scholarly journals Dynamo models of grand minima

2011 ◽  
Vol 7 (S286) ◽  
pp. 350-359
Author(s):  
Arnab Rai Choudhuri
Keyword(s):  
Meridional Circulation ◽  
Nonlinear Effects ◽  
Solar Dynamo ◽  
Dynamo Model ◽  
Generation Process ◽  
The Sun ◽  
Solar Cycles ◽  
Poloidal Field ◽  
Grand Minimum ◽  
Grand Minima

AbstractSince 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.

scholarly journals Does the mean-field α effect have any impact on the memory of the solar cycle?

2020 ◽  
Vol 642 ◽  
pp. A51
Author(s):  
Soumitra Hazra ◽  
Allan Sacha Brun ◽  
Dibyendu Nandy
Keyword(s):  
Solar Cycle ◽  
Mean Field ◽  
Solar Dynamo ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Poloidal Field ◽  
Flux Transport ◽  
Solar Convection ◽  
The Mean ◽  
And Diffusion

Context. Predictions of solar cycle 24 obtained from advection-dominated and diffusion-dominated kinematic dynamo models are different if the Babcock–Leighton mechanism is the only source of the poloidal field. Some previous studies argue that the discrepancy arises due to different memories of the solar dynamo for advection- and diffusion-dominated solar convection zones. Aims. We aim to investigate the differences in solar cycle memory obtained from advection-dominated and diffusion-dominated kinematic solar dynamo models. Specifically, we explore whether inclusion of Parker’s mean-field α effect, in addition to the Babcock–Leighton mechanism, has any impact on the memory of the solar cycle. Methods. We used a kinematic flux transport solar dynamo model where poloidal field generation takes place due to both the Babcock–Leighton mechanism and the mean-field α effect. We additionally considered stochastic fluctuations in this model and explored cycle-to-cycle correlations between the polar field at minima and toroidal field at cycle maxima. Results. Solar dynamo memory is always limited to only one cycle in diffusion-dominated dynamo regimes while in advection-dominated regimes the memory is distributed over a few solar cycles. However, the addition of a mean-field α effect reduces the memory of the solar dynamo to within one cycle in the advection-dominated dynamo regime when there are no fluctuations in the mean-field α effect. When fluctuations are introduced in the mean-field poloidal source a more complex scenario is evident, with very weak but significant correlations emerging across a few cycles. Conclusions. Our results imply that inclusion of a mean-field α effect in the framework of a flux transport Babcock–Leighton dynamo model leads to additional complexities that may impact memory and predictability of predictive dynamo models of the solar cycle.

scholarly journals Flux-transport and mean-field dynamo theories of solar cycles

2012 ◽  
Vol 8 (S294) ◽  
pp. 37-47
Author(s):  
Arnab Rai Choudhuri
Keyword(s):  
Solar Cycle ◽  
Meridional Circulation ◽  
Mean Field ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Poloidal Field ◽  
Flux Transport ◽  
Mean Field Model ◽  
Mean Field Models ◽  
Mean Field Dynamo

AbstractWe point out the difficulties in carrying out direct numerical simulation of the solar dynamo problem and argue that kinematic mean-field models are our best theoretical tools at present for explaining various aspects of the solar cycle in detail. The most promising kinematic mean-field model is the flux transport dynamo model, in which the toroidal field is produced by differential rotation in the tachocline, the poloidal field is produced by the Babcock–Leighton mechanism at the solar surface and the meridional circulation plays a crucial role. Depending on whether the diffusivity is high or low, either the diffusivity or the meridional circulation provides the main transport mechanism for the poloidal field to reach the bottom of the convection zone from the top. We point out that the high-diffusivity flux transport dynamo model is consistent with various aspects of observational data. The irregularities of the solar cycle are primarily produced by fluctuations in the Babcock–Leighton mechanism and in the meridional circulation. We summarize recent work on the fluctuations of meridional circulation in the flux transport dynamo, leading to explanations of such things as the Waldmeier effect.

scholarly journals An Insight into the Solar Dynamo Theory

2017 ◽  
Vol 3 (1) ◽  
pp. 27-36
Author(s):  
Babu Ram Tiwari ◽  
Mukul Kumar
Keyword(s):  
Magnetic Field ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Dynamo Model ◽  
The Sun ◽  
Poloidal Field ◽  
Dynamo Theory ◽  
Dynamo Action ◽  
Flux Transport ◽  
Alpha Omega

The Sun manifests its magnetic field in form of the solar activities, being observed on the surface of the Sun. The dynamo action is responsible for the evolution of the magnetic field in the Sun. The present article aims to present an overview of the studies have been carried on the theory and modelling of the solar dynamo. The article describes the alpha-omega dynamo model. Generally, the dynamo model involves the cyclic conversion between the poloidal field and the toroidal field. In case of alpha-omega dynamo model, the strong differential rotation generates a toroidal field near the base of the convection zone. On the other hand, the turbulent helicity leads to the generation of the poloidal field near the surface. The turbulent diffusion and the meridional circulation are considered as the two important flux transport agents in this model. The article briefly describes the theory of solar dynamo and mean field dynamo model.

scholarly journals Modelling grand minima of solar activity using a flux transport dynamo model

2012 ◽  
Vol 8 (S294) ◽  
pp. 433-438
Author(s):  
Bidya Binay Karak ◽  
Arnab Rai Choudhuri
Keyword(s):  
Solar Activity ◽  
Observational Data ◽  
Meridional Circulation ◽  
Sunspot Cycle ◽  
Maunder Minimum ◽  
Dynamo Model ◽  
Poloidal Field ◽  
Flux Transport ◽  
Grand Minima

AbstractThe occurrence of grand minima like the Maunder minimum is an intriguing aspect of the sunspot cycle. We use the flux transport dynamo model to explain the grand minima, showing that they arise when either the poloidal field or the meridional circulation falls to a sufficiently low value due to fluctuations. Assuming these fluctuations to be Gaussian and determining the various parameters from the data of the last 28 cycles, we carry on a dynamo simulation with both these fluctuations. The results are remarkably close to the observational data.

scholarly journals Origin of solar magnetism

2010 ◽  
Vol 6 (S273) ◽  
pp. 28-36 ◽  
Author(s):  
Arnab Rai Choudhuri
Keyword(s):  
Solar Cycle ◽  
Differential Rotation ◽  
Convection Zone ◽  
Meridional Circulation ◽  
Solar Surface ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Poloidal Field ◽  
Flux Transport ◽  
Solar Magnetism

AbstractThe most promising model for explaining the origin of solar magnetism is the flux transport dynamo model, in which the toroidal field is produced by differential rotation in the tachocline, the poloidal field is produced by the Babcock–Leighton mechanism at the solar surface and the meridional circulation plays a crucial role. After discussing how this model explains the regular periodic features of the solar cycle, we come to the questions of what causes irregularities of solar cycles and whether we can predict future cycles. Only if the diffusivity within the convection zone is sufficiently high, the polar field at the sunspot minimum is correlated with strength of the next cycle. This is in conformity with the limited available observational data.

scholarly journals A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial Impact

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Kazuo Shiokawa ◽  
Katya Georgieva
Keyword(s):  
Solar Wind ◽  
Interplanetary Space ◽  
Solar Wind Plasma ◽  
The Sun ◽  
Scientific Program ◽  
Solar Cycles ◽  
Grand Minimum ◽  
The Earth ◽  
Earth Connection ◽  
Near Future

AbstractThe Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace and atmosphere. This Sun–Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibility of a grand minimum in near future. VarSITI—variability of the Sun and its terrestrial impact—was the 5-year program of the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014–2018, focusing on this variability of the Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs, achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI.

scholarly journals Observing and modeling the poloidal and toroidal fields of the solar dynamo

2018 ◽  
Vol 609 ◽  
pp. A56 ◽  
Author(s):  
R. H. Cameron ◽  
T. L. Duvall ◽  
M. Schüssler ◽  
H. Schunker
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Time Lag ◽  
Solar Observatory ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Dynamo Model ◽  
Flux Emergence ◽  
Poloidal Field ◽  
Poloidal Magnetic Field

Context. The solar dynamo consists of a process that converts poloidal magnetic field to toroidal magnetic field followed by a process that creates new poloidal field from the toroidal field. Aims. Our aim is to observe the poloidal and toroidal fields relevant to the global solar dynamo and to see if their evolution is captured by a Babcock-Leighton dynamo. Methods. We used synoptic maps of the surface radial field from the KPNSO/VT and SOLIS observatories, to construct the poloidal field as a function of time and latitude; we also used full disk images from Wilcox Solar Observatory and SOHO/MDI to infer the longitudinally averaged surface azimuthal field. We show that the latter is consistent with an estimate of the longitudinally averaged surface azimuthal field due to flux emergence and therefore is closely related to the subsurface toroidal field. Results. We present maps of the poloidal and toroidal magnetic fields of the global solar dynamo. The longitude-averaged azimuthal field observed at the surface results from flux emergence. At high latitudes this component follows the radial component of the polar fields with a short time lag of between 1−3 years. The lag increases at lower latitudes. The observed evolution of the poloidal and toroidal magnetic fields is described by the (updated) Babcock-Leighton dynamo model.

scholarly journals Is meridional circulation important in modelling irregularities of the solar cycle?

2011 ◽  
Vol 7 (S286) ◽  
pp. 367-371 ◽  
Author(s):  
Bidya Binay Karak ◽  
Arnab Rai Choudhuri
Keyword(s):  
Solar Cycle ◽  
Convection Zone ◽  
Meridional Circulation ◽  
Dynamo Model ◽  
Turbulent Diffusivity ◽  
Flux Transport ◽  
Grand Minimum

AbstractWe 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.

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