We present a systematic description of the asymmetric shapes the Stokes line profiles exhibit in sunspots. These asymmetries seem to be caused by gradients of both magnetic field and velocity in the photospheres of sunspots.

The vector magnetograph of the Okayama Astrophysical Observatory (Makita et al. 1985a,c) is equipped on the 65cm solar coude telescope with the 10m Littrow spectrograph. Results of observations are vector magnetograms, velocitygrams, maps of the broadband polarizations, maps of the magnetic lines of force, and maps of the electric currents. Their examples are given in figure 1. The data books, which give the vector magnetograms, have been published every year since 1983.

Calibrations of the polarization degree and the overall accuracy were discussed (Makita et al. 1982, 1987; Makita and Li 1992). The accuracy of the polarization measurement is 10−3for the line observation and 10−4 for the continuum observation. Conversion of the polarization degrees to the magnetic field vector has been tried by Sakurai (1987) with the use of the weak field theory and the observed magnetic field strength of sunspots. A simultaneous observation of the same active region was once made with the Sayan Observatory (Makita et al. 1985b). Distributions of the magnetic polarity were quite similar and azimuths of the magnetic field agreed very well.

The magnetic fields of the Sun provide the major incentive to do solar physics. The small spatial extent of the magnetically constrained structures and processes in the solar atmosphere provide the major incentive for high resolution solar telescopes. The visibility of the outer solar atmosphere in the ultraviolet and X-ray domains provide the major incentive for solar space telescopes. Cost provides the major incentive to use interferometric techniques. SIMURIS employs short-wave interferometry from space to measure solar structures and processes with high resolution.

A new method of ‘multi-cloud model’(MCM) is proposed and two application examples are given in the paper.

Stokes I and V profiles of Fel 630.1 nm and Fel 630.2 nm observed in a sunspot with an angular resolution ≥0.5” are analyzed. We find asymmetric V-profiles whose shapes are in agreement with previous determinations having lower angular resolution (~5”). We also find a correlation between penumbral small scale variations of continuum intensity and velocity. Although it involves smaller velocities, such correlation resembles that existing in the quiet sun as a consequence of convection.

Adopting the computational model of papers I and II (Song et al. 1990, 1992) we have found that for a better fit of the center of the Fe I 5324.19 Å line, the effect of turbulent Doppler broadening has to be taken into account. Through theoretical and numerical analysis we conclude that the square root of the modulus of Stokes Q and U is an appropiate observational parameter to represent the transverse magnetic field, since it is approximately linearly proportional to the strength of the transverse magnetic field for suitable positions of the filter passband.

We report observational studies of solar active regions n°6150 and n°6850 during cycle 22. Observations were carried out with a tunable monochromatic birefringent filter coupled with a line-shifter and a Stokesmeter as well as with a spectro-magnetograph, both at Meudon Observatory. AR n°6150 is typical of emerging flux regions, while AR n° 6850, with a complex preceding δ-spot, exhibits characteristic configurations of the transverse magnetic field for flaring activity: shear along the neutral line, and curvature coupled with anomalous Evershed mass motions.

The 20 year old conclusion that more than 90% of the magnetic flux recorded by magnetographs in quiet and active regions is in strong-field, kG form has recently been supported by direct observations of Zeeman splitting in the infrared (near 1.6 μm). The magnetic and thermodynamic properties of the kG fluxtubes have been explored in considerable detail over the past decade, in particular through Fourier transform spectrometer observations combined with Stokes inversion procedures. The weak fields have proven to be much more elusive, and it was not until last year that the first definite identifications of intrinsically weak (less than kG) fields in the low photosphere could be made, using the Stokes V profiles of an infrared line pair.

The problems associated with unresolved flux elements are discussed. It is pointed out that the hypothesis that these fields are strong does explain various problems of solar magnetic fields, but, as all invisible phenomena, is difficult to test. It is pointed out that Zeeman splitting measurements, which give the true field, have revealed field strengths down to the lower limit of conventional spectroscopy (about 400 gauss) for years. Not one spectrogram showing larger splitting in plages or network has been produced. The power-law distribution of weak-field strengths suggests a hierarchy of field strengths, and the simple arithmetic of weak-field elements and tiny pores is on the edge of ruling out strong fields, and further improvement in resolution should do so.

Observations in the 12μ lines have shown plage fields of a few hundred gauss and broadening of the σ components due to field variation within the field of view. These data have been explained away on the basis of height variation in the field, but the requisite transverse field strength or center-limb behavior are not observed.

Spectrograms of high spatial resolution taken every 15s reveal rapid variations of the continuum intensity and line width. Variations of the latter seem to be related to Doppler velocity gradients.

More than 1000 small isolated bright Ca+ structures (facular points) have been observed with the German VTT at the Observatorio del Teide, Tenerife. An analysis of Stokes V and Stokes I profiles of magnetically sensitive lines exhibit some typical properties of these features. The investigation is concentrated on those 40% of the observed structures for which the magnetic filling factor is larger than 10%

Using the 155 hours of coordinated observing data of Huairou and Big Bear Solar Observatories, the lifetimes of network elements have been determined by different ways. The sample of network elements has been chosen on a strict criterion in order to reduce the bias. Two statistical methods with different considerations show a mean lifetime of elements of 49.20 hours and 54.92 hours, respectively. The least-square fit method provides an average lifetime of 55.84 hours.

Relations between horizontal flow and filigree structure obtained from high-resolution observations (~1/4) are discussed. The magnetic flux elements move with the horizontal flow in the supergranulation network, and as downdrafts are approached both magnetic flux and intensity gradually decrease. Reasons for this disappearance are discussed. If the photosphere actually is a turbulent magneto-plasma, as suggested by the good coupling between the magnetic flux elements and the flow field, the integrated magnetic flux in the background field will exceed the flux in the discrete kilogauss structures.

The soft X-ray images taken by the Yohkoh Soft X-ray Telescope (SXT) provide a powerful new tool to solve the mechanism of solar flares. In particular, a limb flare that occurred on 1991, December 2 gives us convincing evidence that magnetic reconnection of a neutral sheet formed at the loop top participates in the flare energy release. The neutral sheet appears to be associated with a destabilized rising loop system (filament) sheared with respect to the flaring loop. Similar formations of X-ray arcades are seen in the quiet Sun associated with filament eruptions on much larger spatial dimension and with a much smaller energy scale.

Major problems of the physics of the solar atmosphere and processes of solar activity are due to the poor knowledge of the magnetic fields outside the photosphere. Unique methods to determine magnetic fields in the corona and chromosphere make use of radio observations in close connection with information obtained in other spectral ranges e.g. the optical and X-ray regions. Based on relevant emission and propagation processes, the basic radio methods providing information on the parent magnetic fields are summarized. Signatures in the microwave and meter wave regions are used to derive magnetic field parameters at different levels in the solar atmosphere of active regions during quiet and flaring conditions. Implications on fine and gross structures are briefly discussed and consequences on acting physical processes mentioned.

We present hard X-ray imaging observations by Yohkoh of the 15 November, 1991 flare. The pre-impulsive and the impulsive phase observations are summarized as follows: (1) Hard X-ray sources in the precursor (or pre–impulsive) phase appear in a much wider area compared with the impulsive phase sources and they show clear evolution just before the onset of the impulsive phase. This suggests that some global re-structuring of coronal magnetic fields led to the impulsive energy release. (2) In the impulsive phase, at the peaks of the individual spikes of the time profile, the bulk of the hard X-ray emission (above 20 keV) originates from the footpoints of the flaring loop. At the valleys between the spikes, X-rays below 30 keV are emitted from near the loop top, while higher energy ones (above 30 keV) are still emitted from the footpoints. Such behavior of hard X-ray sources can be explained by the partial precipitation model.

In this paper, we study the distribution of chromospheric magnetic fields and analyze reversed polarity structures on chromospheric magnetograms in active regions.

We analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.

Three ways of measuring magnetic fields in the corona and chromosphere have been developed based on spectral polarization observations with high spatial resolution using the radio telescope RATAN-600. The methods rely on effects from the theory of the generation and propagation of microwaves in the solar atmosphere: thermal bremsstrahlung, thermal cyclotron emission, and inversion of the polarization sign in quasi-transverse field regions. The new radio spectrograph (PAS) at the RATAN-600 resulted in higher accuracy measurements of the strength and structure of coronal magnetic fields. Using observations made with the PAS on 1992 January 10, we show that the magnetic field strength in the lower corona above all large sunspots can be measured with an accuracy ≈ 3%. The correlation with photospheric magnetic fields is good, ‘radio’ magnetic fields being weaker by ≈ 20%.

According to an active region model proposed in the present paper, i.e. three-dimensional and continuous distributions of the three plasma parameters (electron temperature, electron density, and magnetic field) from the active region to the quiet region, and using the combined mechanisms of gyroresonance radiation and bremsstrahlung, we have researched the solar radio S-component (i.e. the slowly varying component or SVC) variation with the magnetic field of active regions.