:
(l), evaporation without interaction; (2) interaction without evaporation; (3) both interaction and evaporation. The calculations for Case (1) indicate that the numbers of drops in all size classes are diminished with increasing Z, with a preferential reduction at the small-radius end of the spectrum. In Case (2) the interactions of the raindrops introduce considerable detail into n(r), with bimodal curves associated with satellite drop production, the highly efficient consumption of small drops by larger ones and the variations of E and fall-velocity V with drop-radius r.
The main feature of the calculations for Case (3) is the rBle of coalescence in preserving within the spectrum a considerable amount of liquid water that would otherwise be lost by evaporation. For example, whereas the rainwater content at z = 1.5 km for 8 = 20 per cent km- and Lo = 1.0 gm m- is 0.28 gm m-3 if interactions are absent, their presence elevates L to 0.57 gm m-3 at this level. This retention effect is significant for all values considered of 8, L, p, and the initial slope of the raindrop size distribution (varied from half to twice that of the Marshall-Palmerequation). It is alsofound that the structure introduced into the size distributions as a result of interactions is partially smoothed out by evaporation, which replaces a substantial proportion of the smallest drops consumed by coalescence.

Mass absorption Coefficient of natural Aerosol Particles in the 0.4 - 2.4um Wavelength Interval.. Mass absorption Coefficient of natural Aerosol Particles in the 0.4 - 2.4um Wavelength Interval..

Date added: 08/26/1973
Date modified: 07/22/2009
Filesize: 8.15 MB
K. Fischer, "Bestimmung der Absorption von sichtbarer Strahlung durch Aerosolpartikeln," Contrib. Atmos. Phys. 43, 244 (1970); "Mass Absorption Coefficient of Natural Aerosol Particles in the 0.4–2.4 µm Wavelength Interval," Contrib. Atmos. Phys. 46, 89 (1973), "Mass Absorption Indices of Various Types of Natural Aerosol Particles in the Infrared," Appl. Opt. 14, 2851 (1975).

Abstract

 

Theoretical investigation have predicted that absorption of solar radiation by particulate matter- suspended as aerosol particles in the air - plays an important part in the radiation budget of the atmosphere.

In the present study the mass absorption coeffiecnet K/P (i.e. the imaginary part of the refractive index related to density) is determined for the 0.4 - 2.4 um wavelength intercal wavelength interval. The measuremetn are performed on films of aerosol particles which were collected by an automatic jet impactor at several urban and remote sites.

The influence of evaporation and drop-interaction on a rainshaft : Comments and Notes The influence of evaporation and drop-interaction on a rainshaft : Comments and Notes

Date added: 09/14/1974
Date modified: 07/08/2009
Filesize: 326.53 kB

Brazier-Smith, P.R., and Jennings, S.G., and Latham, J. (1974)- The influence of evaporation and drop-interaction on a rainshaft Reply. Quart. J. Roy. Met. Soc., 99, 704-722.


Abstract


Calculations have been made of the variations with fall-depth z of the liquid water content, L, rainfall rate, p, radar reflectivity, Z, drop concentration, NT, and raindrop size distribution n(r), within a steady-state rainshaft as a result of the evaporation and interaction of the drops. The interactions were described by a generalized stochastic equation which takes account, as described by Brazier-Smith, Jennings and Latham (1973), of the variation of coalescence efficiency s with drop radii R, r and the fact that satellite drops are produced when drops separate after collision. The relative humidity is assumed to fall linearly from 100 per cent at cloud base (z = 0, T = 8°C) with a gradient 8. The lapse rate within the rainshaft was taken to be 8°C krn- and the initial size distribution was generally given by the Marshall-Palmer equation. Calculations were made for 3 different situations in order to isolate the physical processes which most affect the rainfall:
(l), evaporation without interaction; (2) interaction without evaporation; (3) both interaction and evaporation. The calculations for Case (1) indicate that the numbers of drops in all size classes are diminished with increasing Z, with a preferential reduction at the small-radius end of the spectrum. In Case (2) the interactions of the raindrops introduce considerable detail into n(r), with bimodal curves associated with satellite drop production, the highly efficient consumption of small drops by larger ones and the variations of E and fall-velocity V with drop-radius r.
The main feature of the calculations for Case (3) is the rBle of coalescence in preserving within the spectrum a considerable amount of liquid water that would otherwise be lost by evaporation. For example, whereas the rainwater content at z = 1.5 km for 8 = 20 per cent km- and Lo = 1.0 gm m- is 0.28 gm m-3 if interactions are absent, their presence elevates L to 0.57 gm m-3 at this level. This retention effect is significant for all values considered of 8, L, p, and the initial slope of the raindrop size distribution (varied from half to twice that of the Marshall-Palmerequation). It is alsofound that the structure introduced into the size distributions as a result of interactions is partially smoothed out by evaporation, which replaces a substantial proportion of the smallest drops consumed by coalescence.

Charge separation due to water drop and cloud droplet interactions in an electric field Charge separation due to water drop and cloud droplet interactions in an electric field

Date added: 01/01/1975
Date modified: 07/01/2009
Filesize: 2.09 MB
Jennings, S.G. (1975)- Charge separation due to water drop and cloud droplet interactions in an electric field. Quart. J. Roy. Met. Soc., 101, 227-233.   
Abstract

Measurements were made of the electric charge acquired by drops of mean radius of about 750m, in the presence of a vertical electric field E, the value of which could be varied from 4·5 to 27kV/m. It was found that the average charge acquired by the water drop as a consequence of the inductive process increased from 0·1fC to about 0·25fC as the electric field strength increased from 5kV/m to about 15kV/m, but there-after decreased with increasing values of electric field.
This work suggests that the collisions between polarized rain-drops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30kV/m; but that significantly larger fields could not be produced since all collisions in the higher fields would result in permanent coalescence.

Electrical charging of water drops in polarizing electric fields. Electrical charging of water drops in polarizing electric fields.

Date added: 08/01/1975
Date modified: 07/01/2009
Filesize: 2.02 MB

Jennings, S.G.  (1974)- Electrical charging of water drops in polarizing electric fields.  J. Electrostatics, 1,  15-25.


Abstract


Measurements were made of the electric charge acquired by drops of mean radius of about 750 μm as they fell through a cloud of water droplets of mean radius 16 μm, in the presence of a vertical electric field E, the value of which could be varied from 4.5 to 27 kV m−1. It was found that the proportion of interactions which resulted in separation (and, therefore, in electric charge transfer, as a consequence of the inductive process of electrification) decreased from about 1% in the weaker fields to about 0.2% in the strongest ones.

This work suggests that the collisions between polarised raindrops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30 kV m−1 but that significantly larger fields could not be produced since all collisions in higher fields would result in permanent coalescence.

Measurements of the number concentration of aitken nuclei at mountain and rural sites Measurements of the number concentration of aitken nuclei at mountain and rural sites

Date added: 08/01/1975
Date modified: 07/03/2009
Filesize: 1.25 MB
Jennings, S.G.  (1975)- Measurements of condensation Aitken nuclei at rural and mountain sites. Jnl. de Rech. Atmos., No. 2,  59-66.

Abstract

 

A study of the number concentration at Aitken nuclei has been carried out using automated Nolan Pollak photoelectric nucleus ountain site, a sparsely populated site and in a rural envirorment. It has been found that the nucleus counter assembly operates very satisfactorily over long periods under field conditions.

The appuratus has proven to be particularly senstive in detecting pertubations in the background count due to localized nuclei sources. Frequency distribution curves of the individual observations follow closely a log-normal distribution for each measurement period. It is shown that te two minute sampling frequency can be increased by about an order of magnitude without causing a significant change in the nuclei number distribution.

The Electrical conductivity within water droplet clouds The Electrical conductivity within water droplet clouds

Date added: 08/01/1975
Date modified: 07/22/2009
Filesize: 1.58 MB
Jennings,S.G.   (1975)- The electrical conductivity within water droplet clouds. Proc.  4th Conf. Static Electrification. Inst. Phys. Conf. Series, No 27,  34-43.

Abstract

 

Studies have been made of the reduction of small positive ion concentration, produced by a weak americium alpha source in the presence of small water droplet clouds. The droplet clouds which possessed values of clou-water content ranging from about 1.0 up to 6 g m-3 and mean radius from 0.75 up to approximately 2.25 μm were produced by a steam condenser method which yielded relatively stable clouds.

High Electric fields from industrial stack plumes High Electric fields from industrial stack plumes

Date added: 01/01/1976
Date modified: 07/02/2009
Filesize: 338.61 kB

Jennings, S.G., and Jones, C.D. (1976)- High electric fields due to industrial stack plumes. Nature, 264, 236-237.


Abstract


THE use of electrostatic precipitators on an industrial stack to remove particulate matter and aerosol particles is now quite common. The plume emanating from such an installation is likely to be highly electrically charged, and consequently associated electrical effects should be observable downwind of the stack.

Continuous Measurements of the natural aerosol size distribution at rural mountain and maritime sites Continuous Measurements of the natural aerosol size distribution at rural mountain and maritime sites

Date added: 08/01/1976
Date modified: 07/01/2009
Filesize: 937.82 kB

Jennings, S.G.  (1976)- Continuous measurements of the natural aerosol size distribution at rural, mountain and maritime sites. Conference on the Atmospheric Aerosols: Their Optical Properties and Effects. NASA Conference Publication CP-2004, MB 4-1  to  4-4.


Abstract


 


A method of measurement of the Dielectric Constant of some liquids A method of measurement of the Dielectric Constant of some liquids

Date added: 01/01/1977
Date modified: 08/06/2009
Filesize: 1.3 MB

Jennings S.G., A method of measurement of the dielectric constant of some liquids. Phys. Educ. Vol 12, January 1977. pp. 40-42.


Abstract


The method depends on the existence of a driving force on a liquid dielectric in an electric field. The force leads to a rise in the liquid level between the plates of a capacitor. The capacitor plates were placed just above a reservoir of the dielectric liquid, the level of which was monitored by a travelling microscope. The rise in liquid level (h) was measured for selected values of voltage (v) until sparking between the plates occurred. A plot of h against V2 was obtained, and the dielectric constant was determined from the slope of the graph.

Aerosol particle size distribution in the 0.25-5.0 micron radius range in Northern England Aerosol particle size distribution in the 0.25-5.0 micron radius range in Northern England

Date added: 07/30/1977
Date modified: 06/30/2009
Filesize: 1.3 MB

Jennings, S.G., and Elleson, R.K. (1977)- Aerosol size distributions in the 0.25 to 5 micrometre radius range. Atmos. Environ., 11, 361-366.


Abstract


An analysis has been made of continuous measurements on the particle size distribution of the atmospheric aerosol in five particle radius categories between 0.25 and 5.0 μm. An automatic Royco model 225 optical particle counter together with a digital line printer was used to obtain the measurements at a 10 min sampling frequency from 21 July to 8 September 1975 at Durham Observatory, 2 km SSW of Durham City in the North East of England. Measurements were also taken every 10 min from 15 December to 6 January 1976 on the summit of Great Dun Fell, 842 msl, on the Northern Pennine Range, England.

Diurnal variation associated with the particle number concentration shows maximum concentration from about 02:00–08:00 h BST and a minimum over the period 14:00–20:00 h BST.

The particle size distribution for both the Durham and Great Dun Fell site follows the shape of a Junge log-radius type distribution with slopes β equal to 3.04 and 2.74 respectively. The distributions show that the number concentration over the five radius intervals is an order of magnitude lower at the mountain site of Great Dun Fell than at Durham Observatory.

An analysis of the sampling frequency of particle concentrations showed that the measurements could be made less frequently by factors up to 20, without loss of accurate information.

Large Electric fields due to industrial chimney stack plumes Large Electric fields due to industrial chimney stack plumes

Date added: 07/30/1977
Date modified: 07/23/2009
Filesize: 2.08 MB

Jones, C.D., and Jennings, S.G. (1977).- Large electric fields due to industrial chimney stack plumes. Atmos. Environ.,11, 1197-1207.


Abstract


Large values of electric field due to a charged plume from an industrial chimney stack have been observed. Downwind and crosswind profiles of the electric field were measured using 4 field mills. Average values of between 5 and 6 kV m−1 over 10 minute periods were measured at distances within 200 m of the stack. Electric field values as large as 3.5 kV m−1 were present at a distance of 3 km from the stack. It was found that the electric field did not return to its normal fair-weather value until the downwind distance from the stack had exceeded 9 km.

The decrease in the average value of the electric field, Ep, under the plume gave good agreement with an equation derived from line charge theory, modified by an empirical decay factor exp(−R/D)

.[1+Image ] where λ is the charge per unit length, h the plume height, R the distance of the position P downwind, and D the distance at which λ is reduced by Image . The experimental results yielded a value for D of about 1.5 km.

 

Point discharge currents as large as 3 μA were measured at a distance of 700 m from the stack. Measurements at heights ranging from 9.25 m to 3.25 m agreed with the theoretical relation i = k(E-E0) where E is the measured value of electric field at a distance 10 m upwind from the discharge point, E0 the critical value of electric field above which point discharge will occur and k is a constant. Values of E0 of about 2kV m−1 were found for the two highest points.

The results suggest that electric field measurements may be a valuable supplement to concentration data in atmospheric diffusion experiments using charged plumes.

Tracking electrically charged puff,....,by ground level electric field measurements Tracking electrically charged puff,....,by ground level electric field measurements

Date added: 07/31/1977
Date modified: 07/08/2009
Filesize: 1003.89 kB

Jennings, S.G., and Jones, C.D. (1977)- Tracking electrically charged puffs, as used in short range atmospheric diffusion investigations, by ground level electric field measurements. J. Electrostatics, 2, 367-373.


Abstract


The use of ionized air as a tracer in short range atmospheric diffusion investigations raises the possibility of cloud location using electric field measurements. In this short communication a simple analysis is developed which enables the trajectory of a charged cloud to be ascertained from electric field measurements at three points at ground level (assuming the charge is known). Alternatively, if the charge is not known, it is shown that five-position electric field measurements are needed to find both its position and magnitude.

The influence of the complex index of refraction on the volume extinction, scattering and absorption The influence of the complex index of refraction on the volume extinction, scattering and absorption

Date added: 08/01/1977
Date modified: 07/08/2009
Filesize: 496.46 kB
The influence of the complex index of refraction on the volume extinction, scattering and absorption coefficient of particle size distributions. Topical Optical Society of America Meeting on Optical Propagation Through Turbulence, Rain and Fog, Boulder, Colorado, U.S.A., pp. WD  7-1  to  7-4.

Abstract

 


Experiments on water drop interactions Experiments on water drop interactions

Date added: 09/06/1977
Date modified: 08/06/2009
Filesize: 1.27 MB

Jennings, S.G. (1977)- Experiments on water drop interactions. Phys. Ed., 12, 381-385.


Abstract

 

A series of experiments is described which demonstrate the interactions of water drops. These experiments were used in a project with second year undergraduates and should be easy to adapt for school use. Photographic, stroboscopic and droplet stream formation techniques are used. Droplet-droplet collisions and collisions with plane and curved air-water interfaces are involved. It is considered that the experiments provide a good basis for the understanding of the relative roles of kinetic energy and surface energy in governing water droplet behaviour.

Combination coefficients of small positive ions with sub micrometer aerosol particles Combination coefficients of small positive ions with sub micrometer aerosol particles

Date added: 02/14/1978
Date modified: 07/01/2009
Filesize: 745.64 kB

Dixon, A.M., and Jennings, S.G. (1978).- Combination coefficients of small ions with submicrometre aerosol particles. J. Phys. D: Appl. Phys., 11, 125-136.


Abstract


The work was concerned with the simultaneous measurement of the combination coefficients b and eta 0, between small ions and aerosol particles, and between small ions and uncharged aerosol particle respectively, for different particle radii. The ion-ion mutual repulsion coefficient gamma had a mean experimental value of 2.39 (+or-0.14)*10-6 cm3 s-1. The decay of ions in the presence of aerosol particles in a mylar vessel was recorded and compared with a family of computed theoretical ion-aerosol decay curves to determine b. eta 0 could then be determined from concentration of uncharged nuclei present. Satisfactory agreement was found between the b eta 0 versus radius results and various theoretically computed values. Possible reasons for discrepancies between theory and experiment are indicated.

Effects of particulate complex refractive index and particle size distribution variations on atmospheric extinction Effects of particulate complex refractive index and particle size distribution variations on atmospheric extinction

Date added: 08/01/1978
Date modified: 07/01/2009
Filesize: 851.05 kB
Jennings, S.G., and Pinnick, R.G.  (1978)- Effects of particulate refractive index and particle size distribution variations on atmospheric extinction and absorption for visible to middle-IR wavelengths. American Meteorological Society Third Conference on Atmospheric Radiation, Davis, California, 6-9.

Abstract


A comprehensive sensitivity study has been made, using Mie theory, to determine the effect of realistic variations in values of real and imaginary parts of the complex index of refraction on volume extinction and absorption coefficients for a wide range of lognormal particle size distributions (defined by geometric mean radius r sub g and geometric standard deviation sigma sub g). Wavelengths lambda from visible (0.55 micrometers) through middle-infrared (10.6 micrometers) were considered. Extinction is independent of complex index to within 20 percent for the majority of realistic particle size distributions, providing lambda < or = 2 micrometers. However, changes in extinction by up to an order of magnitude are caused by realistic variations in refractive indexes for 2 < or = lambda < or = 10.6 micrometers, with real index being more important in affecting extinction than imaginary index.

Use of an Average complex refractive index in atmospheric propagation calculations Use of an Average complex refractive index in atmospheric propagation calculations

Date added: 08/01/1978
Date modified: 07/08/2009
Filesize: 932.35 kB
. B. Gillespie, S. G. Jennings, and J. D. Lindberg, "Use of an average complex refractive index in atmospheric propagation calculations," Appl. Opt. 17, 989-991 (1978)

Abstract

 

In most atmospheric propagation calculation it is generally ssumed that atmospheric dust is composed of homogeneous spherical particles all with the same average complex refractive index and all distributed by the same size distribution. As pointed out by Bergstrom, it is perhaps more realisitc to assume that since diiferent optical constants and each component will have an associated size distribution characteristic of its production. In particular, the free carbon type particles and the soil derived particles should be different. Previous work in our laboratory  with commericallly available cascade impactors has shown that, for some minerals characteristic of the local envirorment, the imaginary refractive index of desert dust is a strong function of particle size.

Vertical Inhomogeneity in Atmospheric Fog and Haze and it's effects on IR extinction Vertical Inhomogeneity in Atmospheric Fog and Haze and it's effects on IR extinction

Date added: 08/01/1978
Date modified: 07/08/2009
Filesize: 2.32 MB
Pinnick, R. G.; Hoihjelle, D. L.; Stenmark, E. B.; Lindberg, James D., Vertical inhomogeneity in atmospheric fog and haze and its effects on infrared extinction, J. Opt. Soc. Am, Vol.68, Page 540

Abstract

 

The presence of atmospheric fog and haze is important to radiative transfer in the atmosphere. For quantitative estimates of scattering and absorption by fod and haze particles, the size distribution is needed. Previously, fog and haze particulate size distributions have been measured by impaction techniques (Garland, 1971; Pilie, 1975; Krasikov and Chikirova, 1956; Kumai, 1973; low, 1975; May, 1961; barteneva and Polyakova, 1965; and Goodman, 1977), by collection of particles on spiderwebs (Arnulf et al., 1957), by a laser hologram camera (Kumkelm, 1971), and by light-scattering single particle counters (Eldridge, 1961; Laktionov, 1967). All of these techniques have serious limitations which restrict their usefulness and require measurements made with them to be regarded with caution. For example, impaction techniques involve laborious microsope measuremtn of droplets or droplet replicas, and corrections must be made to obtain true droplet size. Furthermore, impaction collection efficiencies must be applied to obtain relative particle concentrations.

 

In this article we present measurements of the size distribution of fog and haze particles made with a balloon-borne light-scattering single-particle counter, with emphasis on their effect on Infrared radiation. The primary advantages of using a light-scattering counter is that the measurement is donw in situ in real time, with minimal disturbance to the particles during measurement. Also, measurment of vertical structure is possible with this technique because a statistically significant size distribution measurement can be completed in a relatively short time (on the order of 1/2 minute), permitting a vertical upleg and lownleg to 200m altitude to be completed in 15 to 30 minutes. Measurements made during upleg and downleg portions of each tranverse show that temporal changes during such times scales were relatively small compared to vertical changes for most measurement periods.

Results from measurement of four haze and fog profiles presented here are typical of 19 profiles measured during February 1976 near Grafenwohr, a town located 100 km north of Nurnberg near the eastern border of West Germany. The local terrain consists of rollong hills and is partially forested; some of the land is tilled for farming.

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