A forecast of solar activity in cycle 21

Based on the similarity in the variation of sunspot number in the ascending branch between Cycle 21 and Cycles 3, 8, 18, we predict that the solar activity in Cycle 21 will probably be high, with a maximum smoothed monthly mean relative number of 149.4 and the maximum epoch will be 1979.7.     

On the rotation of large-scale background fields in the 21st cycle of solar activity

We study some peculiarities of the time variation of dipole components in the longitudinal field distribution in individual low-latitude belts of the Sun. For analyzing the horizontal dipole rotation and variations of amplitudes we used magnetic and H data.From 1979 to 1981 the rotation of the dipoles of the northern and southern low-latitude belts (0°–30° N and 10°–40° S) occurs with periods of about 26.8 days (N) and 28.2 days (S), in agreement with the results reported by Antonucci, Hoeksema, and Scherrer (1990) and Hoeksema and Scherrer (1987). A uniform rotation of the low-latitude dipoles of these belts continued until the end of 1981. Following the next coincidence of the magnetic poles in longitude the dipoles change in their rotation character. During about 15–20 rotations the low-latitude dipoles co-rotate with a new period close to the Carrington period. This is followed by a rapid (in 3–5 rotations) transition of the poles to a new stable state, also with the Carrington rotation period. The change in rotation and dynamics of the low-latitude dipoles at the end of 1981-beginning of 1982 can be explained either by a mutual penetration of the fields of different hemispheres to the opposite hemisphere or by the onset of the formation of relatively shortlived (15–20 rotations) structures which cover the entire low-latitude belt.Unlike the trajectories of the poles, the dipole amplitudes of the low-latitude belts showed a significant variability. However, simultaneous increases of the amplitudes in both hemispheres correlated with times at which the dipole poles coincide in longitude, and the greatest increase corresponded to the moment of merging of the dipole poles early in 1982. This suggests that sources of large-scale structures of the background field in the low-latitude belts of the Sun or the related fields interacted when the dipole poles coincided.     

On the short term variations of solar activity during solar cycle 21

Short-term variations of the last solar activity cycle were studied by the flare and coronal indices using Gleissberg method. Systematic short-term variations are found from their course during the 21st solar activity cycle. Comparison of their autocorrelograms constructed by the new set of data obtained from the magnitude of the fluctuations showed us the existence of the phase shift between the temporal variations of the two indices.     

On the increase of solar activity in the southern hemisphere during solar cycle 21

The present paper investigates the north-south asymmetry for major flares (solar cycles 19 and 20), type II radio bursts (solar cycles 19,20 and 21), white light flares (solar cycle 19,20 and 21), and gamma ray bursts, hard X-ray bursts and coronal mass ejections (solar cycle 21). The results are compared with the found asymmetry in favour of the northern hemisphere during solar cycles 19 and 20 in favour of the southern hemisphere during solar cycle 21.     

Occurrence of solar decimetric spike bursts over a period of 4 years during the 21st cycle

A total number of 460 DCIM events, single or groups, were observed during the period of October 1980 to December 1984 with the Weissenau spectrograph as dynamic film spectra. Several parameters describing these data were evaluated statistically and the main features were discussed in context with associated burst types.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

The fuzzy forecast of the activity of solar active regions

In this paper, the theory and method of fuzzy mathematics are applied to forecast the activity of solar active regions. According to the correlation between flares and several solar activity indices of active regions, the membership functions are constructed to comprehensively evaluate and predict the activity of solar active regions. By means of data reduction and analysis, some comparatively accurate results of prediction have been obtained. The accuracy of predicting the activity grades of active regions is higher than 97%. This implies that the method of fuzzy forecast is a good one for solar activity prediction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Double magnetic cycle of solar activity

The source of the poloidal magnetic field was fixed using a uniform series of surface low-resolution magnetic field observations begun at Wilcox Solar Observatory at Stanford. The results obtained confirm the idea that low-frequency dynamo waves with a period approximately equal to 22 years and a high-frequency wave of a quasi-two-year period can coexist. It seems that an interaction between these components in the convection zone takes place on the Sun. Surface large-scale solar magnetic fields are analyzed using a two-dimensional Fourier method technique to study the poloidal field distribution. The first harmonic approximately equals the period of the magnetic cycle, appears at all latitudes, and reaches its the maximum value in the polar regions. Moreover, spectral analyses of axisymmetric magnetic field derivative in time found that the second important harmonic of a period approximately equal to two years appears at all latitudes. This second high-frequency harmonic dominates the polar latitude regions at the same time as the low-frequency one.     

Short-time variations of solar neutrinos and solar activity cycle

It is shown from the statistical analysis of the sunspot data and solar neutrino data that both the data exhibits 5, 10, 15, 20, 25, and 30 months period and these periods may be g-mode oscillation of the core associated with the solar activity.     

On the 11-years cycle of solar activity

Each 11-years cycle of solar activity consists of two processes with different physical properties. The variety of shapes of the 11-years curves depends on the way these processes overlap.All events in the photosphere, chromosphere and corona, and all kinds of emissions like the radio- and corpuscular emissions take part in these two processes.Events taking place in the magnetosphere, ionosphere, troposphere and perhaps some chemical and biological events reflect the essential properties of the 11-years cycle.     

Simulations of the mean solar magnetic field during sunspot cycle 21

Regarding new bipolar magnetic regions as sources of flux, we have computed the evolution of the photospheric magnetic field during 1976–1984 and derived the corresponding evolution of the mean line-of-sight field as seen from Earth. We obtained a good, but imperfect, agreement between the observed mean field and the field computed for a nominal choice of flux transport parameters. Also, we determined the response of the computed mean field to variations in the transport parameters and the source properties. The results lead us to regard the mean-field evolution as a random-walk process with dissipation. New eruptions of flux produce the random walk, and together differential rotation, meridional flow (if present), and diffusion provide the dissipation. The net effect of each new source depends on its strength and orientation (relative to the strength and orientation of the mean field) and on the time elapsed before the next eruption (relative to the decay time of the field). Thus the mean field evolves principally due to the contributions of the larger sources, which produce a strong, gradually evolving field near sunspot maximum but a weak, sporadically evolving field near sunspot minimum.E. O. Hulburt Center for Space Research.Laboratory for Computational Physics.     

Simulations of the gross solar magnetic field during sunspot cycle 21

Regarding new bipolar magnetic regions as sources of flux, we have simulated the evolution of the radial component of the solar photospheric magnetic field during 1976–1984 with a spatial resolution of about 34 000 km, and have derived the corresponding evolution of its absolute value averaged over the visible disk. For nominal values of the transport parameters, this simulated gross field is in close, though imperfect, agreement with the observed gross field and its associated indices of solar activity. By analyzing the response of the simulated gross field to variations in the transport parameters and the source properties, we find that the simulated field originates in newly erupted bipolar regions. The lifetimes of these regions are almost always less than 3 mo. Consequently, the strength of the simulated gross field is a measure of the current level of solar activity, and any recurrent patterns with lifetimes in excess of 6 mo must reflect the continuing eruption of new flux at active longitudes rather than the persistence of old flux in long-lived magnetic structures.E. O. Hulburt Center for Space Research.Laboratory for Computational Physics.Berkeley Research Associates, Springfield, VA.     

Surface magnetic fields during the solar activity cycle

We examine magnetic field measurements from Mount Wilson that cover the solar surface over a 13 1/2 year interval, from 1967 to mid-1980. Seen in long-term averages, the sunspot latitudes are characterized by fields of preceding polarity, while the polar fields are built up by a few discrete flows of following polarity fields. These drift speeds average about 10 m s^-1 in latitude - slower early in the cycle and faster later in the cycle - and result from a large-scale poleward displacement of field lines, not diffusion. Weak field plots show essentially the same pattern as the stronger fields, and both data indicate that the large-scale field patterns result only from fields emerging at active region latitudes. The total magnetic flux over the solar surface varies only by a factor of about 3 from minimum to a very strong maximum (1979). Magnetic flux is highly concentrated toward the solar equator; only about 1% of the flux is at the poles. Magnetic flux appears at the solar surface at a rate which is sufficient to create all the flux that is seen at the solar surface within a period of only 10 days. Flux can spread relatively rapidly over the solar surface from outbreaks of activity. This is presumably caused by diffusion. In general, magnetic field lines at the photospheric level are nearly radial.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Prediction for the amplitude of solar cycle 24 from the pattern of activity near the cycle minimum

Correlations are investigated between the pattern of solar activity described by the smoothed monthly relative sunspot numbers (Wolf numbers) near the minimum of a solar cycle and the cycle amplitude. The closest correlation is found between the amplitude of a solar cycle and the sum of the decrease in activity over two years prior to the cycle minimum and the increase in activity over two years after the minimum; the correlation coefficient between these parameters is 0.92. This parameter is used as a precursor to predict the amplitude of solar cycle 24, which is expected to reach its maximum amplitude (85 ± 12) in February 2014. Based on the correlations between the mean parameters of solar cycles, cycle 24 is expected to last for approximately 11.3 years and the minimum of the next cycle 25 is predicted for May 2020.     

Evidence for two maxima of activity in the 20th solar cycle

Analysis of the 5303 Å coronal line intensity and of the sunspot activity during the period 1962–1970 confirms the existence of two distinct maxima of solar activity, in accordance with the previous findings of Gnevyshev for the period 1954–1960.     

Observation of hysteresis between solar activity indicators andp-mode frequency shifts for solar cycle 22

Using intermediate degreep-mode frequency data sets for solar cycle 22, we find that the frequency shifts and magnetic activity indicators show a “hysteresis” phenomenon. It is observed that the magnetic indices follow different paths for the ascending and descending phases of the solar cycle while for radiative indices, the separation between the paths are well within the error limits.     

A two-component solar cycle

From a previous analysis of a long series of geomagnetic data, we came to the conclusion that, during 91.5% of the time, geomagnetic activity is controlled by the solar wind flow at the Earth's orbit.In this paper, we consider the flow of the solar wind plasma in a coronal field whose source is a dipole. The temporal evolution of the dipole source as well as any small scale evolution occurring in the associated coronal field topology can be closely monitored from the latitudinal distribution of the wind velocity.In the geomagnetic data series, the index Aa is closely linked to the wind velocity at the power 2.25. From this data set, we can reconstruct the behavior of the solar dipole field from 1868 onward.The main results of our analysis are as follows. The solar cycle has two distinct components, dipole and toroidal, of which the respective cycles are out of phase. The toroidal component is strongly linked, with a 5–6 yr delay, to the preceding dipole component. This finding is in contradistinction to the view that the dipole field is a result of the poleward migration of the decaying toroidal field. This result should contribute to improve our understanding of the Sun's cyclical behaviour.     

A technique for predicting the amplitude of the solar cycle

Predictions of the amplitude of the last three solar cycles have demonstrated the value and accuracy of the group of prediction methods known as the precursor techniques. These are based on a correlation between cycle amplitude and phenomena observed on the Sun, or originating from the Sun, during the declining phase of the cycle or at solar minimum. In many cases, precursor predictions make use of the long record of geomagnetic disturbance indices, assuming that these indices are indicative of solar phenomena such as the occurrence of coronal holes.This paper describes a precursor technique for predicting the amplitude of the solar cycle using geomagnetic indices. The technique is accurate — it would have predicted each of the last 11 cycles with a typical error of less than 20 in sunspot number. It has also advantage that a prediction of the lower limit of the amplitude can be made throughout the declining phase, this limit building to a final value at the onset of the new cycle.