Choice of a ‘Reality Index’ for Suspected Cyclic Variations

Gleissberg, W.

doi:10.1038/158915b0

Cited by 16 publications

(19 citation statements)

References 2 publications

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“…Long-term records of sunspot numbers have revealed long-period modulation of Schwabe cycles over 80-100 yr (Gleissberg 1939;Hathaway 2010). This modulation was explained in terms of slow magneto-Rossby waves excited in the lower part of the tachocline (Zaqarashvili et al 2015).…”

Section: Equatorial Slow Magneto-rossby Mode and Gleissberg Cyclementioning

confidence: 99%

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

Zaqarashvili

2018

ApJ

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The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20 0 − 40 0 , coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90-100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1-2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magnetoinertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

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Section: Equatorial Slow Magneto-rossby Mode and Gleissberg Cyclementioning

confidence: 99%

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

Zaqarashvili

2018

ApJ

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“…Until now, however, it is safe to say that this variation persisted during the last 14 cycles. The length of eight cycles nearly corresponds to the Gleissberg cycle (Gleissberg 1939).…”

Section: Conclusion a Long‐term Hemispheric Wavementioning

confidence: 99%

Phase lags of solar hemispheric cycles

Muraközy¹,

Ludmány²

2011

Monthly Notices of the Royal Astronomical Society

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The North-South asymmetry of solar activity is variable in time and strength. We analyse the long-term variation of the phase lags of hemispheric cycles and check a conjectured relationship between these phase lags and the hemispheric cycle strengths. Sunspot data are used from cycles 12-23 in which the separation of northern and southern hemispheres is possible. The centers of mass of the hemispheric cycle profiles were used to study the phase relations and relative strengths of the hemispheric cycles. This approach considers a cycle as a whole and disregards the short-term fluctuations of the cycle time profile. The phase of the hemispheric cycles shows an alternating variation: the northern cycle leads in 4 cycles and follows in 4 cycles. No significant relationship is found between the phase and strength differences of the hemispheric cycles. The period of 4+4 cycles appears to be close to the Gleissberg cycle and may provide a key to its physical background. It may raise a new aspect in the solar dynamo mechanism because it needs a very long memory.Comment: 7 pages, 6 figure

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“…Polarimetric observations from the NSO/Kitt Peak Observatory and magnetograms from the Michelson Doppler Imager (MDI) aboard SOHO and the Helioseismic and Magnetic Imager (HMI) aboard SDO have enabled detailed and continuous study of how sunspots appear in pairs of opposite polarity sense from one cycle to the next, making a 22-year cycle overall (e.g., Hathaway 2015). In addition, a number of other cycles (less obvious and regular than the 22-year cycle) have been identified, from a slow ∼100year modulation of the peak cycle amplitudes called the Gleissberg Cycle (e.g., Gleissberg 1939;Ogurtsov et al 2002), to a rapid 2-year periodicity in the global magnetic field (e.g., Ulrich & Tran 2013). On timescales in between, active longitudes (longitudes at which sunspots appear more frequently and with greater strength) persist for several decades (e.g., Henney & Harvey 2002).…”

Section: Introductionmentioning

confidence: 99%

Exploring Bistability in the Cycles of the Solar Dynamo through Global Simulations

Matilsky

Toomre

2020

ApJ

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The calling card of solar magnetism is the sunspot cycle, during which sunspots regularly reverse their polarity sense every 11 years. However, a number of more complicated time-dependent behaviors have also been identified. In particular, there are temporal modulations associated with active longitudes and hemispheric asymmetry, when sunspots appear at certain solar longitudes or else in one hemisphere preferentially. So far, a direct link between between this asymmetric temporal behavior and the underlying solar dynamo has remained elusive. In this work, we present results from global, 3D magnetohydrodynamic (MHD) simulations, which for the first time display both behavior reminiscent of the sunspot cycle (regular polarity reversals and equatorward migration of internal magnetic field) and asymmetric, irregular behavior that in the simulations we interpret as active longitudes and hemispheric asymmetry. The simulations are thus bistable, in that the turbulent convection can stably support two distinct flavors of magnetism at different times, in superposition, or with smooth transitions from one state to the other. We discuss this new family of dynamo models in the context of the extensive observations of the Sun's surface magnetic field with the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO), as well as earlier observations of sunspot number and synoptic maps. We suggest that the solar dynamo itself may be bistable in nature, exhibiting two types of temporal behavior in the magnetic field.

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Choice of a ‘Reality Index’ for Suspected Cyclic Variations

Cited by 16 publications

References 2 publications

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

Phase lags of solar hemispheric cycles

Exploring Bistability in the Cycles of the Solar Dynamo through Global Simulations

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