Cosmic rays and meteorology

Q U A R T E R L Y J O U R N A L O F THE

R O Y A L M E T E O R O L O G I C A L S O C I E T Y

Vol. 88 OCTOBER 1962 No. 37s

551.513 : 551.521.64 : 5.53.524.73 : 551..517.3

Cosmic rays and meteorology

By G. D. ROCHESTER Physics Department, The Durham Colleges, University of D u T ~ I ~ ~

Symons Memorial Lecture, delivered 4 April 1962

1. INTRODUCTION

The principal components and intensities of the particle radiation outside the earth's atmosphere are shown in Fig. 1. The radiation above the energy lo8 eV is known as the cosmic radiation and it is with two aspects of the relation between this radiation and meteorology that this lecture is concerned.

2. COSMIC RAYS IN THE ATMOSPHERE

The omnidirectional particle intensity of the cosmic radiation beyond the radiation belts is about 2 cm-2 sec-' which means that the energy density of the radiation, 1o-l2 erg ~ r n - ~ , is roughly equal to that of starlight, 6 x erg cmP3, and is very much smaller than the energy density of sunlight at the earth's orbit, 6 x lop4 erg cm-j. Thus cosmic rays bring very little energy into the earth's atmosphere and are therefore unlikely to produce meteorological effects via the energy they dissipate in the atmosphere. The particle intensity of the radiation at the top of the earth's atmosphere in latitude 50"N is 0.2 cm-* sec-l ster-', and at sea-level is cm-2 sec-l ster-l.

-RELATIVISTIC ENERGIES FOR ELECTRONS I

. I I

RELATIVISTIC ENERGIES FOR PROTONS

i . L

~~

0.1 10 m3 105 107 109 10" 10'3 1ot5 10" ~ O ~ ~ E L E C T R O N VOLTS

SOLAR FLARE f-- COSMIC RADIATION (a) __f - PARTICLES 86% PROTONS 13% HELIUM NUCLEI

--TRAPPED(&)* PROTONS - -TRAPPED lob HEAVIER NUCLEI

ELEC~RONS (+

Figure 1. The spectra of enerqetic particles observed in the solar sy5tern.

369

370 G. D. ROCHESTER

INCIDENT PRIMARY PROTON

I I I I I I I

I

!

LOW ENERGY NUCLEONIC COMPONENT (FINAL PRODUCT LOW ENERGY NEUTRONS) I

1

v ---;- ELECTROMAFNETIC MFSON OR I NUCLEONIC COMPONENT

OR ‘SOFT HARD’ COMPONENT COMPONENT1 N, P = HIGH ENERGY NUCLEON:

I n,p =LOW ENERGY NUCLEONS I H = NUCLEAR DISINTEGRATION

I I

Figure 2. A primary cosmic-ray particle and its secondary products in the atmosphere.

The composition of the primary beam at the top of the atmosphere is also shown in Fig, 1, but very few of the particles in this beam reach the earth’s surface because they interact strongly with the nuclei present in the air. A typical chain of transformations through the atmosphere for a very high-energy proton is shown in Fig. 2. The interaction length of such a particle is 60 g cm-’, and since the depth of the atmosphere is 1,034 g cm-* the primary nuclear interactions are confined to a thin layer at the top.

At the first collision the primary particle loses a fraction of its energy (perhaps one-half), and produces the following particles :

Positive and negative r-mesons (pions) which have mean lifetimes of 2.6 x sec and rest masses of 273 times the mass of the electron. These particles dis- integrate into p-mesons (muons) and neutrinos. The muon has a mass of 207 times the electron mass and disintegrates with a mean lifetime of 2.2 i< sec into an electron and two neutrinos.

Neutral pions which have rest masses of 264 times the electron mass and a mean lifetime of about sec. These particles decay into two photons (gamma rays).

Neutrons and protons (nucleons) and nuclear fragments of various sorts which give rise to new, inelastic collisions like the primary collison.

Low-energy nucleons which excite nuclei forming low-energy protons, neutrons, deuterons, a-particles and radioactive isotopes.

Heavy mesons and hyperons. These are rare relative to pions and nucleons and do not seem to play a significant r61e in the atmosphere.

Pions are important in that they give rise to most of the lighter particles and form the main link between these particles and nucleons. Because of their short lifetimes they do

COSMIC RAYS AND METEOROLOGY 371

not accumulate in any part of the atmosphere to any appreciable extent. Charged pions not only decay but also interact in a similar way to nucleons. Slow negative muons can interact weakly with nuclei forming low-energy disintegrations. High-energy muons are also very weakly interacting particles and can penetrate the whole of the earth's atmosphere down to sea-level, where they form 70 per cent of all cosmic rays.

Neutral pions decay very rapidly into photons and form electrons and positrons by the process of pair production. The resulting elzctrons may themselves produce further photons which in turn may lead to more electron pairs. Thus a single, high-energy T"-meson can give rise to a large shower of electrons and photons. The mean-free-path for the process in air is 50 g cm-z, and the process stops when the electron energy falls below the critical energy, which is 84 MeV. Electron showers predominate in the pressure range 100 to G00gcm-2 (or 17 to 5 km in height) and have a maximum at 150g cm-2 (14 km).

The high-energy nucleons form nucleon cascades in which protons and neutrons behave as identical nuclear particles until an energy is reached at which the protons are brought to rest by ionisation before they can interact. This energy is about 300 MeV; below it neutrons continue to produce more neutrons and protons in low-energy disintegrations. Finally, when thermal energies are reached, neutrons are captured by N1+ to form the unstable isotope C4.

3. METEOROLOGICAL EFFECTS IN COSMIC RAYS

( a ) General considerations

Since cosmic rays interact with the atoms present in the atmosphere, marked changes in the intensity and even in the composition of the cosmic rays observed at a given place on the earth's surface, are to be expected from changes in pressure and temperature. The effect of changes in pressure on the muon component is shown in Fig. 3. Indeed, as early as 1026, Myssowsky and Tuwin observed that an increase in the barometric pressure of 1 cm (Hg) caused a decrease in the intensity of cosmic rays of 3.45 per cent and interpreted the effect as due to the absorption of cosmic rays in the atmosphere. The correct explanation is rather more complex because cosmic rays include a wide variety of particles with very different forms of interaction and decay.

A knowledge of the various meteorological effects is necessary in any investigation of the time variations of the radiation when measured by detectors situated within the atmosphere. Such investigations are of interest because of the insight they give into the emission of low-energy cosmic rays and plasma by the sun, and the origin of cosmic rays. Perhaps in the future this type of work will be carried out by means of satellites and space probes but at present the most reliable information comes from continuous monitoring by a world-wide chain of stations at mountain altitudes, at sea-level, and underground. The corrections to be applied to the data from these stations depend upon the various meteorological coefficients of the particles which the detector records.

As illustration the meteorological effects of the neutron and muon components will be considered.

The pressure coeficient of the neutron component

The neutron component is usually measured by the neutron pile developed by Simpson et al. (1953) for continuous recording in the I.G.Y. Part of one of these piles is shown in Fig. 4. The pile consists of between 6 and 12 boron-trifluoride (B'O F3) counters surrounded successively by 3 cm paraffin wax, 5 cm lead and 20 cm paraffin wax. The detected nucleons (mainly neutrons) originate in disintegrations produced in the lead by the high-energy nucleons present in atmospheric nucleon cascades, and the wax acts as a moderator. Production in the lead virtually ensures the absence of spurious effects from ambient slow neutrons. Temperature effects are negligible and the only meteorological parameter for which correction has to be made is pressure.

( b )

372 G. D. ROCHESTER

Figure 3. The baronietric pressure and the intensity of the muon component of the cosmic radiation as functions of time (in days) for February 1 O.%, at Svrrdlovsk.

The intensity of high-energy nucleons in the atmosphere decreases very rapidly with angle from the vertical and hence the pile is sensitive only to the mass of air vertically above it. In the lower atmosphere the intensity varies exponentially with depth, i.e., N,, ot exp (- B/L) where N,, is the nucleon intensity as measured by the pile at atmospheric pressure B, and L is the absorption (or attenuation) length. Thus :

where p,, is the pressure coefficient. L depends somewhat on the energy of the nucleons

PARAFFIN SHIELD AND MODERATOR

.LEAD

.EPF~ COUNTER

'PARAFFIN

0 5 l? 15 Z?CM

Figire 1. The cl-oss-section of a neutron monitor as itsccl fr,r the I C;.Y,


but for

AN/N MAX

A = AL6UQUERQUE 8 BERKELEY C = CHICAGO G = GOT71 NGEN L = LEEDS N = NORIKURO O = OTTAWA S = STOCKHOLM W= WEISENAU

0.1 3 3 5 6 7 8 9 10 12 15 (hr)

10 20 50 k s 200 500 (min) I I I I , , I ( , I 1

Figure 5. The cosmic-ray solar burst of 13 February 1056, at different observing station?.

all atmospheric depths greater than 700 mb in temperate latitudes it is practically constant and equal to I45 g cm-2 giving /3, = -- 0.69 per cent per mb or - (1.2 per cent per cm (Hg).

A neutron pile of the type described has a counting rate of some 25,000 counts per hour and is a very sensitive instrument for detecting variations in the intensity of the primary cosmic radiation, for example, short-period bursts from the sun. In Fig. 5 there is shown the time sequence for different stations of one of the most striking solar bursts.

(c) Pressure and temperature effects qf the muon component

Most muons are produced close to the top of the atmosphere and to reach sea-level must traverse almost the whole of the atmosphere. As they come down they lose energy by ionising the atoms of the air, and some decay spontaneously. The energy lost by ionisation is a function of the mass of the air traversed, and the probability of decay is a function of the length of path, for a given velocity. A negative pressure coefficient is to be expected from the first factor because an increase in pressure will cause an increase in the energy lost by ionisation and therefore a decrease in the number of muons which can reach sea-level. Spontaneous decay effectively removes muons from the muon beam and hence,

3 74 G. D. ROCHESTER

as first shown by Blackett (1938), any meteorological variable, for example, temperature or pressure, which causes an increase in the linear extent of the atmosphere, thereby leading to an increased chance of decay, will cause a decrease in the observed muon intensity.

Duperier (1949), as a result of extensive observations of cosmic rays at sea-level, showed that changes in the muon intensity N, could be correlated with the barometric pressure B , the height of the meson-forming layer H , and the temperature T in the vicinity of the layer, by the equation

where p1 and 8, are the absorption and decay coefficients, and, as already observed, both are negative. p 3 is a positive coefficient arising from the competition between T-p decay and the nuclear interaction of parent pions at the level H. The coefficient is positive because a rise in temperature at H causes a fall in air density resulting in more pion decay and less loss of pions by nuclear interaction. More pion decay means more muons at sea-level.

Duperier estimated the height of the level of production by carrying out a series of multiple correlations between the variables for various assumed levels. Upper-air data were obtained from radiosonde observations. Good correlation was found by taking H as the 100 mb level ( H = 16 km), and the temperature T as the temperature of the atmosphere between the 100 and 200 mb levels, leading to values of /I1, & and p 3 of - 2.3 per cent per cm Hg (- 0.17 per cent per mb), - 5 per cent per km, and + 0.12 per cent per "C respectively.

A more direct theoretical approach by Trefall(10j5 a, b) showed that each of the coefficients /I1 and /I3 contains two terms. The barometer coefficient, for example, consists of terms due to energy loss (pure mass absorption) and decay, because an increase in the pressure not only reduces the number of mesons by preventing slow mesons from reaching sea-level, but also causes an increase in the probability of decay by slowing down the mesons.

Temperature effects do not originate at a particular level but are spread throughout the whole depth of the atmosphere; temperature and pressure are not independent; and p-mesons are not produced at a unique height nor with a unique momentum. It is therefore not surprising that the Duperier type of analysis does not lead to entirely consistent results except in certain cases. In consequence, more elaborate treatments have been suggested, notably by Olbert (1053, 1955) and Dorman (1957). The Dorman analysis leads to an expression of the form

The Duperier treatment oversimplified the problem.

where /3 is the pressure coefficient, ST (b) the change in temperature at pressure level b, and W (b) is the fractional change in intensity due to unit change of temperature in a layer of unit thickness at b. The total change in intensity is found by integrating from the top of the atmosphere ( b = 0) to the level of observation ( b = B). W (b) varies in a complicated way with b and other variables, and results have been given by Dorman in graphical form for different detectors at various depths in the atmosphere and underground. The Dorman formulation seems to fit the observations as accurately as the meteorological data allow, but has not been widely adopted because of the excessive amount of computation involved in its application.

It is clear from the above discussion that the correction of muon intensity for atmospheric changes is a complicated and somewhat unreliable procedure not only because of the complexity of the meteorological effects on muons but because accurate meteorological data for the whole atmosphere do not exist. Meteorological effects are least for very high energy muons because the decay effects decrease with increasing muon energies and production is more nearly confined to the upper parts of the atmosphere. Mathews (1962) has found that for muons at 60 m.w.e. underground (median energy at formation 20 GeV), a


1960 I NOV. I DEC. I JAN. I FEB. MAR.1 APR. I MAY I JUN. I JUL. I AUG. I SEP. ' OCT. I 1961

.r,

..&-.. HEIGHT OF 100 MB LEVEL I I I I I I I I I I I I I

Fiqiire 6. The cosmic-ray intensity at GO m.w.e. underground, the temperature of the region between the 100 and 200 mb levels, and the height of the 100 mb level as functions of time (in months).

formula like (1) involving only two terms, may be used. As shown in Fig. 6, Mathews finds fair correlation with the temperature between the 100 and 200 mb levels. However, as pointed out by Barton (1954), layers of the atmosphere above the 100 mb level may well

OLDER DEBRIS 4

Figure 7. The worl&\vicle circulation of the atmosphere.

376 G. D. ROCHESTER

be important but cannot be taken into account because of the lack of suitable meteorological data. Indeed, Dorman has shown theoretically that more than half of the positive temperature coefficient would be expected to come from variations in the atmosphere above the 100 mb level.

The investigation of the time variations of very high-energy mesons is of particular interest because of the information it could give about the origin of cosmic rays. Thus, as Compton and Getting (1935) first showed, if cosmic rays come from extra-galactic space and if they are isotropic in galactic space, a sidereal time effect will occur due to the rotation of the galaxy, the intensity of the cosmic radiation on the side of the earth facing the direction of motion being 0.6 per cent greater than on the opposite face. This effect is best looked for in high-energy rather than in low-energy cosmic rays because the latter are strongly perturbed by solar fields and radiation. High-energy cosmic rays are, however, relatively rare and hence need large detectors, too large to place on satellites or space probes. These detectors must be run deep in the atmosphere, at ground level, or, if high- energy muons are to be recorded, underground. T o sort out sidereal time effects the readings of such detectors must be corrected for the meteorological effects, and for this purpose good meteorological data involving daily or twice-daily temperature readings accurate to (perhaps) 0.5 "C from the 300 mb level up to about the 20 mb level are needed.

4. METEOROLOGICAL APPLICATIONS OF COSMIC RAYS

(a) General considerations

The principal meteorological application is the use of cosmic-ray-produced radioactive isotopes as tracers in the study of the complex problem of the circulation of the atmosphere. A typical representation of the pattern of circulation, due to Goldsmith and Brown (1961), is shown in Fig. 7. This picture is based on the Dobson-Brewer model and summarizes a large body of experimental and theoretical work on the distribution of water vapour, ozone, helium, carbon dioxide, natural radioactivity and radioactive fall-out. It is assumed that air rises in the tropics and moves polewards with slow meridional velocities in the lower stratosphere. In the upper stratosphere the air is almost stagnant, and after residence times ranging from a few months to a year or two, it descends at the poles. Air also comes down into the troposphere of temperature regions at certain seasons via breaks in the tropopause, and can therefore reach temperate regions some two to three months after leaving the tropics.

This model is applicable up to about 100,000 ft but above this height such evidence as is available, from the distribution of rhodium 102 put into the upper atmosphere by nuclear explosions (Martell 1961), and the theoretical work of Murgatroyd and Singleton (1961), again suggests rapid movement polewards.

To examine the contribution which might be made by the use of cosmic-ray isotopes it is necessary to find out what isotopes are produced in the atmosphere, and how they are distributed in altitude and latitude.

(b) Cosmic-ray-produced isotopes

The known cosmic-ray-produced isotopes are listed in Table 1 (La1 and Peters 1962); of these the most useful for studying atmospheric air movement are H3, NaZ2, S35, Be', P33 and P32. Whether a particular isotope can be used, however, will depend not only on the points outlined in Section 4 (a) but also on such practical considerations as the strength of the activity, the type of radiation emitted, and the effects of artificially-produced isotopes from nuclear explosions. The most useful isotopes appear to be Be7 and P32, although in the case of Be7 there is some evidence that in certain regions of the world serious contamination by artificially-produced Be7 may occur (Bleichrodt 1962).

COSMIC RAYS AND METEOROLOGY

TABLE. 1. COSMIC-RAY PRODUCED ISOTOPES

Isotope Half-Life lcddiat ion Mode of I'rooduction

Be' I' C"

H'

Na2* Q35

Be P'J P 3 2

SiJ?

ct39

2.7 x lO6y 5730 y

710 y 13.5 y

2.6 y 67 d 53 d 25 d

14.3 d 55 min

B- 550 keV 8- 156 keV 8- 8- 1s keV

i3f and y B- Y B- B- 1.7 MeV p- 1.5 MeV

Spallation of NI4 and CYb Neutron capture in N" Spallation of A4" Spallation of N" and OLb Neutron capture in NL4 Spallation of A4" Spallation of A+" Spallation of Ni4 and OL6 Spallation of A'O Spallation of A4" Spallation and muon capture in A4"

( c ) The world-wide production of radioactive isotopes in air

This problem has been considered in a series of papers by Peters, La1 and their co-workers. The isotope, Be7, for example, is produced in small interactions (or ' stars ') in N14 and 0l6 by neutrons and protons with energies above 20 MeV, the largest contribution coming from neutrons in the energy range 100-200 MeV. Three steps are involved in the derivation of the worldwide rates of Be7, namely :

The use of the cloud-chamber data of Brown (1954) and Bullock (1957) to give the absolute production rate of stars of various sizes in nitrogen at a particular altitude and latitude. The extension of these rates to other altitudes and latitudes by use of a parameter, such as the flux of slow cosmic-ray neutrons, which is proportional to the flux of low-energy nucleons.

(3) The determination of the average yield of a particular isotope per star. This has been found by La1 et al. (1960) for Be' by exposing water to the cosmic radiation for periods of 2-4 months (March-August 1959) at Mount Evans and Echo Lake. The chemically measured production rate of Be7 at Echo Lake was 9 x nuclei per g oxygen per sec, a value which is directly applicable to air since experiments with artificially accelerated particles over a wide range of energies show that the yields of oxygen and nitrogen are nearly the same and almost independent of the energy of the incident nucleon. The yield of Be7 is 4.5 per cent per star.

The star rate in the atmosphere as calculated by La1 et al. (1958) is shown in Fig. 8; the total production of Be7 throughout the atmosphere is obtained by multiplying the ordinates of this figure by 0.045. Integration of the curves of this figure gives the global isotope production as a function of latitude, and shows that 70 per cent occurs in the stratosphere. Isotope production is a marked function of geomagnetic latitude, increasing rapidly from the equator to the poles.

The intensity of cosmic rays depends markedly on sunspot activity, being weaker in periods of intense activity because solar plasma prevent low-energy cosmic rays of galactic origin from reaching the earth. It follows that nucleon intensity and isotope production, will also vary in the same way. The average yearly variation in isotope production from this cause is thought to be about 5 per cent; in 1958, an exceptional year, the reduction was 24 per cent. This variation is also strongly latitude sensitive. As La1 and Peters (1962) have pointed out, however, three short-period bursts of solar protons fall upon the earth per day at sunspot maxima and these may partially restore the loss of protons by solar plasma. It is not possible to estimate the magnitude of this effect yet because the form of the low-energy (< 50 MeV) end of the solar flare proton spectrum at the top of the atmosphere is not known.

(1)

(2)

378 G. D. ROCHESTER

Figure 8. various latitudes at intervals of 10".

The total star production rate in the atmosphere as a function of depth in the atmosphere for Curves for successive latitudes are displaced along the abscissa. ss and ST are the mean stratospheric and tropospheric star production iates.

( d ) Cosmic-ray isotopes as tracers

(i) Theoretical

Cosmic-ray isotopes may be used as tracers in meteorology because their production is a known function of latitude and altitude and is almost constant in time. Indeed, as La1 and Peters (1962) have shown, isotopic density provides a natural reference system with geomagnetic latitude and altitude as coordinates. Iso-isotopic production surfaces corres- pond to yn S = constant, where S is the star rate, and y, is the yield per star of isotope n. These quantities are related to the local saturation concentration of the isotope, c,, and the mean lifetime T, by the relation

Lines of isostar production (in a still atmosphere) representing the intersections of the surfaces on a vertical plane, derived from Fig. 8, are shown as dotted lines in Fig. 9. Air motion will displace these surfaces in a manner related to the nature of the motion, whether steady or turbulent, and information may be derived in so far as the surfaces retain their identity during the state of motion. The potential usefulness will depend on the range of lifetimes available, and the sensitivity of the sampling equipment.

La1 and Peters distinguish three cases : The first case, which is also illustrated in Fig. 9, is that of steady motion when the

period of circulation is long compared with the mean lifetime of the isotope. When equilibrium is reached the air velocity v is given by the relation

COSMlC RAYS AND ME'I'EOKOLOGY 379

Figure 9. Schemdtic diagram showing a north-south section of the deformation of iso-concentration surfiaccs with respect to isoproduction surfaces (dotted lines) in dn atmosphere with vertical and meridiunal circulation,

when the period of circulation is very long compared with the half-life of the isotope.

where c, is the local concentration and the other symbols are as previously defined. Non- parallel components of velocity can be obtained by using isotopes of different lifetimes. This relation can be used when steady conditions obtain and it may therefore be applicable to parts of the stratosphere and to the vertical air flow through the equatorial tropopause.

The second and third cases refer to two distinct types of air, namely, air which has remained in the troposphere since it was last cleaned of radioactivity, (cc-air) and air which has descended into the troposphere from the stratosphere (&air). In general, for a given period of irradiation, a-air will clearly have much less radioactivity than /Lair and hence the two types may be distinguished. It can be shown, with certain simplifying assumptions, that for a-air the ratio of the concentrations of long to short-lived isotopes obeys the inequalities :

and for P-air

(ii) Experimental

No results have yet been published to test (4) but according to Peters (private com- munication) sampling is in progress and preliminary results agree with calculation. There are, however, extensive measurements of the radioactivity of airborne dust, at ground level, in Canada, Chicago and England, and of rain and snow in India and Sweden. The results of Parker (1962) in England will be taken to represent the former, and of Peters, Lal, and their co-workers in India, the latter.

Parker has taken continuous readings of the Be7 concentration of surface air at Sutton (Surrey, 51"N, 0") during the years 1960 and 1961 with the result shown in Fig. 10. The maxima in late spring and early summer are very marked and confirm for a cosmic ray produced isotope the similar behaviour of artificially produced radioactive isotopes, for example, CsI3?. As pointed out by Stewart et at. (1957) these maxima are in accordance with the Dobson-Brewer circulation model.

380 G. D. ROCHESTER 1OC

‘JI

81

7(!

6U

50

40 h .3

M s rl I 0 rl

x 30

ii 0) ... L)

I‘U

11

”

I

..., :“ : .’ cI ’. . . . . . .

. . u * :

!+

k

:cI

I

J F h i A M J J A S 0 N U J F M A M J J A S

l0bU lcJb1

I’lgure 10. I k 7 concentration in surface air in England during the years 1960 and 1961

The Bombay workers have measured the concentrations of the isotopes Be’, P3*, and S35 in Indian rains for the years 1956-58. The activity of different samples varies over wide limits and therefore only the average of a long series of measurements is significant. Typical values of the fall-out of Be7 are 4 x lo5 atoms cmp2 year-’ and of P32 3.3 x lo3 atoms cm-2 year-l. If this radioactivity comes from tropospheric air the inequality (5) should hold, that is,

Be7 100 ’< - < 370.

P 3 2

The experimentally measured value of the ratio is 120 showing that the air is tropospheric in origin.

The Indian results also show that the average residence time of the radioactive isotopes in the troposphere in the tropics is about 40 days.


(e ) Conclusion

The results of work with cosmic-ray-produced isotopes are still somewhat meagre but it is concluded that these isotopes offer promising possibilities of investigating the circulation of the atmosphere because their production is a known and unique function of the geomagnetic coordinates and the altitude; and in contrast to all other types of tracer, for example, ozone, their mode of disappearance throughout the greater part of the atmosphere is relatively simple, in that it is governed only by the well-known laws of radioactive decay.

ACKNOWLEDGMENTS

I am indebted to the following authors for permission to use diagrams which have appeared in their papers : Professor J. A. Simpson for Figs. 1, 2 and 4; Dr. L. I. Dorman for Fig. 3 ; Professor C. de Jager for Fig. 5; Dr. T. Mathews for Fig. 6; Drs. P. Goldsmith and F. Brown for Fig. 7; Drs. D. La1 and P. K. Malhotra and Professor B. Peters for Fig. 8; Dr. D. La1 and Professor B. Peters for Fig. 9; and Dr. R. P. Parker for Fig. 10.

Professor Peters kindly let me read an unpublished article by Dr. La1 and himself on ' Cosmic-ray-produced isotopes and their applications to problems in geophysics.' I have used this excellent article freely in the appropriate sections of this lecture.

I wish to thank Dr. A. W. Wolfendale for his helpful comments.

REFERENCES

Barton, J. C. 1954 Blackett, P. M. S. 1938 BLeichrodt, J. F. 1962 Brown, W. W. 1954 Bullock, F. W. 1957 Compton, A. H. and Getting, I. A. 1935 Dorman, L. I. 1957 Duperier, A. 1949 Goldsmith, P. F. and Brown, F. 1961 Lal, D., Malhotra, P. K. and

Peters, B. 1958 Lal, D., Arnold, J. R. and Honda, M. 1960 Lal, D. and Peters, B. 1962

Martell. E. A. 1961

Mathews, T. Murgatroyd, R. J. and Singleton, F. Myssowsky, L. and Tuwin, L. Olbert, S.

Parker, R. P. Simpson, J. A., Fonger, W. and

Stewart, N. G., Osmond, R. G. D.,

Trefall, H.

Treirnan, S. B.

Crooks, R. N. and Fisher, E. M. R.

1962 1961 1926 1953 1955 1962

1953

1957 1955a 1955b

Pror. Phys. SOC. A, 67, p. 637. Phys. Rev., 54, p. 973. Nature, 193, p. 1065. Phys. Rev., 93, p. 528. Proc. Phys. SOC. A, 70, p. 134. Phys. Rev., 47, p. 817. Cosmic-Ray variations, Moscow, U.S.S.R. Proc. Phys. SOC. A, 62, p.684. Nature, 191, p. 1033.

J . Terr. & Atmos. Phys., 12, p. 306. Phys. Rev., 118, p. 1626. Progress in elementary particle and cosmic-ray physics, (Eds.

Wilson and Wouthuysen) North-Holland Publishing Co., Amsterdam, Holland (in press).

Paper presented at I.U.G.G. Symposium on Atmospheric Ozone, Arosa.

Ph.D. Thesis, University of London. Quart. J . R. Met. SOC., 87, p. 125. Zeits. f. Phys., 39, p. 146. Phys. Rev., 92, p. 454. Ibid., 96, p. 1400. Nature, 193, p. 967.

Phys. Rev., 90, p. 934.

A.E.R.E. Report, 2354, Harwell. Proc. Phys. SOC. A, 68, p.893. Ibid., 68, p. 953.

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Cosmic rays and meteorology