Shape of solar cycles and mid-term solar activity oscillations

ABSTRACT The evolution of solar activity comprises, apart from the well-known 11-year cycle, various temporal scales ranging from months up to the secondary cycles known as mid-term oscillations. Its nature deserves a physical explanation. In this work, we have considered the 5–6 year oscillations as derived both from sunspots and solar magnetic dipole time series. Using a solar dynamo model, we have deduced that these variations may be a manifestation of dynamo non-linearities and the non-harmonic shape of the solar activity cycles. We have concluded that the observed mid-term oscillations are related to the non-linear saturation of dynamo processes in the solar interior.

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Global evolution of solar magnetic fields and prediction of activity cycles

Proceedings of the International Astronomical Union ◽

10.1017/s174392132000071x ◽

2019 ◽

Vol 15 (S354) ◽

pp. 147-156

Author(s):

Irina N. Kitiashvili

Keyword(s):

Solar Activity ◽

Magnetic Fields ◽

Activity Cycle ◽

Dynamo Model ◽

Solar Magnetic Fields ◽

Solar Cycles ◽

Multiscale Dynamics ◽

Activity Cycles ◽

Solar Dynamics ◽

Solar Activity Cycles

AbstractPrediction of solar activity cycles is challenging because physical processes inside the Sun involve a broad range of multiscale dynamics that no model can reproduce and because the available observations are highly limited and cover mostly surface layers. Helioseismology makes it possible to probe solar dynamics in the convective zone, but variations in differential rotation and meridional circulation are currently available for only two solar activity cycles. It has been demonstrated that sunspot observations, which cover over 400 years, can be used to calibrate the Parker-Kleeorin-Ruzmaikin dynamo model, and that the Ensemble Kalman Filter (EnKF) method can be used to link the modeled magnetic fields to sunspot observations and make reliable predictions of a following activity cycle. However, for more accurate predictions, it is necessary to use actual observations of the solar magnetic fields, which are available only for the last four solar cycles. In this paper I briefly discuss the influence of the limited number of available observations on the accuracy of EnKF estimates of solar cycle parameters, the criteria to evaluate the predictions, and application of synoptic magnetograms to the prediction of solar activity.

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Cosmic-ray intensities near the heliospheric current sheet throughout three solar activity cycles

Journal of Physics G Nuclear and Particle Physics ◽

10.1088/0954-3899/27/4/303 ◽

2001 ◽

Vol 27 (4) ◽

pp. 773-785 ◽

Cited By ~ 7

Author(s):

M A El-Borie

Keyword(s):

Solar Activity ◽

Current Sheet ◽

Cosmic Ray ◽

Heliospheric Current Sheet ◽

Activity Cycles ◽

Solar Activity Cycles

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MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

PHYSICS OF AURORAL PHENOMENA ◽

10.51981/2588-0039.2021.44.020 ◽

2021 ◽

Vol 44 ◽

pp. 85-91

Author(s):

V.N. Obridko ◽

◽

D.D. Sokoloff ◽

V.V. Pipin ◽

A.S. Shibalova ◽

...

Keyword(s):

Solar Activity ◽

Activity Cycle ◽

Solar Interior ◽

Local Fields ◽

Lower Atmosphere ◽

High Solar Activity ◽

Dynamo Model ◽

Sunspot Activity ◽

Geomagnetic Variations ◽

Near Surface

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

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Solar spectral irradiance variability of some chromospheric emission lines through the solar activity cycles 21-23

Serbian Astronomical Journal ◽

10.2298/saj160126001g ◽

2017 ◽

pp. 71-86

Author(s):

Ü.D. Göker ◽

M.Sh. Gigolashvili ◽

N. Kapanadze

Keyword(s):

Solar Activity ◽

Chemical Elements ◽

Wave Length ◽

Spectral Lines ◽

Spectral Irradiance ◽

Close Connection ◽

Solar Chromosphere ◽

Solar Spectral Irradiance ◽

Activity Cycles ◽

Solar Activity Cycles

A study of variations of solar spectral irradiance (SSI) in the wave-length ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used various data for ultraviolet (UV) spectral lines and international sunspot number (ISSN) from interactive data centers such as SME (NSSDC), UARS (GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by using the MATLsoftware package. In this respect, we revealed negative correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines originating in the solar chromosphere with the ISSN index during the unusually prolonged minimum between the solar activity cycles (SACs) 23 and 24. We also compared our results with the variations of solar activity indices obtained by the ground-based telescopes. Therefore, we found that plage regions decrease while facular areas are increasing in SAC 23. However, the decrease in plage regions is seen in small sunspot groups (SGs), contrary to this, these regions in large SGs are comparable to previous SACs or even larger as is also seen in facular areas. Nevertheless, negative correlations between ISSN and SSI data indicate that these variations are in close connection with the classes of sunspots/SGs, faculae and plage regions. Finally, we applied the time series analysis of spectral lines corresponding to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data. We found an unexpected increase in the 298.5 nm line for the Fe II ion. The variability of Fe II ion 298.5 nm line is in close connection with the facular areas and plage regions, and the sizes of these solar surface indices play an important role for the SSI variability, as well. So, we compared the connection between the sizes of faculae and plage regions, sunspots/SGs, chemical elements and SSI variability. Our future work will be the theoretical study of this connection and developing of a corresponding model.

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Does the mean-field α effect have any impact on the memory of the solar cycle?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937287 ◽

2020 ◽

Vol 642 ◽

pp. A51

Author(s):

Soumitra Hazra ◽

Allan Sacha Brun ◽

Dibyendu Nandy

Keyword(s):

Solar Cycle ◽

Mean Field ◽

Solar Dynamo ◽

Dynamo Model ◽

Solar Cycles ◽

Poloidal Field ◽

Flux Transport ◽

Solar Convection ◽

The Mean ◽

And Diffusion

Context. Predictions of solar cycle 24 obtained from advection-dominated and diffusion-dominated kinematic dynamo models are different if the Babcock–Leighton mechanism is the only source of the poloidal field. Some previous studies argue that the discrepancy arises due to different memories of the solar dynamo for advection- and diffusion-dominated solar convection zones. Aims. We aim to investigate the differences in solar cycle memory obtained from advection-dominated and diffusion-dominated kinematic solar dynamo models. Specifically, we explore whether inclusion of Parker’s mean-field α effect, in addition to the Babcock–Leighton mechanism, has any impact on the memory of the solar cycle. Methods. We used a kinematic flux transport solar dynamo model where poloidal field generation takes place due to both the Babcock–Leighton mechanism and the mean-field α effect. We additionally considered stochastic fluctuations in this model and explored cycle-to-cycle correlations between the polar field at minima and toroidal field at cycle maxima. Results. Solar dynamo memory is always limited to only one cycle in diffusion-dominated dynamo regimes while in advection-dominated regimes the memory is distributed over a few solar cycles. However, the addition of a mean-field α effect reduces the memory of the solar dynamo to within one cycle in the advection-dominated dynamo regime when there are no fluctuations in the mean-field α effect. When fluctuations are introduced in the mean-field poloidal source a more complex scenario is evident, with very weak but significant correlations emerging across a few cycles. Conclusions. Our results imply that inclusion of a mean-field α effect in the framework of a flux transport Babcock–Leighton dynamo model leads to additional complexities that may impact memory and predictability of predictive dynamo models of the solar cycle.

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