Reprinted from Aeronautics and Astronautics, Vol. 13, No.4,pp. 10-19, April 1975, with the permission of the publisher,the American Institute for Aeronautics and Astronautics, andof the author.

Sun-Weather RelationshipsByJ. W. KINGAppleton Laboratory, Slough, England

As they profoundly influence civilization, and have not been wellexplored, Sun-weather relationships should become a major fieldof research in the decade being ushered in by GARP and the IMS

Many people have suggested in the pastthat the weather is influenced by the11- and 22-year sunspot cycles. I believethat the accumulated evidence is socompelling that it is no longer possibleto deny the existence of strong con-nections between the weather andradiation changes (electromagneticand/or corpuscular) associated with 'I

whole range of solar phenomena. Eve"the most skeptical scientist who in-vestigates the literature thoroughly willbe forced to concede that importantaspects of lower-atmosphere behaviorare associated with solar phenomenaranging from short-lived events such assolar flares, through 27-day solarrotations to the l I-year, 22-year, andeven longer solar cycles. The com-plicated pattern of sun-weatherrelationships undoubtedly needs muchfurther clarification, but progress inthis field will be hindered if the viewprevails that such relationships shouldnot be taken seriously simply becausethe mechanisms involved in explainingthem are not yet identified.

What must be sought now are themechanisms responsible for thecomplicated sun-weather relationshipsthat exist and greater insight into theirpractical consequences for agriculture,energy consumption, and nationaleconomies.

Weather and the Solar Cycle

F-l summarizes a rainfall analysis byXanthakis (1973). He observed that athigh northern latitudes (70-80 deg) thell-year solar cycle was positivelycorrelated with a lO-cm oscillation inthe annual rainfall total; at latitudesbetween 60 and 70 deg N the oppositebehavior occurred while at still lower

latitudes a negative correlation existedbefore about 1915 A.D. and a positiveone after that. Bowen (1974) drewattention to the fact that in thesouthern hemisphere the rainfall

JOE W. KING received a Ph.D. atCambridge University, England, in1955 and was awarded theHamilton Prize by the Universityfor his dissertation. He is an"individual merit senior principalscientific officer" at the AppletonLaboratory. At Appleton hereceived the 1966 Wolfe Awardfrom the U.K. Ministry of Technol-ogy for his upper-atmosphericresearch. For four years Dr. Kingchaired the European SpaceResearch Organisation's ion groupand is now vice-president of theICSU special committee on solar-terrestrial physics and chairman-elect of the URSI commission onthe ionosphere. He is a member ofthree British national committees(for radio science, geomagnetismand aeronomy and solar-terrestrialphysics).

109

oscillations associated with the ll-yearsunspot cycle exhibit opposite phases at17 deg Sand 43 deg S (see F-2).Moreover, the sunspot cycle appears toinfluence the rainfall in opposite waysat 55 deg Nand 35 deg N (King, 1973).

The solar-cycle-induced rainfalloscillations referred to range fromabout 3 to some 50% of the normalannual total. Obviously, a reduction ofrainfall by 25% in each of several yearsaround one of the extremes of thesunspot cycle is of considerable im-portance. .Anillyses comb in in data~ zones exhibiting opposite solar-cycle effects will inevitably lead to theerroneous conclusion that no solar-cycle effect exists, as will an ana ySIS ofrainfall data from regions situatedbetween zones in which the sunspot-cycle effect is opposite.

The annual rainfall totals at For-taleza, Brazil, and at three sites inSouth Africa (F-3 and F-4) werepositively correlated with the "double"sunspot cycle for considerable periodsof time. The modulation associatedwith the double cycle amounted toabout 35% of the average annual totalat Fortaleza and to about 25% of theaverage rainfall at the South Africanstations. Data from Fortaleza areavailable from 1865 onwards. After thefirst 60 years the relationship betweenthe rainfall and the double cycle atFortaleza changed phase. The SO yearsof data available from South Africashow a consistent positive correlationwith the double cycle. The Africanrainfall data for latitudes south of thosewhere the double-sunspot-cycle in-fluence is observed exhibit apronounced oscillation having a periodof about 10 years (Tyson et al, 1974) in

anti-phase with the sunspot cycle (Kinget al, 1974).

F-5 gives particularly impressiveevidence of an association betweenrainfall and the double sunspot cycle. Itshows the date within each year from1844 to 1944 by which one quarter ofthe year's rainfall at Adelaide (35 deg S,139 deg E) had fallen. This "quartiledate" (Cornish. 1936 and 1954)oscillates between about April 15 andMay 25 in phase with the doublesunspot cycle (Whipple. 1936). Thecorrelation coefficient. +0.79. betweenthe 101 dates calculated by Cornish andthe corresponding normalized sunspotnumbers plotted in Fig. 5 is highlysignificant (>99. 9%). Cornish showedthat the dates of the other rainfall"octiles" exhibited similar oscillations.Oscillations of up to six weeks in thedate by which various fractions of theannual rainfall total have fallen ob-viously affect agriculture.

As another striking illustration of theinfluence ofthe double sunspot cycle onthe weather. the July temperature incentral England during the period175O-18SO exhibited an oscillation ofnearly 1 C in phase with the doublesunspot cycle (F-6. King et al, 1974).The temperature curve is somewhatanomalous during the years 1840-1855when the temperature extremes oc-curred around sunspot minima insteadof near sunspot maxima.

The double sunspot cycle appears toinfluence the climate of the UnitedStates in several ways. Thompson(1973) and Roberts (1974) have shownthat droughts in various parts of thecountry occur around every secondsunspot minimum. Newman (1965) hasshown that winter temperatures inBoston exhibit a 22-year periodicity.Thompson (1973) reported a"remarkable" correlation between theJuly/August temperature in the cornbelt ofthe United States and the doublesunspot cycle. Striking evidence byMather (1974) relating the double cycleand temperatures in the U.S. will bedescribed toward the end of this article.

Possible relationships between theweather and the "SO-year sunspotcycle" have been discussed by Willett(1 %1).

A sunspot-cycle-induced meteoro-logical variation may suddenly reversephase (e.g .• see Fig. 1). Two classicalexamples of such phase changes shouldbe mentioned:

1. In his review of the relationshipsbetween solar and meteorological phe-nomena. Brooks (1951) observed: "Theone fact which appears to be firmlyestablished is that over the world as awhole. and especially in the tropical

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F:1 Smoothed mean "excess" annual rainfall in three northern-hemispherezones (after Xanthakis. 1973) compared with the corresponding "normalized"annual sunspot numbers. The normalized sunspot number for a particular year isgiven by 100 (Ny-NN)/(NX-NN) where Ny is the annual mean sunspot number forthe year concerned and NX and N N are respectively the annual mean sunspotnumbers for the maximum and minimum years between which the particular yearfalls. It should be noted that data from the American, European and Asian sectorshave been analysed, but that, in the 500-600N zone, data from only the Americansector are shown; the rainfall in the European and Asian sectors of this zonebehaved differently.

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F-2 Difference between the actual and normal annual rainfalls at two latitudesin Australia, The curves were obtained by applying an 8-15-year fi Iter to theannual differences, but it is significant that the extremes of the resultingoscillations occur very close to sunspot minima and maxima. After Bowen (1974).

110

F-3 CORRELATION OF RAINFALL AND "DOUBLE"SUNSPOT CYCLE

A. Smoothed annual rainfall totals at Fortaleza in SouthAmerica derived from data pub Iished by Markham (1974).B. Annual sunspot numbers plotted in the conventional"double sunspot cycle" form; the period shown includessix sunspot minima.

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F-4 Smoothed annual rainfall totals at three places inSouth Africa (after Tyson, 1974) compared with the doublesunspot cycle; the period studied includes six sunspotminima.

regions, the mean air temperature atthe Earth's surface varies in oppositionto the sunspot cycle, being lowest atsunspot maxima and highest at sunspotminima. This was suspected by Her-schel as early as 1801 but was firstclearly demonstrated by Koppen (1873)and has since been confirmed byMielke (1913), Hildebrandsson (1914),Walker (1915, 1923), Mecking (1918),Clayton (1923), Droste (1924) andothers." In their Handbook ofStatistical Methods. in Meteorology,Brooks and Carruthers (1953)examined the significance of some ofthe negative correlations betweentropical temperatures and sunspotnumbers and concluded that they were"undoubtedly significant." Althoughthe tropical temperatures examined bythe early workers referred to by Brookscorrelated negatively with sunspotnumber, Troup (1962) pointed out arelatively recent reversal of this: "Overthe tropics as a whole, the correlationsbetween sunspot number and tropicaltemperatures which were negative priorto 1920 have become zero or evenpositive subsequently. Of recent yearsthere has apparently been a reversal inthe phase of the temperature cycle."

2. The level of the water in LakeVictoria, positively correlated withsunspot number before about 1930, hasbeen negatively correlated since about1950; during the interim period littlecorrelation existed between sunspotnumber and the water level.

Lightning events in Great Britain (F-7, plotted on an arbitrary scaledesigned to indicate variations in thenumber of power failures associatedwith lightning strikes) during foursunspot cycles varied by a factor ofnearly two in phase with the sunspotcycle (Stringfellow, 1974). Brooks(1934) first showed that a significantrelationship exists between the oc-currence of thunderstorms and theannual sunspot numbers: correlationcoefficients up to 0.91 were obtainedfrom long series of data, the largestcorrelation coefficients relating to highlatitudes. In 1953 Brooks andCarruthers made this observation:"There is a correlation coefficient of +0.88 between the number of thun-derstorms recorded in Siberia andmean annual sunspot relative number.Since it 'is inconceivable that thun-derstorms in Siberia cause sunspots, itis reasonable to assume that sunspots

III

or some other solar phenomenonassociated with sunspots causethunderstorms." They also establishedstatistically that the observed variationof the frequency of thunderstorms inthe West Indies during the sunspotcycle was "definitely significant," theprobability of obtaining the correlationby chance being less than 0.1% "Wehave established," they said, "a highprobability that thunderstormfrequency ill the West Indies is relatedin some way to the sunspot maximum."

Cornish (1954) concluded that theoscillations in the Adelaide rainfallrecords (F ·5), "must be due to secularchanges in the latitudinal paths ofanticyclones with their attendantcyclones across southern Australia."Bodurtha (1952) reported that thesunspot cycle strongly influences boththe frequency and the intensity ofanticyclogenesis, so it may be con-cluded that the number and intensity ofanticyclones and the latitudes at whichthey occur all vary during the solarcycle.

Schostakowitsch made one of themost comprehensive investigations ofthe influence of the solar cycle on theweather. He prepared detailed global

F-5 Ten-year smoothedmeans (lower curve) of theannual rainfall "quartile" (thedate by which one quarter ofthe annual rai nfall had oc-curred) for Adelaide,Australia. After Cornish(1954). The date fl uctuates byabout six weeks in phase withthe double sunspot cycleplotted in the form shown inthe upper curve. The Cornishdata points are sl ightlydisplaced because he usedsmoothed means for an evennumber of years.

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F-6 Smoothed means of the July central-Englandtemperatures (upper curve) published by Manley (1974)compared with the conventional double sunspot cycle(lower curve). The period includes 12 sunspot minima.Since 1880 the influence of the double sunspot cycle onthe temperature in Britain has been less apparent than theinfl uence of the 11-year cycle.

maps '(reproduced by Clayton, 1933)showing how the temperature, pressureand rainfall over the Earth vary be-tween sunspot minimum andmaximum.

Response of the Lower AtmosphereTo Short-Lived Solar Phenomena

In recent years, several analyses haveindicated that short-lived solarphenomena may trigger a response inthe lower atmosphere. To investigatethe tropospheric response to solar

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flares, Schuurmans (1965) computedthe change in height of the SOO-mb levelover much of the northern hemisphereduring the first 24 hr after each of 53flares. He concluded that the pattern ofheight changes "shows a remarkableregularity with a symmetry with respectto the geomagnetic rather than to thegeographic pole. The main featuressuggested by the picture are a rise inheight in the region of the geomagneticpole and a wide region of fall in heightcoinciding quite well with the auroral

112

zone." Reiter (1973) showed that theinflux of stratospheric air to the 3-kmlevel increases on the second or thirdday after an H 0: and/or X-ray flare. Heconcluded that "the use of thisstatistically evident solar-terrestrialrelationship would be in order in thepractical forecasting of influxes ofstratospheric air into the biosphere."

Results such as these show that thecirculation of the lower atmosphere issignificantly modified after solar flares.

As measured by the "vorticity area

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-4 -2 0 2 4 6DAYS AFTER CROSSING SECTOR BOUNDARY

F-B Average behaviour of the northern-hemisphere "vorticity area index" aroundthe dates of 53 interplanetary-magnetic-tield sector boundary crossings; winter,1964-70. The data have been divided into two groups in three different ways. Ineach case, the hem ispheric vorticity index shows an oscillation of about 10%.After Wilcox et al (1974).

index" at various heights in thetroposphere (Wilcox et al, 1974), thecirculation also appears to be modifiedaround times when the interplanetarymagnetic field sector boundaries crossthe Earth. These boundaries originateat the Sun and sweep across the Earthas they rotate during the 27-day solarrotation. F-8 shows how the vorticityarea index of the northern hemispherevaried on average during the 53 sectorboundary crossings for which dateswere known. It appears significant thatsim ilar results were obtainedirrespective of how the data set wassubdivided: Three different methods(see F-8) each showed the averagevorticity area index varying by about10%. A change of this magnitude in theindex is of considerable importance.Because only limited data are availableat the present time, further informationabout the behaviour of the troposphereduring sector boundary crossings willbe awaited with interest. Mansurov et

al (1974) have also reported arelationship between sector crossingsand the lower atmosphere.

Solar phenomena tend to recur withperiods of the order of 27 days, thesynodic period of revolution of the Sun.Panofsky (1967) has shown that "thisperiod is close to the period of themaximum fluctuations of mean westwinds" at upper-middle latitudes.Similar behaviour is not observed atlower latitudes.

After an investigation of the 5OO-mbcirculation along the auroral belt, Riehl(1956) concluded that "circulationincreases and decreases take place witha period which can be related to themean solar rotation in the (solar)equatorial zone."

Rosenberg and Coleman (1974)studied the southern California rainfallpower spectrum and concluded that"there is a significant peak at almostexactly 27.0 days." Their study showedthat the 27-day rain cycle is "probably

113

not related to" the Moon. Studies of thephase of the cycle suggest that, if theperiodicity has a solar origin, its phasemust be determined by anothermechanism. Berkes (1955) has reportedthe existence of a 27-day periodicity inwind speed and Egyed (1961) noted a27-day periodicity in soil temperature.

Many authors including Sazonov(1%5), Mustel (1%6), Beynon andWinstanley (1969), Roberts and Olson(1973), Stolov and Shapiro (1974), andSidorenkov (1974) have reportedassociations between magnetic activityand lower atmospheric phenomena.But Hines (1973) pointed out that, sincegeomagnetic activity may be caused bylower-atmosphere disturbances, it isnot possible to come to any definiteconclusion about the origin of theassociated geomagnetic and meteoro-logical disburbances. Further evidenceis needed to resolve this point, althoughit may be significant that at least someof the atmospheric phenomena occurseveral days after the associatedgeomagnetic activity. For example, F-9shows that the vorticity area index fortroughs preceded by a sharp rise inmagnetic activity increases 40% fivedays after the magnetic disturbance.

This behaviour, and some of theother s un-weat her relationshipsmentioned, occurs only during wintermonths. Stolov and Shapiro (1974)analysed 24 years of 700·mb heightsfrom 200N to 700N and concluded that"the 7oo·mb height difference between200N and 550N increases significantlyin winter four days followinggeomagnetic disturbance." Even insummer a statistically significant in-crease was found, but "the effect ismost clear in: winter in the quadrant900 to 1750W and corresponds to a 7%increase in the mean geostrophicwesterly flow." Their analysis of the700·mb heights following geomagneticdisturbances reveals that "the effectproceeds with the growth anddevelopment of large negative centresin the latitude belt 400N to 600N."

Role of Earth'sMagnetic Field

Several studies have shown that sun-weather relationships are mostpronounced in the vicinity of theauroral zone. Sarukhanyan andSmirnov (1970), for example, concluded"the pattern of the amplitudedistribution of the l l-year variation ofatmospheric pressure shows that theamplitude increases only up to 700N.Further north the amplitudes decrease.Thus the maximum amplitudes of thel l-year variations are observed in the65- 700N zone. This zone is known tohave the maximum density of solar

corpuscular radiation, maximumoccurrence of auroras, and maximumfrequency of magnetic disturbances."

F-lO shows the latitudinal variationof the change in surface pressure(averaged around the Earth at par-ticular latitudes) between sunspotminimum and maximum. calculated byme from data published by Miles(1974). The pressure variationassociated with the ll-year sunspotcycle is particularly large in the auroralbelt. (Unfortunately, Miles did notpublish data for higher latitudes.) Theobservation of Sarukhanyan andSmimov-that the effect decreases atlatitudes above 700N-has beenconfirmed by several investigators,including Clayton (Wexler, 1953).

F-lO also shows the latitudinalvariation of the mean amplitude of the"wavenumber I" longitudinal at-mospheric variation; this is clearly mostpronounced in the auroral belt. If it hasnot been demonstrated conclusivelythat the auroral zone influences thelower atmosphere. we certainly mayhypothesize that energetic particlesenter the atmosphere at aurorallatitudes and, through some unknownmechanism, influence the circulation ofthe lower atmosphere.

If this were the case. it would beexpected that the geomagnetic field asa whole would influence the loweratmosphere. Several authors. includingSazonov (1974) and myself (1974a).have in fact drawn attention to thesimilarity between meteorological andgeomagnetic contour maps. F-ll.published by me (1974b), illustrates theremarkable similarity between thespatial variations of three differentmeteorological parameters and theintensity of the geomagnetic field.

To give a measure of the similaritybetween the meteorological andgeomagnetic variations at 600N, F-12compares the longitudinal variations ofthe height of the SOO-mb level and thegeomagnetic intensity. The correlationcoefficient between the two variations is- 0: %3 (the lowest atmosphere beingcolder where the magnetic field is mostintense). Although such a highcorrelation coefficient is unusual ingeophysics, it does not prove anything;nevertheless. its implications shouldnot be lightly dismissed. particularlysince existing models of the atmospheredo not satisfactorily explain thebehaviour observed at high latitudes.Manabe and Terpstra (J 974), forexample, reported: "The agreementbetween the distributions ofgeopotential height of the SOO-mb levelsurface in the mountain-model at-mosphere and that in the actual at-mosphere is particularly poor in higher

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114

latitudes." It is at these latitudes thatmost Sun-weather relationships appearto be pronounced. I have argued (King,1974b) that we still lack good at-mospheric models and need furtherinterdisciplinary research to discoverwhich geophysical processes have beenomitted from the existing models.Green (1974), writing from ameteorological point of view, agreedwith me.

If the Earth's magnetic field in someway controls the morphology of thelower atmosphere, changes of the fieldwhich occur as the nondipole com-ponent "rotates." or as the dipole fielditself changes, may well be ac-companied by climatic variations. F-13shows that variations of temperatureand magnetic intensity in the United

600 2 4 6 8 10DAYS AFTER FIRST IDENTIFICATION OFTROUGH (ADD 3 DAYS ON AVERAGE TOGET INTERVAL AFTER INCREASE INGEOMAGNETIC ACTIVITY)

F-9 Average variation of the vorticity area index associated with winter troughsover the North Pacific and North America during the first ten days after thetroughs were identified. Broken curve indicates troughs preceded (by three dayson average) by magnetic disturbances. Continuous curve indicates troughspreceded by ten magnetically quiet days. The vorticity index rises about 40% fouror five days after the disturbance. After Roberts and Olson (1973).

Kingdom appear to have beenassociated during this century. Theseresults, and many similar ones reportedby Wollin et al (1973,1974), show thatthe temporal variations of magneticintensity and temperature at variousplaces are inversely correlated. Strongnegative correlations have occurred notonly over decades, but over muchlonger time spans. F-14, for example,shows oxygen-isotope data (whichprovide a measure of temperature) andmagnetic-intensity values obtainedfrom a single deep-sea core formedduring a SOO.OOO-year period. Coldepochs occurred when the magneticintensity was relatively high and viceversa. The temperature and magneticmeasurements were not made at exactlycorresponding epochs, but the

800,--,--,---,--,--,---,--,---,--,

00 30 60 90LATITUDE (ON)

F-10 Latitudinal variations of two atmosphericparameters showing particularly large effects in theauroral belt. The val ues in the upper and lower curves werecalculated from data published by Van Loon et al (1973)and Miles (1974) respectively.

600

400

200

0-6

0-4

0-2

AURORAL---.BELT

LONGITUDE (OE)

F-11 Spatial variations of three different meteorologicalparameters compared with the intensity of thegeomagnetic field (after King, 1974b)_ The upper threeboxes contain maps, published by Bean et al (1966), thatindicate how average tropospheric temperature, surfacehumidity and surface pressure vary over most of thenorthern hemisphere in November. The lowest boxcontains a map of the intensity of Earth's magnetic field.

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LONGITUDE (DEGREES EAST)the geomagnetic field.

115

correlation coefficient between pairs ofvalues read off the two curves at in-tervals of SO,OOO years is 0.67, in-dicating a very high probability (greaterthan 99.9%) that the two parametersare related. King and Willis (1974) havesuggested that the "Little Ice Age"which occurred in Europe between15SO and 1850 A.D. was associatedwith the unusually high values ofmagnetic inclination that existed atthat time.

MechanismsThe Earth's magnetic field, as we

see, may playa role in bringing somesun-weather relationships about. Whatgeophysical phenomena that varyduring the solar cycle, we might thenask, does the Earth's magnetic fieldinfluence?

One is cosmic rays. Ney (1959) drewattention to the fact that at the 500-mblevel the amount of ionizationassociated with cosmic rays decreasesby a factor of about 4 between sunspotminimum and maximum, and madethis suggestion: "If there is a con-nection between atmospheric ionizationand thunderstorm activity for example,a solar-cycle modulation might beobserved in climatological data." Theeffects of the sunspot-cycle-inducedchanges of lower-atmosphere con-ductivity on atmospheric electric fields,cloud formation, tem peratures,thunderstorm activity and rainfall donot appear to be clearly known at thepresent time. The possibility that thesolar-cycle variation of cosmic rays maylead to certain sun-weather relation-ships cannot be rejected.

The total ozone content of the at-mosphere also varies during thesunspot cycle and possibly during theshort-lived solar events. Variousauthors, including Willet and Prohaska(1965), Christie (1973) and Paetzold(1973), have described variations ofozone content that occurred during thesunspot cycle while Dobson et at (1929)said "there is a small but definitetendency for days with much ozone tobe associated with magneticallydisturbed conditions." Weeks et at(1972) concluded that the ozone contentis reduced during strong solar protonevents.

It is not known whether such tem-poral variations of ozone cause or arecaused by weather effects, but it has atleast been established that ozone andweather disturbances are associated.Dobson (1936) wrote: "One of the mostinteresting results that has come out ofthe study of the amount of ozone in theatmosphere is the relation which isfound between the amount of ozoneand the weather conditions. At the

present time we know that largechanges in the amount of ozone maytake place within a few days-changesof the order of±2S%-and these areclosely associated with changes in theweather conditions."

The spatial variation of ozone overthe Earth is not yet fully understood,and it seems reasonable to suggest thatattention should be paid to theremarkable similarity which existsbetween the global map of ozone andthe intensity of the geomagnetic field.F-15 shows the regions where mostozone is observed in the northern andsouthern hemispheres (London andKelley, 1974), and I have comparedthese with the regions of extrememagnetic Band L values. It may be thatthe ozone content is controlled in someway by the Earth's magnetic field and,

as a consequence of this, the field mayinfluence the weather. It should beborne in mind that "the correlationcoefficient between the temperature ofthe troposphere and the ozone contentof the atmosphere is about -0.7"(Dobson, 1936).

Apart from cosmic rays and ozone,other mechanisms which may affectSun-weather relationships include thefollowing:

1. The influence of energeticallyweak upper-atmosphere phenomena onlower-atmosphere systems that areclose to resonance (Green, 1974). Theeffective amplification (of anenergetically weak driving force) thatmay occur in an atmosphere whichreacts nonlinearly has not yet beenadequately investigated.

2. The solar-cycle variation of the

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~ 48,600 3'8 ~iJizw~ 47,600

u 47,700i=~ 47,800

~ 47,900~48,00048,100L----L_-'--_..I...---''----'-_....L_-'----'_-'-_-'-_'----'_-L.---..J

1900 1920 1940 1960YEAR A.D.

F-13 Smoothed variations of the magnetic intensity 'at Eskdalemuir andStonyhurst in Great Britain, central-England winter temperatures (calculatedfrom data published by Wollin et ai, 1973), and rainfall for England and Wales(from annual values reported by Wales-Smith, 1973) during this century. Notethat the magnetic-intensity scale decreases upwards.

UiwIU~...J

~z<la::

1920 1940 1960

~ Or---~~--'---rr------.-----------'-----~r---'-----------,cc

~~T-I~g1-0SSu---2zw~xo

>-I-iJi-2z,wO'

~~~~ICJQz-(9~~ °5~------~4------3~----~2~--~-~-----~O

105YEARS B.P.

F-14 Magnetic intensity and information about the temperature obtained from asingle deep-sea core. After Wall in et al (1974).

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F-15 OZONE AND MAGNETIC-FIELD VALUESThe upper box .shows the regions in the northern and southern hemisphereswhere the total ozone content, averaged over 13 years, is greatest. The ozonecontent decreases from the high values shown to about 240 m illiatmospherecentimetres at low latitudes. After London and Kelley, (1974). The lower boxshows the regions of greatest magnetic-B and magnetic-L values in eachhemisphere.

90.---------~--------~--------~-------.6

30o

-30 320

-60-:;'2-0

z.e.....

C340>wo 60::Jr-~ 30-.J

B=O'50

o-30-60 &~o.ss

-90~------~---------L--------~------~-180 -90 0 90 180LONGITUDE (OE)

60,-------------,-------------,-------------,

1875 1900YEAR A.D.

F-16 Evidence from which Vibe (1967) concluded that the sunspot cycle in-fluences the motion of sea ice around Greenland.

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frequency of occurrence of short-livedphenomena. The response of thetroposphere to the ll-year sunspotcycle may represent merely an in-tegration of the effects caused by short-lived phenomena such as solar flares orgeomagnetic storms, which are muchmore frequent at sunspot maximumthan minimum.

3. The effect of water vapour formedfrom solar-wind protons as suggestedby de Turville (1%la, 1961 b).

4. The effects of possible, but as yetunknown, solar-cycle changes in the"Solar Constant," that is, in the totalelectromagnetic energy radiated by theSun.

S. Variations of the efficiency of thecoupling between the solar wind andthe magnetosphere as the direction ofthe interplanetary magnetic field varies(Svalgaard and Wilcox, 1974) or as thesolar-wind velocity varies (Intriligator,1974) during the sunspot cycle.

6. Variable reflection by the upperatmosphere of upward-propagatinggravity-wave energy (Hines, 1974).

Implications of Sun- WeatherRelationships

Sun-weather relationships affect ourlives in numerous ways, many of whichare not appreciated. The following areexamples:

Energy budgeting and electricitydistribution. Mather (1974) has shownthat between 1900 and 1960 inMaryland, Delaware, and Virginiatemperature oscillations averaging 2.SC (4.S F) occurred with "a markedcyclic movement with about 22 yearsbetween success ive peaks." Theseoscillations are 180 deg out of phasewith the double sunspot cycle plotted inF-S, and there seems little doubt thatthey are associated with the doublecycle. A 2.S C temperature oscillationextending over large areas will ob-viously affect the demand for energy. Itshould be noted in this connection thatthe frequency of lightning strikes af-fecting electricity supplies (F -7)correlates strongly with the sunspotcycle in certain parts ofthe world.

Food production and famines.Several authors have drawn attention tothe influence of the sunspot cycle onagricultural productivity; relationshipsbetween the solar cycle and agricultureare hardly surprising since the phase ofthe annual rainfall can vary by sixweeks during the double solar cycle (F-S).

Filewicz (1962) discussed the effectsof severe winters on fruit-growing inNorth America and Europe. He andothers (particularly Baur-see Lamb,1972) believe severe winters to be

1925

associated with the extremes of thesunspot cycle. After a study of forestgrowth, Bray (1965) saw a "relationshipbetween growing season, climate andsolar activity." I have shown (King.1973) that the length of the growingseason estimated for 'agriculturalpurposes varies in phase with thesunspot cycle. King et al (1974) used theworld wheat-production figures for1949-73 to show how the sunspot cycleinfluences food production and con-cluded that the present low level ofworld food reserves may be associatedwith the decline in solar activity duringthe approach to the 1974-75 sunspotminimum. The modulation of wheatproduction associated with the l l-yearsunspot cycle seems to be at least 100/0in many parts of the world; in certaincountries it may even exceed 50%.

The decline of solar activity betweenthe 1968 sunspot maximum and theminimum due in about 1974 may wellaccount for the shortfalls of the Sovietwheat crops in recent years.

Thompson (1973) and Roberts (1974)drew attention to the fact that droughtsin certain agriculturally importantregions of the United States occur inthe years around every second sunspotminimum. The last drought wascentered on the sunspot-minimum yearof 1954, and it seems significant thatthe wheat crop in the United States inthat year fell 12% short of the averagefor the five previous years. In 1974,when the next drought was to be ex-pected, lack of rain adversely affectedthe U.S. corn crop.

Further examples of solar-cycleeffects on agriculture have been citedby Gamow (1965): "The correlationbetween the number of sunspots andthe growth of trees indicates that treesgrow faster during the years of sunspotmaxima. A related correlation seems toexist between the number of sunspotsand the price of wheat: the smaller thenumber of sunspots, the higher theprice of wheat. This can probably beexplained by saying that during thelean sunspot years less wheat grows peracre."

In a recent analysis (to be publishedelsewhere), I show that 29 of the 68major famines since 1700 A.D. came insunspot-minimum years or in the yearsimmed iately preceding sunspotminimum. The probability of such ahigh proportion of the famines oc-curring by chance in these two yearsfrom each sunspot cycle is smaller than10-4. Of the ten "sunspot minimumminus one" years during the period1866 to 1963, eight produced famineskilling a total of at least 26 millionpeople.

It is interesting that famines, whichoccur mainly in the eastern half of thenorthern hemisphere around sunspotminimum, tend to migrate northward.Famine swept China in the periods1887-89,1919-21 and 1929-30 and thenin Russia in 1891-92, 1921-22 and1932-33. This northward migration offamine regions resembles themovement of drought regions in NorthAmerica. As Thompson (1973) pointsout, "The droughts of the 1930s and1950s began in the southwestern statesseveral years before the peak of thedroughts in Nebraska and Kansas. Thetendency apparently is for droughts tomigrate northward gradually forseveral years."

Drift of sea ice. The upper part of F-16 contains information kindly drawnto my attention by E. Ungstrup. Thecurve shows the "polar-bear bag" insouthwest Greenland-the number ofpolar bears caught there each year(Vibe, 1967). Vibe, a zoologist, pointedout that the polar bear bag follows thesunspot cycle (delayed, as F-16 shows,by about two years). He says that thesunspot cycle appears to "influence theacceleration of drift ice which serves thepolar bear as a means of trans-portation." If Vibe's interpretation iscorrect, the solar cycle exerts asignificant influence on the behaviourof sea ice in the north Atlantic. Thepossible implications of this for nor-thern countries and also for the scienceof oceanography .and the theory ofocean-atmosphere coupling should beassessed.

Inadvertent man-made weathermodification. Helliwell and Katsufrakis(1974) reported that the Canadianelectrical power d istribu tion systemappears to trigger VLF emissions in themagnetosphere. Such emissions induceelectron precipitation, and if particleevents do indeed affect the circulationof the troposphere, a real possibilityexists that electricity distributionsystems may influence the lower at-mosphere.

National economic systems. Severalauthors have gone so far as to suggestthat solar-cycle-induced meteorologicaleffects may be sufficiently important toinfluence the economies of in-dustrialized nations. A review of thissubject has been published by Williams(1961). Sparkes (1974) supports theopinion of the economist J. M. Keynes(1961). The possibility of solar-cycle-induced meteorological phenomenaplaying a part in harvest fluctuationswhich in turn affect the trade cycle,concluded Keynes, "is not to be lightlydismissed."

It will take satellite observations to

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resolve several problems in the field ofsun-weather relations, including thefollowing:-How does the efficiency of thecoupling between the solar wind andthe magnetosphere vary during thesunspot cycle?-What physical phenomena ac-company interplanetary magnetic fieldsector boundaries?-How constant is the Solar Constant?-What properties of the 22-yearsunspot cycle may be associated withlower-atmosphere effects?

All the "mechanisms" describedearlier require further study todetermine whether or not they playarole in sun-weather relationships. Itappears unlikely that significantprogress will be made in this field untilwe know the general morphology of theSun-weather relationships that existand the role played in these by theauroral zone. We need further com-parisons of geomagnetic andclimatological data from differentepochs to establish the relationshipsbetween magnetic-field and climaticchanges.

It appears highly desirable that theeffects of geophysical phenomenashould be included somehow inmeteorological models. If, for example,the wavenumber 1 and wavenumber 2tropospheric patterns are associatedwith Earth's magnetic field, theyshould probably not be expected tomove as though they were Rossbywaves. The accuracy of calculationsmade using divergent barotropicmodels could perhaps be improved bymaking allowance for certaingeophysical processes.

The coincidence of major in-ternational meteorological andgeophysical programs, the GlobalAtmospheric Research Program(GARP) and the InternationalMagnetospheric Study OMS), later inthis decade provides a golden op-portunity for collaboration between twogroups of scientists who must surelyinteract more than they do at present-meteorologists and space physicists.

Acknowledgment

I owe thanks to J. A. Saxton,Director of the Appleton Laboratory,for supporting this work, and I amindebted to Mrs. A. 1. Slater for helpwith data analysis.

References

Full details of the papers referred tocan be obtained from me on request.Please use the following address: Dr. J.W. King, Appleton Laboratory, DittonPark, Slough SL3 9JX, England. •