Zonal flows and grand minima in a solar dynamo model

Bushby, P. J.

doi:10.1111/j.1365-2966.2006.10706.x

Cited by 64 publications

(72 citation statements)

References 43 publications

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“…Eventually, the symmetric modes decay in amplitude, allowing the antisymmetric family and thus the dipole mode to reassert its dominance. In earlier studies of simpler though nonlinear mean-field dynamo models, there is a clear variability between the dominance of antisymmetric and symmetric dynamo modes in those models (e.g., Tobias 1997; Moss & Brooke 2000;Brooke et al 2002;Bushby 2006). Such variability can lead to intervals of deep minima.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

Augustson

Brun

Miesch

et al. 2015

ApJ

114

145

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The 3D MHD Anelastic Spherical Harmonic code, using slope-limited diffusion, is employed to capture convective and dynamo processes achieved in a global-scale stellar convection simulation for a model solar-mass star rotating at three times the solar rate. The dynamo-generated magnetic fields possesses many timescales, with a prominent polarity cycle occurring roughly every 6.2 years. The magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation. The polarity reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. An equatorial migration of the magnetic field is seen, which is due to the strong modulation of the differential rotation rather than a dynamo wave. A poleward migration of magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families. This intermittent dynamo state potentially results from the simulation's relatively low magnetic Prandtl number. A mean-field-based analysis of this dynamo simulation demonstrates that it is of the α-Ω type. The timescales that appear to be relevant to the magnetic polarity reversal are also identified.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

Augustson

Brun

Miesch

et al. 2015

ApJ

114

145

View full text Add to dashboard Cite

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“…In stochastically forced kinematic dynamo models, persistence in the solar-cycle-averaged level of activity (hereafter "memory") can extend from less than one and up to three cycles, depending on details of the models and of the physical parameter regime in which they operate (e.g., St-Jean and Charbonneau, 2007;Yeates et al, 2008;Cameron et al, 2013;Muñoz-Jaramillo et al, 2013). In nonkinematic dynamo models incorporating the magnetic back reaction on large-scale inductive flows, deterministic modulation of the primary cycle amplitude can be produced, amounting to a form of memory that can extend over tens of activity cycles in a wide range of parameter regimes (e.g., Tobias, 1997;Bushby, 2006). Among models that do succeed in producing deep activity minima similar to the Maunder minimum, most show onsets occurring surprisingly fast, typically within one or two cycles.…”

Section: Future Scenarios (2015-2300)mentioning

confidence: 99%

Solar forcing for CMIP6 (v3.2)

et al. 2017

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Abstract. This paper describes the recommended solar forcing dataset for CMIP6 and highlights changes with respect to CMIP5. The solar forcing is provided for radiative properties, namely total solar irradiance (TSI), solar spectral irradiance (SSI), and the F10.7 index as well as particle forcing, including geomagnetic indices Ap and Kp, and ionization rates to account for effects of solar protons, electrons, and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing has been provided for a CMIP exercise. The solar forcing datasets are provided at daily and monthly resolution separately for the CMIP6 preindustrial control, historical (1850CMIP6 preindustrial control, historical ( -2014, and future (2015-2300) simulations. For the preindustrial control simulation, both constant and time-varying solar forcing components are provided, with the latter including variability on 11-year and shorter timescales but no long-term changes. For the future, we provide a realistic scenario of what solar behavior could be, as well as an additional extreme Maunderminimum-like sensitivity scenario. This paper describes the forcing datasets and also provides detailed recommendations as to their implementation in current climate models.For the historical simulations, the TSI and SSI time series are defined as the average of two solar irradiance models that are adapted to CMIP6 needs: an empirical onePublished by Copernicus Publications on behalf of the European Geosciences Union. A new and lower TSI value is recommended: the contemporary solar-cycle average is now 1361.0 W m −2 . The slight negative trend in TSI over the three most recent solar cycles in the CMIP6 dataset leads to only a small global radiative forcing of −0.04 W m −2 . In the 200-400 nm wavelength range, which is important for ozone photochemistry, the CMIP6 solar forcing dataset shows a larger solar-cycle variability contribution to TSI than in CMIP5 (50 % compared to 35 %).We compare the climatic effects of the CMIP6 solar forcing dataset to its CMIP5 predecessor by using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The differences in the long-term mean SSI in the CMIP6 dataset, compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates of −0.35 K day −1 at the stratopause), cooler stratospheric temperatures (−1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (−3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K day −1 at the stratopause), temperatures (∼ 1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar-cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.CMIP6 models wi...

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“…Moreover, the dynamical feedback of the strong dynamo-generated magnetic fields is likely to be significant enough to produce non-linear effects on the activity cycle. A number of models have introduced these non-linear effects (Proctor 1977;Tobias 1997;Moss & Brooke 2000;Bushby 2006;Rempel 2006) and have resulted in the production of grand minima-like periods or other strong modulation of the cyclic activity. However, time delays have hardly been considered and if they were, they were mainly due to the advection time by meridional flow.…”

Section: Introductionmentioning

confidence: 99%

Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models

Jouve¹,

Proctor²,

Lesur³

2010

A&A

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Context. The Sun is a magnetic star whose cyclic activity is thought to be linked to internal dynamo mechanisms. A combination of numerical modelling with various levels of complexity is an efficient and accurate tool to investigate such intricate dynamical processes. Aims. We investigate the role of the magnetic buoyancy process in 2D Babcock-Leighton dynamo models, by modelling more accurately the surface source term for poloidal field. Methods. To do so, we reintroduce in mean-field models the results of full 3D MHD calculations of the non-linear evolution of a rising flux tube in a convective shell. More specifically, the Babcock-Leighton source term is modified to take into account the delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. Results. We find that the time delays introduced in the equations produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. Aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. The strong effects introduced even by small delays is found to be due to the dependence of the delays on the magnetic field strength at the base of the convection zone, the modulation being much less when time delays remain constant. We do not find any significant influence on the cycle period except when the delays are made artificially strong. Conclusions. A possible new origin of the solar cycle variability is here revealed. This modulated activity and the resulting butterfly diagram are then more compatible with observations than what the standard Babcock-Leighton model produces.

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Zonal flows and grand minima in a solar dynamo model

Cited by 64 publications

References 43 publications

Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

Solar forcing for CMIP6 (v3.2)

Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models

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