Several advantages of near infrared spectral lines for magnetic field measurements are listed. In particular, the 10830 Å multiplet of HeI is well suited for observations of chromospheric magnetic fields.

New photoelectric spectroheliograms made with the 10830 Å line reveal a large amount of filamentary fine structure in active regions. This fine structure has important consequences on the interpretation of 10830 Å magnetograms. Except for an association of 10830 Å disk filaments with polarity reversals there is little correlation between absorption features and the 10830 Å longitudinal field. Comparisons of chromospheric and photospheric observations show that the chromospheric field is spatially more diffuse and weaker than the photospheric field.

I have studied the observed concentrations of vertical velocity and vertical magnetic field in the corners of the coarse network. Using a horizontal velocity inferred from the vertical velocity, I have computed the possible rate of concentration of the field. The rate turns out to be much higher than observed. I conclude that the observed motions in supergranules are not concentrating the observed field at the corners of the network. I have suggested four possible alternate situations consistent with the observations.

The Culgoora magnetograph (Ramsay et al., 1970) produces simultaneous filtergrams in opposite circular polarizations at a wavelength selected by a filter bandwidth 0.005 nm (Ramsay et al., 1970). In the blue wing of the 610.27 nm line of CaI, regions of magnetic fields in strong or weak plages are very obvious in one or other polarization, depending on polarity, even before subtraction; in one polarization they are bright, but almost invisible in the other. They are more difficult to discern at equal intervals from the line centre in the other wing (Figure 1). When subtractions are carried out to yield magnetograms of the same sense, the two magnetograms from opposite wings give results which appear to be much the same. An example is shown in Figure 2. Similar results are obtained over a wide range of positions in the wings of the 610.27 nm line.

This paper describes a photographic technique for recording solar spectra. The technique, which we call spectra-spectroheliography, requires the same amount of observing time as conventional spectroheliography but yields much more information. Data reduction techniques have been developed to use this information for the construction of spectroheliograms and other contour maps. Parameters investigated by this method include the vector magnetic field, line-of-sight velocity, continuum intensity, and line strength. Results indicate (1) good correlation between bright regions in spectroheliograms and small vertical magnetic fields; (2) poorer correlation between larger magnetic fields and bright regions; (3) a feature in the continuum resembling a pore but having no vertical magnetic field; and (4) a gradient in the vertical magnetic field of 12 kG/arc s.

Spectroheliogram movies of magnetic, velocity, and intensity fields have been obtained in a wide variety of spectral lines. The time resolution was typically 10–30 s. Some of the lines used were: CN λ 3883; CaI λ 6103; FeI λ 4071; FeI λ 5434; FeII λ 4924; CaII λ 3934; CaII λ 8542.

On filter magnetograms of the Sun made at Lockheed Solar Observatory, small mottles create a salt-and-pepper appearance. Outside plages, the surface seems to be sprinkled with little magnetic elements, with opposite polarities intermingled. The many steps of the photographic subtraction process required to make these elements visible tend to cast doubt on their reality. Independent and stronger evidence for the quantization of magnetic field, recently presented by Livingston and Harvey (1969), stimulates an effort to define more carefully the characteristics of the elements seen on filter magnetograms. The purpose of this contribution is to show that these characteristics are compatible with those of the elements observed at Kitt Peak.

Magnetic field observations made utilizing a 1/7 Å birefringent filter for the FeI line at 5324 Å resolve magnetic field features comparable in scale to the Hα fine structure. Without exception, low lying filaments in the center of the disk coincide with boundaries of polarity change in the line of sight component of the magnetic field. Small filaments can be identified on a scale comparable to the Hα fibril structures. The arch filament systems are associated with areas of mixed polarity. ‘Satellite spots’ may sometimes be identified as small localized enhancements of magnetic field of both polarities around the perimeter of a sunspot.

Zeeman spectroheliograms of photospheric magnetic fields (longitudinal component) in the CaI 6102.7 Å line are being obtained with the new 61-cm vacuum solar telescope and spectroheliograph, using the Leighton technique. The structure of the magnetic field network appears identical to the bright photospheric network visible in the cores of many Fraunhofer lines and in CN spectroheliograms, with the exception that polarities are distinguished. This supports the evolving concept that solar magnetic fields outside of sunspots exist in small concentrations of essentially vertically oriented field, roughly clumped to form a network imbedded in the otherwise field-free photosphere. A timelapse spectroheliogram movie sequence spanning 6 hr revealed changes in the magnetic fields, including a systematic outward streaming of small magnetic knots of both polarities within annular areas surrounding several sunspots. The photospheric magnetic fields and a series of filtergrams taken at various wavelengths in the Hα profile starting in the far wing are intercompared in an effort to demonstrate that the dark strands of arch filament systems (AFS) and fibrils map magnetic field lines in the chromosphere. An example of an active region in which the magnetic fields assume a distinct spiral structure is presented.

The simultaneous measurements of longitudinal magnetic fields in lines λ5250 and λ6103, the line of sight velocities and intensities in these lines at some fixed point (area 2″.3 × 4″.5) within the moderately strong (∼ 100 G) areas of solar magnetic fields were examined to find the possible fluctuations of m.f. with time. No fluctuations were found which cannot be correlated with the simultaneously measured seeing conditions such as contrast, image excursions and scintillations for characteristic periods less than 5m. The possibility of ∼ 5m oscillations of magnetic fields correlated with the well known sight-line velocity oscillations is pointed out.

Evidence for the existence of 5 min oscillations in the photospheric and low chromospheric magnetic fields is presented, their properties discussed, and a possible production mechanism suggested.

The association of Hα flares with photospheric magnetic field patterns is reviewed on the basis of empirical evidence. The insertion of flares in the H∥ and H⊥ patterns is described. Present data on the evolution of magnetic structures in connection with flares suggest that flares result from special trends in this evolution leading to stressed and/or ‘misconnected’ fields. However no sudden changes with a flare-like time scale have been definitely observed in photospheric fields.

A solar radio outburst with its different parts well seen on metric wavelengths is described. A stable source shows successively two kinds of emission before the flash-phase of the event, and a moving type IV burst (V ≃ 1000 km/s), initiated 1/4 solar radius high, is directly associated with a spray-type prominence. Parameters of this radiating source are discussed.

A type II burst seen on lower frequencies with a spectrograph (V ≃ 3200 km/s) seems to start after the flash phase. Two possible cases are considered for the generation of the shock-wave responsible for type II burst.

An investigation of strong magnetic fields associated with flares was made with the 61 cm vacuum telescope and spectroheliograph at the San Fernando Observatory. Magnetograms of the longitudinal component of the field were made daily during the period of September 25–29, 1969. Observations were also made during this same period of the enhanced radio emission at 3.3 mm wavelength. On September 27 an importance class 3 or 4 flare occurred in the region studied. Total magnetic flux was determined for September 25, 26, 28 and 29 for the region which included the flare. In an area of about 190 arc s by 250 arc s the flux values for these dates were respectively 2.4, 2.5, 2.2 and 2.8 × 1022 Mx. Following the flare of September 27 the flux decreased significantly. Magnetic energy change in the region of the flare can be determined if an appropriate height is known. Following Howard and Severny (Astrophys. J. 137, 1242, 1963) a height of 109 cm was used. This yields a value of 5 × 1031 ergs for the decrease of magnetic energy in the longitudinal component of the field.

A balloon observation of an impulsive hard X-ray burst on September 27, 1969 showed the size of the source to be one arc minute or less. It was remarkably smaller than the associated Hα flare with a size of 3 arc min.

The efficient acceleration of electrons and the trigger of the flares are suggested to be attributed to a large scale electric potential field caused by a gas motion near the photosphere. The primary cause of the onset of flares would be the acceleration of electrons. The electrons excite plasma waves which make the conductivity lower by several orders, so that the electromagnetic energy I2L stored before the onset of the flare would be suddenly converted into the heat due to the ohmic loss.

Soft X-ray (3–60 Å) photographs of the solar corona have been obtained on four flights of a rocket-borne grazing incidence telescope having a resolution of a few arc seconds. The configuration of the X-ray emitting structures in the corona has been compared to the magnetic field distribution measured by photospheric longitudinal magnetograms. The X-ray structures trace the three dimensional configuration of the magnetic field through the lower corona.

Active regions in the corona take the form of tubular structures connecting regions of opposite magnetic polarity within the same or adjacent chromospheric active regions.

Higher, larger structures link widely separated active regions into complexes of activity covering substantial fractions of the disk. The complexes are separated by areas of low average field in the photosphere. Interconnections across the solar equator appear to originate over areas of preceding polarity.

Enhanced X-ray emission is observed, outside the active belt, over areas of enhanced general magnetic field. Bright point-like X-ray features are observed above bipolar areas in the general coronal field.

Two, probably related, classes of X-ray features are associated with points of high field gradient along the longitudinal magnetic, ‘neutral line’. Both in the non-flaring active region and in flares the brightest emission is observed from one or more small line sources (at our present resolution). In flares this can account for a substantial fraction of the total soft X-ray emission of the flare.

An expansion of the source of a great solar microwave burst was observed a little beyond the west limb on March 30, 1969. This expansion is interpreted in terms of diffusion of energetic electrons in a turbulent magnetic field in the flare region. The height of the source is estimated to have been 104 km.

It is observed that the change of the net magnetic flux associated with flares can exceed 1017 Mx/s, which corresponds according to Maxwell's equation to the e.m.f. ∼ 109 V which is specific for the high energy protons generated in flares. It is shown that this value of e.m.f. can hardly be compensated by e.m.f. of inductance which should appear due to the actually measured motions in a flare generating active region. The values of electric field strength thus found, together with measured values of electric current density (from rotH), leads to an electric conductivity which is 103 times smaller than usually adopted.

A time sequence of longitudinal magnetograms of two active regions, McMath Regions 9281 and 9760, have indicated magnetic field changes occurring in localized areas with time scales of the order of hours. We believe the observed field changes are evolutionary in nature, rather than related to the occurrence of small flares. Three examples of evolutionary magnetic changes are discussed.

During the period of strong flare activity of the active center McMath No. 9740, from October 25 to November 2, 1968, 32 magnetograph records of longitudinal H∥ and 20 of transverse fields, H⊥, were obtained for this center with the Crimean magnetograph. Sometimes 5–7 daily records were made. Hα and K spectroheliograms, Hα cine film and routine determinations of sunspot magnetic fields were also obtained frequently. However the most important point is that all these optical observations were accompanied by simultaneous and continuous measurements of intensity and polarization of radio emission from this active center at a wavelength of 3 cm, recorded with the aid of the big 22-m radiotelescope of the Crimean Observatory (the resolution is 8′ for this wavelength), (Erushev and Zvetkov, 1970).

In this paper common regularities in flare positions have been studied in relation to spots as the extreme points of the magnetic field. The angular distribution diagrams of flares reveal that equatorial-western shifts of flares occurred during the I.G.Y. period (1957–58) in both hemispheres. This shift with some peculiarities is confirmed in the material of the 19th solar cycle, using the Solar Data bulletins, U.S.S.R., 1955–66. One result is that the western component of the shift does not change its sign and increases steadily during the cycle, while the equatorial component reverses sometimes and decreases steadily in amplitude to the end of the cycle.