Solar Flare Telescope Research Articles

Magnetic reconnection observed in the pre-flare phase of AR 7186 of 1992 June 4

A direct observation of a magnetic reconnection event that occurred in the flare of AR 7186 of 1992 June 4 and observed by both the Soft X-ray Telescope (SXT) aboard the Yohkoh spacecraft and the Solar Flare Telescope (SFT, NAOJ, Mitaka), is reported in this article. Phenomena predicted by the theory of reconnection, such as the necessary inflow of field lines into the current sheet, the outflow of thermal plasma expelled by the current sheet, the evaporation and H αflare kernels caused by the outflow, and the opening-out of magnetic filed lines, have been confirmed in the observations. Based on an analysis of the observations, a phenomenological model of magnetic field line reconnection is sketched.

TOPOLOGY OF MAGNETIC FIELD AND CORONAL HEATING IN SOLAR ACTIVE REGIONS II. The Role of Quasi-Separatrix Layers

The photospheric vector magnetic fields, Hα and soft X-ray images of AR 7321 were simultaneously observed with the Solar Flare Telescope at Mitaka and the Soft X-ray Telescope of Yohkoh on October 26, 1992, when there was no important activity in this region. Taking the observed photospheric vector magnetic fields as the boundary condition, 3D magnetic fields above the photosphere were computed with a new numerical technique. Then quasi-separatrix layers (QSLs), i.e., regions where 3D magnetic reconnection takes place, were determined in the computed 3D magnetic fields. Since Yohkoh data and Mitaka data were obtained in well-arranged time sequences during the day, the evolution of 3D fields, Hα features and soft X-ray features in this region can be studied in detail. Through a comparison among the 3D magnetic fields, Hα features and soft X-ray features, the following results have been obtained: (a) Hα plages are associated with the portions of QSLs in the chromosphere; (b) diffuse coronal features (DCFs) and bright coronal features (BCFs) are morphologically confined by the coronal linkage of the field lines related to the QSLs; (c) BCFs are associated with a part of the magnetic field lines related to the QSLs. These results suggest that as the likely places where energy release may occur by 3D magnetic reconnection, QSLs play an important role in the chromospheric and coronal heating in this active region.

Stray-Light Effect on Magnetograph Observations

To examine the stray-light effect in magnetograph observations, we have determined the point spread functions of the vector magnetograph mounted on the Japanese Solar Flare Telescope based on two indirect methods, one analyzing the solar limb intensity profile, and the other using the Fourier power spectra of photospheric intensity distributions. Point spread functions consist of two parts: a blurring part which describes seeing and small-spread-angle stray light, and a scattering part which describes large-spread-angle stray light. The FWHM spatial resolution is typically 3.0′′, and the amount of scattered light is about 15% on clear days. We find that the blurring part is well described by a Moffat function whose Fourier transform is given by an exponential function. Our results indicate that polarization measurements of low-intensity magnetic elements like sunspots may be significantly underestimated due to the large-spread-angle stray light, and polarization measurements of magnetic elements which are smaller than 5–7′′ appear to be disturbed by small-spread-angle stray light.

Magnetic Field Observation with the Solar Flare Telescope

AbstractThe Solar Flare Telescope was constructed at Mitaka in 1989. This instrument comprises four telescopes which respectively observe (a) Hα images, (b) continuum images, (c) vector magnetic fields, and (d) velocity fields in the photosphere. The instrument aims at the study of energy build-up and energy release in solar flares, in cooperation with the Solar-A satellite. The whole system has been in regular operation since 1992 July. The methods of measuring the magnetic and velocity fields are described.