الفهرس 
ABSTRACTOnly 14 pages are availabe for public view
 |  | from | 168 |  |  |
| | | from | 168 | | |
Abstract
The occurrence of various solar activity features show non-uniformity over the solar
disk. It has also been noticed that more activity features occur in one part of the solar
hemisphere than the other at one time. When these features are examined with respect to
equator of the Sun, they are referred to as the North-South (N-S) asymmetry. The existence of
the north-south asymmetry in solar activity is now an intensively studied phenomenon. It is a
real and systematic phenomenon (not due to random fluctuation) which can be observed in
terms of several activity indicators.
The present work introduced an intensive analysis to study the effect of the
interplanetary magnetic field polarity IMF (Toward (T) or Away (A)) on the interplanetary
parameters, solar & geomagnetic indices, as well as the solar daily variations of the cosmic
rays, over the time interval from 1975 to 2013. The period covers three complete solar cycles
(21st, 22nd, 23rd), and a major part of the solar cycle (24th).
Firstly, daily data for the solar and interplanetary parameters (sunspot number Rz, total
solar irradiance TSI, solar radio flux SF, field magnitude B, proton density n, proton
temperature T, solar wind speed SWS and the dynamic pressure nv2) and the geomagnetic
indices (aa, Ap, Kp, and Dst) have been analyzed as a function of the sense of the
interplanetary magnetic field to examine the north-south asymmetries of the heliospheric
current sheet over the considered period.
The yearly north-south asymmetry of the field magnitude was clear over the
considered period. There was no remarkable N-S asymmetry in the averaged field magnitude
over the considered epochs, as well as there was no magnetic solar cycle dependence. The sign
of the north-south asymmetry in the solar activity as indicated by the sunspot number Rz
depended upon the solar magnetic polarity, where it became positive in negative magnetic
polarity, and negative in positive magnetic polarity. The average solar flux component SF(T)
for toward days north of the current sheet was larger in magnitude than those for the away
days SF(A) south of the current sheet, during the negative polarity epochs (1986-1988 and
2001-2008).
n addition, the solar wind speed were faster by about 22.11 ± 4.5 km/s for away
polarity days than for toward polarity days during the negative polarity epoch (2001-2008),
where the IMF points away from the Sun south of the current sheet and toward the Sun north
of it. Moreover, during cycles 21, and 24, the solar plasma was less dense, hotter, and faster
north of the HCS than north of it. By comparing the north-south asymmetry for the solar &
interplanetary parameters and geomagnetic indices, one can conclude that the asymmetry
which observed in the geomagnetic indices was qualitatively consistent with those observed in
interplanetary parameters.
In order to adequately study of the N-S asymmetry in the cosmic ray diurnal and
semidiurnal variations and achieve significant insights, a considerable database must be used.
In this work, the hourly averages of cosmic-ray counts have been used for fifteen neutron
monitor stations during the interval from 1975 to 2013. The effective threshold rigidity of
these detectors lies in the range 0.0 GV Ro 13 GV.
During the years of minimum solar cycles, lesser amplitude differences were obtained.
While in case of ascending and descending years of the solar activity cycles, a high different
between the amplitude of toward and away days start to appear according to the direction of
the cosmic ray gradient (northward or southward gradient). In addition, north-south
asymmetries of cosmic ray latitudinal gradient of the solar diurnal and semidiurnal amplitudes
are correlated well with the relative frequency of the Sun’s activity in the northern and
southern hemispheres.
When the solar magnetic field is reversed, the time of maximum of solar diurnal vector
(T-A) shifted from 1 to 11 hrs and from 3 to 9 hrs for the northern and southern detections,
respectively. Furthermore, the time of maximum of solar semidiurnal vector (T-A) shifted,
from 1 to 8 hrs and from 1 to 4 hrs for the northern and southern detections, respectively.
Finally, we think that the north-south asymmetry is a fact, and is a good indicator in
studying the solar activity. The asymmetries that observed in the solar, interplanetary
parameters and geomagnetic indices may provide multiple causes for producing the observed
asymmetric modulations of cosmic rays.
CHAPTER 1
INTRODUCTION AND REVIEW OF LITERATURE
1
INTRODUCTION AND REVIEW OF LITERATURE
1.1 Introduction
It is now well known that our Sun is a fairly typical star, nothing more than one of the
variable stars of the Universe. It has a mean radius of about 696000 km, and it is rotating with a
period that increases with latitude from 25 days at the equator to 36 days at poles. For practical
reasons, the period is often taken to be 27 days. Its mass is about 2 x 1030 kg, consisting mainly
of helium (10 %) and hydrogen (90 %). The Sun expels several products of its activity to the
interplanetary medium, namely electromagnetic radiation, energetic particles, solar wind and
transient ejects within their magnetic fields.
The solar radiation is the fundamental source of energy that drives the Earth’s climate and
sustains life. The variability of this output certainly affects our planet. The Earth responds to
solar variability through geomagnetic activity, variations of the high atmosphere and possibly
changes of weather, climate and biota. The solar electromagnetic radiation that reaches the