An analysis of the diurnal anisotropy on geomagnetically quiet days was performed using neutron monitor data at Deep River, Leeds, Rome and Tokyo, well distributed in latitude and longitude for the period 1964-79. The days were separated according to the polarity of IMF on that day. A significant difference in the amplitude and phase was found on towards and away polarity days, particularly during the years of high solar activity and large north-south asymmetry. These results (particularly time of maximum) on geomagnetically quiet days show some better relationship to the expected results as compared to the results obtained using all the days in a year

BADRUDDIN

Yadav, N. R.

Yadav, R. S.

English

151-156A systematic and detailed analysis of the diurnal anisotropy on geomagnetically quiet days has been performed using the cosmic ray intensity data for the period 1964-1979 for neutron monitors at Deep River, Leeds, Rome and Tokyo. The days have been separated according to the polarity of the IMF on that day. Appreciable difference in the amplitude and phase is found for towards and away polarity days, particularly, during the years when the solar activity is high and the north-south asymmetry is also quite large. These results on geomagnetically quiet days show some better relationship with the expected results, especially, the behaviour of the time of maximum; however, these did not show any good relationship with the expected result when all days in a year are considered. The results of the study indicate that the north-south asymmetry in solar activity is influential in determining the latitude gradient of cosmic ray flux

Badruddin

Yadav, R S

Yadav, N R

NOPR

Cosmic Ray Density Gradient & Its Dependence on the North-South Asymmetry in Solar Activity

NASA Technical Reports Server

148 SH 4.5- I7
COSMIC RAY DL_SITY GRADIENT AND ITS DEP_D_CE ON THE
NORTH-SOUTH ASYMMETRY IN SOLAR ACTIVITY
Badruddin, R. S. Yadav and N.R. Yadav
Space Science Group,Dept. of Phys.,A.M.U.,Aligarh (India).
ABSTRACT
An analysis of the diurnal auisotropy on geomanetically quiet
days has been performed using neutron monitor data at Deep
7_ ver(R_ _ T. _ZGV) ,Leeds(R_2.20GV), Rome (R_ 6.32GV) a_d Tokyo
(R_II.61GV),well distributed in latitude and longitude for
the period I964-79.The days have been separated according to
the polarity of IMF on that day. A significant difference in
the _nplitude and phase has been found on towards and away
polarity days particularly during the years of high solar
activity and large north-south asymmetry. These results (part-
icularly time of ma_mum) on geoma_etically quiet days show
some better relationship to the expected results as compared
to the results obtained using all the days in a year.
I.Introduction. The e_zistence of perpendicular gradient has
been studied by separating the cosmic ray diurnal vectors
into groups corresponding to the direction of IMF. This methoa
has been recently applied(Kananen et al. I981;Swinson and
I(ananen,I982)by using the neutron and meson monitor data for
the period 1965-75.These authors have found that the _nplitude
of the diurnal anisotropy on away pola1_lty days exceeds those
of towards polarity days during year I965-68 and that the
reverse is generally the case after the reversal of sun's polar
magnetic field in I969-7I.These data points to a cosmic ray
gradient,perpendicular to the ecliptic plane,pointing ' .
southward prior to 1969 and there was some evidence about
northward pointing gradient after the reversal of sun's polar
magnetic field in lO69-71 except in 1974. However, the phase
does not show the effect expected from the smplitude behaviour.
They found no significant difference,in the _uplitude and
phase both, of the away and towards polarity days in 1969-71,
at neutron monitor energies.
We found in our paper that on day-to -day basis the coher-
ence for the cosmic ray anisotropy is better for days of low
to average solar wind speed,which also is related to geomagn-
etically quiet days,and it would be more mesamingful to use
only these d_ys for determining the annual average of the
cosmic ray daily variation particularly for sunspot maximum
activity period, during which one observed large number of
cases of time varying isotrop%c changes in cosmic ray intens-
. ity.ln this paper we have analysed the neutron monitor data
for 1964-79 period for the stations mentioned above on mag-
netically most quiet days and determined the amplitude and
phase for away and towards polarity days separately. On the
- basis of these results the perpendicular density gradiemt are
c_scussed. Some indirect information about the three dimensional
structure of the heliosphere especially current sheet has been
inferred from these results.
https://ntrs.nasa.gov/search.jsp?R=19850026721 2020-03-20T16:52:17+00:00Z
$44 SH 4.5- 17
2.Result. Fig.l shows that the amplitude on away polarity
days is ,in general, higher than on towards polarity days
during I964-68.But the phase on towards polarity days is
higher than the away polarity days during this peri0d. The
difference in amplitude and phase on away & towards polarity
days are more pronounced during the higher solar activity
period I967 and I968.These results are in agreement with the
results of the earlier workers(Hashimand Bercovitch,I972;
Kananen et al.,I98I;Swinson &Kana_en,I982).However the
results of Kananen et al.(198I) for the time of maximum does
not show the right type of effect as expected.We found using
the data from three neutron monitors, fo_ geomanetically
quiet days that the results for the time of maximum are also
generally in agreement to that expected from the amplitude
behaviour during I964-68,especially in I967 and I968.To give
a better representation,we have plotted the average vectors
for the period I964-68,separately on away and towards .....•
polarity days (Fig.2).
Kananen et al.(I98I) and Swinson & Ka_anen(I982) do _ot
found any significant difference in the amplitude and phase
on away and towards polarity days during I969-TI.Their
results imply no density gradient (pointing northward or _
southward)during this period of reversal of sun'spolar mag-
netic field. The solar activity was high and north-south
asymmetry was also quite large(and positve)throughout the
period I966-70(Badruddin et al._I983).We see from Fig.I that
the _nplitude at Deep River and Leeds,which was higher for
away polarity days than for towards polarity days during the
year I964-68,changed to higher value for towards polarity
days than away polarity days in I969 thougl_,at Rome similar
change has been observed in I970.However,as far as phase is
concerned,it has changed to later hours for towards polarity
days than the avJay polarity days in I969 at all the three
stations Deep RiVer,Leeds,& Rome.In I970,the amplitude was
much higher for towards polarity days than away polarity
days and the time of maximum was quite significantly changed
towards later hours for away polarity days than towards
polarity days. These results are also shown on the vector
diagram in Fig. 2.In many earlier studies it has been assumed
that the IMF in northern and southern hemispheres have
reverse configurations in I964-68 and I969-79.The north-
south asymmetry in solar activity in I969-70 was of the same
sign(positive) as it was in I967-68.Thus if the current
sheet was displaced downward due to positive north'south
asymmetry in 1967-68,it will be the same case in 1969-70.But
since the IMF polarity may be different in northern and
southern hemispheres in 1967-68 a_d 1969-70, the reverse
behaviour of diurnal amplitude and phase on away a_d towards
polarity days in I967-68 and I969-70 may be due thins reason.
However_in I97I,when solar activity was lower as compared to
I969 and I970 and north-south asymmetry was also small i_
this year,no significant difference im amplitude arid time of
maximum for towards and away polarity days is observed at
- 146
SH 4.5- I7
all the four stations(only the su_iplitudeat Deep River shows
some diffrence).Similar difference at Deep River was also
reported by S_wlnson and _ananen (I982).
During the period I97fii972 and I973 there is some _i f _ _
difference in the amplitude ;at towards and away pola_lty
days only at Deep River. The average vectors for the period
I97I-I973 have also been shown in Fig. 2 for all the four
stations. During these periods there was no marked north-south
asymmetry as evidenced form solar flares. Swinson and Kananen
(I982)did not found a consistent northward gradient at meson
monitor energies during I971-73',though their results point to
a northward gradient in I972 and in I973 for Deep River and
Oulu neutron monitors.
In I974 the _uplitude on away polarity days isl higher
than the towards polarity days. Various arguments have been
adw_nced to explain the observed eJ_plitude and phase behavio-
ur in I974(Swinson _I_ananen,I982;Ahluwalia & Riker, I98I).It
is to be mentioned here that the north-south asymmetry in
solar activity was some-what negative as evidenced from solar
flares and moreover in I973-75 the monster type solar wind
strains were prominently observed.
In the solar activity minimum period I975-76, there is no
appreciable difference in the amplitude and phase values for
towards and away polarity days. The north-south asymmetry was
also very small during these years. However, in 1977,there is
some evidence for a northward pointing gradient as seen from
amplitude at Deep River and the amplitude and phase at Tokyo
for towards and away polarity days. The solar activity in I977
was not high and north-south asymmetry was also small. However
there was an accelerated increase in solar activity after
mi d-I977.
In I978 & I979 the solar activity was very high. However,
the north-south asymmetry was _nall.We see from results for
amplitude and phase on away and towards polarity days that
there is no appreciable difference in amplitude and phase
for the two types of days both at Deep River and Tokyo.
3.Conclusion. From the above results we see that there is an
appreciable difference in the amplitude and/or phase on
towards and away plarity days during years of l_gh solar
activity and large north-south asymmetry. During the years of
lower solar activity and/or small north-south asymmetry this
difference is not appreciable. These results support the view
that at least during the period of kigh solar activity and
appreciable north-south asymmetry,either the density gradient
pointing away from the solar equatorial plane is not symmeh_±c
or the current sheet might ,. _have been displaced fro_ the
ecliptic plane Thus it seems right to suggest(Swinson/E983)
that in order _o detect any _ x_N anisotropy the position
of the current sheet(on average)would have to be displaced
from the ecliptic plane due to asymmetric activity on the sty.
References
Ahluwslia, H.S. and Riker,J.F., (I981),I7th ICRC,IO,230.
Badruddin,Yadav,R.S. and Yadav,N.R. (I983) ,Ind. J.Radio Space,
14@_ SH 4.5- I7
Phys. ,I2,I24.
Hashim,A, and Bercovitch,M. (I972) ,Planet. Space Sci. ,20,79I.
Kananen ,H. ,Komari, H., Tamskanen ,P.and Oksman, J., (I98I),
I7th ICRC,IO, I90 .
$winson, D.B.and Kananen,H., (I982) ,JoGeophys. Res. ,87,I685.
Swinson,D.B.,(I983),I8th ICRC, IO, 55 •
Fig.I shows average amplitude(A) and phase(P) of away
polarity days(solid line) and towards polarity days(broke_
line)from I964-79.The diagram in the bottom shows the major
solar flares numbers in respective years in northern(circle)
and southern (crosses) hemi spheres.
Fig. 2 shows the average diurnal vectors on away polarity
days(solid line)and towards polarity days(broken line) for
the years and stations indicated.
@


Cosmic ray density gradient and its dependence on the north-south asymmetry in solar activity

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Cosmic ray density gradient and its dependence on the north-south asymmetry in solar activity

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