The absence of flares in λ3835 and the heating of the chromosphere

Simultaneous observations of flares in H and a band 15 Å wide centered on 3835 Å show no change whatever in 3835 Å at the time of several flares, although the chromospheric network is easily visible. Flares are therefore transparent in this wavelength.Since the flare represents a test heat input from above, and no brightening of the network appears, we conclude it is impossible for the corona to produce the bright network by downward convection.     

The solar flares of August 28 and 30, 1966

We describe observations of the class 3+ flare of August 28, 1966, made at the Mount Wilson Observatory. This great proton flare followed the sequence: (1) Precursor flare; (2) Filament eruption; (3) Beginning in penumbra of large spot; (4) Rapid elongation in two strands; (5) Great spray and surface wave; (6) Rapid separation of two strands to maximum brightness; and (7) Slow spread of brightness and decay.The soft X-ray burst coincides with stages 3–6, decaying through stage 7; the hard (> 80 keV) burst coincides, but decays more rapidly.Considering a demi-cylinder of emitting material, the soft X-rays are explained by a 4-million-degree plasma, or at least a large flux of electrons with that amount of energy. Given this flux, the microwave burst is explained by synchrotron emission with the low frequency cut-off due to coronal absorption.The class-2 flare of August 30, 1966, is also discussed.This research was supported by the Advanced Research Projects Agency under the Office of Naval Research Grant N00014-67-C-0140 and the National Aeronautics and Space Administration under Grant NGR 05 002 034.NASA International University Fellow at the California Institute of Technology, 1967–1968, now at Arcetri Astrophysical Observatory.     

Arch filaments associated with the formation of sunspots by umbral merging

The formation of a sunspot during the emergence of a new group is described. The spot forms from a cluster of small umbrae that do not converge. Rather, the individual umbrae enlarge and merge into a spot covering the same area. The formation of each umbra is accompanied by an intensification of the arch filament anchored in it. The formation of the sunspot produces no apparent change in the total field.     

Electromagnetic and corpuscular emission from the solar flare of 1991 June 15: Continuous acceleraton of relativistic particles

Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to 0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data.     

Emerging flux in active regions

We have compared the rates at which flux emerges in active and quiet solar regions within the sunspot belts. The emerging flux regions (EFRs) were identified by the appearance of arch filament structures in H. All EFRs in high-resolution films of active regions made at Big Bear in 1978 were counted. The comparable rate of flux emergence in quiet regions was obtained from SGD data and independently from EFRs detected outside the active region perimeter on the same films. The rate of flux emergence is 10 times higher in active regions than in quiet regions. A sample of all active regions in 31 days of 1983 gave a ratio of 7.5. We discuss possible mechanisms which might funnel new magnetic flux to regions of strong magnetic field.     

Properties and Motions of Ellerman Bombs

We studied the properties and proper motions of Ellerman bombs (EBs) around a sunspot in a mature active region using high-resolution off-band H filtergrams together with nearly simultaneous magnetograms. Sixty-four percent of the EBs (class I) did not correspond accurately to enhanced magnetic field elements while the rest corresponded well to such elements (class II), which all were moving magnetic features (MMFs). We studied the lifetimes, shapes and dimensions, contrasts and time profiles of the EBs. These properties were essentially the same for both classes, in agreement with previous authors. Class I EBs did not move but class II EBs tracked the MMFs well, with horizontal proper motions up to a maximum of 1.1 km s–1 and their velocity pattern was similar to the velocity pattern of the MMFs.     

A 10-Year Set of Ca II K-Line Filtergrams

We have processed a 10-year set of BBSO Caii K-line filtergrams covering most of solar cycle 22. The excess K-line emission is integrated to form linear and square-root activity indices that are fitted to UV data from UARS and SME. Good fits are found both for the Mgii core–wing ratio (linear) and total L irradiance (square root) and the indices are thus good proxies for UV data. The SME L irradiance is systematically lower by 20% than predicted from our corresponding K-line indices. The 10.7 cm radio data confirms that SME underestimated the flux. The network is partly responsible for the solar cycle variation of the indices and is relatively more important in L than in Mgii and Caii K. This is due to the saturation of L equivalent width. We also report on substantial improvements to the equipment and reduction software. The system is now based on a digital CCD camera which promises more accurate measurements in the upcoming solar cycle 23.     

Study of Hα Jets on the Quiet Sun

High-speed jets of solar quiet regions have been observed at Big Bear Solar Observatory in H–1.0 Ú, and compared with high-resolution magnetograms. Over the whole Sun, the birthrate of the H–1.0 Ú jets is about 19±3 events s^–1, which is much lower than the birthrate of spicules. The average lifetime of these jets is 2±1 min. H–1.0 Ú jets are very different from spicules, in the sense of birthrate, lifetime, and shape. Jets tend to recur in the same sites, always located in boundaries of supergranules. Under the best observing conditions, we found that 80% of the major jet sites are associated with converging magnetic dipoles – mainly the sites where intranetwork elements are canceling with opposite polarity network elements. In order to establish a possible relationship between the disk H jets and limb macrospicules, we have also obtained time sequences of H center-line images at the limb. These images are enhanced by median filtering so that jet structures over the limb are easily studied. We found that these limb H jets (above the spicule forest) repeatedly occur in the same sites, which is the property shared by the disk H–1.0 Ú jets. However, their mean lifetime is 10 min, substantially longer than that of disk jets. Comparison with simultaneous SOHO/EIT Heii 304 Ú images shows that every Heii 304 Ú jet over the limb coincides with an H jet, although Heii 304 Ú jets extend much farther out. Some H jets do not have associated He jets, probably due to the difference in image resolutions. H spectra of selected jets are analyzed, and we found that jets are not simply blue-shifted; instead, the line profiles are broadened with significantly larger broadening on the blue side. Two-component fitting finds that the velocity of the blue-shifted component (an optically-thin component) is around 20 to 40 km s^–1.     

Sunspot motion,flares and type III bursts in McMath 11482

We have studied a series of flares in McMath 11482, 1972 August 19–22, with particular reference to the basis for the flares and comparison with dekameter radio data. We find that the flares were produced by rapid ( 1000 km h^–1) westward motion of a large new p spot. Many flares occur just in front of the spot, and they cease when the motion stops. All flares occurring in front of the spot produce type III bursts, while even strong flares elsewhere in the region produce little or no type III. The time of type III emission agrees perfectly with the start of the H flare. Thus type III bursts are only produced in favorable configurations.Simultaneous K-line movies are compared with H films and show little difference in flare appearance.     

Coronagraph observations of the coronal condensation of 4 February 1962

Climax coronagraph observations of the accessible Fe lines, as well as the Caxv 5694 line at the time of the 1962 total eclipse, are analyzed. The spectra show that the ionization equilibrium of iron is not substantially changed in an intense coronal condensation, at least for the stages x through xv. The only exception is Fexv 7059, for which density effects are important. The stability of the ionization distribution is explained by the dynamic nature of the Fe ionization, with ions entering on the high side (Fexvi and up) due to rapid heating and then cooling through the visible stages.Comparison of the ionization distributions inferred from radiative and collisional excitation of the iron lines shows that the excitation must be by collisions everywhere at the heights examined (less than 50 000 km).The iron abundance in the corona is found to be 10^–4 that of hydrogen, but this figure would be reduced by the amount of cyclic excitation.The peak electron density in the condensation is 8 × 10⁹, and the peak value of the 5694 line/ continuum ratio is 2.5, in good agreement with calculations by Chevalier and Lambert.The ratio of the infrared Fexiii lines is measured along the limb and found to vary with electron density as expected, the 10 747/10 798 ratio is 7 or less at densities much below 10⁹ and saturates at a value of 2 for densities above that amount.