Download Chapter 7 - Shodhganga

Chapter 7
7.1 Summary
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Summary and Future Plan
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In this thesis, we have worked out and presented the various aspects of solar activity
features such as solar flares, solar active prominences (SAP) etc. on the Sun. We have
studied the variation of SAP and flare activity with the evolution of sunspot cycle. We
have also studied the spatial distribution and asymmetry of these features over the
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solar hemisphere.
Multi–wavelength study is important to understand the dynamics of solar
flares and other associated phenomena at various heights in the solar atmosphere.
Therefore multi–wavelength analyses of solar flares and associated phenomena during
the period of October–November 2003 have also been deal with.
The solar activity features (specially the larger solar flares, eruptive
prominences and CMEs) are the major sources of various interplanetary and
geoeffective disturbances. Hence the present work includes various aspects of space–
weather. Relationship of various interplanetary parameters and geomagnetic indices
and their behavior during major geomagnetic storms has been reported. We have
found out key parameters which are important for space weather and geomagnetic
storm/substorm predictions using various statistical methods.
The complete work contains seven chapters. In Chapter 1 a brief description
about the Sun’s structure and solar activity aspects has been given. Here we have also
presented the current knowledge and theoretical understanding of solar activity
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7.1. Summary
phenomena and their interplanetary/Earth’s magnetospheric and ionospheric
perturbations. A description of various instruments (both ground and space) and
sources from where data have been taken are discussed in Chapter 2.
In Chapter 3 we present the results of a study of the spatial distribution and
asymmetry of SAP for the period 1996 through 2007 (Joshi et al., 2009). This period
contains the solar cycle 23. For more meaningful statistical analyses we analysed the
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distribution and asymmetry of SAP in two subgroups viz. Group 1 (G1) and Group 2
(G2). Here Group 1 contains structures belonging to prominences/filaments and
Group 2 contains structures belonging to active region. During the period of 4383
days a total number of 8778 SAP are reported. This study shows that the SAP activity
during this cycle is low compared to previous solar cycles. This result shows the
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violation of G–O rule for SAP activity for event–odd pair of cycle for the cycles 22–
23. Most of the SAP lie in low latitude band (i.e., latitude from 1–40°). The present
study also indicates that during the rising phase of the cycle the number of SAP
events is roughly equal in the northern and the southern hemispheres. However,
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activity in the southern hemisphere has been dominant since 1999 till the end of cycle
23. From the equator of the Sun the frequency of SAP, G1 and G2 events increases
from 1 to 30°. The SAP events are at maximum between latitudes 21 to 30° for solar
cycle 23. It is different from the solar cycles 20, 21 and 22 where the SAP activity are
at maximum between 11 to 20° latitude band on either side of the solar equator. From
the central meridian of the Sun the frequency of SAP, G1 and G2 events decreases
from 1 to 80° and the frequency increases between 81–90°. The SAP events are most
numerous between 81–90° central meridian band. Our statistical study shows N–S
asymmetry to be more significant than the E–W asymmetry.
In Chapter 4 we have presented the statistical analysis of soft X–ray (SXR)
flares during the period January 1976 to December 2007 (Joshi et al., 2010). This is
the period covering the solar cycles 21, 22 and 23. During this period the occurrence
of 63594 single SXR flares are reported. A detailed analysis of north–south and east–
west asymmetry of SXR flares at total (1–90°), low (1–40°) and high (50–90°)
latitude and center meridian distances are given here. North–south and east–west
asymmetry of different intensity classes (B, C, M and X) for the period of
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7.1. Summary
investigation have also been presented. Slight southern and eastern hemisphere
dominance is found during solar cycles 21, 22 and 23. North–south distribution shows
that the SXR flare events are most prolific in the 11–20° latitude band in the northern
and southern hemispheres whereas east–west distribution does not show any preferred
prolific band. It is also observed that the low latitudes (1–40°) are the active latitudes
and produce maximum number of SXR flares. In our study the north–south and east–
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west asymmetry peaks have been found to occur near the activity minimum. It is
revealed that the SXR flare activity for M and C class flares during solar cycle 23 is
low as compared to the cycle 22, indicating the violation of Gnevyshev–Ohl rule. It is
also found that the class B flare activity is higher for cycle 23 while the other class
activities are dominant for solar cycle 21. Along with these studies this chapter deals
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with the analysis of flare evolution parameters viz. duration, rise time, decay time and
event asymmetry for total as well as for different classes. It has been observed that the
duration, rise time and decay time increase with increasing intensity class. The
increase is more pronounced for the duration and decay time than for the rise time for
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solar cycles 21 and 22 while for cycle 23 it is the same for duration, rise time and
decay time. The most important conclusion on the basis of investigations presented in
Chapters 3 and 4 is the fact that north–south asymmetry is a real feature and not due
to random fluctuations and also that north–south asymmetry is more significant than
the east–west asymmetry.
In Chapter 5 multi–wavelength analysis of two major flares (M1.2 and M1.7)
which erupted on October 25, 2003 from active region NOAA 10486 is presented.
This active region was one of the most magnetic active regions of the solar cycle 23.
The eruptive flares were observed in Hα at ARIES, Nainital, in UV and EUV by
TRACE and in X–ray by GOES and RHESSI. Both these show multiple eruptive
center e.g., kernels or ribbons and seen to be initiated by different mechanisms. Both
the flares are eruptive in nature and associated with CMEs. We co–align the data from
different instruments and compared the spatial locations of different energy sources.
The first flare initiated with the eruption of huge sigmoid filaments in south–east
direction while the second one initiated by the interaction and eruption of complex
loop system and the sigmoid filament in the northern side of the active region.
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7.2. Future Plan
Temporally the flares exhibits long duration event (LED). The interpretation of results
has been carried in the light of existing theories.
In Chapter 6 we carry out a correlative study between the geomagnetic activity
indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (B,
Bz, E and σB) and plasma (T, D, V, P and β) parameters and their various products
(BV, BzV and B2V) during intense geomagnetic storms (GMSs) (Dst ≤ –100 nT) for
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rising, maximum and decay phases as well as for complete solar cycle 23 (Joshi et al.,
2011). We have selected 92 intense GMSs separately for CME–driven GMSs (group
G1) and CIR–driven GMSs (group G2) in all observed during solar cycle 23 for a
more meaningful analysis. It can be concluded that the peak values of different
geomagnetic activity indices are in good correlation with B, Bz, σB, V, E, BV, BzV
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and B2V, hence these parameters are most useful for predicting GMSs and substorms.
These parameters are also reliable indicators of the strengths of GMSs. The average of
peak values of geomagnetic activity indices and various field/plasma parameters are
large in decay phase compared to rising and maximum phase of cycle 23. We have
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also presented the lag/lead time analysis between the maximum of Dst and the peak
values of geomagnetic activity indices, various interplanetary field/plasma parameters
for all GMSs. The average value of lag (–)/lead (+) time lie in the ~ –4.00 hour
interval for Kp, ap and AE indices as well as for B, Bz, σB, E, D and P. These
parameters play a significant role in prediction of storm/substorms. Correlation
coefficients between various interplanetary field/plasma parameters, their various
products and geomagnetic activity indices for G1 and G2 groups show different
nature. Three GMSs and associated solar sources observed during three different
phases of this solar cycle have also been studied and we find that GMSs are
associated with large flares, and halo CMEs and their active regions are close to the
solar equator.
7.2 Future Plan
Study of long term variation, spatial distribution over the solar disk and asymmetry of
different solar activity features provide key information about the solar cycle and
variation of Sun’s magnetic field. The multi–wavelength analyses of eruptive activity
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7.2. Future Plan
features provide crucial information about the physics behind these eruptions. These
eruptive events have a great influence on interplanetary space and near Earth
environment. These include drag on Earth–orbiting satellites as a result of which their
lifetime in the orbits is shortened. Geomagnetic storms/substorms are the outcome of
these activities and may cause power break out etc. It is important to predict these
Our focus for future will be
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disturbances and disruptions before they reach near any spacecraft and the Earth.
1. To study the temporal variation, latitudinal and longitudinal distribution and
asymmetry over the solar disk and various periodicities of different solar activity
features for the upcoming and the present solar cycles.
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2. Multi–wavelength analyses of solar eruptive features such as solar flare,
prominences and CMEs etc. from wavelength range from γ to radio waves using
various ground and space based instruments.
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3. To study the various aspects of space weather predictions such as solar source
identification of geomagnetic storms/substorms and investigation of behavior of
different interplanetary field/plasma parameters and their relationship with
different geomagnetic indices during geomagnetic storms/substorms.
To achieve these futures planes we will use the long term data from various
catalogues available online. For multi–wavelength analysis we will use high
resolution data from various ground and space based instrument, which are recently
launched such as solar dynamic observatory (SDO), etc. We will continue our
observations at ARIES in H–alpha wavelength.
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