Periodicities in the north-south asymmetry of solar activity

This paper tries to cast additional evidence on the proposed periodic behaviour of the N-S asymmetry in sudden disappearances (SD) of solar prominences (Vizoso and Ballester, 1987). We have performed a Blackman-Tukey power spectrum of the values of the SD N-S asymmetry and the results shows a significant peak, above 95% confidence level, at 12.4 years, another peak at 2.3 years fails to be statistically significant. Moreover, power spectrum performed with the values of N-S asymmetry of flare number and flare index (Vizoso and Ballester (1987) display significant peaks, above 95% confidence level, around 3.1–3.2 years.     

Periodic variation of the north-south asymmetry of solar activity phenomena

We report here a study of various solar activity phenomena occurring in both north and south hemispheres of the Sun during solar cycles 8–23. In the study we have used sunspot data for the period 1832–1976, flare index data for the period 1936-1993, Hα flare data 1993–1998 and solar active prominences data for the period 1957–1998. Earlier Verma reported long-term cyclic period in N-S asymmetry and also that the N-S asymmetry of solar activity phenomena during solar cycles 21, 22, 23 and 24 will be south dominated and the N-S asymmetry will shift to north hemisphere in solar cycle 25. The present study shows that the N-S asymmetry during solar cycles 22 and 23 are southern dominated as suggested by Verma.     

On the north-south asymmetry in the solar wind

The orientations of tangential discontinuities seen by Mariner 4 are interpreted as implying a sector dependent asymmetry in the north-south component of the solar-wind flow. In two sectors, fast solar wind streams had a southward motion relative to slow streams, in one sector the reverse obtained, and in the remaining sector the asymmetry was not clearly defined. We interpret this as being due to greater pressure in the north hemisphere in two sectors and greater pressure in the south hemisphere in one. It is possible this asymmetry could produce a small average southward magnetic field component.     

Polarization of Jupiter: Semiannual variations in the north-south asymmetry

The analysis of the previous (1981–1999) and recent (2000–2007) observations of Jupiter has confirmed the semiannual variations in the north-south asymmetry of polarized radiation in the polar regions of the planet. The processes of polar aerosol formation are modulated by the position of the planet relative to the solar equator.     

Seasonal north-south asymmetry in solar radiation incident on jupiter's atmosphere

Although the orbital eccentricity and axial tilt are small, the near-temporal coincidence of perihelion and the northernmost excursion of the subsolar point produce asymmetries in the solar radiation incident on Jupiter's atmosphere. Calculations of the incident radiation and the latitudinal gradient of the insolation are presented. North-south asymmetries in the zonal wind and morphology of the large-scale cloud systems observed by Voyagers 1 and 2 are cited. In the absence of an identified internal mechanism capable of generating the observed asymmetries, seasonal forcing of this magnitude should be considered.     

The north-south asymmetry of sunspot areas during solar cycle 22

We have analyzed the asymmetry of sunspot areas during the current solar cycle 22, finding that it has been statistically significant and that the shape of the underlying trend within the full asymmetry time series (1874–1993) indicates that the dominance of solar activity has started to shift, during the current cycle, from the northern hemisphere to the southern one.     

The north-south asymmetry of solar filaments separately at low and high latitudes in solar cycle 23

We present the results of a study on the north-south asymmetry of solar filaments at low(50°) and high(60°) latitudes using daily filament numbers from January 1998 to November 2008(solar cycle 23). It is found that the northern hemisphere is dominant at low latitudes for cycle 23. However, a similar asymmetry does not occur for solar filaments at high latitudes. The present study indicates that the hemispheric asymmetry of solar filaments at high latitudes in a cycle appears to have little connection with that at low latitudes. Our results support that the observed magnetic fields at high latitudes include two components: one comes from the emergence of the magnetic fields from the solar interior and the other comes from the drift of the magnetic activity at low latitudes.     

The north-south asymmetry of polarization of Jupiter: The causes of seasonal variations

We present new results obtained from the analysis of the seasonal variations in the asymmetry of polarization of light reflected by Jupiter. From the 23-year set of observations, the anticorrelation between the asymmetries of polarization and insolation has been revealed. The mechanism explaining the observed seasonal variations of polarization has been proposed. The core of this mechanism is the effect of temperature changes in the planetary stratosphere on the processes of the stratospheric aerosol haze formation. Additional irregular factors that may influence the observed polarization asymmetry are considered.     

Long-term variations in total solar irradiance

For more than a decade total solar irradiance has been monitored simultaneously from space by different satellites. The detection of total solar irradiance variations by satellite-based experiments during the past decade and a half has stimulated modeling efforts to help identify their causes and to provide estimates of irradiance data, using proxy indicators of solar activity, for time intervals when no satellite observations exist. In this paper total solar irradiance observed by the Nimbus-7/ERB, SMM/ACRIM I, and UARS/ACRIM II radiometers is modeled with the Photometric Sunspot Index and the Mg II core-to-wing ratio. Since the formation of the Mg II line is very similar to that of the Ca II K line, the Mg core-to-wing ratio, derived from the irradiance observations of the Nimbus-7 and NOAA9 satellites, is used as a proxy for the bright magnetic elements. It is shown that the observed changes in total solar irradiance are underestimated by the proxy models at the time of maximum and during the beginning of the declining portion of solar cycle 22 similar to behavior just before the maximum of solar cycle 21. This disagreement between total irradiance observations and their model estimates is indicative of the fact that the underlying physical mechanism of the changes observed in the solar radiative output is not well-understood. Furthermore, the uncertainties in the proxy data used for irradiance modeling and the resulting limitation of the models should be taken into account, especially when the irradiance models are used for climatic studies.     

Spatial distribution of the N-S asymmetry of solar activity and its time variations

The 1943–2001 data on the brightness of the coronal green λ530.3 nm line are used to investigate the surface distribution of the north-south (N-S) asymmetry index A. Synoptic maps of the asymmetry index in 784 successive Carrington rotations have been constructed. The results are presented in the form of a movie that visualizes the time variation in the spatial distribution of the asymmetry. Examination of a series of synoptic maps shows that the time variation in the general distribution of the A index over the solar surface has a number of peculiar features. In particular, the latitude-longitude regions with the dominance of the green line brightness in one of the hemispheres are replaced by similar (in shape) regions with its dominance in the other hemisphere after 14–18 rotations-in other words, the map, as it were, turns into its negative. This may be a manifestation of the quasi-biennial oscillations in the N-S asymmetry. The synodic rotation period of the asymmetry “structures” has been determined. It has turned out to be equal to the period of the fast coronal rotation mode found previously from the large-scale brightness distribution of the coronal green line, i.e., this is 27 days on the equator and slightly more than 28 days at high latitudes. The N-S asymmetry and its characteristics should be taken into account when considering the dynamo mechanism.     

On time variations of the solar differential rotation law and asymmetry of the global distribution of the solar activity

The relation between the systematic time variations of the solar differential rotation at middle latitudes and the asymmetry of global distribution of the solar activity is discussed in connection with the study of the maintenance of the solar differential rotation. The systematic variations at middle latitudes are inferred from a peculiar correlation in the time variations of the solar differential rotation which is shown in this paper to be implied in the data of Howard and Harvey (1970) of spectroscopic measurements of rotational velocities. If we adopt the working hypothesis of the solar equatorial acceleration maintained by the angular momentum transport due to the very large scale convection, the two phenomena are related through the concurrent presence of the neighboring modes with the presumed dominant mode of the very large scale convection.     

Long-term persistence of solar activity

We examine the question of whether or not the non-periodic variations in solar activity are caused by a white-noise, random process. The Hurst exponent, which characterizes the persistence of a time series, is evaluated for the series of¹⁴C data for the time interval from about 6000 BC to 1950 AD. We find a constant Hurst exponent, suggesting that solar activity in the frequency range from 100 to 3000 years includes an important continuum component in addition to the well-known periodic variations. The value we calculate,H 0.8, is significantly larger than the value of 0.5 that would correspond to variations produced by a white-noise process. This value is in good agreement with the results for the monthly sunspot data reported elsewhere, indicating that the physics that produces the continuum is a correlated random process and that it is the same type of process over a wide range of time interval lengths.     

Long-term prediction of solar activity

After reviewing the various methods used so far in the long-term prediction of solar activity, we have opted to use methods based on the 80-year period and probability considerations. Our predictions for Cycle No. 21 are:

• 1.Maximum of the annual average Wolf number: 54 – 94
• 2.Minimum of the annual average Wolf number: 0 – 4
• 3.Epoch of maximum: first half of 1981 - first half of 1983
• 4.Epoch of minimum: first half of 1976 - first half of 1977

A comparison of our predictions with others is made.     

Long-term persistence of solar activity

The solar irradiante has been found to change by 0.1% over the recent solar cycle. A change of irradiante of about 0.5% is required to effect the Earth's climate. How frequently can a variation of this size be expected? We examine the question of the persistence of non-periodic variations in solar activity. The Hürst exponent, which characterizes the persistence of a time series (Mandelbrot and Wallis, 1969), is evaluated for the series of¹⁴ C data for the time interval from about 6000 BC to 1950 AD (Stuiver and Pearson, 1986). We find a constant Hürst exponent, suggesting that solar activity in the frequency range of from 100 to 3000 years includes an important continuum component in addition to the well-known periodic variations. The value we calculate,H ≈ 0.8, is significantly larger than the value of 0.5 that would correspond to variations produced by a white-noise process. This value is in good agreement with the results for the monthly sunspot data reported elsewhere, indicating that the physics that produces the continuum is a correlated random process (Ruzmaikin et al., 1992), and that it is the same type of process over a wide range of time interval lengths. We conclude that the time period over which an irradiance change of 0.5% can be expected to occur is significantly shorter than that which would be expected for variations produced by a white-noise process. The full paper has been submitted to Solar Physics. Part of the research decribed here was carried out by JPL, Caltech under a contract with NASA.     

Chaotic behavior of the north-south asymmetry of sunspots?

North-south asymmetry in the distribution of sunspots was examined. Weak correlations between north-south asymmetry and sunspot number were found in several time lags. Higuchi's fractal dimension (1988) was calculated to evaluate irregularity in north-south asymmetry. The fractal dimension obtained is 1.90 ± 0.01 and this implies that the north-south asymmetry is highly irregular. The method of Sugihara and May (1990), based on the nonlinear prediction method, was used to distinguish between deterministic chaos and noise. The results do not confirm the idea that north-south asymmetry is an example of deterministic chaos.     

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.     

Long term variations in solar flare activity

A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm^-2 in an event with kinetic energy above 10 MeV) andR ₀ (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R₀ values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged flux (ˉJ, cm^-2 S^-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average flux estimates for time durations 〈T〉 exceeding 10³ yr, are free from such uncertainties. The long-term averaged ˉJ values obtained over different time scales (10⁴ - 10⁶ yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 10⁵ yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 10¹⁵ cm^-2 during the last million years.     

North-South asymmetry of solar dynamo in the current activity cycle

An explanation is suggested for the north-south asymmetry of the polar magnetic field reversal in the current cycle of solar activity. The contribution of the Babcock-Leighton mechanism to the poloidal field generation is estimated using sunspot data for the current activity cycle. Estimations are performed separately for the northern and southern hemispheres. The contribution of the northern hemisphere exceeded considerably that of the southern hemisphere during the initial stage of the cycle. This is the probable reason for the earlier reversal of the northern polar field. The estimated contributions of the Babcock-Leighton mechanism are considerably smaller than similar estimations for the previous activity cycles. A relatively weak (<1 G) large-scale polar field can be expected for the next activity minimum.     

Evolution and nature of north-south asymmetry in the heliospheric current sheet

The nature and evolution of north-south asymmetry in the heliospheric current sheet (HCS) has been investigated using solar and interplanetary magnetic field (IMF) observations for the past few solar cycles. The mean heliographic latitude of the HCS (averaged over the solar longitude) a ₀ is found to be non-zero during many solar rotations indicating that the large-scale solar magnetic field is more ordered in a system where the origin is shifted away from the centre of the Sun. We have shown that the asymmetry in HCS manifests in different forms depending on the transition heliographic latitude of the reversal of dominant polarity of the IMF ( _T) and the difference in the maximum latitudinal extension of the HCS in the two solar hemispheres (). The classification of the observed asymmetry during 1971–1985 and its effect on IMF observations near Earth has been studied. We have also inferred the sign of _T during 1947–1971 using inferred IMF polarity data. The observed sign reversals of _T suggest the importance of periodicities less than the solar cycle period to be associated with the evolution of asymmetry in HCS. Asymmetry in sunspot activity about the solar equator does not seem to relate consistently well with the asymmetry in HCS about the heliographic equator.     

Rescaled range analysis of the asymmetry of solar activity

Previous studies of the north-south asymmetry of solar activity (e.g., Carbonell, Oliver, and Ballester, 1993; Oliver and Ballester, 1994) suggest that the asymmetry time series can be represented by means of a multicomponent model made up of a long-term trend, a weak sinusoidal component (with a period close to 12.1 years) and a dominant random process. Here, we have used the rescaled range analysis to study the valuation of the stochastic component of the asymmetry. To avoid the influence of the trend and the sinusoidal component on the result, we have removed both from the original time series. The value obtained for the Hurst exponent (0.717 ± 0.002) suggests that the non-periodic component is a correlated random process.