Jongchul Chae

The Formation of a Prominence in NOAA Active Region 8668. II. Trace Observations of Jets and Eruptions Associated with Canceling Magnetic Features

Our previous study has shown that the formation of a reverse S-shaped filament in NOAA active region 8668 was closely associated with a large canceling magnetic feature. In the present paper we investigate the response of the upper atmosphere at the region of this canceling magnetic feature. The UV and EUV data taken by the Transition Region and Coronal Explorer (TRACE) reveal that a series of jets and small eruptions took place there during the formation of the prominence. Plasma in each jet originated from a single site of flux cancellation and moved in opposite directions at a transverse speed of 80-250 km s-1 across the plane of the sky. Plasma eruptions showing complex morphology and dynamics started from two or more sites of flux cancellation and appear to have the same physical origin as the jets. The two filter ratio technique indicates that the EUV-emitting plasma in the jets and eruptions have transition-region temperatures of (2-3) × 105 K. It is also found from emission-measure analysis that the electron density is (0.7-1.9) × 1010 cm-3 and that each jet carries plasma mass of (1.7-4.6) × 1013 g and each eruption carries additional mass of (9-25) × 1013 g. Our results are consistent with the current pictures that (1) flux cancellation observed in the photosphere is a consequence of magnetic reconnection occurring in the chromosphere and (2) that a series of such magnetic reconnection events is able to supply the mass necessary for the formation of a solar prominence.

Flux Cancellation Rates and Converging Speeds of Canceling Magnetic Features

Canceling magnetic features are commonly believed to result from magnetic reconnection in the low atmosphere. According to the Sweet–Parker type reconnection model, the rate of flux cancellation in a canceling magnetic feature is related to the converging speed of each pole. To test this prediction observationally, we have analyzed the time variation of two canceling magnetic features in detail using the high-resolution magnetograms taken by the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). As a result, we have obtained the rate and converging speed of flux cancellation in each feature: 1.3×1018xa0Mxxa0hr−1 (or 1.1×106xa0Gxa0cmxa0s−1 per unit contact length) and 0.35xa0kmxa0s−1 in the smaller one, and 3.5×1018xa0Mxxa0hr−1 (1.2×106xa0Gxa0cmxa0s−1) and 0.27xa0kmxa0s−1 in the bigger one. The observed speeds are found to be significantly bigger than the theoretically expected ones, but this discrepancy can be resolved if uncertainty factors such as low area filling factor of magnetic flux and low electric conductivity are taken into account.

Temperatures of Extreme-Ultraviolet-emitting Plasma Structures Observed by the Transition Region and Coronal Explorer

The Transition Region and Coronal Explorer has revealed, in unprecedented detail, various kinds of EUV-emitting plasma structures in the solar upper atmosphere. The filter ratio 195 A/171 A has been conventionally used to determine the plasma temperatures, but this method has a shortcoming in that it may not yield a unique temperature value for a given ratio. Therefore, we introduce a new method employing two filter ratios (195 A/171 A and 284 A/195 A). It is demonstrated that this color-color method is effective in determining a wide range of unambiguous plasma temperatures. We have obtained a temperature of 1 × 106 K for a loop that is bright in 171 A but hardly visible in 284 A, a higher temperature of 2 × 106 K for a loop that is clearly visible in 195 and 284 A but not in 171 A, and a transition-region temperature of 2.5 × 105 K for a low-lying loop that is clearly visible in all the EUV wavelengths. In addition, we have found that moss structures have temperatures of around 1 × 106 K and that EUV jets have temperatures of about 2.5 × 105 K.

DEVELOPMENT OF THE FAST IMAGING SOLAR SPECTROGRAPH FOR 1.6 m NEW SOLAR TELESCOPE

KASI and Seoul National University developed the Fast Imaging Solar Spectrograph (FISS) as one of major scientific instruments for the 1.6 m New Solar Telescope (NST) and installed it in the Coude room of the NST at Big Bear Solar Observatory (BBSO) in May, 2010. The major objective of the FISS is to study the fine-scale structures and dynamics of plasma in the photosphere and chromosphere. To achieve it, the FISS is required to take data with a spectral resolution higher than at the spectrograph mode and a temporal resolution less than 10 seconds at the imaging mode. The FISS is a spectrograph using Echelle grating and has characteristics that can observe dual bands (H and CaII 8542) simultaneously and perform fast imaging using fast raster scan and two fast CCD cameras. In this paper, we introduce briefly the whole process of FISS development from the requirement analysis to the first observations.