Engineering topics

Hirayama, Tadashi

Publications and source records attributed to Hirayama, Tadashi.

5 records

NASA NTRS1992

The morphology of 20 x 10 exp 6 K plasma in large non-impulsive solar flares

We have examined images of 10 flares observed by the Soft X-ray Telescope on-board the Yohkoh spacecraft. These images show that the hottest portion of the soft X-ray flare is located in compact regions that appear to be situated at the tops of loops. These compact regions form at, or shortly after, flare onset, and persist well into the decay phase of the flares. In some cases, the compact regions are only a few thousand kilometers in size and are small compared to the lengths of flaring loops. This is inconsistent with the smoother intensity distribution along the loops expected from models of chromospheric evaporation.

Acton, Loren W.↗

NASA NTRS1992

White-light flares observed by Yohkoh

The Yohkoh observatory is producing a first sample of white-light flares observed from space. We present observations of four of them, all X-class events. The Yohkoh Soft X-ray Telescope white-light data typically have a 12-s cadence for images with 2.46 arcsec pixels over a field of view of 2.62 arcmin in one of two broad-band optical filters, and the November 15, 1991 flare produced a brightness increase of about 38 percent over the photospheric brightness in the 30 A passband filter centered at 4308 A. The white-light flare morphology in the best-observed flares displays a double 'footpoint' character, establishing a close relationship with the compact magnetic flux tubes involved with both hard and soft X-ray emissions. We describe the data in the context of the soft and hard X-ray observations simultaneously carried out on board the Yohkoh satellite, emphasizing energetics and timing.

Hudson, Hugh S.↗

NASA NTRS1992

Observations of the variability of coronal bright points by the Soft X-ray Telescope on Yohkoh

We present the initial results of a study of X-ray bright points (XBPs) made with data from the Yohkoh Soft X-ray Telescope. High temporal and spatial resolution observations of several XBPs illustrate their intensity variability over a wide variety of time scales from a few minutes to hours, as well as rapid changes in their morphology. Several XBPs produced flares during their lifetime. These XBP flares often involve magnetic loops, which are considerably larger than the XBP itself, and which brighten along their lengths at speeds of up to 1100 km/s.

Strong, Keith T.↗

NASA NTRS1992

Observations of X-ray jets with the Yohkoh Soft X-ray Telescope

The features of the multiple X-ray jets in the solar corona, revealed by the time series of the Yohkoh Soft X-ray Telescope images are described. The typical size of a jet was from 5 x 10 exp 3 to 4 x 10 exp 5 km, the translational velocity was 30-300 km/s, and the corresponding kinetic energy was estimated to be from 10 exp 25 to 10 exp 28 erg. Many of the jets were found to be associated with flares in X-ray bright points, emerging flux regions, or active regions, and they sometimes occurred several times from the same X-ray feature. One of the jets associated with a flaring bright point was identified as being an H-alpha surge.

Shibata, Kazunari↗

NASA NTRS1986

The density and thickness of quiescent prominences

The electron density was determined for a number of quiescent prominences at various positions from the Stark effect. It was found that the intensity ratio of Mg I emission lines to SrII lines is independent of the observed electron density in the range of ten to the 10.2 power to 10 to the 11.4 power cm-3. This contrasts with Landman's (1984) theoretical expectation that the ratio is proportional to the electron density. From the intensity of Balmer lines and the electron density, it is inferred that the true diameter of a thread in prominence of high electron density may be smaller than 0.2". The averaged total number density of hydrogen N sub H sub of was found to be 3-6 times 10 to the 11th power cm-3, leading to a total gas pressure P =0.6 dyn cm-2 and a total density of approx. 10 to the minus twelth power g cm-3. Landman's large value of N sub H approx. 6 times 10 to the 12th power and P sub g approx. 6 may have resulted either from the fact that he has treated very bright prominences and/or from the derivation of the high electron density for all prominences he studied.

Hirayama, Tadashi↗