Christoffersen Kokholm posted an update 3 weeks, 2 days ago
Much criticism has been leveled at these dynamo model-primarily based cycle forecasting schemes, and typically unfairly so. To dismiss the whole idea on the grounds that the photo voltaic dynamo is a chaotic system is likely too extreme a stance, especially since (1) even chaotic programs might be amenable to prediction over a finite temporal window, and (2) input of data (even if not via true knowledge assimilation) can in principle result in some correction of the system’s trajectory in section area.
This concept finds help in the 10Be radioisotope report, which exhibits a clear and uninterrupted cyclic sign by way of the Maunder Minimum (see Panels B and C of Determine 22 ; also Beer et al., 1998 ). Strictly talking, thresholding a variable controlled by a single dynamical state topic to amplitude modulation isn’t intermittency, though the ensuing time series for the variable might effectively look quite intermittent.
The presence of a large-scale, quasi-steady magnetic area of fossil origin within the photo voltaic inside has lengthy been recognized as a attainable explanation of the Gnevyshev-Ohl rule (Panel E of Figure 22 ). The essential thought is sort of simple: The slowly-decaying, deep fossil area being effectively steady on photo voltaic cycle timescales, its superposition with the eleven-yr polarity reversal of the overlying dynamogenerated area will lead to a 22-yr modulation, whereby the cycle is stronger when the fossil and dynamo area have the same polarity, and weaker when these polarities are opposite (see, e.g., Boyer and Levy, 1984 ; Boruta, 1996 ). The magnitude of the effect is immediately associated to the energy of the fossil field, versus that of the dynamo-generated magnetic field.
Fitting equilibrium solutions to their low-order model to the smoothed SSN time collection, one magnetic cycle at a time ( Figure 26A ), they can plausibly interpret variations of their becoming parameters as being attributable to systematic, persistent variations of the meridional circulation speed on decadal timescales ( Determine 26B ). They then enter these variations within the kinematic axisymmetric Babcock-Leighton mannequin of Chatterjee et al. ( 2004 ), conceptually similar to that described in Section four.8 but replacing the nonlinearity on the poloidal supply term by a threshold function for magnetic flux loss by means of magnetic buoyancy.
Determine 18 shows N-hemisphere time-latitude diagrams for the toroidal magnetic subject on the core-envelope interface (Panel A), and the floor radial subject (Panel B), for a Babcock-Leighton dynamo resolution now computed following the closely similar mannequin implementation of Dikpati and Charbonneau ( 1999 ). Be aware how the polar radial subject modifications from unfavourable (blue) to optimistic (red) at just about the time of peak constructive toroidal field at the core-envelope interface; that is the section relationship inferred from synoptic magnetograms (see, e.g., Figure four herein) in addition to observations of polar faculae (see Sheeley Jr, 1991 ).
Within the context of Babcock-Leighton fashions, introducing stochastic forcing of the dynamo numbers leads to amplitude fluctuation patterns qualitatively just like those plotted in Figure 25 : lengthy timescale amplitude modulation, spread in cycle interval, (non-solar) optimistic correlations between cycle amplitude and rise time, and (solar-like) positive correlation between period and rise time, with the fascinating addition that in some model formulations cycle-to-cycle amplitude variation patterns reminiscent of the Gnevyshev-Ohl Rule are additionally produced (see Charbonneau et al., 2007 ). Charbonneau and Dikpati ( 2000 ) have presented a series of dynamo simulations together with stochastic fluctuations in the dynamo number as well as within the meridional circulation.
Equally striking is the pronounced dearth of sunspots within the interval 1645 – 1715 (see Panel C of Figure 22 ); this isn’t attributable to lack of observational information (see Ribes and Nesme-Ribes, 1993 ; Hoyt and Schatten, 1996 ), however represents as an alternative a part of strongly suppressed activity now referred to as the Maunder Minimal (Eddy, 1976 , 1983 , and references therein).
It appears likely that in the foreseeable future, the less complicated, mean-area and imply-discipline-like solar cycle models reviewed right here will remain the workhorses of analysis on long timescale phenomena comparable to grand activity minima and maxima, on the evolution of surface magnetic flux, on dynamo-mannequin-based mostly solar cycle prediction, and on the modelling and interpretation of stellar activity cycles.