Solar neutrino in relation to solar wind particles

A relationship was found earlier (Basu, 1982, 1992) between the solar neutrino flux and the flux of solar wind particles received on the Earth. However, the data used in these analyses have recently been revised and extended. This prompted us to re-examine the relationship using the new updated solar neutrino data base. The present analysis confirms the earlier findings and establishes that the two quantities are related at statistically significant levels. This suggests that the two may have a common cause of origin in the interior of the solar atmosphere and needs further investigation.     

Solar neutrino and solar particles

Examination of the most recent data on solar neutrino shows that there is a statistically significant relationship between solar neutrino and solar particles.     

Solar neutrino data and the 11-year solar activity cycle

Recent data on solar neutrino flux have been analysed and it is shown that there is a statistically significant variation of solar neutrino flux data with the solar activity cycle. Thus the observation suggests that the solar activity cycle is due to the pulsating characters of the nuclear energy generation in the interior of the Sun.     

Solar neutrino flux,cosmic rays,and the solar activity cycle

It is suggested that the experimental data on the solar neutrino flux as measured by Davis and his collaborators from 1970 to 1982 vary with the solar activity cycle to a very high level of statistical significance for all the available tests of the hypothesis (e.g., (t-test, ²-test, run test, Wilcoxon-Mann-Whitney test) when the solar neutrino flux data are computed from the weighted moving averages of order 5. The above tests have also been applied to the data that have been generated by the Monte Carlo simulation with production rate and background rate parameters that are typical of those in the actual experiment. It is shown that the Monte Carlo simulated data do not indicate a variation within the solar cycle. Thus the moving average data strongly favours the variation within the solar activity cycle.     

Quasi-biennial periodicity in the solar neutrino flux and its relation to the solar structure

By analysing the observed results on the neutrino flux from the Sun for the years 1970–1978, it is shown that the production rate of the neutrinos at the central core of the Sun had been varying with a period almost equal to 26 months for these years. This so-called quasi-biennial periodicity in this rate suggests that the physical state of the central core of the Sun must have been modulated with this period through the variation of physical parameters as temperature and the chemical composition at the central core of the Sun. An idea to interpret this observed periodicity is thus proposed by taking the variations of these parameters into consideration. Some supporting evidence on this periodicity can be found on the variations of the solar activity as the relative sunspot numbers and the equatorial rotation speed of the Sun.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Radius of the Sun in relation to solar activity

Radius of the Sun has been measured by many researchers using various techniques over more than three centuries, which demonstrated that the solar radius is not constant in time, but exhibits significant variations. As in cases of variations in most other observed features of the Sun, correlation has been saught between solar radius and sunspot numbers, the latter being recognized as the best index of solar activity. However, such studies have so far produced completely contradictory results, viz., both correlation and anticorrelation have been reported. The reason appears to be the data used, which is highly inhomogeneous. I report here a statistically significant relationship between solar radius and sunspot numbers in the sense that a larger diameter of the Sun is associated with higher levels of solar activity, when a homogenised data base covering observations over the last three centuries is used for solar radius.     

Solar neutron observations and their relation to solar flare acceleration problems

We review the current observational knowledge on the production of neutrons in association with solar flares. From a study of the observations it is shown that unique information can be obtained on the spectral properties of accelerated ions produced during the flare. Also, the abundance of ³He/H in the photosphere can be directly determined. We also review the current interpretations of all available neutron observations and in particular highlight the uncertainties, and provide guide posts for future experiments.     

Solar soft X-rays and solar activity

Flare-associated soft X-ray bursts (8–12 Å) are examined for 283 events observed by OSO-III. These bursts are shown to be predominantly thermal in nature. Their time-profiles are roughly similar to those of the associated H flares, although the X-ray burst begins about two minutes earlier, on the average. The strength of the soft X-ray burst is directly related to the area and brilliance of the flare, the age and flare-richness of the associated plage, and the general level of solar activity at the time of the burst. The peak enhancements in the soft X-ray and H emission rates during flares are of the same order of magnitude, as are the total flare energies radiated at these wavelengths. We estimate that soft X-radiation accounts for up to 10% of a flare's total electromagnetic emission.NRC/NAS Resident Research Associate.     

Solar soft X-rays and solar activity

Peak fluxes of flare-associated 8–12 Å X-ray bursts occur at or near the time of the maximum energy content of the soft X-ray source volume. The amplitudes of flare-associated bursts may thus be used as a measure of the energy deposited in the source volume by non-thermal electrons and other processes. In the mean, the soft X-ray burst amplitude is apparently independent of the occurrence of a type III event. This is interpreted to indicate that electrons accelerated by the type III process do not directly participate in establishing the soft X-ray source volume.     

Solar soft X-rays and solar activity

Soft solar X-rays (8 gl 12 Å) were observed from OSO-III. An analysis of the X-ray enhancements associated with 165 solar flares revealed that there is a tendency for a weak soft X-ray enhancement to precede the cm- burst and H flare. The peak soft X-ray flux follows the cm- peak by about 4 min, on the average. Additionally, it was found that flare-rich active centers tend to produce flares which are stronger X-ray and cm- emitters than are flares which take place in flare-poor active centers.     

Solar energy cycle and its relation to geomagnetic activity

It is suggested that recurrent and nonrecurrent geomagnetic disturbances which are related to the release of solar magnetic energy in the form of unipolar and bipolar magnetic regions respectively, are connected with the variations in the solar energy source. The true beginning of the solar cycle takes place when unipolar magnetic regions start to develop, i.e, when nuclear energy generation becomes dominant over the neutrino energy loss according to the photon-neutrino coupling theory.     

The solar neutrino problem

The observed capture rate for solar neutrinos in the ³⁷Cl detector is lower than the predicted capture rate. This discrepancy between theory and observation is known as the ‘solar neutrino problem’. I review the basic elements in this problem: the detector efficiency, the theory of stellar (solar) evolution, the nuclear physics of energy generation, and the uncertainties in the predictions. I also answer the questions of: So What? and What Next?

     

Small scale solar magnetic fields and their relation to various solar activity indices

Correlation studies between various solar activity indices and a long time series of annual sums of the maximum value of solar magnetic field intensity, observed for each group of sunspots during each passage of it over the visible solar hemisphere, have pointed out a couple of interesting points. First, the faculae have a significant contribution to the numerical representation of the small scale solar magnetic coefficients and low standard errors of estimation to the above mentioned maximum values of the solar magnetic field. These properties give to the area index an important physical meaning which is a first approximation to the small scale solar magnetic fields expressed by the above-mentioned maximum values of it. Finally, the main point which comes out is that long term studies of the solar magnetic fields, especially extrapolated studies to the past, could be supported by photospheric indices of the solar activity. This paper constitutes the expanded version of a report presented to theIAU Symposium No. 102 ‘Solar and Stellar magnetic fields: Origins and coronal effects’, held in Zürich 2–6 August, 1982.     

The nature of the solar activity and its relation to solar cosmic-ray production

The long-term variation of the solar activity and its nature are statistically analysed by using the data on the relative sunspot numbers for the last two hundred years. Based on this analysis, the occurrence frequency of large solar flares in the past is estimated to find a clue to deduce the production rate of high-energy particles from the Sun in the past. According to the results from the present study, during the period that the solar activity was much higher than that observed during solar cycle No. 19, this production rate must have been very much higher than that being currently observed. Such a period might have been hazardous to life on Earth because of the destruction of the ozone layer by the bombardment of solar cosmic rays.     

Effect of neutrino magnetic moment on solar neutrino observations

Neutrino spin precession effects in the magnetic field of the Sun are considered as an explanation of the outcome of Davis' solar neutrino experiments. Theoretically, it is possible to account for a neutrino magnetic moment only as the result of the interaction of the electromagnetic field with charged particles into which the neutrino can transform virtually. The currently accepted theory of weak interactions (the two component neutrino andV-A interactions) forbids a resulting magnetic moment interaction with the electromagnetic field for all such virtual processes. Modifications of this theory are considered to find out whether an appreciable precession effect is permitted within the experimentally established limits. It is found that the value for the neutrino magnetic moment evaluated under these theoretically anomalous circumstances is still so small that only the largest possible estimate for the magnetic field strength in the Sun's interior would cause the required effect.The author has received scholarship support from the Latin American Scholarship Program of American Universities during the preparation of this work.     

On the solar neutrino puzzle

Based on the available solar neutrino and helioseismic data a possible astrophysical solution of the solar neutrino problem is proposed. Forthcoming high and low energy neutrino measurements and helioseismic experiments will allow one to check the considered possibility.     

Solar radio fluxes as indices of solar activity

The daily solar radio flux values at 9400, 3750, 2000 and 1000 MHz and at 2800 MHz observed since 1957 at Toyokawa and Ottawa, respectively, have been used to provide new information on the solar radio fluxes as indices of solar activity. After an examination of the yearly mean values at each frequency, another investigation based on mean ratios during periods of 18 or 6 months indicates that a close connection is observed between the radio fluxes in the cm region and that anomalies related to calibration problems can be detected. The regression analysis of the daily values of the fluxes during at least 25 years and a special test on the sensitivity may provide final information on the stability of the data with respect to time and solar activity. The method is capable of detecting long-term trends corresponding to instrumental drifts. Such information is essential to our understanding of anomalies detected in the observations of u.v. and X-ray irradiances. However, such a method is based on a linear relationship. When a quadratic form, as it is observed in the decimeter region, is adopted, the effect of the various levels of activity in a solar cycle must be considered.     

A model independent approach to future solar neutrino experiments

We discuss here what model independent information about properties of neutrinos and of the sun can be obtained from future solar neutrino experiments (SNO, Super-Kamiokande). It is shown that in the general case of transitions of solar ν_e's into νμ and/or ντ the initial ⁸B neutrino flux can be measured by the observation of NC events. From the CC measurements the ν_e survival probability can be determined as a function of neutrino energy. The general case of transitions of solar ν_e's into active as well as sterile neutrinos is considered. A number of relations between measurable quantities the test of which will allow to answer the question whether there are sterile neutrinos in the solar neutrino flux on the earth are derived. Transitions of solar ν_e's into active and sterile states due to neutrino mixing and Dirac magnetic moments or into active left-handed neutrinos and active right-handed antineutrinos due to neutrino mixing and Majorana transition magnetic moments are also considered. It is shown that future solar neutrino experiments will allow to distinguish between the cases of Dirac and Majorana magnetic moments.     

Chemistry of the solar neutrino experiment

The possibility of chemical ‘trapping’ of the Ar⁺ ion in the reaction $$v{\text{ }} + {\text{ }}^{{\text{37}}} {\text{Cl}} \to {\text{ }}^{{\text{37}}} {\text{Ar}}^{\text{ + }} + {\text{ e}}^ - ,$$ when it takes place in tetrachloroethylene (C₂Cl₄) liquid, is examined in detail. It is concluded that if trapping does take place, the rate is much smaller than the charge neutralization rate. Therefore, this niechanism cannot explain the observed small rate of Ar production in the Brookhaven solar neutrino experiment. A detailed examination of a number of experiments which are sensitive to possible trapping lends strong support to this conclusion.     

On the proposed associations of solar neutrino flux with solar particles,cosmic rays,and the solar activity cycle

It has been proposed that the observed solar neutrino flux exhibits important correlations with solar particles, galactic cosmic rays, and the sunspot cycle, with the latter correlation being opposite in phase and lagging behind the sunspot cycle by about one year. Re-examination of the data-available interval 1971–1981, employing various tests of statistical significance, however, suggests that such a claim is, at present, unwarrantable. For example, on the associations of solar neutrino flux and cosmic-ray flux with the Ap geomagnetic index, neither were found to be statistically significant (at the 95% level of confidence), regardless of the choice of lag (-1, 0, or +1 yr). Presuming linear fits, all correlations with Ap had coefficients of determination (r ², where r is the linear correlation coefficient) less than 16%, meaning that 16% of the variation in the selected test parameters could be explained by the variation in Ap. Similarly, on the associations of solar neutrino flux and cosmic ray flux with sunspot number, only the latter association proved to be of statistical importance. Using the best linear fits, the correlation between yearly averages of solar neutrino flux and sunspot number had r ² 19%, the correlation between weighted moving averages (of order 5) of solar neutrino flux and sunspot number had r ² 45%, and the correlation between cosmic-ray flux and sunspot number had r ² 76%, all correlations being inverse associations. Solar neutrino flux was found not to correlate strongly with cosmic-ray flux, and the Ap geomagnetic index was found not to correlate strongly with sunspot number.