T h e mutual relations between solar activity, thunderstorms 

and Vertical Gradients of Electro Atmospheric Potential 

A . M U R R I - R . F U S A R I - C. SCUTERINI ( * ) 

R e c e i v e d on December 4th, 1973 

SUMMARY. — T h e mutual relations are established between solar 
a c t i v i t y expressed in W o l f numbers, the vertical gradient of electro atmo-
spheric potential measured in the Geophysical Observatory of Macerata, 
the geomagnetic field measured in the Observatory of the nearby t o w n of 
A q u i l a , and the thunderstorm a c t i v i t y o v e r the whole of the Italian ter-
r i t o r y . 

T h e mutual relationship between the vertical gradient, the geomagnetic 
field and the frequency of thunderstorms and solar a c t i v i t y are clearly 
evident. In particular the antiparallel behavior between solar a c t i v i t y 
and the vertical gradient, as w e l l as thunderstorm frequency lias been made 
clear b y observations carried out o v e r a period of 22 years. 

T h e results obtained f r o m a study of the geomagnetic field and the 
vertical gradients agree w i t h the research on a much shorter period of t i m e 
recently carried out b y R a o . 

Observational values h a v e been treated as statistical elements ( 2 ) t o 
enable smoother readings, w i t h o u t h o w e v e r m o v i n g the m a x i m u m s and 
mínimums of the phenomenon in the g i v e n period of t i m e so that paral-
lelisms and antiparallelisms resulting f r o m theso observational values are 
kept. 

T h e average values of the vertical gradients of electro atmospheric 
potential were derived f o r electrically calm days. 

F r o m these 5 days per month were chosen b y probability m e t h o d ; 
the averages were then calculated on these five days chosen stochastically. 
W e considered an electrically calm day one in which the sky was absolutely 
clear, w i t h no thunderstorms either in the v i c i n i t y or far f r o m the obser-
v a t o r y , w i t h neither f o g or haze present. 

RIASSUNTO. — V e n g o n o stabilite le correlazioni fra a t t i v i t à solare 
espressa attraverso il numero di W o l f , il gradiente verticale di potenziale 
elettroatmosfcrico misurato nell'Osservatorio Geofisico di Macerata, il campo 

( * ) Geophysical Observatory, Macerata. 



38 A . M U K E I - R . F U S A R I - C. SCTJTERINI 

geomagnetico rilevato nel prossimo Osservatorio della città dell'Aquila, la 
a t t i v i t à temporalesca di tutto il territorio italiano. 

L e correlazioni fra gradiente verticale, campo geomagnetico, frequenza 
dei temporali ed a t t i v i t à solare appaiono evidenti. In particolare l'anda-
mento antiparallelo f r a attività solare e gradiente verticale, come pure con 
la frequenza dei temporali è messa in evidenza da osservazioni che vertono 
su di un periodo di 22 anni. 

L e considerazioni dell'andamento del campo geomagnetico e del gra-
diente sono concordanti con quanto recentemente t r o v a t o por un periodo 
assai più breve da Rao. 

I valori grezzi sono stati trattati come elementi statistici ( 2 ) onde 
avere andamenti più lisci, senza peraltro che i massimi ed i minimi del fe-
nomeno vengano spostati nel tempo, in modo che le condizioni (li paralle-
lismo ed antiparallelismo che risultano dai dati grezzi siano p e r f e t t a m e n t e 
conservate. 

I valori medi del gradiente verticale di potenziale elettroatmosferico 
sono stati dedotti per i giorni elettricamente calmi. Fra questi sono stati 
scelti con metodi probabilistici 5 giorni per mese; le medie sono state cal-
colate su questi cinque giorni prelevati stocasticamente. P e r giorno elettri-
camente calmo è stato scelto quello nel quale il cielo si è presentato assolu-
tamente sereno, non si sono verificati temporali né prossimi all'Osservatorio 
né lontani, non si sono avuto nebbie o foschie. 

1. - P R E L I M I N A R Y REMARKS 

I n a r e c e n t s t u d y ( 1 3 ), o n e of our g r o u p e x p o u n d e d t h e results 

of r e s e a r c h on t h e b e h a v i o r of t h e Y . G . E . A . P . , also r e l a t i n g i t t o 

solar a c t i v i t y e x p r e s s e d b y t h e B z i n d e x . O n t h a t o c c a s i o n t h e cor-

r e l a t i o n v a l u e s b e t w e e n t h e t w o p h e n o m e n a w e r e c a l c u l a t e d , a n d i t 

w a s seen t h a t t h e t w o p r e s e n t e d a d e f i n i t e a n t i p a r a l l e l b e h a v i o r , 

w h i c h w a s also i n d i c a t e d b y t h e e x p e r i m e n t a l c u r v e s . 

O n l y d u r i n g t h e p r e s e n c e of d i s t u r b i n g f a c t o r s in t h e l o w e r a t m o -

s p h e r e , l i k e f a l l - o u t caused b y a n u c l e a r e x p l o s i o n , d i d t h e c o r r e l a t i o n 

i n d e x d e n o t e d e f l e c t i o n w h i c h w a s t o b e a t t r i b u t e d t o m o d i f i c a t i o n s 

i n t h e e l e c t r i c f i e l d caused b y t h e e n t r a n c e of a l a r g e q u a n t i t y of r a d i o -

a c t i v e p a r t i c l e s w h i c h r e s u l t e d in a s c r e e n i n g of t h e e l e c t r o a t m o s p h e r i c 

f i e l d a n d c o n s e q u e n t i n t e r f e r e n c e w i t h i t s i n t e r d e p e n d e n c e on solar 

a c t i v i t y . 

F u r t h e r s t u d i e s h a v e b e e n m a d e w i t h a w i d e r r a n g e of V . G . E . A . P . 

r e a d i n g s as w e e x t e n d e d our research o v e r a p e r i o d of 22 y e a r s in-

c l u d i n g 3 y e a r s f r o m c y c l e 18 (1944,3 - 1954,4), t h e w h o l e of c y c l e 

19 (1954,4 - 1964,8) a n d p a r t of c y c l e 20 f r o m 1964,8 up t o a n d 

i n c l u d i n g t h e w h o l e of 1972 (2 3'2 4). 



T I I E M U T U A L R E L A T I O N S B E T W E E N S O L A R A C T I V I T Y E T C . 39 

W e also compared the behavior of the geomagnetic field and 
storm activity over the whole of the Italian territory. 

Regarding the representation of solar activity w-e chose the Wolf 
numbers for sunspots which, at least as a first approximation, offer 
an effective measurement of this activity, these numbers were sup-
plied by the observatories at Arcetri, Rome and Catania. 

Finally all the observational data was treated statistically to 
smooth the curves representing the phenomena, without however 
altering the maximum and minimum positions (2'12). 

As in previous studies, the V.G.E.A.P. was calculated with values 
taken on electrically calm days. From these days, five were drawn 
by date, and from them wre calculated the average hourly and monthly 
values. W e only intended as suitable days those with fair weather, 
without any cloud formations, fog or electric disturbances. 

2 . - C O R R E L A T I O N O F T H E V . G . E . A . P . W I T H S O L A R A C T I V I T Y 

Research on the V.G.E.A.P., begun in 1951 with a quadrant 
electrometer and then continued with a valve electrometer, enabled 
the examination of the parameter values over a period of 22 years 
from 1951 up to 1972, and this research is still being continued today. 

The curves in Fig. 1 illustrate the antiparallelism between solar 
activity and the V.G.E.A.P. Solar activity being represented by its 
log graph. If variations in solar activity are in fact the primary cause 
of variations in the V.G E.A.P.; the effect, which is very often in 
logarithmical relation to the cause and therefore the correlation, 
should be more apparent with the log Wm (solar activity) curve. In 
fact this correlation is represented in fig. 1 and the antiparallelism is, 
wre think, quite significant. 

To the minimum solar activity recorded in 1954 there corre-
sponds, with marked adherence in time, the V.G.E.A.P. maximum, 
the latter being one of the highest recorded during the whole period 
of research. 

The solar maximum of 1957 which coincided with the maximum 
of the 80 years period of solar activity did not apparently determine 
a major decrease in the V.G.E.A.P., even if comparisons with suc-
cessive recordings have been rendered quite difficult owing to the 
fact that during recent years there has been an erosion of daily values 
and averages of the gradient due to the progressive increase in pol-



40 A . M U K E I - R . F U S A R I - C. SCTJTERINI 

lution in the area where recordings are effected, with consequent 
alterations in the local electro atmospheric field. 

This pollution by markedly increasing the relative humidity and 
thus favouring the formation of fog and nigh mists, has altered the 
vertical gradient by lowering its average, as is to be expected since the 
V.G.E.A.P. is inversely proportional to atmospheric humidity (6'9-21). 

The following minimum in solar activity, which extended over 
a longer period of time than the previous one, is correlated with a 
much less evident gradient maximum, as is easily seen by the figures 
in table 1 and illustrated in Fig. 1. 

Pig. 1 - The vertical potential gradients smoothing; the geomagnetic field; 
thunderstorm frequency, and logs of solar activity expressed in W o l f numbers. 

The following solar maximum of 1970 was preceded by quite a 
long period of fluctuating activity which presented a decrease in 1968 
and 1969 compared with values reached in .1967. 



T I I E M U T U A L R E L A T I O N S B E T W E E N S O L A R A C T I V I T Y E T C . 4 1 

I t was possible to note yet once again that these variations in 
solar activity were accompanied by fluctuations in an antiparallel 
manner in the Y.G.E.A.P. even though these fluctuations were limited. 

In fact there corresponds to the secondary minimum in solar 
activity thus formed in 1968, a halt in the gradual decrease in the 
gradient values with a tendency to return to higher values. 

I t can also be seen that, while for the solar minimums and maxi-
mums recorded in 1951 and 1957 the corresponding minimums and 
maximums in the gradient appeared during the same period (the 
time lapse not exceeding 2 months), the following coincidences were 
slightly displaced in time, as the minimums and maximums of the 
gradient appeared a few months after the maximums and minimums 
in solar activity. 

This fact can be justified by the seasonal variations of the gra-
dient, which sometimes slightly modify its behavior. 

This is what happened during the solar maximum of July 1970 
which was followed by the gradient minimum during the last months 
of that year. 

The fluctuations in solar activity also have their influence in 
establishing a slight time lapse in the coincidence between the maxi-
mums and minimums of the two although they still maintain in their 
general behavior a clearly antiparallel structure. 

3 . - C O R R E L A T I O N W I T H T H E G E O M A G N E T I C F I E L D 

During our research we also considered the values of the geo-
magnetic field and its average behavior, which has been illustrated 
together with the other values in Fig. 1. 

The values of this parameter were taken from the bulletin issued 
by the Aquila Observatory. The field values recorded in Aquila 
were chosen in consideration of the fact that it is the nearest geo-
magnetic observatory to our research station. 

The behavior of this parameter is already known, presenting, 
as it does, its maximums and minimums in agreement with those of 
solar activity. The values at our disposition start from 1958 and clear-
ly state their antiparallel behavior respecting Y.G.E.A.P. values. 
This behavior had already been illustrated by Rao in 1970 (25) for 
the same period. 



42 A . M U K E I - R . F U S A R I - C. SCTJTERINI 

I t can be seen that, although the antiparallelism between the 
two parameters is maintained, the maximums and minimums of the 
two phenomena do not always coincide in time, but are separated by 
variable periods, as lias already been noted regarding the solar and 
V.G.E.A.P. maximums and minimums. 

On the other hand this observation, limited to the period con-
sidered, can also be applied to the very short periods considered by 
Eao in this work which we have already quoted. 

4. - CORRELATION W I T H THUNDERSTORMS I N I T A L I A N REGION 

The frequency of thunderstorms over the whole of the Italian 
territory from 1953 until 1970 has also been considered, and is indi-
cated in Pig. 1. As can easily be seen, the frequency of thunderstorms 
presents a minimum in relation to the solar maximum of 1957, a maxi-
mum in correspondence with the solar minimum of 1954 and a mini-
mum in relation to the maximum of 1970. 

Therefore we can add that what has already been said regarding 
the other phenomena examined can also be applied to thunderstorm 
activity, i.e. the correspondence between thunderstorms and solar 
activity is marked when the latter is well evidenced, and less notice-
able during other periods, as can be seen by the thunderstorm activity 
1968/1972. 

I t is however evident that, during the period considered and in 
our area the Y.G.E.A.P. and thunderstorm activity are correlated 
in a positive manner with parallel behavior, even if the coincidences 
in time between the maximums and minimums, as has already been 
noted, present slight discrepancies. 

In a significant recent publication Sarukhanyan and Smirnov (2fl) 
have determined the correlation between the atmospheric circulation 
in the northern hemisphere and solar activity over the past 50 years 
and reach interesting conclusions, which, we think, confirm what we 
have discovered regarding thunderstorms. 

In fact the two Russian authors determine that the frequency 
of atmospheric zonal processes in the northern hemisphere decrease 
with the increasing solar activity during the 11 years cycle, whilst 
the frequency of these processes increases when the sun's activity 
diminuishes. 



T I I E M U T U A L R E L A T I O N S B E T W E E N S O L A R A C T I V I T Y E T C . 4 3 

Since the frequency of zonal processes determines and establishes 
the formation of thunderstorms, the Russian publication would 
confirm the antiparallel correlation between the solar cycle and thun-
derstorm activity, as we have said, or at least this has been so for 
the past 50 years. 

5 . - D I S C U S S I O N A N D C O N C L U S I O N S 

From what has been briefly set forth above it can be seen that, 
in the area of observation from 1951 to 1972, the V.G.E.A.P.; was 
antiparallel to solar activity, indicated by the number of W„, sunspots 
recorded at the observatories of Arcetri, Catania ,and Rome. 

A t the same time, having considered the behavior of the geo-
magnetic field (measured at the nearby observatory of Aquila) it was 
noticed that the Y.G.E.A.P. and the geomagnetic field (in this area 
and for the given period of time) could be considered as very near 
antiparallels, thus confirming what has been discovered by other for 
shorter periods of time. 

Our study of thunderstorm activity, covering the whole of Italy 
for further precision in determining stormy days, has enabled us to 
point out the parallelism between thunderstorm activity and the 
V.G.E.A.P., and that both of these are antiparallel to the solar ac-
tivity curve as defined above. 

On the other hand it is necessary to point out that the authors 
are well aware that what has been found during their research ap-
pears at least partially in opposition to the findings of others (16.17) 
as for example Bauer, who when considering sunspots from 1902 to 
1922 and the behavior of the electric field found a parallelism (19 -
vol. I I - pag. 52) or Brooks who discovered that thunderstorm activity 
and sunspots during a cycle were parallel, whilst in our research we 
have found them to be decidedly antiparallel. 

According to Eussian research workers (Likter I . Ya and coll. 
written communication to the E.A.'s fourth international conference 
Tokyo 1968 - quoted by Markson) (20) the antiparallel behavior simi-
lar to the one observed by us is typical of the equatorial regions. 

Eao, already quoted by us, found antiparallel behavior between 
the V.G.E.A.P. and the geomagnetic field for alpine stations. 

The behavior of the V.G.E.A.P. was compared to the polarity 
of the sunspots (northern hemisphere) and to the sun's poloidal field 



4 4 A . M U K E I - R. F U S A R I - C. SCTJTERINI 

in t h e v a r i o u s cycles w h i c h w e considered, a n d in our o p i n i o n t h e r e 

is no i m m e d i a t e c o r r e l a t i o n b e t w e e n these p h e n o m e n a . 

I n conclusion w e can a d d t h a t , c o n t i n u i n g our s y s t e m a t i c research 

on t h e Y . G . E . A . P . in our o b s e r v a t o r y w e h a v e d u r i n g this p e r i o d , 

f o l l o w i n g t h e m a x i m u m solar a c t i v i t y of 1970,8, n o t i c e d a c o n s t a n t 

a n d p r o g r e s s i v e increase, m o n t h b y m o n t h , of t h e v e r t i c a l g r a d i e n t 

v a l u e s . 

T h i s leads us t o suppose t h a t also d u r i n g t h e f u t u r e m i n i m u m 

solar a c t i v i t y , t h e g r a d i e n t v a l u e s w i l l p r e s e n t a r e l a t i v e m a x i m u m , 

thus p r o b a b l y c o n f i r m i n g f o r t h e solar c y c l e 20 t h e a n t i p a r a l l e l 

b e h a v i o r a l r e a d y n o t e d d u r i n g p r o c e d i n g cycles. 

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