The marked N-S asymmetry in solar activity (with predominant activity in the Sun's Northern Hemisphere) during the 1960's could certainly account for a S-pointing cosmic ray gradient. It is also clear from the data that the response to this change in solar activity asymmetry, and the related change in the perpendicular cosmic ray density gradient, is different for cosmic ray telescopes in the Earth's Northern and Southern Hemispheres. Northern Hemisphere detectors see a S-pointing gradient in the 60's and a N-pointing gradient after 1971, while Southern Hemisphere telescopes see a S-pointing gradient both before and after the reversal

Humble, J. E.

Shea, M. A.

Swinson, D. B.

English

NASA Technical Reports Server

437
SH 4.2-7
NORTH-SOUTH ASYMMETRY IN ACTIVITY ON THE SUN AND
COSMIC RAY DENSITY GRADIENTS
D.B. Swinson I, M.A. Shea 2 and J.E Humble 3
1
Department of Physics and Astronomy, The University of New
Mexico, 800 Yale N.E., Albuquerque, New Mexico 87131.
2
Air Force Geophysics Lab., Hanscom AFB, Bedford, MA 01731.
3
Department of Physics, University of Tasmania, Hobart,
Tasmania, Australia 7001.
INTRODUCTION. One method of detecting a perpendicular
cosmic ray density gradient (VN_) Is to make use of the
contribution of the drift term B x VNp to the solar cosmic
ray dlurnal varlatlon. This method has been descrlbed by
Swlnson [_970, 1976] and by Hashlm and Bercovltch [1972].
The B x VNp term produces a flow In the ecllptlc plane
perpendicular to the IMF B& wlth the sense of the flow de-
pending upon the sense of B; thls fleld-dependent flow adds
vectorlally to the usual azimuthal streaming which produces
a cosmlc ray Intensity maximum at 18 hours solar tlme (after
correction for geomagnetic bending). In the case of a
southward perpendicular gradient, when the IMF Is away from
the sun, the resultant dlurnal variation should have a
larger amplitude, and the tlme of maximum should occur a
llttle earller, whereas If the IMF Is toward the sun, the
resultant dlurnal varlatlon should have a smaller amplltude
wlth a later tlme of maxlmum. Swlnson and Kananen [1982]
have used this method to analyze neutron monitor and under-
ground muon data, separated according to IMF sense, from
1965 to 1975, to show that there Is a perpendlcular cosmic
ray gradlent that polnted southward prlor to 1969, and a
suggested northward pointing gradlent after the reversal of
the sun's polar magnetlc field in 1969-71.
DATA. In this paper we will consider data from four under-
ground cosmic ray telescopes, two in the northern and two in
the southern hemisphere. The telescopes are Embudo Cave
(35.20°N, threshold rlgldlty 19 GV, medlan rlgldlty 132 GV),
Socorro (34.04°N, threshold rigidity 45 GV, median rigidity
305 GV), Bolivia (16.31°S, threshold rlgldlty 16 GV, medlan
rlgldlty 125 GV) and Hobart, (42.85°S, threshold rlgldity 30
GV, median rigidity 162 GV). The data presented are for the
periods 1965-83, 1968-83, 1965-76 and 1965-83, respectively.
The yearly average solar diurnal variatlon for each tele-
scope has been determined for days when the IMF was toward
(T) and away from (A) the sun. The amplitude data are
presented (the A amplitude should exceed the T amplitude for
a southward gradient).
In Figure 1 the annual A and T amplitudes for each
station, for all available data, are plotted for 1965 to
 
RTH-SOUTH METRY IN TIVITY   S   
S IC  SITY DIENTS 
. . Winson l  . . ea2 , a  J. . ble3 
SH 4 :-7 
 Depa~tment f PhYSICS and Ast~onomy, he Unlve~slty f e  
exlco,  ale . ., que~que, e  eXICO 31. 
2 l~ ~ce eophysICS ab., anscom B, fo~d,  31. 
3 a~tment f YSICS, lve~slty f s anla, a~t, 
asmania, t~alla 1. 
INTR DUCTION. ne ethod of detectlng a pe~pendlcula~ 
cosmIC ray densIty gradIent (VNe) I~ to make use of the 
t~lbutlon f t  rIft t r    p t  t  lar c s IC 
r  I rnal arIatIon. IS ethod as een scrIbed  
WInson [1 70, 76]   ashIm  ercovltch [ 72]. 
The H x vNp te~m p~oduces a flow In the ecllptlc plane 
perpendIcular to the IMP a, WIth the sense of the flow de-
pendlng upon the sense of Hi thIS fIeld-dependent flo  adds 
vectorlally to the usual aZI uthal strea ing which produces 
a cos IC ray I tensity aXI um at 18 hours s lar tI e (after 
rrection f r omagnetic ending). I  t  se f a 
southward perpendIcular gradIent, hen the I P IS a ay fro  
 n,  sultant Iurnal ariatIon uld ve  
r er plitude,  e I e f aXImum ould cur  
Ittle ar Ier, hereas  e I P IS t ard  n, e 
resultant dIurnal varIatIon should have a s aller a plItude 
WIth a l ter tI e f aXImum. WInson  ananen [ 82] 
ave sed is ethod  alyze eutron onitor d der-
round uon ata, s parated cording t  I F s nse, fr  
1965 t  1975, t  sho  t at t ere IS a perpendIcular cos ic 
r y radIent t at OInted s thward rIor t  69, a d a 
gested orthward ointIng radIent fter t e versal f 
t e n's olar agnetIC I ld i  69-71. 
ATA. I  t is aper e WIll nSIder ata fr  f ur nder-
~ound cos 1C ~ay t l scopes, t o I  t e ~the~n d t o 1  
t e southe~n hemlsphe~e. he telescopes a~e Embudo ave 
(35.20 0 N, threshold rIgIdIty 19 GV, edIan rIgIdIty 132 GV), 
Socorro (34.04°N, threshold rIgIdIty 45 GV, edIan rIgIdIty 
305 GV), olIVIa (16.31 0 g, threshold rIgIdIty 16 GV, ed1an 
rIgIdIty 125 V) and obart, (42.85 o g, t reshold rI 1dity 30 
V, edlan ~lgldlty 62 V). he ata ~esented ~e o~ t e 
pe~iods 1965-83, 1968-83, 1965-76 and 1965-83, ~espectlvely. 
he ea~ly ve~age o1a~ lu~nal ariatlon ~ ach t le-
scope as en ete~mlned o~ ays hen t e I P as owa~d 
( ) nd ay ~om ( ) t e n. he plitude ata ~e 
~esented (t e  a plltude s ould e ceed t e  a plltude fo~ 
a outhwa~d rad1ent). 
I  lgu~e 1 t e nual  and  plitudes o~ ach 
tat lon, f r ll vallable ata, re lotted f r 965 t  
https://ntrs.nasa.gov/search.jsp?R=19850026532 2020-03-20T17:00:51+00:00Z
438 SH 4.2-7
1983. The A amplitude points , . , ............ i
are 3olned by solid lines and ,, J
the T amplltude points by ,Msuoo
dashed lines; shading occurs ,0
when A amplitudes are greater
than T amplitudes, indicatlng
a southward perpendicular gra- 0s
dlent. The vertical lines on _ Aik_ ' soco,,o I '_!the d iagram indlcate the end ,[_JL_.,_, .."-._.l"of the solar po ar field re- ,0
81. Prior to 1971 there is a z
consistent predominance of A _,5_ A_ Z_
amplitudes over T amplitudes _ / Ill['!!''_ %l"h'_,'°''v'"
in both hemlspheres, which Is : ,V' " _perpendicular gradient dur ing _
this period. After 1971, the A A
(Embudo and Socorro) show some !11:',',ii,
domlnance of T-amplltudes,
whlle the southern hemisphere IA_ _'-/j',OAR,
it" \" vtelescopes (Bolivia and l I i i l I l I I ! I I I I I i i , * i
Hobart) show little change ,AR 656 , , _70,2 _ 4 s 6 , , 9 ,0,2 3
from the pre-reversal sltua- Figure I. Yearly average
tlon. The average annual amplitudes of away polar-
errors for the amplltudes polarlty days (solld llne)
plotted In Figure 1 are and toward polarity days
±.014% for Embudo, +0.165% (dashed llne) for under-
for Socorro, ±0.16% for ground muon telescopes in
Bolivia and ±0.125% for Hobart. Embudo, Socorro, Bolivia,
In order to look for a and Hobart, 1965-1983.
possible cause for a perpen- The shaded areas occur
dlcular cosmic ray gradient when the amplitude for the
we have examined data on away polarity exceeds that
the N-S asymmetry In activity for the toward polarity.
on the sun. One might expect
that when activity is greater on the sun's northern hemis-
phere, that activity might be more effective in sweeping
cosmic rays out of the heliosphere above the ecliptic plane
or in preventing galactic cosmic rays from entering, leading
to a S-polntlng perpendicular gradient. Here, we extend a
study by Roy [1977], which used the "major" flares as
defined by the comprehensive flare index, CFI, [Dodson and
Hedeman, 1971] to show that between 1959 and 1970 there was
a greater frequency of flares in the northern hemisphere of
the sun than in the southern hemisphere; this northern
hemisphere asymmetry was not evident from 1971 to 1974.
This paper extends the results of Roy through 1980.
The number of flares in each hemisphere was counted as a
function of month and year, using observations from the
worldwide network of solar optical and radio patrol
stations. From these data, an annual average for the per-
38 
1983. The  a plltude pOlnts 
ate JOIned by SOlld Ilnes and 
t e T a plltude pOlnts by 
dashed lInes; shadlng occurs 10 
when A amplltudes are greater 
t a  T a pllt es, l icatl  
05 
a s t ar  r ndlcular r -
dlent. The vertlcal lines on lor 
th  dlagram Indlcate the end ~ 
f  l  l   ~ 05 
versals of 1969-71 and 1980- : 
. r l r t   t r  IS a ... ! 
conslstent predomlnance of A ~ 
ampll.t~udes ov r T amplitudes e 15 
in both hemlspheres, WhlCh IS ~ 
conslstent wlth a southward i 10 
r dicul r l t rln  C 
thls per lod. After 1971, the 05 
northern hemlsphere telescopes 
10 ( budo d ocorro) s  s e 
do lnance f -a pllt des, 
05 hlle t e southern he lsphere 
t lesc s ( oli I  and 
obart) s  llttl   
fro  the pre-reversal sltua-
tl . e r  ual 
YEAR 
   p lt es 
l tt  I  l r    
.014   budo, ±O.  
f r corr , 0.l6% f r 
oll l   .12S  f r obart. 
   o    
ssi l  s   a r -
l l r c s lc r  ra  l t 
e  e a I e  t   
t e -S asy etry In tl lt  
 t  .  i ht ect 
SH 4.2-7 
T' 
 
65 6 7 8 9 70 1 2 3 4 5 6 7 8 9 80 1 2 3 
Flgure 1. early average 
pllt  f a  lar-
l rI   SOlI  I  
 to r  l rit  s 
 ln   er-
r  uon t lesc s I  
budo, corr , olivla, 
 obart, - 83. 
   r 
hen t  a plit e f r t  
a a  larIt  s t t 
f r t e to ard l rIt . 
t t hen tl it  lS r at r  t  s 's rt r  e ls-
~  t t tl lt  lght  or  ff tl  I  s ee I  
c s lC r s t f t  li s ere a e t  ll tl  l  
or In preventIng galactlc cos IC rays from entering, leadlng 
t  a - I tl  er endlcular ra Ient. ere, e e te  a 
st  by oy [ ), hich used t e " aj r" fl r s as 
defIned by the co prehensive flare Index, FI, [ odson and 
e e an, ] t  s  t t t   a   t r  as 
a gredter frequency of flares in the northern he isphere of 
t  s  t a  I  t  s t r  e Isphere; t IS rt r  
he isphere asy etry as not eVldent from 1971 to 1974. 
IS er t s t  r lt  f  thro  . 
he nu ber f fl r s i  each he lsphere as counted as a 
f tI  f ont  a  ar, Sl  s r atl s from t  
orld lde net ork of s lar tIcal and radIO atr l 
t tio . r  t s  t , a  al r  f r t  r-
439 SH 4.2-7
YE_
Figure 2(a) The percentage of "ma3or" flares, as defined by
the comprehensive flare index, that occurred in the northern
hemisphere of the sun from 1955 through 1980, and (b) the
percentage of flares wlth Type [I radio emission that
occurred in the northern hemisphere of the sun from 1955
through 1980. See text for further explanation.
centage of major events in the northern solar hemisphere was
determined, and these annual averages are displayed as solid
dots in Figure 2(a). The data have also been arranged into
groups of years, and the average for each group of years
falls within the shaded regions in Figure 2(a). It is clear
that there is a strong, statistically significant dominance
of solar northern hemisphere activity from 1959 to 1970,
with an essentially even distribution of activity between
the two solar hemispheres before and after that period.
This same method was applied to a sub-set of these
"major" events -- the events for which metric Type II solar
radio emission has been associated. These events were
selected primarily because a Type II radio burst is
Indicative of a shock passing through the corona between 1.5
and 2 solar radii, which could subsequently effect the
cosmic ray intensity in the Inner heliosphere, particularly
at that latitude. This sub-set of Type II events is
displayed in Figure 2(b), where the results are comparable
to those In Figure 2(a). Data in Figure 2 are preliminary;
a complete analysis will be published later.
DISCUSSION AND CONCLUSION: The marked N-S asymmetry In
solar activity (with predominant activity In the sun's
northern hemisphere) during the 1960's could certainly
account for a S-poant/ng cosmic ray gradient. It ,s also
clear from the data in Figure I that the response to thls
change in solar activity asymmetry, and the related change
in the perpendicular cosmic ray density gradient, is
different for cosmic ray telescopes in the earth's northern
and southern hemispheres. Northern hemisphere detectors see
a S-polnting gradient in the 60's and a N-pointlng gradient
after 1971, while southern hemisphere telescopes see a S-
pointing gradient both before and after the reversal.
These results can be accounted for by a combination of a
39 SH 4.2-7 
60 65 10 1980 60 65 10 1960 
YEAR YEAR 
~  ( )  ~  f J ~  ~   f1   
t  ~ 1  ~  1 , t ~~  1  t  ~ ~  
1 ~  f t  s  ~  1955 ~  1980, and ( ) t  
~  f ~  1t  ype II ~ 1  e 1SS1on t t 
~~  i  t  ~ ~  1 ~  f t  s  ~   
~ough .  t t ~ ~ ~ planat1on. 
centage f majo~ e ents 1n t e no~the~n sola~ hem1sphe~e as 
~  a  t s  al ~  ~  1s l  s SOll  
t  i  1 ~  . e t   l   ~~  1 t  
I s f aIs,  t  l  fOI  I  f l  
f ll  it i  t  s a e  ~ 1  1n 1 ~  ( ). It lS ~ 
t t ~  lS a ~  st t1st1 l1  slg 1f1 t 1nance 
of sola~ no~the~n hemisphe~e acti it  f~om 1959 t  1970, 
it   t1all   1 ~l 1  f t1 1t  t  
t  t  ~ ~  ~   ~ t ~l  
h1S sa e ethod as a lie  t  a s -set f t s  
~  ts t  ts ~ Wh1C  ~  e II ~ 
~ 1  1SS1on   1at .  t  ~  
s l t  ~l ~l  s  a e II ~ 1  ~  lS 
1 1cat1 e f a s c  ass1  ~  t  ~  et ee  .  
  ~ ~ 11  Wh1Ch l  s s uentl  ff t t  
cosm1C ~ay 1 te sit  1n t e 1nne~ hel1osphe~e, pa~t1cula~ly 
t t t l t1t . his s -set f e II ts lS 
displayed 1n F1gu~e 2(b), whe~e the ~esults a~e compa~able 
t  t se 1n Figu~e (a). ata 1n F1gu~e 2 a~e p~el1m1na~y; 
a co plete analys1s 1ll be publ1shed 1ate~. 
IS SSI   CLUSI : he alked -S asy etlY 1n 
s l r ti it  ( it  ~  ~ ~  ~n t  s 's 
northern hem~sphere) dur~ng the 1960's could certai l  
acc t f r a - l tl  cos ic ra  r i t. It IS ls  
clear from the data in Figure 1 that the response to th~s 
change in solar act~v~ty asy etry, and the relate  change 
~n t  r ndicular ~  r  ~  ~  i  
different for cosm~c ray telescop~s ~n the earth's northern 
and southern he ispheres. orthern hem~sphere detectors see 
a - i ti  r i t ~n t  's a  a -pointi  ~  
t  , ~  t r  ~  t lesc    -
~  r i t t  ef re and ft r t  ~  
es  lt    t  f r  a ~ ~  f a 
440 Sl-I 4.Z-7
"9°° qA -- qA + "9°°
Flgure 3. Schematzc _ i €_o.s) €,o.sj tI
representatIon of
perpend_cular cosmlc /
ray density gradlents. l
North-South symmetr i- SOLA,0o , o•
cal (dashed llnes) and _AT,TUD, %
North-South asymme- //, _ _
trlcal (solid llnes) \\
are shown for the two
IMP configuration qA- _
i \
and qA+. .,0o "'°o
; > > >
INCREASING INCaEASING
DENSITY DENSITy
N-S symmetrical gradient, and a significantly larger N-S
asymaetr lcal gradient that is present only dur lng the 1960's
(dashed llnes and solid lines, respectlvely, In Figure 3).
The N-S symmetrlcal gradient arlses naturally as the result
of cosmlc ray tra3ectorles In the hellosphere [Erdos and
Kota, 1981; Kota and Joklpli, 1983]; for these symmetric
gradients, the cosmic ray intenslty decreases wlth increa-
slng helio]atltude before the 1969-71 reversal, and in-
creases wlth increasing hellolatitude after the reversal as
shown schematically in Figure 3. The N-S asymmetrical gra-
dlent Is greater In magnitude than the symmetrical gra-
dlents, and zs S-polntlng above and below the equator before
the reversal, as shown schematlcally by the solld llne in
Figure 3; the asymmetrlcal gradient is attrlbuted to the N-S
asymmetry in solar actlvlty demonstrated in Figure 2. After
the reversal there is no N-S solar activity asymmetry and
therfore no N-S asymmetrlcal cosmic ray denslty gradient.
Cosmic ray telescopes in the northern hemisphere therefore
see a density gradient above the ecllptic plane that Is S-
polntlng before the reversal and N-pointing after it, while
telescopes In the southern hemlsphere see a gradient below
the ecllptlc plane whose resultant effect is S-polntlng
before and after the reversal, leading to the cosmic ray
effects seen in Figure i.
ACKNOWLEDGEMENTS. The work of one of the authors (DBS) was
supported by the Atmospheric Sciences Sectlon, Natlonal
Science Foundation, under grant ATM-8305098.
REFERENCES.
Dodson, H.W. & E.R. Hedeman, UAG-14, World Data Center A, 1971.
Erdos, G. & J. Kota, Proc. 17th ICRC (Paris), 10, 105, 1981.
HashJm, A & M. Bercovltch, Planet. Space Scl., 20, 791, 1972.
Kota, J. & J.R. Joklp11, Astrophys. J., 256, 573, 1983.
Roy, J.-R., Solar Physics, 52, 53, 1977.
SWlnson, D.B., J. Geophys. Res., 75, 7303, 1970.
Swlnson, D.B., J. Geophys. Res., 81, 2075, 1976.
Swlnson, D.B. & H. Kananen, J. Geophys. Res., 87, 1685, 1982.
F 19lue 3. Schemat1c 
representat10n of 
perpend1cular cosm1C 
ray density grad1ents. 
North-South sy metr1-
cal (dashed llnes) and 
North-South asymme-
tr1cal (solid llnes) 
are shown for the two 
IMP configuration qA-
and qA+. 
440 
qA-
) ') 
INC.IASING 
DENSITY 
qA + 
(70'S) I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
INCRIASING 
DUnlTY 
\ 
\ 
SH 4.'2-7 
o· 
N-S sy metr1cal gradlent, and a sIgn1f1cantly larger N-S 
asymmetrlcal gradlent that 1S pr sent only dur1ng the 1960's 
(dashed llnes and SOlld llnes, respectlvely, In Flgure 3). 
The N-S symmetr1cal gradlent arl es naturally as the result 
of cosmlC ray traJectorles 1n the hellosphere [Erdos and 
Kota, 1981; Kota and JOklpli, 1983J; for th se symmetrlc 
gradIents, the cosmic ray Intenslty decr ases wlth increa-
slng he1iolat1tude before the 1 69-71 r versal, and in-
creases w1th 1ncreas1ng hellolatitude after the reversal as 
shown schem tically in Flgure 3. The N-S asymmetrlcal gra-
dlent 1S greater 1n magnltude than the sy metrlcal gra-
dlents, and IS S-pol tlng above and below the equator before 
the reversal, as shown schematlcally by the SOlld llne in 
Flgure 3; the asymmet~lcal gradlent is attrlbuted to the N-S 
asy metry 1n solar actIv1ty demonstrated 1n Flgure 2. After 
the reversal there 1S no N-S solar act1vity asy metry and 
therfore no N-S asy metrlcal cosmIC ray denslty gradlent. 
Cosm1c ray telescopes in the northern hemlsph re therefore 
see a denslty gradlent above the ecllptic plane that IS S-
p<Jlnt1ng before the reversal and N-pointing after it" wh1le 
telescopes 1n the southern hem1sph re see a grad lent below 
the ecl1ptic plane whose resultant effect IS S-polntlng 
before and after the reversal, leadlng to the cosmic ray 
effects seen 1n Flgure 1. 
ACKNOWLEDGEMENTS. The work of one of the authors (DBS) was 
supported by the Atmospheric SCIences SectIon, NatIonal 
Science FoundatIon, under grant ATM-83 5098. 
REFERENCES. 
Dodson, H.W. & E.R. Hedeman, UAG-14, World D ta Center A, 1971. 
Erdos, G. & J. Kota, Proc. 17th ICRC (Parls), 10, 105, 1981. 
Hashim, A & M. Bercovltch, Planet. Space SCI., 20, 791, 1972. 
Kota, J. & J.R. JOklpll, Astrophys. J., 256, 573, 1983. 
Roy, J.-R., Solar PhYSICS, 52, 53, 1977. 
SWlnson, D B., J. Geophys. Res., 75, 7303, 1970. 
SWInson, D B., J. Geophys. Res., 81, 2075, 1976. 
SW1nson, D.B. & H. K a en, J. Geophys. Res., 87, 1685, 1982. 


North-south asymmetry in activity on the Sun and cosmic ray density gradients

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