Magnetic Helicity as a Predictor of the Solar Cycle

Hawkes, Gareth; Berger, Mitchell A.

doi:10.1007/s11207-018-1332-3

Cited by 27 publications

(18 citation statements)

References 35 publications

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“…1, and is seen to be close to those used inthe present paper. The Hawkes & Berger (2018) helicity fluxes follow F v φ from the W18 model reasonably closely for Cycle 22, but are a factor two stronger for Cycles 21 and 23. These discrepancies can be attributed to the different spatial resolutions used for the two studies: in Hawkes & Berger (2018) the authors use only the first few degrees from the WSO spherical harmonic decomposition, and as such calculate the large scale winding without accounting for the contribution of active regions.…”

Section: Comparison With Earlier Workmentioning

confidence: 69%

“…The third row of Table 2 shows the helicity fluxes estimated by Hawkes & Berger (2018) using WSO data, using the differential rotation profile of Berger & Ruzmaikin (2000). This profile is shown by the black dashed line in the right panel of Fig.…”

Section: Comparison With Earlier Workmentioning

confidence: 99%

“…Previously, Berger & Ruzmaikin (2000) estimated that 4 × 10 46 Mx 2 of helicity were injected into each coronal hemisphere by solar rotation over a 22 year period from 1976 to 1998 (solar cycles 21 and 22), using low resolution magnetogram data from Wilcox Solar Observatory. This calculation was extended to 2018 by Hawkes & Berger (2018), who found, in particular, that the injected helicity in solar cycle 23 was lower than in the previous two cycles. Here we use surface flux transport modelling to extend this calculation to multiple solar cycles, considering magnetic flux distributions with higher spatial resolution and including also the helicity flux from meridional flow and supergranular diffusion.…”

Section: Introductionmentioning

confidence: 97%

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Hemispheric injection of magnetic helicity by surface flux transport

Hawkes

Yeates

2019

A&A

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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.

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Section: Comparison With Earlier Workmentioning

confidence: 69%

Section: Comparison With Earlier Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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Hemispheric injection of magnetic helicity by surface flux transport

Hawkes

Yeates

2019

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“…The forecasting potential of the global dipole may also provide the ground for the findings of Hawkes and Berger (2018) who proposed the ''helicity flux'' as a cycle precursor. Perhaps more aptly called helicity input rate by the differential rotation, their helicity flux is defined by a weighted hemispheric surface integral of (a functional of) the radial magnetic field, where the weight function is fixed by the differential rotation profile.…”

Section: Extending the Range Of The Polar Precursor: Early Forecasts mentioning

confidence: 99%

Solar cycle prediction

Petrovay

2020

Living Rev Sol Phys

194

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A review of solar cycle prediction methods and their performance is given, including early forecasts for Cycle 25. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. Prediction methods form three main groups. Precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. The choice of a good precursor often implies considerable physical insight: indeed, it has become increasingly clear that the transition from purely empirical precursors to model-based methods is continuous. Model-based approaches can be further divided into two groups: predictions based on surface flux transport models and on consistent dynamo models. The implicit assumption of precursor methods is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. Extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variations are the same at any point of time, and therefore it lends itself to analysis and forecasting by time series methods. In their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. One method that has This article is a revised version of

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“…where we note that the z-spatial co-ordinate has been dropped again (k = lm). This is a multiresolution form of the helicity flux used in studies of the solar helicity flux through the hemisphere Hawkes & Berger (2018). Using the surface flux transport model simulations of Jiang et al (2011), we calculate the helicity flux associated with seven spatial scales in Figure 22 This data covers their simulations for Solar Cycles 21 and 22, where time is counted from the beginning of cycle 21.…”

Section: Flux Of Magnetic Helicitymentioning

confidence: 99%

Spatial scales and locality of magnetic helicity

Prior

Hawkes

Berger

2020

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Context. Magnetic helicity is approximately conserved in resistive MHD models. It quantifies the entanglement of the magnetic field within the plasma. The transport and removal of helicity is crucial in both the dynamo in the solar interior and active region evolution in the solar corona. This transport typically leads to highly inhomogeneous distributions of entanglement.Aims. There exists no consistent systematic means of decomposing helicity over varying spatial scales and in localised regions. Spectral helicity decompositions can be used in periodic domains and is fruitful for the analysis of homogeneous phenomena. This paper aims to develop methods for analysing the evolution of magnetic field topology in non-homogeneous systems. Methods. We apply a multiresolution wavelet decomposition to the magnetic field and demonstrate how it can be applied to various quantities associated with magnetic helicity, including the field line helicity. We use a geometrical definition of helicity which allows these quantities to be calculated for fields with arbitrary boundary conditions. Results. It is shown that the multiresolution decomposition of helicity has the crucial property of local additivity and demonstrate a general linear energy-topology conservation law which is a significant generalisation of the two point correlation decomposition used in the analysis of homogeneous turbulence and periodic fields. The localisation property of the wavelet representation is shown to characterise inhomogeneous distributions which a Fourier representation cannot. Using an analytic representation of a resistive braided field relaxation we demonstrate a clear correlation between the variations in energy at various length scales and the variations in helicity at the same spatial scales. Its application to helicity flows in a surface flux transport model show how various contributions to the global helicity input from active region field evolution and polar field development are naturally separated by this representation. Conclusions. The multiresolution wavelet decomposition can be used to analyse the evolution of helicity in magnetic fields in a manner which is consistently additive. This method has the advantage over more established spectral methods in that it clearly characterises the inhomogeneous nature of helicity flows where spectral methods cannot. Further its applicability in aperiodic models significantly increase the range of potential applications.

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Magnetic Helicity as a Predictor of the Solar Cycle

Cited by 27 publications

References 35 publications

Hemispheric injection of magnetic helicity by surface flux transport

Hemispheric injection of magnetic helicity by surface flux transport

Solar cycle prediction

Spatial scales and locality of magnetic helicity

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