A remark on the statistical distribution of radio burst duration during solar noise storms

We reanalyze histograms of durations and frequency bandwidths of individual bursts during solar radio noise storms. We find that the well-known maxima these histograms exhibit towards small durations and bandwidths actually correspond to a constant burst emission probability over the whole range of observed durations and bandwidths.     

Limits on radiative decays of solar neutrinos from measurements during a total solar eclipse

During the 1999 total solar eclipse we intended to search for photons emitted by a possible radiative decay of the heavier component of solar neutrinos, using two telescopes: an airborne one, and another at mountain altitude, in Romania(the NOTTE experiment). The weather conditions did not allow us to perform the measurements. Alternatively, we analyzed a video tape of the eclipse offered to us by a local television, obtaining some qualitative estimations on the neutrino lifetimes. We present also a first report on the observations made 21 June 2001, from Zambia. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of short-period variation in solar activity

We introduce two methods to detect short-period variation in solar activity.These are called amplitude of low frequency fluctuation(ALFF) and fractional amplitude of low frequency fluctuation(FALFF). We find a positive correlation between short-period variation and 11-year variation of solar activity using these two methods.Through ALFF,we find that solar activity over a short period becomes intensive when the 11-year solar activity is intensive. The ALFF value of the short period activity varies with the peak in sunspot number as a quadratic function. Through FALFF we find that the ratio of short-period spectral intensity to intensity over the whole period of solar activity will increase when the 11-year period of solar activity is intensive.The short-period FALFF value varies with the peak in sunspot number according to a cubic function. Using ALFF,we obtain a yearly series of solar activity that varies over a short period of 1–5 yr from 1860 to 2003,which shows an obvious periodicity of about 22 yr,33 yr,11 yr and a century. These short period variations show good correlations with long term variations in solar activity.     

A solar cycle variation of the interplanetary magnetic field

Measurements of the north-south (B _z component of the interplanetary field as compiled by King (1975) when organized into yearly histograms of the values of ¦B _z ¦ reveal the following. (1) The histograms decrease exponentially from a maximum occurrence frequency at the value ¦B _z ¦ = 0. (2) The slope of the exponential on a semi-log plot varies systematically roughly in phase with the sunspot number in such a way that the probability of large values of ¦B _z ¦ is much greater in the years near sunspot maximum than in the years near sunspot minimum. (3) There is a sparsely populated high-value tail, for which the data are too meager to discern any solar cycle variation. The high-value tail is perhaps associated with travelling interplanetary disturbances. (4) The solar cycle variations of B _z and the ordinary indicators of solar activity are roughly correlated. (5) The solar cycle variation of B _z is distinctly different than that of the solar wind speed and that of the geomagnetic Ap disturbance index.Now at the Aerospace Corporation, El Segundo, Calif. 90245, U.S.A.     

A solar cycle variation of the interplanetary magnetic field configuration

The representation of the sector boundaries, published by Svalgaard (1974, 1975) in a superposed 27-days Bartels format showed that they have a significant preference to occur in certain days of the solar rotation. Further study of these data, as well as of the polarized days in the vicinity of them, pointed out that during the epoch of extrema of the 11-year cycle there is a well-established 2-sector structure, on the average. On the contrary, a mean 4-sector structure is more prominent during the intermediate years.     

A cyclical period variation detected in the updated orbital period analysis of TV Columbae

Two CCD photometries of the intermediate polar TV Columbae are made for obtaining two updated eclipse timings with high precision. There is an interval time ～17 yr since the last mid-eclipse time observed in 1991. Thus, the new mid-eclipse times might offer an opportunity to check the previous orbital ephemerides. A calculation indicates that the orbital ephemeris derived by Augusteijn et al. (Astron. Astrophys. Suppl. Ser. 107:219, 1994) should be corrected. Based on the proper linear ephemeris (Hellier in Mon. Not. R. Astron. Soc. 264:132, 1993), the new orbital period analysis suggests a cyclical period variation in the O–C diagram of TV Columbae. Using Applegate’s mechanism to explain the periodic oscillation in the O–C diagram, the required energy is larger than the energy that a M0-type star can afford over a complete variation period of ～31.0(±3.0) yr. Thus, the light travel-time effect indicates that the tertiary component in TV Columbae may be a dwarf with a low mass, which is near the lower mass limit of ～0.08M _⊙ as long as the inclination of the third body is high enough.     

A remark on the apsidal motion in slose binary systems

Dynamics of the apsidal motion in close binary systems are discussed. A comparison between the solution for the perfect fluid system and the solution for the rigid system reveals that some overall viscosity in the interior of distorted star has a right tendency to reconcile the observation of apsidal motion with the theory of internal structure.     

A search for 5 min periodic structure in solar 2 cm emission

Two hundred and eighty-five hours of solar data obtained from the University of Iowa 2 cm radiometer during 1968–1969 were analyzed for evidence of periodic structure related to the 5 min periodic chromospheric oscillations detected in optical line emissions. A power spectral analysis of the data failed to show any statistically significant (> 96 % confidence) periodic activity in the frequency range 1–15 mHz (periods of 1–16 min) for data organized according to solar activity in H, soft solar X-rays (2–12 ), and several microwave frequencies (3–15 GHz).A small shift in power from low to higher frequencies in the power spectrum of the 2 cm data was found to be correlated with H and X-ray activity. This power shift is attributed to a relative increase in chromospheric turbulence at altitudes common to H, X-ray, and 2 cm emission.Consistent statistical analyses of previous works reporting evidence for oscillations at microwave and extreme-ultraviolet frequencies indicate that confidence in these previous results is marginal.A model for chromospheric oscillation bursts in quiescent supergranules is incorporated into a statistical analysis of the power spectrum detectability of the oscillations to understand the negative results obtained.     

Note on a periodic intensity variation of the radio source Cassiopeia-A

Data in addition to our previous paper are presented in order to confirm a periodicity in the radiant flux from the radio source Cassiopeia-A. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 253–257 (May 2007).     

Latitudinal variation of the solar limb-darkening function

In an effort to monitor solar limb-darkening variability, the continuum radiation intensity at 550 nm over the outermost 32 arcseconds of the limb is measured at various solar latitudes. Using the Finite Fourier Transform Definition, the edge location of the Sun is determined for a series of scan amplitudes at each of the observed positions. The differential radius is the difference between edge locations for a fixed pair of scan amplitudes, and is a quantity which characterizes the slope of the solar limb-darkening function. Utilizing the differential radius, such observations offer the possibility of revealing a latitudinal variation of the photospheric temperature gradient and could provide clues to the mechanisms and variability of energy transport out of the Sun. These observations began in 1988 with measurements at 24 separate limb positions and include observations since 1990 when 36 positions were observed. The daily differential radius measurements for each position that is free of contamination from solar active regions are weighted according to the corresponding daily variance and averaged to obtain an overall value at each position for the observing season. The results indicate that during the 1991 observing season, there were regions near 20°N latitude and 30°S latitude on the Sun where the differential radius values were significantly greater than surrounding regions. This suggests that perturbations to the temperature gradient occur in latitudinally localized regions and persist for at least several months. It is shown that this phenomenon could have the same origin as the observed latitudinal variations of surface temperature and could also speak to the question of a lag time between the cycles of irradiance and magnetic variation.     

Quasi-periodic variation in the solar neutrino flux revisited

Neutrino capture rate data from the Homestake chlorine experiment (1970–1990) has been spectrally analysed. The data were smoothed by a 4-month equally-spaced sequence and by a cubic spline polynomial approximation. Fourier (FFT), maximum entropy spectrum analysis (MESA), and power spectrum analysis (PSA) employing the Blackman-Tukey window were used. The significant periodicities obtained are: 1 ± 0.1, 1.4 ± 0.2, 2.4 ± 0.2, 5 ± 0.2, and 11 ± 1.5 years. A possible correlation with similar coincident periods in other solar-terrestrial phenomena is discussed.     

A quantity characterizing variation of observed magnetic twist in solar active regions

An alternative parameter R_J_z is introduced as the ratio of one of two kinds of opposite-sign current to the total current and is used to investigate the relationship between this quantity and the hemispheric helicity sign rule(HSR) that has been established by a series of previous statistical studies. The classification of current in each hemisphere obeys the following rule: if the product of the current and the corresponding longitudinal field component contributes a consistent sign with respect to the HSR,it is called "HSR-compliant" current,otherwise it is called "HSR-noncompliant" current. Firstly,consistency between the butterfly diagram of R_J_z and current helicity was obtained in a statistical study.Active regions with R_J_zsmaller than 0.5 tend to obey the HSR whereas those with R_J_z greater than 0.5 tend to disobey it. The "HSR-compliant" current systems have a 60% probability of realization compared to 40% for "HSR-noncompliant" current systems. Overall,the HSR is violated for active regions in which the "HSR-noncompliant" current is greater than the "HSR-compliant" current. Secondly,the parameter R_J_z was subsequently used to study the evolution of current systems in the case analyses of flare-productive active regions NOAA AR 11158 and AR 11283. It is found that there is a "R_J_z-quasistationary" phase that is relatively flare quiescent and "R_J_z-dynamic" phase that is characterized by the occurrence of large flares.     

The horizontal variation of temperature in the low solar photosphere

Observations of the rms intensity fluctuations in the continuum obtained by Pravdjuk et al. (Solnechnye Dannye, No. 2, p. 70, 1974) from white-light photographs made with the Soviet Stratospheric Solar Observatory are analyzed to obtain a horizontal temperature-fluctuation amplitude as a function of depth. The results indicate that temperature fluctuations increase with depth monotonically from a small value at ₅₀₀₀0.5 (cf. Figure 2). The initial rise of T appears quite steep, having a slope of approximately 20 K km^–1. The model of Wilson (Solar Phys. 9, 303, 1969) is incompatible with the data. Convective flux in the present model is approximately 6% of the total flux at ₅₀₀₀ = 1.     

Radial variation of differential rotation in the solar electron corona

Long-lived brightness structures in the solar electron corona persist over many solar rotation periods and permit an observational determination of coronal magnetic tracer rotation as a function of latitude and height in the solar atmosphere. For observations over 1964–1976 spanning solar cycle 20, we compare the latitude dependence of rotation at two heights in the corona. Comparison of rotation rates from East and West limbs and from independent computational procedures is used to estimate uncertainty. Time-averaged rotation rates based on three methods of analysis demonstrate that, on average, coronal differential rotation decreases with height from 1.125 to 1.5 R _S. The observed radial variation of differential rotation implies a scale height of approximately 0.7 R _S for coronal differential rotation.Model calculations for a simple MHD loop show that magnetic connections between high and low latitudes may produce the observed radial variations of magnetic tracer rotation. If the observed tracer rotation represents the rotation of open magnetic field lines as well as that of closed loops, the small scale height for differential rotation suggests that the rotation of solar magnetic fields at the base of the solar wind may be only weakly latitude dependent. If, instead, closed loops account completely for the radial gradients of rotation, outward extrapolation of electron coronal rotation may not describe magnetic field rotation at the solar wind source. Inward extrapolations of observed rotation rates suggest that magnetic field and plasma are coupled a few hundredths of a solar radius beneath the photosphere.     

Temporal variation of large scale flows in the solar interior

We attempt to detect short-term temporal variations in the rotation rate and other large scale velocity fields in the outer part of the solar convection zone using the ring diagram technique applied to Michelson Doppler Imager (MDI) data. The measured velocity field shows variations by about 10 m/s on the scale of few days.     

Prediction of maximum sunspot number in solar cycle 23

Instantaneous predictions of the maximum monthly smoothed sunspot number in solar cycle 23 have been made with a linear regressive model, which gives the predicted maximum value as a function of the smoothed sunspot numbers corresponding to a given month from the minimum in all preceding cycles. These predictions indicate that the intensity of solar activity in the current cycle will be at an average level.     

Fluctuations of energetic particle flux during solar cycle based on measurements in the solar wind,in the magnetosphere,and at Earth

We present the results of our studies of the cosmic-ray fluctuations in the frequency range 10⁻⁴−1.67 × 10⁻³ Hz based on energetic particle flux measurements on spacecraft in the solar wind, in the magnetosphere, and at Earth in the 11-year solar cycle. The cosmic-ray fluctuation spectrum is shown to have an 11-year modulation related to the solar cycle. A different behavior of the level of energetic particle fluctuations measured in different regions of space is observed for cosmic rays of different origins. We conclude that the new, previously unknown phenomenon of 11-year modulation of the cosmic-ray fluctuation spectrum has been established. A possible explanation of this phenomenon is given.     

The solar cycle influence on the lunar magnetic variation at Istanbul

The dependence of the amplitude of the lunar daily geomagnetic variation on sunspot number and magnetic activity is investigated using data from Istanbul for the years 1952–1968. Annual and seasonal values of the amplitudes of the lunar diurnal and lunar semidiurnal variation are determined, and compared with sunspot number and magnetic activity using partial correlation techniques.