3,216 research outputs found
A theoretical model of torsional oscillations from a flux transport dynamo model
Assuming that the torsional oscillation is driven by the Lorentz force of the
magnetic field associated with the sunspot cycle, we use a flux transport
dynamo to model it and explain its initiation at a high latitude before the
beginning of the sunspot cycle.Comment: 3 pages, 2 figures. proceedings of IAU symposium 273, Physics of Sun
and star spots, Ventura, California 22-26 August 201
A possible explanation of the Maunder minimum from a flux transport dynamo model
We propose that the poloidal field at the end of the last sunspot cycle
before the Maunder minimum fell to a very low value due to fluctuations in the
Babcock--Leighton process. With this assumption, a flux transport dynamo model
is able to explain various aspects of the historical records of the Maunder
minimum remarkably well on choosing the parameters of the model suitably to
give the correct growth time
The Waldmeier effect and the flux transport solar dynamo
We confirm that the evidence for the Waldmeier effect WE1 (the
anti-correlation between rise times of sunspot cycles and their strengths) and
the related effect WE2 (the correlation between rise rates of cycles and their
strengths) is found in different kinds of sunspot data. We explore whether
these effects can be explained theoretically on the basis of the flux transport
dynamo models of sunspot cycles. Two sources of irregularities of sunspot
cycles are included in our model: fluctuations in the poloidal field generation
process and fluctuations in the meridional circulation. We find WE2 to be a
robust result which is produced in different kinds of theoretical models for
different sources of irregularities. The Waldmeier effect WE1, on the other
hand, arises from fluctuations in the meridional circulation and is found only
in the theoretical models with reasonably high turbulent diffusivity which
ensures that the diffusion time is not more than a few years.Comment: Being reviewed in MNRA
Is meridional circulation important in modelling irregularities of the solar cycle?
We explore the importance of meridional circulation variations in modelling
the irregularities of the solar cycle by using the flux transport dynamo model.
We show that a fluctuating meridional circulation can reproduce some features
of the solar cycle like the Waldmeier effect and the grand minimum. However, we
get all these results only if the value of the turbulent diffusivity in the
convection zone is reasonably high.Comment: 4 pages, 4 figures. Proceedings of IAU Symposium 286: Comparative
Magnetic Minima: Characterizing quiet times in the Sun and sta
Dynamo models of grand minima
Since a universally accepted dynamo model of grand minima does not exist at
the present time, we concentrate on the physical processes which may be behind
the grand minima. After summarizing the relevant observational data, we make
the point that, while the usual sources of irregularities of solar cycles may
be sufficient to cause a grand minimum, the solar dynamo has to operate
somewhat differently from the normal to bring the Sun out of the grand minimum.
We then consider three possible sources of irregularities in the solar dynamo:
(i) nonlinear effects; (ii) fluctuations in the poloidal field generation
process; (iii) fluctuations in the meridional circulation. We conclude that (i)
is unlikely to be the cause behind grand minima, but a combination of (ii) and
(iii) may cause them. If fluctuations make the poloidal field fall much below
the average or make the meridional circulation significantly weaker, then the
Sun may be pushed into a grand minimum.Comment: 10 pages, 5 figures. Proceedings of IAU Symposium 286: Comparative
Magnetic Minima: Characterizing quiet times in the Sun and star
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