Production of a short-lived filament by a surge

A large surge was observed on September 17, 1971 part of which, after travelling 200,000 km across the surface, returned to the surface to form a filament. The filament lasted about 30 minutes, then rose up and returned to the source of the surge. This was interpreted as the filling of a semi-stable magnetic trap. Analysis of the microwave radio burst showed it to have been produced by a source optically thick at 8,800 MHz, with area 4 (arc min)squared and T approximately 275,000 deg, N squared sub eV approximately 7 x 10 to the 48th power. The soft x-ray burst showed a component at 12 x 1,00.000 deg with N squared sub eV approximately 3 x 10 to the 48th power

Further observations of the lambda 10830 He line in stars and their significance as a measure of stellar activity

Measurements of the lambda 1030 He line in 198 stars are given along with data on other features in that spectral range. Nearly 80% of all G and K stars show some lambda 10830; of these, half are variable and 1/4 show emission. It was confirmed that lambda 10830 is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars, along with P gamma, but P gamma is not in emission in G and K stars with lambda 10830 emissions. Variable He emission and Ti I emission are found in the RV Tauri variables R Scuti and U Mon. In R Aqr the Fe XIII coronal line lambda 10747 and a line at lambda 11012 which may be singlet He or La II are found, as well as lambda 10830 and P gamma. The nature of coronas or hot chromospheres in the various stars is discussed. It was concluded that the lambda 10830 intensity must be more or less proportional to the energy deposited in the chromosphere corona by non-thermal processes

The flares of August 1972

Analysis is made of observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra. In each flare the observations fit a model of particle acceleration in the chromosphere with emission produced by impart and by heating by the energetic electrons and protons. The region showed twisted flux and high gradients from birth, and flares appear due to strong magnetic shears and gradients across the neutral line produced by sunspot motions. Post flare loops show a strong change from sheared, force-free fields parallel to potential-field-like loops, perpendicular to the neutral line above the surface

The velocities of intranetwork and network magnetic fields

We analyzed two sequences of quiet-Sun magnetograms obtained on June 4, 1992 and July 28, 1994. Both were observed during excellent seeing conditions such that the weak intranetwork (IN) fields are observed clearly during the entire periods. Using the local correlation tracking technique, we derived the horizontal velocity fields of IN and network magnetic fields. They consist of two components: (1) radial divergence flows which move IN fields from the network interior to the boundaries, and (2) lateral flows which move along the network boundaries and converge toward stronger magnetic elements. Furthermore, we constructed divergence maps based on horizonal velocities, which are a good representation of the vertical velocities of supergranules. For the June 4, 1992 data, the enhanced network area in the field of view has twice the flux density, 10% higher supergranular velocity and 20% larger cell sizes than the quiet, unenhanced network area. Based on the number densities and flow velocities of IN fields derived in this paper and a previous paper (Wang et al., 1995), we estimate that the lower limit of total energy released from the recycling of IN fields is 1.2 × 10²⁸ erg s⁻¹, which is comparable to the energy required for coronal heating

Magnetic fields, bremsstrahlung and synchrotron emission in the flare of 24 October 1969

Magnetic fields, bremsstrahlung, and synchrotron emission in solar flare of October 24, 196

Reproduction of the Lyman α irradiance variability from analysis of full-disk images in the CaII K-line

We have compared three years of daily CaII K-line images from the Big Bear Solar Observatory (BBSO) with HI Lymanα irradiance data from the Upper Atmosphere Research Satellite (UARS). The daily full-disk CaII K-line images are reduced to a new index of integrated excess emission, which reproduces both the 27 day rotational modulation and the solar cycle decrease in Lyα irradiance. Our analysis shows that while plages reproduce the 27-day variation quite well, the total K-line emission excess above the quiet background is needed to reproduce the secular solar cycle trend in the Lyα irradiance. The resulting K-line index exhibits a high degree of correlation (0.9) with the time series of measured Lyα flux

Active regions. II: Mount Wilson 16997: A small spot with big flares

We describe the great activity associated with Mount Wilson 16997, a single αp spot without plage that produced a number of large flares and developed into a substantial center. The activity was signalled by the emergence of f polarity and weak plage ahead of the spot on 24 September 1968 (although the region was already seen at the limb at the 22 September 1968 eclipse as a active center). A number of explosive flares with X-rays on the 25th were climaxed by a large flare a 0036 UT 26 September; the latter was associated with the splitting of the old spot and the emergence of a new one. The polarity axis rotated around to a normal configuration by the 29th, but a large flare occurred on that day, too. Several of the flares show interesting details such as the return of spray material to the surface at the boundary of the region. The behavior of this region shows that: (1) Large flares may come from small, round spots; (2) The magnetic field rotation due to the action of the Hale-Nicholson force is a possible source of flare energy; and (3) Appearance and disappearance of spots is clearly connected with flare activity

Studies of solar flares using optical, X-ray and radio data

I have studied a number of flares for which good X-ray and optical data were available. An average lag of 5.5 s between hard X-ray (HXR) start and Hα start, and HXR peak and Ha peak was found for 41 flares for which determination was possible. Allowing for time constants the time lag is zero. The peak Hα lasts until 5–6 keV soft X-ray (SXR) peak. The level of Hα intensity is determined by the SXR flux. Multiple spikes in HXR appear to correspond to different occurrences in the flare development. Flares with HXR always have a fast Hα rise. Several flares were observed in the λ 3835 band; such emission appears when the 5.1–6.6 keV flux exceeds 5 × 10⁴ ph cm⁻² s⁻¹ at the Earth. Smaller flares produce no λ3835 emission; we conclude that coronal back conduction cannot produce the bright chromospheric network of that wavelength. The nearly simultaneous growth of Hα emission at distant points means an agent travelling faster than 5 × 10³ km s⁻¹ is responsible, presumably electrons. In all cases near the limb an elevated Ha source is seen with the same time duration as HXR flux; it is concluded that this Hα source is almost always an elevated cloud which is excited by the fast electrons. A rough calculation is given. Another calculation of Hα emission from compressed coronal material shows it to be inadequate. In several cases homologous flares occur within hours with the same X-ray properties. Radio models fit, more or less, with field strengths on the order of 100G. A number of flares are discussed in detail

Active regions. II: Mount Wilson 16997: A small spot with big flares

We describe the great activity associated with Mount Wilson 16997, a single αp spot without plage that produced a number of large flares and developed into a substantial center. The activity was signalled by the emergence of f polarity and weak plage ahead of the spot on 24 September 1968 (although the region was already seen at the limb at the 22 September 1968 eclipse as a active center). A number of explosive flares with X-rays on the 25th were climaxed by a large flare a 0036 UT 26 September; the latter was associated with the splitting of the old spot and the emergence of a new one. The polarity axis rotated around to a normal configuration by the 29th, but a large flare occurred on that day, too. Several of the flares show interesting details such as the return of spray material to the surface at the boundary of the region. The behavior of this region shows that: (1) Large flares may come from small, round spots; (2) The magnetic field rotation due to the action of the Hale-Nicholson force is a possible source of flare energy; and (3) Appearance and disappearance of spots is clearly connected with flare activity