Pragmatic Information in Nonlinear Dynamo Theory for Solar Activity

Author(s):  
Jürgen Kurths ◽  
Ulvike Feudel ◽  
Wolfgang Jansen
2020 ◽  
Vol 17 (1) ◽  
Author(s):  
Kristóf Petrovay

AbstractA 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 yielded predictions consistently in the right range during the past few solar cycles is the polar field precursor. Nevertheless, some extrapolation methods may still be worth further study. Model based forecasts are quickly coming into their own, and, despite not having a long proven record, their predictions are received with increasing confidence by the community.


1980 ◽  
Vol 91 ◽  
pp. 29-32
Author(s):  
A. Bratenahl ◽  
P. J. Baum ◽  
W. M. Adams

In orthodox dynamo theory (Stix, 1976), the two basic processes, generation of toroidal from poloidal field and conversion of toroidal into reversed poloidal field, are both located in the high β regime convection zone. Generation requires that regime, since its function demands it be driven by mechanical forces. But the function and therefore the operating requirements of conversion are entirely different, and there seems to be no à priori reason, other than historical tradition coupled with failure to recognize those differences, for the assumption that conversion must also operate there. Conversion transforms the topological structure of generated flux by altering the field line connectivity, so that the principal task performed is reconnection. Reconnection is a spontaneous process which must compress and accelerate plasma if any is present. Obviously it must perform much more work in the high β convection zone than in the low β solar atmosphere. It seems natural, therefore, to expect the reconnection aspect of conversion to be located there, where the least work needs to be performed. To transfer the generated flux there, we may add to conversion another spontaneous process: eruption of bipolar structure (Parker, 1955). To transfer the reconnected flux back down, we add to generation another mechanically driven process called topological pumping (Drobyshevski and Yuferev, 1974). Topological pumping depends on the diamagnetic effect of eddy-motion (Wiess, 1966), the kind possessed by supergranulation: 3-dimensional arrangement of isolated rising plumes, surrounded by a continuous network of descending sheet-like flow. In the two-level dynamo presented here, conversion may be observed directly, since we expect it to express itself in terms of all forms of solar activity: sunspots, flares, faculae, filaments, coronal structures including coronal holes, etc., and their organization and evolution in a “solar meteorology”. It is clearly important to investigate a model that thus unites the two disciplines of solar activity and dynamo theory. Each strengthens the other and brings a greater unity to solar physics.


2003 ◽  
Vol 409 (3) ◽  
pp. 1097-1105 ◽  
Author(s):  
N. Kleeorin ◽  
K. Kuzanyan ◽  
D. Moss ◽  
I. Rogachevskii ◽  
D. Sokoloff ◽  
...  

2005 ◽  
Vol 23 (4) ◽  
pp. 1505-1511 ◽  
Author(s):  
H. Lundstedt ◽  
L. Liszka ◽  
R. Lundin

Abstract. In order to improve the forecasts of the impact of solar activity on the terrestrial environment on time scales longer than days, improved understanding and forecasts of the solar activity are needed. The first results of a new approach of modelling and forecasting solar activity are presented. Time series of solar activity indicators, such as sunspot number, group sunspot number, F10.7, E10.7, solar magnetic mean field, Mount Wilson plage and sunspot index, have been studied with new wavelet methods; ampligrams and time-scale spectra. Wavelet power spectra of the sunspot number for the period 1610 up to the present show not only that a dramatic increase in the solar activity took place after 1940 but also that an interesting change occurred in 1990. The main 11-year solar cycle was further studied with ampligrams for the period after 1850. time-scale spectra were used to examine the processes behind the variability of the solar activity. Several interesting deterministic and more stochastic features were detected in the time series of the solar activity indicators. The solar nature of these features will be further studied. Keywords. Solar physics, astrophysics and astronomy (Magnetic fields; Stellar interiors and dynamo theory) – Space plasma physics (nonlinear phenomena)


2013 ◽  
Vol 39 (10) ◽  
pp. 729-735 ◽  
Author(s):  
E. P. Popova ◽  
N. A. Yukhina
Keyword(s):  

2004 ◽  
Vol 2004 (IAUS223) ◽  
pp. 65-68
Author(s):  
N. Kleeorin ◽  
K. Kuzanyan ◽  
D. Moss ◽  
I. Rogachevskii ◽  
D. Sokoloff ◽  
...  

2020 ◽  
Vol 495 (4) ◽  
pp. 3788-3794 ◽  
Author(s):  
R Stepanov ◽  
N I Bondar’ ◽  
M M Katsova ◽  
D Sokoloff ◽  
P Frick

ABSTRACT The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time-scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate ‘true’ cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record – photometric monitoring of V833 Tau for more than 100 yr. We find that the observed variations of V833 Tau with time-scales of 2–50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from the stellar dynamo theory.


1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.


1979 ◽  
Vol 44 ◽  
pp. 357-372
Author(s):  
Z. Švestka

The following subjects were discussed:(1)Filament activation(2)Post-flare loops.(3)Surges and sprays.(4)Coronal transients.(5)Disk vs. limb observations.(6)Solar cycle variations of prominence occurrence.(7)Active prominences patrol service.Of all these items, (1) and (2) were discussed in most detail and we also pay most attention to them in this report. Items (3) and (4) did not bring anything new when compared with the earlier invited presentations given by RUST and ZIRIN and therefore, we omit them.


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