scholarly journals The Sunspot Cycle and Solar Magnetic Fields. II. The Interaction of Flux Tubes with the Convection Zone

1985 ◽  
Vol 38 (6) ◽  
pp. 1067 ◽  
Author(s):  
Ronald G Giovanelli
Keyword(s):  
Convection Zone ◽  
Torsional Oscillation ◽  
Sunspot Cycle ◽  
Solar Magnetic Fields ◽  
Field Reversal ◽  
Flux Tubes ◽  
Dynamo Mechanism ◽  
Floating Criteria ◽  
New Type ◽  
Major Cycle

Mechanisms of interaction between flux tubes or ropes and the convection zone are examined insofar as they are relevant to the sunspot cycle. These include floating, transport, and the penetration of gas from outside the tubes. It is found that all previous studies contain one or more major errors of physics which render their conclusions invalid. The errors include invariably the assumption that Archimedes' principle is applicable to flux ropes, that gas entry can be disregarded, and usually that floating criteria depend solely or primarily on local phenomena. Some of the results presented here are explanations of (i) the transport of flux tubes by the slow observed poleward motions and the even slower systems which carry extensions of these tubes downwards to depths of ~ 150 Mm and then equatorwards; (ii) their magnetic field strengths ( ~ 104 G at a depth 10 Mm to (6-12) x 104 G at ~ 150 Mm); and (iii) the amplitudes of the torsional oscillation. Taken in conjunction with Part I, where the mechanism of polar field reversal is described and the variation of the phase of the torsional oscillation explained, all major cycle observations are accounted for in what turns out to be a new type of dynamo mechanism.

scholarly journals The Sunspot Cycle and Solar Magnetic Fields. I. The Mechanism as Inferred from Observation

1985 ◽  
Vol 38 (6) ◽  
pp. 1045 ◽  
Author(s):  
Ronald G Giovanelli
Keyword(s):  
Magnetic Fields ◽  
Differential Rotation ◽  
Torsional Oscillation ◽  
Sunspot Cycle ◽  
Polar Field ◽  
Lower Latitude ◽  
Polar Regions ◽  
Sunspot Maximum ◽  
Field Reversal ◽  
Opposite Hemisphere

Observations of solar magnetic and velocity fields can be used to derive the course of events involved in the solar cycle. These differ in three important respects from those of conventional dynamo theories: (i) Polar field reversal. Following the outbreak of a new cycle, magnetic flux released by sunspots diffuses initially by Leighton's random-walk process, but this is soon dominated by the observed poleward flow of about 20 m s - 1 which carries flux to polar regions in about 12 months. Since follower spots lie about 2� higher in latitude than leaders, follower flux arrives in polar regions some two weeks ahead of leader flux, providing a net inflow of follower polarity there until sunspot maximum, reversing the polar field from the previous sunspot cycle and building it up to a maximum. After sunspot maximum, the flux arriving in polar regions is predominantly of follower polarity until or unless spots occur at latitudes so low that flux can diffuse towards and across the equator, predominantly from the lower latitude leader; the effect is doubled by a complementary migration from the opposite hemisphere. This prevents the change in polar flux over the cycle from dropping to zero, and leaves the polarity there reversed at the end of the cycle. (ii) The sunspot cycle. A slow, deeper counterflow, essential for continuity, carries flux strands down in the polar zones and then equatorwards. The concentration of strands is increased continually by differential rotation, and they are dragged continually into contact. Reconnection occurs rapidly except between tubes that are inclined at very small angles. This results in the formation of ropes of flux strands twisted very gently. At some stage they are large enough to float, forming sunspots. The mean sunspot latitude decreases continuously as the flux is carried equatorwards, dying out as the flux ropes become exhausted. The whole process repeats, once again reversing the polar and spot group magnetic fields. Hale's polarity laws follow immediately, and Sporer's law requires only minor adjustments to the predicted velocity of the deep equatorward counterflow. The estimated velocity of this flow is compatible with the observed sunspot and magnetic cycles of 11 and 22 years. (iii) The torsional oscillation. Shear by differential rotation increases the concentration of flux strands; the reaction to strongly sheared flux strands is a tendency to reduce differential rotation. This results in cyclic variations of differential rotation, the phase with respect to sunspot formation being in good agreement with the torsional oscillation observations of Howard and LaBonte (1981) at all latitudes up to 50-55�.

Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as a Cosmic Dynamo

2000 ◽  
Vol 179 ◽  
pp. 365-371
Author(s):  
Hirokazu Yoshimura
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Convection Zone ◽  
Dimensional Space ◽  
Solar Dynamo ◽  
Magnetic Cycle ◽  
Plasma Flows ◽  
Flux Tubes ◽  
Solar Magnetic Cycle ◽  
Dynamo Mechanism

Abstractwe briefly describe historical development of the concept of solar dynamo mechanism that generates electric current and magnetic field by plasma flows inside the solar convection zone. The dynamo is the driver of the cyclically polarity reversing solar magnetic cycle. The reversal process can easily and visually be understood in terms of magnetic field line stretching and twisting and folding in three-dimensional space by plasma flows of differential rotation and global convection under influence of Coriolis force. This process gives rise to formation of a series of huge magnetic flux tubes that propagate along iso-rotation surfaces inside the convection zone. Each of these flux tubes produces one solar cycle. We discuss general characteristics of any plasma flows that can generate magnetic field and reverse the polarity of the magnetic field in a rotating body in the Universe. We also mention a list of problems which are currently being disputed concerning the solar dynamo mechanism together with observational evidences that are to be constraints as well as verifications of any solar cycle dynamo theories of short and long term behaviors of the Sun, particularly time variations of its magnetic field, plasma flows, and luminosity.

scholarly journals Magnetic fields in the solar convection zone

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Yuhong Fan
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Active Regions ◽  
Toroidal Magnetic Field ◽  
Near Surface ◽  
New Developments ◽  
Solar Convection Zone ◽  
Flux Tubes ◽  
Solar Convection ◽  
Dynamo Mechanism

AbstractIt has been a prevailing picture that active regions on the solar surface originate from a strong toroidal magnetic field stored in the overshoot region at the base of the solar convection zone, generated by a deep seated solar dynamo mechanism. This article reviews the studies in regard to how the toroidal magnetic field can destabilize and rise through the convection zone to form the observed solar active regions at the surface. Furthermore, new results from the global simulations of the convective dynamos, and from the near-surface layer simulations of active region formation, together with helioseismic investigations of the pre-emergence active regions, are calling into question the picture of active regions as buoyantly rising flux tubes originating from the bottom of the convection zone. This article also gives a review on these new developments.

scholarly journals A 3D kinematic Babcock Leighton solar dynamo model sustained by dynamic magnetic buoyancy and flux transport processes

2019 ◽  
Vol 623 ◽  
pp. A54 ◽  
Author(s):  
Rohit Kumar ◽  
Laurène Jouve ◽  
Dibyendu Nandy
Keyword(s):  
Large Scale ◽  
Convection Zone ◽  
Meridional Circulation ◽  
Sunspot Cycle ◽  
Transport Processes ◽  
Solar Dynamo ◽  
Dynamo Model ◽  
Flux Transport ◽  
Field Reversal ◽  
Magnetic Buoyancy

Context. Magnetohydrodynamic interactions between plasma flows and magnetic fields is fundamental to the origin and sustenance of the 11-year sunspot cycle. These processes are intrinsically three-dimensional (3D) in nature. Aims. Our goal is to construct a 3D solar dynamo model that on the one hand captures the buoyant emergence of tilted bipolar sunspot pairs, and on the other hand produces cyclic large-scale field reversals mediated via surface flux-transport processes – that is, the Babcock-Leighton mechanism. Furthermore, we seek to explore the relative roles of flux transport by buoyancy, advection by meridional circulation, and turbulent diffusion in this 3D dynamo model. Methods. We perform kinematic dynamo simulations where the prescribed velocity field is a combination of solar-like differential rotation and meridional circulation, along with a parametrized turbulent diffusivity. We use a novel methodology for modeling magnetic buoyancy through field-strength-dependent 3D helical up-flows that results in the formation of tilted bipolar sunspots. Results. The bipolar spots produced in our simulations participate in the process of poloidal-field generation through the Babcock-Leighton mechanism, resulting in self-sustained and periodic large-scale magnetic field reversal. Our parameter space study varying the amplitude of the meridional flow, the convection zone diffusivity, and parameters governing the efficiency of the magnetic buoyancy mechanism reveal their relative roles in determining properties of the sunspot cycle such as amplitude, period, and dynamical memory relevant to solar cycle prediction. We also derive a new dynamo number for the Babcock-Leighton solar dynamo mechanism which reasonably captures our model dynamics. Conclusions. This study elucidates the relative roles of different flux-transport processes in the Sun’s convection zone in determining the properties and physics of the sunspot cycle and could potentially lead to realistic, data-driven 3D dynamo models for solar-activity predictions and exploration of stellar magnetism and starspot formation in other stars.

scholarly journals Can short time delays influence the variability of the solar cycle?

2010 ◽  
Vol 6 (S271) ◽  
pp. 288-296
Author(s):  
Laurène Jouve ◽  
Michael R. E. Proctor ◽  
Geoffroy Lesur
Keyword(s):  
Solar Cycle ◽  
Convection Zone ◽  
Mean Field ◽  
Period Doubling ◽  
Temporal Modulation ◽  
Solar Convection Zone ◽  
Flux Tubes ◽  
Solar Convection ◽  
Short Time ◽  
Period Doubling Bifurcations

AbstractWe present the effects of introducing results of 3D MHD simulations of buoyant magnetic fields in the solar convection zone in 2D mean-field Babcock-Leighton models. In particular, we take into account the time delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. We find that the delays produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. The study of a reduced model reveals that aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. We also discuss the memory of such systems and the conclusions which may be drawn concerning the actual solar cycle variability.

Mechanisms and Mitigation of 3D Coupled Vibrations in Drilling with PDC Bits

2021 ◽  
Author(s):  
Shilin Chen ◽  
Chris Propes ◽  
Curtis Lanning ◽  
Brad Dunbar
Keyword(s):  
Torsional Oscillation ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Coupled Vibration ◽  
Stick Slip ◽  
Rock Interaction ◽  
Bottom Hole ◽  
New Type ◽  
Design Characteristics ◽  
Axial Resonance

Abstract In this paper we present a new type of vibration related to PDC bits in drilling and its mitigation: a vibration coupled in axial, lateral and torsional directions at a high common frequency (3D coupled vibration). The coupled frequency is as high as 400Hz. 3D coupled vibration is a new dysfunction in drilling operation. This type of vibration occurred more often than stick-slip vibration. Evidences reveal that the coupled frequency is an excitation frequency coming from the bottom hole pattern formed in bit/rock interaction. This excitation frequency and its higher order harmonics may excite axial resonance and/or torsional resonance of a BHA. The nature of 3D coupled vibration is more harmful than low frequency stick-slip vibration and high frequency torsional oscillation (HFTO). The correlation between the occurrence of 3D coupled vibration and bit design characteristics is studied. Being different from prior publications, we found the excitation frequency is dependent on bit design and the occurrence of 3D coupled vibration is correlated with bit design characteristics. New design guidlines have been proposed to reduce or to mitigate 3D coupled vibration.

Sign in / Sign up

Export Citation Format

Share Document