scholarly journals Solar dynamo model with nonlocal alpha-effect and diamagnetic pumping

2012 ◽  
Vol 8 (S294) ◽  
pp. 429-430
Author(s):  
L. L. Kitchatinov ◽  
S. V. Olemskoy
Keyword(s):  
Field Data ◽  
Large Scale ◽  
Solar Magnetic Field ◽  
Convection Zone ◽  
Dynamo Model ◽  
Cycle Period ◽  
Magnetic Cycle ◽  
Magnetic Field Data ◽  
Sunspot Data ◽  
Alpha Effect

AbstractSunspot data and large-scale solar magnetic field data are used to demonstrate the operation of the Babcock-Leighton mechanism on the Sun. A dynamo model is developed that employs jointly a nonlocal alpha-effect of the Babcock-Leighton type and diamagnetic downward pumping. The pumping concentrates magnetic fields to the base of the convection zone. The magnetic cycle period, equatorial symmetry of the generated fields, their meridional drift, and the polar-to-toroidal field ratio obtained in the model agree with observations.

scholarly journals Grand Minima in a spherical non-kinematic α2Ω mean-field dynamo model

2020 ◽  
Vol 10 ◽  
pp. 9 ◽  
Author(s):  
Corinne Simard ◽  
Paul Charbonneau
Keyword(s):  
Differential Rotation ◽  
Large Scale ◽  
Mean Field ◽  
Cyclic Behavior ◽  
Dynamo Model ◽  
Cycle Period ◽  
Cycle Amplitude ◽  
Primary Cycle ◽  
Mean Field Dynamo ◽  
Grand Minima

We present a non-kinematic axisymetric α2Ω mean-field dynamo model in which the complete α-tensor and mean differential rotation profile are both extracted from a global magnetohydrodynamical simulation of solar convection producing cycling large-scale magnetic fields. The nonlinear backreaction of the Lorentz force on differential rotation is the only amplitude-limiting mechanism introduced in the mean-field model. We compare and contrast the amplitude modulation patterns characterizing this mean-field dynamo, to those already well-studied in the context of non-kinematic αΩ models using a scalar α-effect. As in the latter, we find that large quasi-periodic modulation of the primary cycle are produced at low magnetic Prandtl number (Pm), with the ratio of modulation period to the primary cycle period scaling inversely with Pm. The variations of differential rotation remain well within the bounds set by observed solar torsional oscillations. In this low-Pm regime, moderately supercritical solutions can also exhibit aperiodic Maunder Minimum-like periods of strongly reduced cycle amplitude. The inter-event waiting time distribution is approximately exponential, in agreement with solar activity reconstructions based on cosmogenic radioisotopes. Secular variations in low-latitude surface differential rotation during Grand Minima, as compared to epochs of normal cyclic behavior, are commensurate in amplitude with historical inferences based on sunspot drawings. Our modeling results suggest that the low levels of observed variations in the solar differential rotation in the course of the activity cycle may nonetheless contribute to, or perhaps even dominate, the regulation of the magnetic cycle amplitude.

scholarly journals Wavelet analysis of long-term variations in neutron monitor, sunspot number and interplanetary magnetic field data

2021 ◽  
pp. 39-42
Author(s):  
Fraser Baird ◽  
Alexander MacKinnon
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Solar Magnetic Field ◽  
Cosmic Ray ◽  
Negative Polarity ◽  
Neutron Monitors ◽  
Magnetic Field Data ◽  
First Time ◽  
Long Term Variations

For the first time, based on the experimental data of AMS-02, a three-parameter spectrum of variations of ga - lactic cosmic rays was obtained in the range of rigidity 1- 20 GV, to which neutron monitors are most sensitive. It was found that during the period of negative polarity of the solar magnetic field, a power-law spectrum of va - riations is observed with a strong exponential decay in the region of high rigidity. When the polarity changes to positive at the beginning of the new 24th solar cycle, the spectrum of cosmic ray variations becomes purely po- wer-law. The transition to the experimentally obtained spectrum of variations will make it possible to remove a number of uncertainties and increase the accuracy of the analysis of data from the ground network of detectors. This will make it possible to retrospectively obtain fluxes of galactic protons with an average monthly resolution for the period of the space era based on ground-based monitoring.

scholarly journals Dynamics of Variable Dusk-Dawn Flow Associated with Magnetotail Current Sheet Flapping

2021 ◽  
Author(s):  
James Henry Lane ◽  
Adrian Grocott ◽  
Nathan Anthony Case ◽  
Maria-Theresia Walach
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Field Data ◽  
Large Scale ◽  
Magnetic Field Data ◽  
Analysis Technique ◽  
Upstream Solar Wind ◽  
Magnetotail Dynamics ◽  
Magnetotail Current Sheet

Abstract. Previous observations have provided a clear indication that the dusk-dawn (v⊥y) sense of both slow (< 200 km s−1) and fast (> 200 km s−1) convective magnetotail flows is strongly governed by the Interplanetary Magnetic Field (IMF) By conditions. The related “untwisting hypothesis” of magnetotail dynamics is commonly invoked to explain this dependence, in terms of a large-scale magnetospheric asymmetry. In the current study, we present Cluster spacecraft observations from 12 October 2006 of earthward convective magnetotail plasma flows whose dusk-dawn sense disagrees with the untwisting hypothesis of IMF By control of the magnetotail flows. During this interval, observations of the upstream solar wind conditions from OMNI, and ionospheric convection data using SuperDARN, indicate a large-scale magnetospheric morphology consistent with positive IMF By penetration into the magnetotail. Inspection of the in-situ Cluster magnetic field data reveals a flapping of the magnetotail current sheet; a phenomenon known to influence dusk-dawn flow. Results from the curlometer analysis technique suggest that the dusk-dawn flow perturbations may have been driven by the J x B force associated with a dawnward-propagating flapping of the magnetotail current sheet, locally overriding the expected IMF By control of the flows. We conclude that invocation of the untwisting hypothesis may be inappropriate when interpreting intervals of dynamic magnetotail behaviour such as during current sheet flapping.

Coronal Large-Scale Structure in Odd and Even 11-Year Cycles

1994 ◽  
Vol 144 ◽  
pp. 96
Author(s):  
V. I. Makarov ◽  
V. P. Mikhailutsa ◽  
M. P. Fatianov ◽  
T. V. Stepanova
Keyword(s):  
Large Scale ◽  
Radial Direction ◽  
Solar Magnetic Field ◽  
Essential Difference ◽  
The Sun ◽  
High Latitudes ◽  
Solar Cycles ◽  
Magnetic Cycle ◽  
Solar Magnetic Cycle ◽  
Odd Cycles

AbstractObservations of 22 solar eclipses (1914-1991) have been processed. Radial deviations of streamers in the polar and equatorial zones of the Sun in odd and even solar cycles have been studied. An essential difference of the degree of non-radiality of coronal rays at the same latitudes in odd and even cycles has been found. Deviations from the radial direction of streamers are large in the polar zones in the epoch of the maxima of even cycles and in the equatorial zones at the minima of odd cycles. Deviations from radiality at high latitudes are observed mainly in the poleward direction. The results obtained are interpreted in terms of a new model of the cycle, in which the properties of the solar magnetic field depend on the phase of a 22-year solar magnetic cycle.

scholarly journals Stellar dynamos with solar and antisolar differential rotations: Implications to magnetic cycles of slowly rotating stars

2019 ◽  
Vol 491 (3) ◽  
pp. 3155-3164 ◽  
Author(s):  
Bidya Binay Karak ◽  
Aparna Tomar ◽  
Vindya Vashishth
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Rotation Period ◽  
Toroidal Field ◽  
Dynamo Model ◽  
Cycle Period ◽  
Rotating Stars ◽  
Magnetic Cycles

ABSTRACT Simulations of magnetohydrodynamics convection in slowly rotating stars predict antisolar differential rotation (DR) in which the equator rotates slower than poles. This antisolar DR in the usual αΩ dynamo model does not produce polarity reversal. Thus, the features of large-scale magnetic fields in slowly rotating stars are expected to be different than stars having solar-like DR. In this study, we perform mean-field kinematic dynamo modelling of different stars at different rotation periods. We consider antisolar DR for the stars having rotation period larger than 30 d and solar-like DR otherwise. We show that with particular α profiles, the dynamo model produces magnetic cycles with polarity reversals even with the antisolar DR provided, the DR is quenched when the toroidal field grows considerably high and there is a sufficiently strong α for the generation of toroidal field. Due to the antisolar DR, the model produces an abrupt increase of magnetic field exactly when the DR profile is changed from solar-like to antisolar. This enhancement of magnetic field is in good agreement with the stellar observational data as well as some global convection simulations. In the solar-like DR branch, with the decreasing rotation period, we find the magnetic field strength increases while the cycle period shortens. Both of these trends are in general agreement with observations. Our study provides additional support for the possible existence of antisolar DR in slowly rotating stars and the presence of unusually enhanced magnetic fields and possibly cycles that are prone to production of superflare.

scholarly journals Long-term variability of the solar cycle in the Babcock-Leighton dynamo framework

2018 ◽  
Vol 13 (S340) ◽  
pp. 293-296
Author(s):  
Bidya Binay Karak ◽  
Mark Miesch
Keyword(s):  
Solar Cycle ◽  
Flux Distribution ◽  
Convection Zone ◽  
Dynamo Model ◽  
Mixed Polarity ◽  
Alpha Effect ◽  
Polarity Field ◽  
South Asymmetry ◽  
Grand Minima

AbstractWe explore the cause of the solar cycle variabilities using a novel 3D Babcock–Leighton dynamo model. In this model, based on the toroidal flux at the base of the convection zone, bipolar magnetic regions (BMRs) are produced with statistical properties obtained from observed distributions. We find that a little quenching in BMR tilt is sufficient to stabilize the dynamo growth. The randomness and nonlinearity in the BMR emergences make the poloidal field unequal and cause some variability in the solar cycle. However, when observed scatter of BMR tilts around Joy’s law with a standard deviation of 15°, is considered, our model produces a variation in the solar cycle, including north-south asymmetry comparable to the observations. The morphology of magnetic fields closely resembles observations, in particular the surface radial field possesses a more mixed polarity field. Observed scatter also produces grand minima. In 11,650 years of simulation, 17 grand minima are detected and 11% of its time the model remained in these grand minima. When we double the tilt scatter, the model produces correct statistics of grand minima. Importantly, the dynamo continues even during grand minima with only a few BMRs, without requiring any additional alpha effect. The reason for this is the downward magnetic pumping which suppresses the diffusion of the magnetic flux across the surface. The magnetic pumping also helps to achieve 11-year magnetic cycle using the observed BMR flux distribution, even at the high diffusivity.

scholarly journals The Alpha-Effect in Galaxies is Highly Anisotropic

1990 ◽  
Vol 140 ◽  
pp. 113-114
Author(s):  
G. Rüdiger
Keyword(s):  
Large Scale ◽  
Rotation Axis ◽  
Mean Field ◽  
Dynamo Model ◽  
Mean Flow ◽  
Dynamo Theory ◽  
Input Quantity ◽  
Alpha Effect ◽  
The Mean ◽  
Mean Field Dynamo

Besides the mean flow the alpha is the other input quantity for any mean-field dynamo model. It describes the generation of turbulent electromotive force <u × B> from a large-scale field <B> for a given turbulence. The necessary helicity of the turbulence results from the joint action of Coriolis force and density stratification. The standard estimate of 1 km/s for alpha in galaxies is a surely well-established approximation. One of the essentials, however, remains open. Due to the extremely anisotropic structure of disks the tensorial character of alpha can no longer be ignored. In stellar applications anisotropy in the α-tensor leads to a preferred excitation of non-axisymmetric magnetic fields. That is true for α2 -dynamos if the alpha parallel to the rotation axis, α||, is much smaller than that in the equatorial plane, α⊥. The idea is that also for disk-like configurations a similar behaviour makes the existence of the observed large-scale non-axisymmetric magnetic BSS modes understandable within the frame of the mean-field dynamo theory.

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