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A close relationship between flares and magnetic flux cancellation at the photospheric layer has been observationally established in a number of active regions. The flux cancellation precedes the flares by a few hours up to a day. During this time a specific pattern appears in the radial velocity field in the chromosphere, namely, the magnetic separatrix appears as a narrow blue-shifted band while the flares all occur in the red-shifted regions on either side. This observation supports the identification of flux cancellation with magnetic reconnection in the lower atmosphere and confirms that the reconnection is closely related to fast energy release in the corona.

A full-disk magnetogram obtained with the full-disk magnetograph of Huairou Solar Observing Station shows similar morphological features and magnetic field intensities as in traditional small scale magnetograms obtained by the solar magnetic field telescope at the same site.

At the chromospheric level, a localized magnetic feature with polarity opposite to the underlying photospheric magnetic field has been observed in a rapidly formed sunspot. The strength of this reversed polarity is several hundred gauss. Seven subflares, centering around the reversed polarity, have been identified in observation of nine hours. The flares showed progressive increase in size and extent with the develop- ment of the reversed polarity. The bipolar feature above the unipolar magnetic flux can only mean that a bundle of magnetic lines of force has been kinked or knotted, or a self-closed flux system has been developed above the photosphere.

The twisting motion of a quiescent filament in AR5572 was observed on 8 July 1989. Based on the time sequence of magnetograms, Hβ fitergrams and Hβ Dopplergrams obtained at Huairou Solar Observing Station of Beijing Astronomical Observatory, the twisting motion of the filament is identified to be related to three cancelling magnetic features in the filament channel.

In view of an approximate description of magnetic shear by non-potential character of a force-free magnetic field, the force-free factor α would be a measure of magnetic shear, and the shear development would be analytically described by a differential equation dα dt = 1 β 2 ∇· G + V ·∇α, where, G = ∂B ∂t × B , might be called as the generation function of magnetic shear. It is clearly shown by this equation that the magnetic shear is generated by local dynamo action resulting from the interaction between magnetic field and plasma motion. It is also illustrated that the squeezing and pressing of opposite polarity fields, the flux emergence and submergence would be as effective as shear motion in producing magnetic shear.

A direct indication of magnetic reconnection in solar photosphere has been found for the first time with the aid of the time sequence of vector magnetograms. The reconnection takes place in the interface between one pole of an emerging flux region and the old flux of opposite polarity. It occurs well after a subflare with X-ray classification of C2.9 when flux cancellation in the interface had lasted for several hours. It is suggested that the reconnection in the photosphere would be a common phenomenon on the sun.

There are 4 types of evolution patterns of network magnetic fields: (1) flux cancellation, the mutual disappearance of encountering fluxes of opposite polarity, (2) flux increase by emergence of ephemeral regions, (3) flux decrease of one polarity and (4) flux increase of one polarity, without emergence of ephemeral regions. From a time sequence of magnetograms of a quiet region of 1983 October 14, the evolution of 300 network features was measured. The magnetograms have a spatial resolution of 2 to 3 arcsec and a time resolution of about 2 hr. The statistics show that the contribution to flux decrease by Type 3 is 1.28 times that by Type 1, and the contribution to flux increase by Type 4 is 7 times that by Type 2.

On 1984 July 9, we obtained continuous magnetograms with 1“−2” spatial resolution, 2.5min time resolution and noise level below 5 Gauss at Big Bear Solar Observatory. Analysis of' these magnetograms after calibration and empirical corrections shows that, in addition to the transient, mixed polarity field described by Livingston and Harvey (1975), there is a stable type of uni-polar flux forms. These features have a typical size of 2“−5” in one dimension, a total flux of (+18) Mx, a field strength of approximately 40G and a lifetime of several hours. We call these Intra-Network Flux Concentrations (INFC).

We give a formal expression for the dependence of hydrogen line oscillator strength on departure from LTE and propose a method for determining this departure in the various sub-levels of the hydrogen atom in solar prominences. Results for 10 solar prominences are given. Finally, we discuss the possible implications of a smaller population in the 2p level than in the 2s level.