Engineering topics

Shibata, Kazunari

Publications and source records attributed to Shibata, Kazunari.

4 records

NASA NTRS1995

Coronal x-ray jets: Observation and theory

The Soft X-ray Telescope (SXT) aboard Yohkoh has revealed that the solar corona is much more dynamic that had been thought. Among various newly discovered dynamic phenomena, one of the most surprising findings is the discovery of coronal x-ray jets. The length of these jets is a few 10(exp 3) - a few 10(exp 5) km, their (apparent) velocity is a few 10 - a few 100 km/s (some reached 1000 km/s), and the corresponding kinetic energy is estimated to be 10(exp 25) - 10(exp 28) erg. They occur in association with small flares in active regions, emerging flux regions, and x-ray bright points, and show the following common characteristics: recurrency, whip-like motion, change in morphology at the footpoint ARs, and often converging (or inverted-Y) shape. Large scale loop brightenings observed by SXT seem to correspond to jets occurring in closed loop systems. These observations suggest that the magnetic reconnection between the emerging magnetic flux (or expanding loop) and the overlying coronal/chromospheric magnetic field is a key physical process for producing these jets. We shall summarize characteristics of these coronal X-ray jets observed by SXT, and also discuss the theoretical interpretation of them, especially in the framework of a magnetic reconnection model.

Shibata, Kazunari↗

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 NTRS1992

The structure of the coronal soft X-ray source associated with the dark filament disappearance of 1991 September 28 using the Yohkoh Soft X-ray Telescope

The structure of the coronal soft X-ray source associated with the dark filament disappearance on September 28, 1991, observed with the Soft X-ray Telescope, is examined as a possible example of the 'eruption-reconnection' model of filament disappearance. The results suggest, however, that this model may not fit. There is a strong possibility that much of the dark filament mass remains in the heated unwinding axial field.

Mcallister, Alan↗

NASA NTRS1991

Numerical simulations of microflare evolution in the solar transition region and corona

Several observers report transient ultraviolet brightenings, often referred to as microflares, in the solar atmosphere. In this paper, the results are presented of a series of one-dimensional numerical simulations examining possible relationships between microflares and the generation of dynamical chromospheric and transition region features. Low-energy and medium-energy microflares eject long-lived cool, dense gas plugs into the corona, with the gas plug traversing the loop apex in the medium energy case. In the case of high-energy microflares, the gas plug is rapidly heated to the temperature of the surrounding corona, and the results resemble the dynamics occurring in standard solar flare thick-target electron beam models.

Sterling, Alphonse C.↗