130 research outputs found
A Model of the Double Magnetic Cycle of the Sun
It has been argued that the solar magnetic cycle consists of two main
periodic components: a low-frequency component (Hale's 22-year cycle) and a
high-frequency component (quasi-biennial cycle). The existence of the double
magnetic cycle on the Sun is confirmed using Stanford, Mount Wilson and Kitt
Peak magnetograph data from 1976 to 1996 (solar cycles 21 and 22). In the frame
of the Parker's dynamo theory a model of the double magnetic cycle is
presented. This model is based on the idea of two dynamo sources separated in
space. The first source of the dynamo action is located near the bottom of the
convection zone, and the second operates near the top. The model is formulated
in terms of two coupled systems of non-linear differential equations. It is
demonstrated that in the case of weak interaction between the two dynamo
sources the basic features of the double magnetic cycle such as existence of
two component and observed temporal variations of high-frequency component can
be reproduced.Comment: 6 pages, 2 figure
The G-O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups
We have analysed the combined Greenwich and Solar Optical Observing Network
(SOON) sunspot group data during the period of 1874-2011 and determined
variations in the annual numbers (counts) of the small, large and big sunspot
groups (these classifications are made on the basis of the maximum areas of the
sunspot groups). We found that the amplitude of an even-numbered cycle of the
number of large groups is smaller than that of its immediately following
odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl
rule or G-O rule of solar cycles, generally described by using the Zurich
sunspot number (Rz). During cycles 12-21 the G-O rule holds good for the
variation in the number of small groups also, but it is violated by cycle pair
(22, 23) as in the case of Rz. This behaviour of the variations in the small
groups is largely responsible for the anomalous behaviour of Rz in cycle pair
(22, 23). It is also found that the amplitude of an odd-numbered cycle of the
number of small groups is larger than that of its immediately following
even-numbered cycle. This can be called as `reverse G-O rule'. In the case of
the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated
the G-O rule. In many cycles the positions of the peaks of the small, large,
and big groups are different and considerably differ with respect to the
corresponding positions of the Rz peaks. In the case of cycle 23, the
corresponding cycles of the small and large groups are largely symmetric/less
asymmetric (Waldmeier effect is weak/absent) with their maxima taking place two
years later than that of Rz. The corresponding cycle of the big groups is more
asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the
same time as that of Rz.Comment: 13 pages, 5 figures, 1 table, accepted by Solar Physic
A solar cycle lost in 1793--1800: Early sunspot observations resolve the old mystery
Because of the lack of reliable sunspot observation, the quality of sunspot
number series is poor in the late 18th century, leading to the abnormally long
solar cycle (1784--1799) before the Dalton minimum. Using the newly recovered
solar drawings by the 18--19th century observers Staudacher and Hamilton, we
construct the solar butterfly diagram, i.e. the latitudinal distribution of
sunspots in the 1790's. The sudden, systematic occurrence of sunspots at high
solar latitudes in 1793--1796 unambiguously shows that a new cycle started in
1793, which was lost in traditional Wolf's sunspot series. This finally
confirms the existence of the lost cycle that has been proposed earlier, thus
resolving an old mystery. This letter brings the attention of the scientific
community to the need of revising the sunspot series in the 18th century. The
presence of a new short, asymmetric cycle implies changes and constraints to
sunspot cycle statistics, solar activity predictions, solar dynamo theories as
well as for solar-terrestrial relations.Comment: Published by Astrophys. J. Let
Solar-Cycle Characteristics Examined in Separate Hemispheres: Phase, Gnevyshev Gap, and Length of Minimum
Research results from solar-dynamo models show the northern and southern
hemispheres may evolve separately throughout the solar cycle. The observed
phase lag between the hemispheres provides information regarding the strength
of hemispheric coupling. Using hemispheric sunspot-area and sunspot-number data
from Cycles 12 - 23, we determine how out of phase the separate hemispheres are
during the rising, maximum, and declining period of each solar cycle.
Hemispheric phase differences range from 0 - 11, 0 - 14, and 2 - 19 months for
the rising, maximum, and declining periods, respectively. The phases appear
randomly distributed between zero months (in phase) and half of the rise (or
decline) time of the solar cycle. An analysis of the Gnevyshev gap is conducted
to determine if the double-peak is caused by the averaging of two hemispheres
that are out of phase. We confirm previous findings that the Gnevyshev gap is a
phenomenon that occurs in the separate hemispheres and is not due to a
superposition of sunspot indices from hemispheres slightly out of phase. Cross
hemispheric coupling could be strongest at solar minimum, when there are large
quantities of magnetic flux at the Equator. We search for a correlation between
the hemispheric phase difference near the end of the solar cycle and the length
of solar-cycle minimum, but found none. Because magnetic flux diffusion across
the Equator is a mechanism by which the hemispheres couple, we measured the
magnetic flux crossing the Equator by examining magnetograms for Solar Cycles
21 - 23. We find, on average, a surplus of northern hemisphere magnetic flux
crossing during the mid-declining phase of each solar cycle. However, we find
no correlation between magnitude of magnetic flux crossing the Equator, length
of solar minima, and phase lag between the hemispheres.Comment: 15 pages, 7 figure
North-South Distribution of Solar Flares during Cycle 23
In this paper, we investigate the spatial distribution of solar flares in the
northern and southern hemisphere of the Sun that occurred during the period
1996 to 2003. This period of investigation includes the ascending phase, the
maximum and part of descending phase of solar cycle 23. It is revealed that the
flare activity during this cycle is low compared to previous solar cycle,
indicating the violation of Gnevyshev-Ohl rule. The distribution of flares with
respect to heliographic latitudes shows a significant asymmetry between
northern and southern hemisphere which is maximum during the minimum phase of
the solar cycle. The present study indicates that the activity dominates the
northern hemisphere in general during the rising phase of the cycle
(1997-2000). The dominance of northern hemisphere is shifted towards the
southern hemisphere after the solar maximum in 2000 and remained there in the
successive years. Although the annual variations in the asymmetry time series
during cycle 23 are quite different from cycle 22, they are comparable to cycle
21.Comment: 6 pages, 2 figures, 1 table; Accepted for the publication in the
proceedings of international solar workshop held at ARIES, Nainital, India on
"Transient Phenomena on the Sun and Interplanetary Medium" in a special issue
of "Journal of Astrophysics and Astronomy (JAA)
Hemispheric Sunspot Numbers R_n and R_s: Catalogue and N-S asymmetry analysis
Sunspot drawings are provided on a regular basis at the Kanzelhoehe Solar
Observatory, Austria, and the derived relative sunspot numbers are reported to
the Sunspot Index Data Center in Brussels. From the daily sunspot drawings, we
derived the northern, R_n, and southern, R_s, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International Sunspot Numbers
R_i, the R_n and R_s have been normalized to the R_i, which ensures that the
relation R_n + R_s = R_i is fulfilled. For validation, the derived R_n and R_s
are compared to the international northern and southern relative sunspot
numbers, which are available from 1992. The regression analysis performed for
the period 1992-2000 reveals good agreement with the International hemispheric
Sunspot Numbers. The monthly mean and the smoothed monthly mean hemispheric
Sunspot Numbers are compiled into a catalogue. Based on the derived hemispheric
Sunspot Numbers, we study the significance of N-S asymmetries and the
rotational behavior separately for both hemispheres. We obtain that about 60%
of the monthly N-S asymmetries are significant at a 95% level, whereas the
relative contributions of the northern and southern hemisphere are different
for different cycles. From the analysis of power spectra and autocorrelation
functions, we derive a rigid rotation with about 27 days for the northern
hemisphere, which can be followed for up to 15 periods. Contrary to that, the
southern hemisphere reveals a dominant period of about 28 days, whereas the
autocorrelation is strongly attenuated after 3 periods. These findings suggest
that the activity of the northern hemisphere is dominated by an active zone,
whereas the southern activity is mainly dominated by individual long-lived
sunspot groups.Comment: 9 pages, 8 figures, data catalogue online available at
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/70
Sun's retrograde motion and violation of even-odd cycle rule in sunspot activity
The sum of sunspots number over an odd numbered 11 yr sunspot cycle exceeds
that of its preceding even numbered cycle, and it is well known as Gnevyshev
and Ohl rule (or G--O rule) after the names of the authors who discovered it in
1948. The G--O rule can be used to predict the sum of sunspot numbers of a
forthcoming odd cycle from that of its preceding even cycle. But this is not
always possible because occasionally the G--O rule is violated. So far no
plausible reason is known either for the G--O rule or the violation of this
rule. Here we showed the epochs of the violation of the G--O rule are close to
the epochs of the Sun's retrograde orbital motion about the centre of mass of
the solar system (i.e., the epochs at which the orbital angular momentum of the
Sun is weakly negative). Using this result easy to predict the epochs of
violation of the G--O rule well in advance. We also showed that the solar
equatorial rotation rate determined from sunspot group data during the period
1879--2004 is correlated/anti-correlated to the Sun's orbital torque during
before/after 1945. We have found the existence of a statistically significant
17 yr periodicity in the solar equatorial rotation rate. The
implications of these findings for understanding the mechanism behind the solar
cycle and the solar-terrestrial relationship are discussed.Comment: 13 pages, 4 figures, accepted by MNRA
Predicting the Amplitude of a Solar Cycle Using the North-South Asymmetry in the Previous Cycle: II. An Improved Prediction for Solar Cycle~24
Recently, using Greenwich and Solar Optical Observing Network sunspot group
data during the period 1874-2006, (Javaraiah, MNRAS, 377, L34, 2007: Paper I),
has found that: (1) the sum of the areas of the sunspot groups in 0-10 deg
latitude interval of the Sun's northern hemisphere and in the time-interval of
-1.35 year to +2.15 year from the time of the preceding minimum of a solar
cycle n correlates well (corr. coeff. r=0.947) with the amplitude (maximum of
the smoothed monthly sunspot number) of the next cycle n+1. (2) The sum of the
areas of the spot groups in 0-10 deg latitude interval of the southern
hemisphere and in the time-interval of 1.0 year to 1.75 year just after the
time of the maximum of the cycle n correlates very well (r=0.966) with the
amplitude of cycle n+1. Using these relations, (1) and (2), the values 112 + or
- 13 and 74 + or -10, respectively, were predicted in Paper I for the amplitude
of the upcoming cycle 24. Here we found that in case of (1), the north-south
asymmetry in the area sum of a cycle n also has a relationship, say (3), with
the amplitude of cycle n+1, which is similar to (1) but more statistically
significant (r=0.968) like (2). By using (3) it is possible to predict the
amplitude of a cycle with a better accuracy by about 13 years in advance, and
we get 103 + or -10 for the amplitude of the upcoming cycle 24. However, we
found a similar but a more statistically significant (r=0.983) relationship,
say (4), by using the sum of the area sum used in (2) and the north-south
difference used in (3). By using (4) it is possible to predict the amplitude of
a cycle by about 9 years in advance with a high accuracy and we get 87 + or - 7
for the amplitude of cycle 24.Comment: 21 pages, 7 figures, Published in Solar Physics 252, 419-439 (2008
Photospheric Magnetic Field: Relationship Between North-South Asymmetry and Flux Imbalance
Photospheric magnetic fields were studied using the Kitt Peak synoptic maps
for 1976-2003. Only strong magnetic fields (B>100 G) of the equatorial region
were taken into account. The north-south asymmetry of the magnetic fluxes was
considered as well as the imbalance between positive and negative fluxes. The
north-south asymmetry displays a regular alternation of the dominant hemisphere
during the solar cycle: the northern hemisphere dominated in the ascending
phase, the southern one in the descending phase during Solar Cycles 21-23. The
sign of the imbalance did not change during the 11 years from one polar-field
reversal to the next and always coincided with the sign of the Sun's polar
magnetic field in the northern hemisphere. The dominant sign of leading
sunspots in one of the hemispheres determines the sign of the magnetic-flux
imbalance. The sign of the north-south asymmetry of the magnetic fluxes and the
sign of the imbalance of the positive and the negative fluxes are related to
the quarter of the 22-year magnetic cycle where the magnetic configuration of
the Sun remains constant (from the minimum where the sunspot sign changes
according to Hale's law to the magnetic-field reversal and from the reversal to
the minimum). The sign of the north-south asymmetry for the time interval
considered was determined by the phase of the 11-year cycle (before or after
the reversal); the sign of the imbalance of the positive and the negative
fluxes depends on both the phase of the 11-year cycle and on the parity of the
solar cycle. The results obtained demonstrate the connection of the magnetic
fields in active regions with the Sun's polar magnetic field in the northern
hemisphere.Comment: 24 pages, 12 figures, 2 table
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