Differential rotation of the sun determined tracing sunspots and oscillations of sunspot tilt angle

The time and spatial characteristics of 324 large sunspots (S50 millionths of the solar hemisphere) selected from the Abastumani Astrophysical Observatory photoheliogram collection (1950–1990) have been studied. The variations of sunspot angular rotation velocity residuals and oscillations of sunspot tilt angle were analyzed. It has been shown that the differential rotation rate of selected sunspots correlates on average with the solar cycle. The deceleration of differential rotation of large sunspots begins on the ascending arm of the activity curve and ends on the descending arm reaching minimum near the epochs of solar activity maxima. This behavior disappears during the 21st cycle. The amplitudes and periods of sunspot tilt-angle oscillations correlate well with the solar activity cycle. Near the epochs of activity maximum there appear sunspots with large amplitudes and periods showing a significant scatter while the scatter near the minimum is rather low. We also found evidence of phase difference between the sunspot angular rotation velocity and the amplitudes and periods of tilt-angle oscillations.     

Propagation of a quasi bi-annual impulse close to the moment of the solar magnetic field polarity changing

Some particular features of solar differential rotation have been recently revealed in Abastumani Astrophysical Observatory: in the northern hemisphere of the Sun a propagation of a quasi bi-annual impulse of the rotation residual from the high latitudes to the equator, during the time interval of 1979–1981, was statistically demonstrated. Japaridze and Gigolashvili (1992) proposed that this event might be related with the change of magnetic polarity in the northern hemisphere of the Sun in 1981.To prove this hypothesis an investigation of the MHD equations in the local system of coordinates has been carried out. A homogeneous equation with partial derivatives in the linear approximation was obtained. Its solution is presented analytically. The disturbance of velocity enhances especially at the moment of reversal of magnetic field polarity.     

Fine structure of motions in a quiescent prominence

The Ca⁺ K line of the quiescent prominence of 15 October 1969 observed at the Abastumani Astrophysical Observatory of the Academy of Sciences of Georgia, U.S.S.R. is studied in detail. The behaviour of various fragments of the prominence with the line-of-sight Doppler velocities is investigated for different places of the prominence along the spectrum height. Due to superposition of the fragments and the radial velocities a complex non-gaussian profile of the spectral line is formed. Decomposition of the non-gaussian profile into suitable gaussian ones is made with a computer yielding objectivity and high accuracy. The rms error for the intensities in the decomposition is about 5%.It is found that the components into which the Ca⁺ K line decomposes at each level, are traced while proceeding from one photometric section to another throughout the spectral height.A hypothesis on the preferably filamentary structure of the prominence is put forward.     

A study on the various types of arrhythmias in relation to the polarity reversal of the solar magnetic field

Over the last few years, various researches have reached the conclusion that cosmic ray variations and geomagnetic disturbances are related to the condition of the human physiological state. In this study, medical data concerning the number of incidents of different types of cardiac arrhythmias for the time period 1983–1992, which refer to 1902 patients in Tbilisi, Georgia, were used. The smoothing method and the Pearson r-coefficients were used to examine the possible effect of different solar and geomagnetic activity parameters and cosmic ray intensity variations on the different types of arrhythmias. The time interval under examination was separated into two different time periods, which coincided with the polarity reversal of the solar magnetic field occurred in the years 1989–1990, and as a result, a different behavior of all the above-mentioned parameters as well as of the different types of arrhythmias was noticed during the two time intervals. In addition, changing of polarity sign of the solar magnetic field was found to affect the sign of correlation between the incidence of arrhythmias and the aforementioned parameters. The primary and secondary maxima observed in the solar parameters during the solar cycle 22, also appeared in several types of arrhythmias with a time lag of about 5 months.     

A model of a quiescent prominence on the basis of studying the K Ca+ line fine structure

A model of a quiescent prominence with nonparallel structural elements, based on a study of the K Ca⁺ line fine structure of two quiescent prominences. The dependences of the radial velocities on the height found for the structural elements making up the prominence (Gigolashvili and Zhugzhda, 1982) gives the information on the inner spatial structure of the prominence. Analysis of the available data allows us to suggest an alternative model of a quiescent prominence.     

Determination of the total amount of hydrogen atoms in a quiescent prominence

A brief quantitative review of the determination of the chemical composition of the Sun and stars is given. The method of estimation of the total amount of hydrogen atoms in a prominence is considered.The values of relative abundances of some infrequent elements in the solar atmosphere are refined using metal emission lines in the spectrum of a quiescent prominence. The most probable values of relative abundances for itrium _Y1×10^–9, zirconium _Zr2×10^–9, and scandium _Sc3.8×10^–9 are derived.     

Investigation of the Differential Rotation by H�� Filaments and Long-Lived Magnetic Features for Solar Activity Cycles 20 and 21

For solar activity Cycles 20 and 21 (1966??C?1985) the solar differential rotation has been investigated using H?? filaments and relatively small-scale long-lived magnetic features with negative and positive polarities. We used annual averaged angular velocities of quiescent H?? filaments from H?? photoheliograms of the Abastumani Astrophysical Observatory film collection and selected long-lived magnetic features from the McIntosh atlas (McIntosh, Willock, and Thompson, Atlas of Stackplots, NGDC, 1991). We have determined coefficients of Faye??s formulas for H?? filaments as well as for long-lived magnetic features and have found that for Solar Cycles 20 and 21 the H?? filaments have lower rotation rates and rotated more differentially than the long-lived magnetic features.     

An investigation of macroscopic motions using the Ca+ lines in the prominence of 15 October 1969

The fine structure of the quiescent prominence of 15 October 1969, observed at Abastumani Astrophysical Observatory of the Academy of Sciences of Georgia, U.S.S.R. with the horizontal telescope, is studied.The complex non-gaussian Ca⁺ K line profiles are decomposed into gaussian components and the distribution of the velocity field is plotted.Estimating the direction of the motion by the appearance of the spectral line and by the distribution of the velocity field, we conclude that there is a left-handed screw. Having used the high dispersion spectral data published, we find that prominences showing left-handed screws fall in the northern hemisphere of the Sun and those with right-handed screws in the southern hemisphere.The influence of Coriolis acceleration on quiescent prominences is discussed.     

Revealing of periodicities in the variations of differential rotation of the Sun

It is presumed that a north-southern asymmetry of a solid-body rotation of large spots, depending on even and odd solar activity cycles (Gigolashvili and Khutsishvili 1 1989, 1990) may possibly be explained by the asymmetry of the appearance of large structures with strong magnetic fields in the corresponding hemispheres. Spectral analysis of the observational data shows the presence of cyclic variations of differential rotation of large- and middle-sized spots. Variations of differential rotation of small spots are either absent or overlapped by noise. It is also supposed that the discovered and most frequently realized component of the spectrum of solar differential rotation variations — a four-years periodicity — may be either a real phenomenon or the result of overlapping of multiple quasi bi-annual variations.