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 Towards an algebraic method of solar cycle prediction

2020 ◽  
Vol 10 ◽  
pp. 50 ◽  
Author(s):  
Kristóf Petrovay ◽  
Melinda Nagy ◽  
Anthony R. Yeates
Keyword(s):  
Dipole Moment ◽  
Solar Cycle ◽  
Active Regions ◽  
Surface Flux ◽  
Algebraic Method ◽  
Meridional Flow ◽  
Activity Level ◽  
Dynamo Model ◽  
Flux Transport ◽  
Axial Dipole

We discuss the potential use of an algebraic method to compute the value of the solar axial dipole moment at solar minimum, widely considered to be the most reliable precursor of the activity level in the next solar cycle. The method consists of summing up the ultimate contributions of individual active regions to the solar axial dipole moment at the end of the cycle. A potential limitation of the approach is its dependence on the underlying surface flux transport (SFT) model details. We demonstrate by both analytical and numerical methods that the factor relating the initial and ultimate dipole moment contributions of an active region displays a Gaussian dependence on latitude with parameters that only depend on details of the SFT model through the parameter η/Δu where η is supergranular diffusivity and Δu is the divergence of the meridional flow on the equator. In a comparison with cycles simulated in the 2 × 2D dynamo model we further demonstrate that the inaccuracies associated with the algebraic method are minor and the method may be able to reproduce the dipole moment values in a large majority of cycles.

scholarly journals Hemispheric injection of magnetic helicity by surface flux transport

2019 ◽  
Vol 631 ◽  
pp. A138 ◽  
Author(s):  
G. Hawkes ◽  
A. R. Yeates
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Solar Rotation ◽  
Surface Flux ◽  
Magnetic Helicity ◽  
Solar Cycles ◽  
Flux Transport ◽  
Transport Models ◽  
Radial Magnetic Field ◽  
Helicity Injection

Aims. We estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700–2009). Methods. We determine the radial magnetic field evolution using two separate surface flux transport models: one driven by magnetogram inputs and another by statistical active region insertion guided by the sunspot number record. The injection of relative magnetic helicity is then computed from this radial magnetic field together with the known electric field in the flux transport models. Results. Neglecting flux emergence, solar rotation is the dominant contributor to the helicity injection. At high latitudes, the injection is always negative/positive in the northern/southern hemisphere, while at low latitudes the injection tends to have the opposite sign when integrated over the full solar cycle. The overall helicity injection in a given solar cycle depends on the balance between these two contributions. This net injected helicity correlates well with the end-of-cycle axial dipole moment.

Meridional Flow and the Solar Cycle Variation of the Sun’s Open Magnetic Flux

2002 ◽  
Vol 580 (2) ◽  
pp. 1188-1196 ◽  
Author(s):  
Y.‐M. Wang ◽  
N. R. Sheeley, Jr. ◽  
J. Lean
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Meridional Flow ◽  
Solar Cycle Variation ◽  
Cycle Variation ◽  
Open Magnetic Flux

scholarly journals Predicting cycle 24 using various dynamo-based tools

2008 ◽  
Vol 26 (2) ◽  
pp. 259-267 ◽  
Author(s):  
M. Dikpati
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Active Regions ◽  
Flux Transport ◽  
Delayed Onset ◽  
Drift Speed ◽  
Sensitivity Tests ◽  
The Mean ◽  
Cycle 24

Abstract. Various dynamo-based techniques have been used to predict the mean solar cycle features, namely the amplitude and the timings of onset and peak. All methods use information from previous cycles, including particularly polar fields, drift-speed of the sunspot zone to the equator, and remnant magnetic flux from the decay of active regions. Polar fields predict a low cycle 24, while spot zone migration and remnant flux both lead to predictions of a high cycle 24. These methods both predict delayed onset for cycle 24. We will describe how each of these methods relates to dynamo processes. We will present the latest results from our flux-transport dynamo, including some sensitivity tests and how our model relates to polar fields and spot zone drift methods.

scholarly journals Optimization of surface flux transport models for the solar polar magnetic field

2019 ◽  
Vol 632 ◽  
pp. A87 ◽  
Author(s):  
K. Petrovay ◽  
M. Talafha
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Parameter Space ◽  
Large Scale ◽  
Surface Flux ◽  
Supporting Evidence ◽  
Flux Transport ◽  
Polar Magnetic Field ◽  
Flow Profiles ◽  
Magnetic Diffusivity

Context. The choice of free parameters in surface flux transport (SFT) models describing the evolution of the large-scale poloidal magnetic field of the Sun is critical for the correct reproduction of the polar magnetic flux built up during a solar cycle, which is known to be a good predictor of the amplitude of the upcoming cycle. Aims. For an informed choice of parameters it is important to understand the effects of and interplay among the various parameters and to optimize the models for the polar magnetic field. Methods. Here we present the results of a large-scale systematic study of the parameter space in an SFT model where the source term representing the net effect of tilted flux emergence was chosen to represent a typical, average solar cycle as described by observations. Results. Comparing the results with observational constraints on the spatiotemporal variation of the polar magnetic field, as seen in magnetograms for the last four solar cycles, we mark allowed and excluded regions in the 3D parameter space defined by the flow amplitude u0, the magnetic diffusivity η and the decay time scale τ, for three different assumed meridional flow profiles. Conclusions. Without a significant decay term in the SFT equation (i.e., for τ >  10 yr) the global dipole moment reverses too late in the cycle for all flow profiles and parameters, providing independent supporting evidence for the need of a decay term, even in the case of identical cycles. An allowed domain is found to exist for τ values in the 5–10 yr range for all flow profiles considered. Generally higher values of η (500–800 km2 s−1) are preferred though some solutions with lower η are still allowed.

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 Magnetic solar surface flux transport simulation

2019 ◽  
Vol 13 (28) ◽  
pp. 33-43
Author(s):  
Loay K. Abood
Keyword(s):  
Magnetic Flux ◽  
Flux Distribution ◽  
Solar Surface ◽  
Surface Flux ◽  
Surface Velocity ◽  
Advection Equation ◽  
Implicit Methods ◽  
Flux Transport ◽  
Tilted Angle ◽  
Angle Parameter

In this paper, the solar surface magnetic flux transport has been simulated by solving the diffusion–advection equation utilizing numerical explicit and implicit methods in 2Dsurface. The simulation was used to study the effect of bipolar tilted angle on the solar flux distribution with time. The results show that the tilted angle controls the magnetic distribution location on the sun’s surface, especially if we know that the sun’s surface velocity distribution is a dependent location. Therefore, the tilted angle parameter has distribution influence.

scholarly journals Forward modelling of brightness variations in Sun-like stars

2018 ◽  
Vol 620 ◽  
pp. A177 ◽  
Author(s):  
E. Işık ◽  
S. K. Solanki ◽  
N. A. Krivova ◽  
A. I. Shapiro
Keyword(s):  
Magnetic Flux ◽  
Rotation Rate ◽  
Activity Patterns ◽  
Surface Flux ◽  
Magnetic Activity ◽  
Threshold Field ◽  
Flux Emergence ◽  
Flux Transport ◽  
Rotation Rates ◽  
Set Up

Context. The latitudinal distribution of starspots deviates from the solar pattern with increasing rotation rate. Numerical simulations of magnetic flux emergence and transport can help model the observed stellar activity patterns and the associated brightness variations. Aims. We set up a composite model for the processes of flux emergence and transport on Sun-like stars to simulate stellar brightness variations for various levels of magnetic activity and rotation rates. Methods. Assuming that the distribution of magnetic flux at the base of the convection zone follows solar scaling relations, we calculate the emergence latitudes and tilt angles of bipolar regions at the surface for various rotation rates, using thin-flux-tube simulations. Taking these two quantities as input to a surface flux transport (SFT) model, we simulate the diffusive-advective evolution of the radial field at the stellar surface, including effects of active region nesting. Results. As the rotation rate increases, (1) magnetic flux emerges at higher latitudes and an inactive gap opens around the equator, reaching a half-width of 20° for 8 Ω⊙; and (2) the tilt angles of freshly emerged bipolar regions show stronger variations with latitude. Polar spots can form at 8 Ω⊙ by accumulation of follower-polarity flux from decaying bipolar regions. From 4 Ω⊙ to 8 Ω⊙, the maximum spot coverage changes from 3 to 20%, respectively, compared to 0.4% in the solar model. Nesting of activity can lead to strongly non-axisymmetric spot distributions. Conclusions. On Sun-like stars rotating at 8 Ω⊙ (Prot ≃ 3 days), polar spots can form, owing to higher levels of flux emergence rate and tilt angles. Defining spots by a threshold field strength yields global spot coverages that are roughly consistent with stellar observations.

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