General solution for interplanetary magnetic field produced from stationary sources on the sun

It is well known that interplanetary space contains Parker's Archimedean spiral magnetic field, the components of which are respectively radial and longitudinal in the solar polar coordinates (r, θ, φ) and are intimately related to each other, depending on the solar wind velocity. In this paper, we present a general solution of the interplanetary magnetic field which is produced from time-independent sources fixed on the solar surface and contains the Parker field as a particular solution. The field is first classified broadly into two types called the φ-dependent (or nonzonal) and the φ-independent (or zonal) fields. The former field is further subdivided into two types, one is the so-called Parker type and the other is the vortex type which has no radial component. The resultant of these two fields exhibits the helical (or twisted) structure in space, tentatively introduced by Lee and Fisk. The zonal field is also subclassified into two; one is the radial-type zonal field and the other is the toroidal field. These two fields are mutually independent and therefore their resultant does not always coincide in direction with the Parker field.     

On the large-scale diffuse magnetic field of the sun

Although the sunspots migrate towards the equator, the large-scale weak diffuse magnetic fields of the Sun migrate poleward with the solar cycle, the polar field reversing at the time of the sunspot maxima. We apply the vector model of Dikpati and Choudhuri (1994, Paper I) to fit these observations. The dynamo layer at the base of the convection zone is taken to be the source of the diffuse field, which is then evolved in the convection zone subject to meridional circulation and turbulent diffusion. We find that the longitudinally averaged observational data can be fitted reasonably well both for positive and negative values of the-effect by adjusting the subsurface meridional flow suitably. The model will be extended in a future paper to include the decay of active regions as an extra source of the diffuse field, which may be necessary to explain the probable phase lag betweenB _r andB at lower latitudes.     

Differential rotation of the photospheric magnetic field

The differential rotation of the large-scale photospheric magnetic field has been investigated with an autocorrelation technique using synoptic charts of the photospheric field during the interval 1959–66. Near the equator the rotation period of the field is nearly the same as the rotation rate of long-lived sunspots studied by Newton and Nunn. Away from the equatorial zone the field has a significantly shorter rotation period than the spots. Over the entire range of latitudes investigated the average rotation period of the photospheric magnetic field was about 1 1/4 days less than the average rotation period of the material observed with Doppler shifts by Livingston and by Howard and Harvey. Near the equator the photospheric field results agree with the results obtained from recurrent sunspots, while above 15° the photospheric field rotation rates agree with the rotation rates of the K corona and the filaments.     

E-W motions of large-scale magnetic field structures of the sun

By applying a new method of processing daily full-disk magnetograms obtained at the Wilcox Solar Observatory at Stanford University, it has become possible to reveal the pattern of global E-W motions of field structures which appears to reflect large-scale convective plasma motions beneath the photosphere.Structures of E-W velocity of different sign extend from north to south, traversing the equator. The extent of the structures in longitude is 25°–45°, and the velocity amplitude reaches 0°.4–0°.5 day^-1 (60–70 m s^-1 at the equator). Boundaries of E-W flows of different sign correlate with strong, large-scale magnetic field hills. The lifetime of the velocity structures is comparable with that of magnetic field structures.     

New pulsar rotation measures and the Galactic magnetic field

We measured a sample of 150 pulsar rotation measures (RMs) using the 20-cm receiver of the Parkes 64-m radio telescope. 46 of the pulsars in our sample have not had their RM values previously published, whereas 104 pulsar RMs have been revised. We used a novel quadratic fitting algorithm to obtain an accurate RM from the calibrated polarization profiles recorded across 256 MHz of receiver bandwidth. The new data are used in conjunction with previously known dispersion measures and the NE2001 electron-density model to study models of the direction and magnitude of the Galactic magnetic field.     

White dwarfs with magnetic field and differential rotation

We compute classical white-dwarf models distorted by magnetic field and differential rotation. In the computations we implement a complex-plane strategy and a multiple-partition technique, which have been developed recently by the first author.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Interpretation of faraday rotation in the galactic magnetic field

The autocorrelation function of Faraday rotation measures is discussed in terms of different types of galactic field configurations. The autocorrelation function evaluated from published data of 139 radio galaxies and quasars is found to resemble a form typical for a quasi-longitudinal field, whereas the autocorrelation function of 38 pulsars turns out to be of the form expected for a longitudinal field. These observations are interpreted with respect to the position of the solar system relative to the neutral sheet in a quasi-longitudinal field configuration.Rotation measures calculated theoretically using a mathematical formulation of the quasi-longitudinal field model are adapted to experimental data. The resulting polarity of the global field structure is discussed in connection with the original dipole-like configuration the magnetic momentum vector of which is found to have been antiparallel to the angular momentum vector of the Galaxy. The relation between the field strength and the density of electrons is found to be consistent with earlier results.     

Photospheric magnetic field rotation: Rigid and differential

An autocorrelation of the direction of the large-scale photospheric magnetic field observed during 1959–1967 has yielded evidence that the field structure at some heliographic latitudes can display both differential rotation and rigid rotation properties.     

Small-scale background magnetic field on the sun in solar cycle 23

Based on SOHO/MDI data (an archive of magnetic maps with a resolution of ～2″), we have investigated the dynamics of the small-scale background magnetic field on the Sun in solar cycle 23. The cyclic variations and surface structure of the background magnetic field have been analyzed using the mean estimates of 〈B〉 and 〈B ²〉 of the observed magnetic field strength B for various solar surface areas and at various B levels. We have established that the cyclic variations of 〈2〉 at latitudes below 30° are essentially similar to those of the total radio flux F _10.7. A significant difference between the background magnetic fields in the northern and southern solar hemispheres persisting throughout the solar cycle has been detected. We have found the effect of background magnetic field growth toward the solar limb and concluded that the transversal component in the background magnetic field is significant. The relatively weak small-scale background magnetic fields are shown to form a special population with its own special laws of cyclic variation.     

Simulating the generation of the solar toroidal magnetic field by differential rotation

Within the kinematic dynamo theory, we construct a mathematical model for the evolution of the solar toroidal magnetic field, excited by the differential rotation of the convective zone in the presence of a poloidal field of a relic origin. We use a velocity profile obtained by decoding the data of helioseismological experiments. For the model of ideal magnetic hydrodynamics, we calculate the latitudinal profiles of the increasing-with-time toroidal field at different depths in the solar convection zone. It is found that, in the region of differential rotation, the excited toroidal field shows substantial fluctuations in magnitude with depth. Based on the simulations results, we propose an explanation for the “incorrect polarity” of magnetic bipolar sunspot groups in solar cycles.     

Turbulent viscosity,magnetic diffusivity,and heat conductivity under the influence of rotation and magnetic field

The old problem of turbulent diffusion is addressed to define the influence of rotation and magnetic field - the usual ingredients of astrophysical bodies - on the effective transport coefficients. Either rotation and magnetism produce the anisotropy and quenching. The tensorial structures of the diffusivities and their dependences on the angular velocity and the field strength are explicitly defined. An example of application of the theory to the global stellar circulation model is given and the implications for cosmic dynamos are briefly discussed.     

The relationship between meridional drift and rotation of the large-scale solar magnetic field

The pattern of torsional oscillations was detected in the rotation of the large-scale magnetic field using the method of two-dimensional correlation functions. The position of areas of fast and slow rotation agrees with the Doppler picture obtained by Ulrich et al. (1988). The torsional wave amplitude is 20–40 ms^–1 and increases with latitude. A strong correlation of the pattern of residual E-W rate with the meridional drift pattern, obtained from the same data, was determined. The sign of correlation is consistent with the results reported by Ward (1965).     

Solar rotation in the subphotospheric layers

The solar rotation rate at latitudes 0°, 15° and 30° has been inferred by averaging the results of 120 regions of 15°×15°, which have been studied over a total area of about 75° in latitude and 360° in longitude. A local helioseismology technique, the ring diagram analysis method, has been used to analyse the horizontal velocity vectors from about 0.95 R up to the surface. Our results are in very good agreement with those of other authors over most of the depth range. However, near the surface we find sharp local features which are not reported in other studies. The independent measurements of the rotation rate in the north and south hemispheres show asymmetries below 0.975 R . The data used are full-disc dopplergrams taken by Solar Oscillation Investigation/Michelson Doppler Imager (SOI/MDI) on board of the SOlar and Heliospheric Observatory (SOHO) during its first Dynamic Program, between 1996 May and June.     

Periodicities in the solar differential rotation,surface magnetic field and planetary configurations

Using Greenwich data on sunspot groups during 1874–1976, we have studied the temporal variations in the differential rotation parametersA andB by determining their values during moving time intervals of lengths 1–5 yr successively displaced by 1 yr. FFT analysis of the temporal variations ofB (orB/A) shows periodicities 18.3 ± 3 yr, 8.5 ± 1 yr, 3.9 ± 0.5 yr, 3.1 ± 0.2 yr, and 2.6 ± 0.2 yr at levels 2. This analysis also shows five more periodicities at levels 1–2. The maximum entropy method is used to set narrower limits on the values of these periods. The reality of the existence of all these periodicities ofB (orB/A ) except the one at 2.8 yr is confirmed by analyzing the simulated time series ofB andB/A with values ofA andB randomly distributed within the limits of their respective uncertainties. Four of the prominent periods ofB agree, within their uncertainties, with the known periods in the the large-scale photospheric magnetic field. The deviations from the average differential rotation are larger near the sunspot minima. On longer time scales, the variations in the amount of sunspot activity per unit time are well correlated to the variations in the amplitudes of the torsional oscillation represented by the 22-yr periodicity inB. All the periods inB found here are in good agreement with the synodic periods of two or more consecutive planets. The possibility of planetary configurations providing perturbations needed for the Sun's MHD torsional oscillations is speculated upon and briefly discussed.     

Rayleigh-Taylor instability of a two-fluid layer under a general rotation field and a horizontal magnetic field

In this paper the Rayleigh-Taylor instability (RTI) of a two-fluid layer system under the simultaneous action of a general rotation field and a horizontal magnetic field is presented. An approximate and an exact solution of the eigenvalue equation are calculated. These solutions are important not only to understand more deeply the physical problem but also to determine the correct numerical solutions. Numerical calculations are done for an unstable density stratification in the cases of horizontal magnetic field parallel and perpendicular to the horizontal component of the angular velocity. For an adverse density stratification, it is shown that in comparison to previous works, the horizontal magnetic field creates new angular areas (of the angle of propagation of the perturbation) at which the perturbation is stable and propagates as traveling waves. It is also shown that the vertical component of the angular velocity has a destabilizing effect because it works to eliminate the stable angular areas.     

The effect of toroidal magnetic field and differential rotation on self-gravitating polytropic models

In this paper we construct a polytropic model distorted by toroidal magnetic field and differential rotation. We then compute states of critical rotation of this model. In the computations we implement the so-called complex-plane strategy and multiple partition technique which are numerical methods deviced recently by the first author.