New indications of the 4-month oscillation in solar activity,atmospheric circulation and Earth's rotation

The 4-month oscillation, detected earlier by the same authors in geophysical and solar data series, is now confirmed by the analysis of other observations. In the present results the 4-month oscillation is better emphasized than in previous results, and the analysis of the new series confirms that the solar activity contribution to the global atmospheric circulation and consequently to the Earth's rotation is not negligeable. It is shown that in the effective atmospheric angular momentum and Earth's rotation, its amplitude is slightly above the amplitude of the oscillation known as the Madden-Julian cycle.     

50-day Oscillation of Length-of-day Change

Variations of Earth’s rotation rate (length-of-day, LOD) occur over a wide range of time scales from a few hours to the geological age. Studies showed that the 50-day fluctuation exists in LOD change. In the present paper, the authors use wavelet technique to study the 50-day oscillation in LOD series. Temporal variations of the oscillation are presented in this work. After analyzing the axial component of atmospheric angular momentum (AAM) and oceanic angular momentum (OAM), the 50-day periodic signal is also found in atmospheric and oceanic motion with remarkable time-variation. Meanwhile, the 50-day oscillation of the axial AAM is in good consistence with that of LOD change. This suggests that the 50-day oscillation of LOD change is mainly excited by the axial AAM. Possible origin of the oscillation for Earth system is discussed in the end of this paper.     

The sun's rotation and perturbations of geopotential height and temperature fields in the stratosphere

The morphology of a solar activity effect apparently connected with the Sun's rotation and showing up in 25-day and 13.6-day oscillations of stratospheric geopotential and temperature fields is analysed in this study. The used data cover the height range between roughly 20 and 30 km and a timespan from July 1965 to October 1971. Most prominent responses are found for zonal harmonic wave number 1 at the oscillation period of 25 days (solar rotation period modulated by seasonal changes) and for the zonally averaged meteorological quantities at the oscillation period of 13.6 days. Additional statistically significant effects show up in the zonal harmonics with wave number 1 and 3 at half the solar rotation period and in the zonal means with periodicities near 25–27 days. The results point towards a modulation of the quasistationary stratospheric planetary wave with a positive geopotential anomaly around roughly 180° longitude by solar activity changes. The direct physical mechanisms of this Sun-climate relationship are not yet clear, but it can be concluded that atmospheric dynamics is an important factor for its morphology and that downward propagation of such effects seems possible and should be investigated in future studies.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Torsional oscillations of the Sun

A series of digitized synoptic observations of solar magnetic and velocity fields has been carried out at the Mount Wilson Observatory since 1967. In recent studies (Howard and LaBonte, 1980; LaBonte and Howard, 1981), the existence of slow, large-scale torsional (toroidal) oscillations of the Sun has been demonstrated. Two modes have been identified. The first is a travelling wave, symmetric about the equator, with wave number 2 per hemisphere. The pattern-alternately slower and faster than the average rotation-starts at the poles and drifts to the equator in an interval of 22 years. At any one latitude on the Sun, the period of the oscillation is 11 years, and the amplitude is 3 m s^-1. The magnetic flux emergence that is seen as the solar cycle occurs on average at the latitude of one shear zone of this oscillation. The amplitude of the shear is quite constant from the polar latitudes to the equator. The other mode of torsional oscillation, superposed on the first mode, is a wave number 1 per hemisphere pattern consisting of faster than average rotation at high latitudes around solar maximum and faster than average rotation at low latitudes near solar minimum. The amplitude of the effect is about 5 m s^-1. For the first mode, the close relationship in latitude between the activity-related magnetic flux eruption and the torsional shear zone suggests strongly that there is a close connection between these motions and the cycle mechanism. It has been suggested (Yoshimura, 1981; Schüssler, 1981) that the effect is caused by a subsurface Lorentz force wave resulting from the dynamo action of magnetic flux ropes. But, this seems unlikely because of the high latitudes at which the shear wave is seen to originate and the constancy of the magnitude of the shear throughout the life time of the wave.     

Possible dynamical evolution of the rotation of Venus since formation

The past evolution of the rotation of Venus has been studied by a numerical integration method using the hypothesis that only solar tidal torques and core-mantle coupling have been active since formation. It is found quite conceivable that Venus had originally a rotation similar to the other planets and has evolved in 4.5×10⁹ years from a rapid and direct rotation (12-hour spin period and nearly zero obliquity) to the present slow retrograde one.While the solid tidal torque may be quite efficient in despinning the planet, a thermally driven atmospheric tidal torque has the capability to drive the obliquity from 0° towards 180° and to stabilize the spin axis in the latter position. The effect of a liquid core is discussed and it is shown that core-mantle friction hastens the latter part of the evolution and makes even stronger the state of equilibrium at 180°. The model assumes a nearly stable balance between solid and atmospheric tides at the current rotation rate interpreting the present 243 day spin period as being very close to the limiting value.A large family of solutions allowing for the evolution, in a few billions years, of a rapid prograde rotation to the present state have been found. Noticeably different histories of evolution are observed when the initial conditions and the values of the physical parameters are slightly modified, but generally the principal trend is maintained.The proposed evolutionary explanation of the current rotation of Venus has led us to place constraints on the solid bodyQ and on the magnitude of the atmospheric tidal torque. While the constraints seem rather severe in the absence of core-mantle friction (aQ15 at the annual frequency is required, and a dominant diurnal thermal response in the atmosphere is needed), for a large range of values of the core's viscosity, the liquid core effect allows us to relax somewhat these constraints: a solid bodyQ of the order 40 can then be allowed. ThisQ value implies that a semi-diurnal ground pressure oscillation of 2 mb is needed in the atmosphere in order for a stable balance to occur between the solid and atmospheric tides at the current rotation rate. No model of atmospheric tides on Venus has been attempted in this study, however the value of 2 mb agrees well with that predicted by the model given in Dobrovolskis (1978).     

High-frequency oscillations in the corona observed at the 1983 eclipse

We detected excess oscillatory power at 0.25–2.0 Hz in a coronal loop in the 1983 Indonesian total solar eclipse. In this second-generation experiment enlarging upon the work of Pasachoff and Landman (1984), we observed in two frequency channels, one coronal and one continuum, to monitor atmospheric and instrumental effects. We briefly discuss the effects of an oscillation near 1 Hz on the coronal heating problem.Visiting Colleague, Institute for Astronomy, University of Hawaii.     

The common oscillations of solar activity,the geomagnetic field,and the Earth's rotation

An oscillation with a period around 5.5 years is identified as being common to the geomagnetic field, the Earth's rotation, and solar activity variations. The large extrema of the cross-correlation functions and their oscillatory character are considered to be indicators of a physical relation between geophysical and solar phenomena.     

Evidence for the phi-dependent rotation-oscillation of the Sun (and for the driving mechanism of the asymmetric dynamo)

Longitude-dependent oscillations of the solar rotation are derived from the 27-day averages of the photospheric velocity data. Two pairs of prominent periods are obtained. Their harmonic means correspond to a semiannual variation and to the first harmonic of the latter. To explain the origin of the oscillation the corona and the interplanetary material are supposed to rotate parallel to the planetary plane with an inclination to the solar equator. The non-uniform shearing around the equator is assumed to result in oscillation with a period of half of a year.     

Comparative Analyses of Brookhaven National Laboratory Nuclear Decay Measurements and Super-Kamiokande Solar Neutrino Measurements: Neutrinos and Neutrino-Induced Beta-Decays as Probes of the Deep Solar Interior

An experiment carried out at the Brookhaven National Laboratory over a period of almost 8 years acquired 364 measurements of the beta-decay rates of a sample of \({}^{32}\mbox{Si}\) and, for comparison, of a sample of \({}^{36}\mbox{Cl}\). The experimenters reported finding “small periodic annual deviations of the data points from an exponential decay?…?of uncertain origin”. We find that power-spectrum and spectrogram analyses of these datasets show evidence not only of the annual oscillations, but also of transient oscillations with frequencies near 11 year^?1 and 12.5 year^?1. Similar analyses of 358 measurements of the solar neutrino flux acquired by the Super-Kamiokande neutrino observatory over a period of about 5 years yield evidence of an oscillation near 12.5 year^?1 and another near 9.5 year^?1. An oscillation near 12.5 year^?1 is compatible with the influence of rotation of the radiative zone. We suggest that an oscillation near 9.5 year^?1 may be indicative of rotation of the solar core, and that an oscillation near 11 year^?1 may have its origin in a tachocline between the core and the radiative zone. Modulation of the solar neutrino flux may be attributed to an influence of the Sun’s internal magnetic field by the Resonant Spin Flavor Precession (RSFP) mechanism, suggesting that neutrinos and neutrino-induced beta decays can provide information about the deep solar interior.     

Helioseismic Constraints on Rotation and Magnetic Fields in the Solar Core

In recent years, more and more precise measurements have been made of solar oscillation frequencies and line widths. From space, the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data has led to much progress. From the ground, networks, like Global Oscillation Network Group (GONG), Taiwanese Oscillation Network (TON), and Birmingham Solar Oscillations Network (BiSON) have also led to much progress. The sharpened and enriched oscillation spectrum of data have been critically complemented by advances in the treatments of the opacities and the equation of state. All of this has led to a significantly more precise probing of the solar core. Here we discuss the progress made and suggest how the core may be better probed with seismic data on-hand. In particular, we review our knowledge of the rotation and structure of the core. We further argue that much may be learned about the core by exploiting the line width data from the aforementioned sources. Line-width data can be used to place sharper constraints on core properties, like the degree to which the Sun rotates on a single axis and the upper limit on magnetic fields that may be buried in the core.     

Solar magnetic cycle dependence in corotating modulation of galactic cosmic rays

We study the temporal evolution of cosmic ray intensity during ～27-day Carrington rotation periods applying the method of superposed epoch analysis. We discuss about the average oscillations in the galactic cosmic ray intensity, as observed by ground based neutron monitors, during the course of Carrington rotation in low solar activity conditions and in different polarity states of the heliosphere (A<0 and A>0). During minimum and decreasing phases in low solar activity conditions, we compare the oscillation in one polarity state with that observed in other polarity state in similar phases of solar activity. We find difference in the evolution and amplitude of ～27-day variation during A<0 and A>0 epoch. We also compare the average variations in cosmic ray intensity with the simultaneous variations of solar wind parameters such as solar wind speed and interplanetary magnetic field strength. From the correlation analysis between the cosmic ray intensity and the solar wind speed during the course of Carrington rotation, we find that the correlation is stronger for A>0 than A<0.     

Periodic variation and phase analysis of grouped solar flare with sunspot activity

Studies on the periodic variation and the phase relationship between different solar activity indicators are useful for understanding the long-term evolution of solar activity cycles.Here we report the statistical analysis of grouped solar flare(GSF) and sunspot number(SN) during the time interval from January 1965 to March 2009.We find that,(1) the significant periodicities of both GSF and SN are related to the differential rotation periodicity,the quasi-biennial oscillation(QBO),and the eleven-year Schwabe cycle(ESC),but the specific values are not absolutely identical;(2) the ESC signal of GSF lags behind that of SN with an average of 7.8 months during the considered time interval,which implies that the systematic phase delays between GSF and SN originate from the inter-solar-cycle signal.Our results may provide evidence about the storage of magnetic energy in the corona.     

Helioseismology and the solar cycle: Past, present and future

A major goal of helioseismology is to understand the mechanism of the solar cycle. In this paper, some results of helioseismic observations relevant to the cycle are briefly reviewed, the current state-of-the-art is discussed, and near-term future directions are sketched out. Topics covered include the internal rotation rate; activity-related parameter variations; the tachocline; far-side imaging; the torsional oscillation; and meridional flows.     

Radiative transfer and solar oscillations

Solar Physics - We consider the atmospheric behaviour of solar oscillations in a model including a detailed, semi-empirical atmosphere. Equations of radial and non-radial oscillation, with...     

4.7s nearly periodic oscillations superimposed on the solar microwave great burst of 28 March 1976

An unusual fast oscillation was found superimposed on the solar great burst of 28 March 1976, as measured at 7 GHz. The period of the osculation was 4.7 ± 0.9s, defined over the entire duration of the event. The amplitude of the oscillation was proportional to the flux density, in the range 50 < S < 3000 solar flux units. The degree of circular polarization has not shown any fast periodic time structures.Presently merged with CNP, Observatório Nacional.     

Test of a differential photometer for extinction gradient correction in full-disk helioseismology

The ground based full disk velocity Doppler measurements used in helioseismology suffer from an atmospheric noise component when the sky transparency is not perfect. It is due to the non uniform integration of the line of sight component of the solar rotation produced by the differential atmospheric extinction across the direction of the solar equator. A simple two-channel differential photometer is proposed for measuring this differential extinction. The first laboratory tests of this instrument show that it has the capability of performing the required correction without adding a significant level of new instrumental noise contribution.

     

Rotation of Plasma in Sunspots

In this paper we present the results of a sunspot rotation study using Abastumani Astrophysical Observatory photoheliogram data for 324 sunspots. The rotation amplitudes vary in theinebreak 2–64° range (with maximum at 12–14°), and the periods around 0–20 days (with maximum atinebreak 4–6 days). It could be concluded that sunspot rotations are rather inhomogeneous and asymmetric, but several types of sunspots are distinguished by their rotational parameters.During solar activity maximum, sunspot average rotation periods and amplitudes slightly increase. This can be affected by the increase of sunspot magnetic flux tube depth. So we can suppose that sunspot formation during solar activity is connected to a rise of magnetic tubes from deeper layers of the solar photosphere, strengthening the processes within the tube and causing variations in rotation.There is a linear relation between tilt-angle oscillation periods and amplitudes, showing higher amplitudes for large periods. The variations of those periods and especially amplitudes have a periodical shape for all types of sunspots and correlate well with the solar activity maxima with a phase delay of about 1–2 years.     

Variations in air density,satellite drag coefficient and atmospheric rotation rate from analysis of the orbit of 1966-92D

Variations in air density, the satellite drag coefficient, and the atmospheric rotation rate at 60°S lat and 120–130 km height during the period September 1968–June 1969 have been determined from analysis of the high-eccentricity orbit of the 4th Molyniya 1 upper-stage rocket body, 1966-92D. The results show good correlation between density increases and strong geomagnetic activity, although solar flares of equal geomagnetic index value do not consistently produce density changes of equal magnitude. A 30 per cent semi-annual variation was observed, but there was no indication of the 50 per cent lower thermosphere seasonal-latitudinal variation that was predicted from the CIRA 1972 atmosphere. The satellite drag coefficient was observed to begin decreasing with height at an altitude where the molecular mean free path, λ, was twice the satellite's length. The coefficient decreased to a value approaching 1.0 as the satellite's perigee height fell below the altitude where λ was one-half the length. A mean atmospheric rotation rate of 1.1 ± 0.1 Earth rot/day was obtained for the last 20 days of decay. However, variations were observed with west-to-east wind speeds of ?100 m/sec measured for a local time of 13 hr.     

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.     

On the calculation of spurious velocity signal produced by atmospheric differential extinction in whole-disk oscillation measurements

The systematic diurnal signal drift in full-disk solar oscillation measurements has been calculated taking into account differential rotation, the inclination of the rotational axis of the Sun with respect to the picture plane, the limb-darkening function and a realistic estimation of the sky transparency, slightly variable during the day. An illustration of this method on the Kumbel (U.S.S.R.) IRIS data is presented and discussed.