scholarly journals Differential rotation and meridional flows in stellar convection zones

2013 ◽  
Vol 9 (S302) ◽  
pp. 194-195 ◽  
Author(s):  
Manfred Küker ◽  
Günther Rüdiger
Keyword(s):  
Differential Rotation ◽  
Main Sequence ◽  
Mean Field Theory ◽  
Mean Field ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Meridional Flow ◽  
Flux Transport ◽  
Stellar Convection ◽  
Stellar Dynamo

AbstractDifferential rotation and meridional flow are key ingredients in flux transport dynamo models of the solar activity cycle. As the subsurface flow pattern is not sufficiently constrained by observations, it is a major source of uncertainty in solar and stellar dynamo models. We discuss the current mean field theory of stellar differential rotation and meridional flows and its predicitons for the Sun and stars on the lower main sequence.

scholarly journals Impact of nonlinear surface inflows into activity belts on the solar dynamo

2020 ◽  
Vol 10 ◽  
pp. 62
Author(s):  
Melinda Nagy ◽  
Alexandre Lemerle ◽  
Paul Charbonneau
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Activity Cycle ◽  
Surface Flux ◽  
Meridional Flow ◽  
Cycle Model ◽  
Flux Transport ◽  
Bona Fide ◽  
Nonlinear Surface ◽  
The Impact

We examine the impact of surface inflows into activity belts on the operation of solar cycle models based on the Babcock–Leighton mechanism of poloidal field regeneration. Towards this end we introduce in the solar cycle model of Lemerle & Charbonneau (2017. ApJ 834: 133) a magnetic flux-dependent variation of the surface meridional flow based on the axisymmetric inflow parameterization developped by Jiang et al. (2010. ApJ 717: 597). The inflow dependence on emerging magnetic flux thus introduces a bona fide nonlinear backreaction mechanism in the dynamo loop. For solar-like inflow speeds, our simulation results indicate a decrease of 10–20% in the strength of the global dipole building up at the end of an activity cycle, in agreement with earlier simulations based on linear surface flux transport models. Our simulations also indicate a significant stabilizing effect on cycle characteristics, in that individual cycle amplitudes in simulations including inflows show less scatter about their mean than in the absence of inflows. Our simulations also demonstrate an enhancement of cross-hemispheric coupling, leading to a significant decrease in hemispheric cycle amplitude asymmetries and temporal lag in hemispheric cycle onset. Analysis of temporally extended simulations also indicate that the presence of inflows increases the probability of cycle shutdown following an unfavorable sequence of emergence events. This results ultimately from the lower threshold nonlinearity built into our solar cycle model, and presumably operating in the sun as well.

scholarly journals Solar activity and differential rotation

2010 ◽  
Vol 6 (S273) ◽  
pp. 298-302
Author(s):  
Hari Om Vats ◽  
Satish Chandra
Keyword(s):  
Solar Activity ◽  
Differential Rotation ◽  
Rotation Rate ◽  
Rotation Period ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
X Ray ◽  
Sunspot Numbers ◽  
Sidereal Rotation

AbstractThe coronal sidereal rotation rate as a function of latitude for each year, extending from 1992 to 2001 for soft X-ray images and from 1998 - 2005 for radio images are obtained. The present analysis reveals that the equatorial rotation rate of the corona is comparable to the photosphere and the chromosphere, However, at the higher latitudes, the corona rotation quite differently than the photosphere and chromosphere. The latitude differential obtained by both radio and X-ray images is quite variable throughout the period of the study. The equatorial rotation period seems to vary almost systematically with sunspot numbers which indicates its dependence on the phases of the solar activity cycle.

scholarly journals Dynamo Processes Constrained by Solar and Stellar Observations

2018 ◽  
Vol 13 (S340) ◽  
pp. 275-280
Author(s):  
Maria A. Weber
Keyword(s):  
Differential Rotation ◽  
Meridional Circulation ◽  
Mean Field ◽  
Magnetic Activity ◽  
Flux Emergence ◽  
Dynamo Theory ◽  
M Dwarfs ◽  
Dynamo Action ◽  
Solar Type ◽  
Stellar Dynamo

AbstractOur understanding of stellar dynamos has largely been driven by the phenomena we have observed of our own Sun. Yet, as we amass longer-term datasets for an increasing number of stars, it is clear that there is a wide variety of stellar behavior. Here we briefly review observed trends that place key constraints on the fundamental dynamo operation of solar-type stars to fully convective M dwarfs, including: starspot and sunspot patterns, various magnetism-rotation correlations, and mean field flows such as differential rotation and meridional circulation. We also comment on the current insight that simulations of dynamo action and flux emergence lend to our working knowledge of stellar dynamo theory. While the growing landscape of both observations and simulations of stellar magnetic activity work in tandem to decipher dynamo action, there are still many puzzles that we have yet to fully understand.

scholarly journals Various scenarios for the equatorward migration of sunspots

2019 ◽  
Vol 15 (S354) ◽  
pp. 134-137
Author(s):  
Detlef Elstner ◽  
Yori Fournier ◽  
Rainer Arlt
Keyword(s):  
Shear Layer ◽  
Differential Rotation ◽  
Linear Relation ◽  
Rise Time ◽  
Meridional Flow ◽  
Wave Direction ◽  
Flux Transport ◽  
Surface Shear ◽  
Alpha Effect ◽  
Dynamo Wave

AbstractThe profile of the differential rotation together with the sign of the alpha-effect determine the dynamo wave direction. In early models of the solar dynamo the dynamo wave often leads to a poleward migration of the activity belts. Flux transport by the meridional flow or the effect of the surface shear layer are possible solutions. In a model including the corona, we show that various migrations can be obtained by varying the properties of the corona. A new dynamo of Babcock-Leighton type also leads to the correct equatorward migration by the non-linear relation between flux density and rise time of the flux.

scholarly journals Magnetohydrodynamic Simulation of the Evolution of Bipolar Magnetic Regions

1993 ◽  
Vol 141 ◽  
pp. 98-107 ◽  
Author(s):  
S. T. Wu ◽  
C. L. Yin ◽  
P. Mcintosh ◽  
E. Hildner
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Solar Surface ◽  
Effective Diffusion ◽  
Three Dimensional ◽  
Meridional Flow ◽  
Flux Transport ◽  
Turbulence Effects ◽  
Convective Motions

AbstractIt has been recognized that the magnetic flux observed on the solar surface appears first in low latitudes, and then this flux is gradually dispersed by super granular convective motions and meridional circulation. Theoretically, the magnetic flux transport could be explained by the interactions between magnetic fields and plasma flows on the solar surface through the theory of magnetohydrodynamics.To understand this physical scenario, a quasi-three-dimensional, time-dependent, MHD model with differential rotation, meridional flow and effective diffusion as well as cyclonic turbulence effects is developed. Numerical experiments are presented for the study of Bipolar Magnetic Regions (BMRs). When the MHD effects are ignored, our model produced the classical results (Leighton, Astrophys. J., 146, 1547, 1964). The full model’s numerical results demonstrate that the interaction between magnetic fields and plasma flow (i.e., MHD effects), observed together with differential rotation and meridional flow, gives rise to the observed complexity of the evolution of BMRs.

scholarly journals Cycle times of early M dwarf stars: mean field models versus observations

2019 ◽  
Vol 15 (S354) ◽  
pp. 116-119
Author(s):  
Manfred Küker ◽  
Günther Rüdiger ◽  
Katalin Oláh ◽  
Klaus G. Strassmeier
Keyword(s):  
Mean Field ◽  
Meridional Flow ◽  
Rotating Stars ◽  
Early Type ◽  
Flux Transport ◽  
Dwarf Stars ◽  
Cycle Times ◽  
Mean Field Models ◽  
M Stars ◽  
M Dwarf Stars

AbstractObservations of early-type M stars suggest that there are two characteristic cycle times, one of order one year for fast rotators (Prot < 1 day) and another of order four years for slower rotators. For a sample of fast-rotating stars, the equator-to-pole differences of the rotation rates up to 0.03 rad d−1 are also known from Kepler data. These findings are well-reproduced by mean field models. These models predict amplitudes of the meridional flow, from which the travel time from pole to equator at the base of the convection zone of early-type M stars can be calculated. As these travel times always exceed the observed cycle times, our findings do not support the flux transport dynamo.

scholarly journals Dipolar and Quadrupolar Magnetic Field Evolution over Solar Cycles 21, 22, and 23

2010 ◽  
Vol 6 (S271) ◽  
pp. 94-101 ◽  
Author(s):  
M. L. DeRosa ◽  
A. S. Brun ◽  
J. T. Hoeksema
Keyword(s):  
Magnetic Field ◽  
Spherical Harmonic ◽  
Transport Model ◽  
Activity Cycle ◽  
Surface Flux ◽  
Solar Activity Cycle ◽  
Solar Photosphere ◽  
Solar Cycles ◽  
Flux Transport ◽  
The Past

AbstractTime series of photospheric magnetic field maps from two observatories, along with data from an evolving surface-flux transport model, are decomposed into their constituent spherical harmonic modes. The evolution of these spherical harmonic spectra reflect the modulation of bipole emergence rates through the solar activity cycle, and the subsequent dispersal, shear, and advection of magnetic flux patterns across the solar photosphere. In this article, we discuss the evolution of the dipolar and quadrupolar modes throughout the past three solar cycles (Cycles 21–23), as well as their relation to the reversal of the polar dipole during each solar maximum, and by extension to aspects of the operation of the global solar dynamo.

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