Engineering topics

Zirin, Harold

Publications and source records attributed to Zirin, Harold.

27 records · Page 2

NASA NTRS1989

Study of supergranules

Results of a detailed study on supergranule lifetime and velocity fields are presented. The correlation between the observed downdraft velocity and the network magnetic flux elements on the quiet sun is shown. After excluding areas with magnetic flux density 25 G or greater, it is found that the upper limit of the supergranule vertical speed is 0.1 km/s for both downdraft and updraft, and the rms speed is 0.03 km/s. By observing the evolution of individual supergranules, it is found that the average lifetime of supergranules might be 50 hours or greater. Different ways of formation and decay of supergranular cells are described. New cells usually form in an area containing no preexisting supergranule velocity fields. Cells may disappear in two ways: fragmentation and fading away.

Wang, Haiman↗

NASA NTRS1988

Coordinated videomagnetograph observations by the Big Bear and Huairou Observatories

A videomagnetograph patterned after the BBSO system was installed at Huairou in 1987, and five days of coordinated observing were carried out from September 24 to 29, 1987. The data were combined to make a continuous movie of the fields abound a stable spot. A 57 hour magnetograph run with two seven hour gaps were achieved from 2330 UT, September 24 to 0830 UT, September 27. The frames were reregistered and justified to eliminate the change of scale with meridian distance. The intensities were corrected for cosine effect. Preliminary examination of the data shows continuous decrease of the total magnetic field during this period by more than 50 percent. The principal loss of flux appears to be due to cancellation at the main neutral line. Some flux disappears due to fragmentation, which makes the elements fall below the threshold, while only a tiny loss due to diffusion can be detected. It is planned to continue this program during Max 1991, including transverse field measurements as well. Several long runs were already obtained in 1988.

Wang, Haimin↗

NASA NTRS1988

The vertical structure of arch filament systems in solar emerging flux regions

The paper studies the vertical velocity of arch filaments in emerging flux regions by measuring their proper motion near the limb in H-alpha filtergrams and their radial velocity near the disk center in H-alpha spectrograms. Both show that arch filaments rise at a velocity between 10 and 15 km/s. The possible mechanisms producing this high velocity are discussed. None of them is satifactory, but it appears that the unloading of the arches by outflow must play a role. From the strength of H-alpha emission and D3 absorption, the temperature of arch filaments is estimated at 6000-15,000 K and the density at 10 to the 11th-12th/cu cm.

Chou, Dean-Yi↗

NASA NTRS1987

High-resolution continuum observations of the Sun

The aim of the PFI or photometric filtergraph instrument is to observe the Sun in the continuum with as high resolution as possible and utilizing the widest range of wavelengths. Because of financial and political problems the CCD was eliminated so that the highest photometric accuracy is only obtainable by comparison with the CFS images. Presently there is a limitation to wavelengths above 2200 A due to the lack of sensitivity of untreated film below 2200 A. Therefore the experiment at present consists of a film camera with 1000 feet of film and 12 filters. The PFI experiments are outlined using only two cameras. Some further problems of the experiment are addressed.

Zirin, Harold↗

NASA NTRS1987

Weak solar fields and their connection to the solar cycle

Videomagnetograph observations of the weak solar magnetic fields are discussed. Intranetwork (IN) elements are found to emerge in bipolar form, but to flow in a random pattern rather than toward the network elements. Merging of IN fields is found to be more important than the ephemeral regions as a source of new network elements. Arguments for and against the hypothesis that all solar fields are intrinsically strong are considered. It is noted that reconnection and merging of magnetic fields take place continually under the conditions presently examined.

Zirin, Harold↗

NASA NTRS1987

Delta spots and great flares

The development of delta spots and the great flares they produce are reviewed based on 18 years of observations. Delta groups are found to develop in three ways: (1) by the eruption of a single complex active region formed below the surface; (2) by the eruption of large satellite spots near a large older spot; and (3) by the collision of spots of opposite polarity from different dipoles. It is shown that the present sample of 21 delta spots never separate once they lock together, and that the driving force for the shear is spot motion. Indicators for the prediction of the occurrence of great flares are identified.

Zirin, Harold↗

NASA NTRS1987

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.

Zirin, Harold↗

NASA NTRS1986

Observation of flares in the helium lines

Observations of flares in the visible and UV lines are discussed. Observations in He I 5876 and He II 4686 permit isolation of footpoints and effects of footpoint heating, as well as valuable insight into physical conditions in both loops and footpoints. Interpretation of UV line intensities permits assessment of chromospheric heating in the flares. In general these observations point to temperatures of 30,000-100,000 C and densities above 10 to the 12th in the helium-emitting areas.

Zirin, Harold↗

NASA NTRS1986

White light flare of 24-25 April 1984

The temporal correlation between white light brightenings that appeared 4 min after the start of the April 24-25, 1984 H-alpha flare and its X-ray flux is noted to be good; it is in addition found that the bright patches moved in the same direction as the H-alpha white strands of the flare. Another noteworthy aspect of this flare is the lateness of white light emission relative to H-alpha emission and the blue-shifted soft X-ray emission.

Hiei, Eijiro↗