The 180° ambiguity of the transverse magnetic field measured by a heliomagnetograph is an intrinsic problem due to the linear polarization in Zeeman effect(Harvey, 1969). Thus we have to make use of some criteria for calibrating the transverse magnetic fields in vector magnetograms. Up to now, a few criteria have been suggested by some solar physicists (Harvey, 1969; Krall et al., 1982; Sakurai et al., 1985; Aly, 1989; Wu and Ai, 1990; Canfield et al., 1991. The existing criteria could be classified as observational criteria and mathematical criteria. The former is based on the observation facts, such as the fibrils and the filaments in solar filtergrams, and the latter is derived from the mathematical model of solar magnetic field, such as divergence equation (∆. B = 0), potential field model and force-free field model. These criteria, however, are not applicable to all solar active regions, especially to those with complicated magnetic fields. For this reason, we suggest a synthesized method for calibrating the transverse magnetic fields in solar vector magnetograms.

Electric conductivity tensor of partly-ionized plasma is deduced. Four atmospheric models are used then to estimate the conductivity in the lower atmosphere. The parallel conductivity reaches its minimum value in the temperature minimum zone, which is 1 to 2 orders smaller than the conductivity of fully-ionized plasmas of the same condition; the effective perpendicular conductivity, or Cowling conductivity, becomes 5 to 6 orders smaller than the fully-ionized value in the lower chromosphere.

We review the present status of our understanding of the structure and dynamics of emerging flux regions which form the first stage of active regions. We review the observations of the emerging flux regions, and discuss their structure, dynamics, and physical conditions derived from these observations. We also discuss implications about magnetic fields below the surface.

Recurrent solar activity on a time-scale of the Sun’s rotation rate has for a long time been attributed to quasi-periodic disturbances in the solar interior. The following brief survey discusses recent attempts to come to grips with the Sun’s episodic activity.

Stackplot displays of the photospheric magnetic field show long-lived patterns that often rotate at rates differing from the intrinsic photospheric rate. These complex patterns are produced naturally by the flux-transport model, in which magnetic flux emerging in the form of active regions is dispersed over the solar surface by differential rotation, supergranular diffusion, and a poleward meridional flow. Numerical simulations show that long-lived patterns with slopes similar to the observed ones arise even when the longitudes of the erupting flux are randomized, suggesting that a deep-seated longitudinal organization is not required to explain the qualitative nature of the patterns. Both autocorrelation analysis and visual comparison between the slopes of the observed and simulated patterns indicate that the equatorial rotation period of the Sun is close to 26.75 days, significantly shorter than the traditional 26.9 day value of Snodgrass and Newton & Nunn but in agreement with the recent measurements of Komm, Howard, & Harvey. A complete discussion of these results may be found in Sheeley, Wang, & Nash, ApJ, 401, 378 (1992).

Characteristics and the emergence pattern of bipolar active regions are investigated using NSO/KP full disk magnetograms. Discussed in this paper are two samples of newly emerged bipolar regions: 9492 ephemeral regions and 978 active regions. Their distributions in size, latitude, and orientation are compared. It is concluded that ephemeral regions are the small scale end of a wide spectrum of active regions.

It is shown that the growth and decay rates of sunspot groups are both a function of the axial tilt angles of the groups. Both of these rates reach a maximum near the average tilt angle, which is around +5°, not 0°. (A positive tilt angle represents the situation where the leading spots are equatorward of the following spots). The fact that this peak angle is close to the average tilt and not 0° suggests that this may be the orientation of the subsurface toroidal flux tube(s) from which the sunspot groups form. In general, spot groups with positive tilt angles show faster average percentage growth rates for greater positive tilt angles. For negative tilt angles (following spots equatorward of leading spots) the situation is quite different. Within certain well-defined ranges of tilt angles the average group percentage area growth rates are quite high and the dispersion in this quantity is large. In other well-defined tilt angle ranges the percentage growth rates are uniformly (relatively) small. The difference between these average growth rates is more than a factor two. The reality of this result can be demonstrated by selecting for analysis various subsets of the data. It may be hypothesized that in general the dispersion measured in group tilt angles results from the random action of large-scale convection on the rising magnetic flux loops. Both growth and decay are facilitated in the case of flux loops that have a minimum twist. The percentage growth and decay rates are affected by the fact that groups with tilt angles near the average value tend to be larger than groups with different tilt angles. The ‘quantized’ behavior of the percentage growth rates for negative tilt angles is difficult to fit into any rough model of flux emergence. The more or less ‘quantized’ nature of the growth-tilt angle relationship for negative tilt angles is quite puzzling and may reflect some characteristic of the subsurface flux orientation or development which is at present unknown.

Long-term evolution of solar large-scale magnetic fields in relation to the local active phenomena is studied. The changes of the magnetic flux distribution are influenced by the horizontal transport of magnetized plasma. The whole system of magnetic field changes is interpreted as a global process which is controlled by the large-scale convective patterns. The large-scale horizontal velocity field of transporting motions is determined in various approaches with similar results. Regions with positive divergence in the field of horizontal flow field are found to be closely connected with the occurrence of solar active regions. The process of the horizontal flow was analysed by the “cork” method. The corks reveal a pattern of giant cells which are persistent for several solar rotations. These large cells are interpreted as giant convective elements. Occurrence of new strong magnetic flux in regions of positive divergence is then interpreted as a result of emergence of flux in the upflowing parts of that pattern.

Two-dimensional (2D) magnetohydrodynamic (MHD) numerical simulations have been performed to study magnetic reconnection between emerging flux and the overlying coronal magnetic field, taking into account of gravity. It is found that (1) reconnection starts when most of chromospheric mass in the current sheet between the emerging flux and the coronal field has drained down along the loop because of gravity, (2) multiple magnetic islands, which confine cool, dense chromospheric plasma, are created in the sheet; the islands coalesce dynamically and are ejected along the sheet, together with the ambient hot plasma, at Alfven speed. The coexistence of hot and cool plasmas in the mass ejection (jet) associated with the reconnection seems to explain those X-ray jets observed by Yohkoh, which are identified with Hα surges.

We analyse Greenwich sunpot group position data for one solar cycle (1952-1963) in order to study the rotation rate of clusters of sunspot groups, so-called active nests. We find that the latitude-dependent rotation rate of nests shows an intrinsic spread. This spread appears to be caused by extensive and dense clusters of sunspot nests (superclusters or nested nests), and by very compact single nests of short duration. The ‘best’ rotation rate is defined as the rate at which the highest number of sunspot groups appear to form nests. This latitude-dependent best rotation is close to the rotation rate of individual recurrent sunspots, although nests seem to rotate slightly more rigidly than sunspot groups.

We present a new observational evidence of the magnetic field reconnection in emerging flux regions (EFR). Our observations show that Hα surges are the first active manifestation of emerging magnetic field in some EFRs. We call them EFR-surges. Examining their morphological and evolutionary characteristics, we conclude that they are produced by the magnetic field reconnection between the EFR and the pre-existing surrounding region.

Progress in sunspot seismology is briefly reviewed. New observations of the absorption of p-modes by a sunspot (Bogdan, Brown, Lites, and Thomas 1993) show that the absorption coefficient (averaged over frequency and azimuthal order) increases with horizontal wavenumber to a maximum near k = 0.9 Mm−1 and then decreases monotonically to zero at about k = 1.5 Mm−1. The absorption along individual p-mode ridges shows a sinusoidal-like modulation, which may be an important feature for comparison with theory. Results for the quiet Sun show no net absorption, but do show apparent emission along p1 over the same range of k where the sunspot shows its greatest absorption. This behavior, and the overall decrease in absorption at higher wavenumbers, can be explained as an effect of the decreasing lifetime of p-modes with increasing wavenumber k (increasing mode degree l).

We study the oscillatory behaviour of small-scale magnetic flux-tube concentrations and their immediate surroundings by analysing high spatial resolution time series of spectra of four Zeeman sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, Fe I 5250.7) taken simultaneously in left-hand and right-hand circularly polarized light with the Echelle spectrograph at the Vacuum Tower Telescope in Izaña, Tenerife. The velocity field inside the magnetic elements is dominated by the 5-min oscillations which also show up as periodic variations in the relative amplitude asymmetry of the Stokes V profiles. In other parameters as for instance the Stokes V peak separation we cannot detect an oscillatory component. Neither the magnetic line ratio nor the thermal line ratio is affected by the 5-min oscillations, although the latter reveals remarkable spatiotemporal variations.

Observations of the Stokes I and V profiles of the Ca II H and K lines in solar magnetic regions are presented. Least-squares fits of dI/dλ to V are obtained and the wavelength variation of the residuals, i. e. V-kdI/dλ, calculated. We find significant symmetric residuals in umbrae, which are in agreement with the effect on the V profiles due to atomic orientation, i.e. with the existence of an unequal population of the Zeeman sublevels with M>0 with respect to those with M<0.

We present high-quality power spectra of oscillations in the quiet solar chromosphere measured from the Ca II H line. They show unambiguously that the network does not participate in chromospheric three-minute oscillations, but that instead it oscillates in slow wave motions which are neither present in the surrounding non-magnetic chromosphere, nor in the underlying photosphere.

We present accurate measurements, based on the g = 3 line at 1.5648/µm, of the field strength and longitudinal velocity in the vicinity of the magnetic neutral-line of a solar active region. We find that very close to the neutral line the field strength and the flow velocity are correlated in the sense that the magnetic polarity with the larger field strength is associated with a downflow, while the polarity with the weaker field shows an upflow. This is exactly the signal predicted by theoretical models of siphon flows, and constitutes the first reliable detection of a siphon flow on the sun.

Nonlinear MHD waves forced into a bounded cavity exhibit structural instability of their equilibria and periodic orbits as the forcing varies. For some values of the forcing the computed Poincaré maps, Lyapunov exponents and phase-space correlation reveal that the waves become chaotic; the Haussdorff dimension of the waves’ attracting set lies between its correlation dimension (≈ 2.2) and its information dimension (≈ 2.25).

We use imaging spectroscopy from the MSDP of the VTT telescope in Tenerife (collaboration Paris-Meudon Observatory and Kiepenheuer Institut) to analyse Doppler velocities of arch filaments in Hα and NαD1. The geometry of the magnetic loops is deduced from perspective effects with a simple dynamical model. Velocities are correlated in both lines.

Further results are expected from simultaneous observations with other instruments (SVST of La Palma and Huairou magnetograph).

The Sun’s rotation rate near the base of its convection zone might be expected to vary over the solar cycle because of related changes there in the magnetic field. Helioseismic analyses have taught us that much of the Sun’s convection zone rotates with surface-like differential rotation and a transition toward solid body rotation beneath. For a review of what we know about the Sun’s internal rotation, see Goode, et al.(1991). We now have sufficient solar oscillation data to look for changes in the internal rotation near the base of the convection zone. The relevant data are from the 1986, 1988, 1989 and 1990 Big Bear Solar Observatory( BBSO) sets, Libbrecht and Woodard(1992, private communication). These four datasets were gathered at the same site for roughly the same number of days, reduced in the same way and span the same temporal and spatial frequency ranges—the differences between the sets should arise primarily because they were obtained in different years.

Nonlinear effects in dynamics of solar magnetic fields which, in particular, determine the evolution of solar magnetic structures and their lifetimes, are discussed. By some analogy with the effects of acoustic streaming in usual hydrodynamics the general definition of these effects as “magneto acoustic streaming” is proposed.