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11.
Inference of magnetic fields from very high spatial, spectral, and temporal resolution polarized images is critical in understanding the physical processes that form and evolve fine scale structures in the solar atmosphere. Studying high spectral resolution data also helps in understanding the limits of lower resolution spectral data. We compare three different methods for calibrating the line-of-sight component of the magnetic field. Each method is tested for varying degrees of spectral resolution on both synthetic line profiles computed for known magnetic fields and real data. The methods evaluated are: (a) the differences in the center of gravity of the right and left circular components for different spectral resolution, (b) conversion of circular polarization, at particular wavelengths, to magnetic fields using model-dependent numerical solutions to the equations of polarized radiative transfer, and (c) the derivative method using the weak field approximation. Each method is applied to very high spatial and spectral resolution circular polarization images of an active region, acquired in the Fei 5250 Zeeman-sensitive spectral line. The images were obtained using the 20 m pass-band tunable filter at NSO/Sacramento Peak Observatory Vacuum Tower Telescope. We find that the center-of-gravity separation offers the best way of inferring the longitudinal magnetic field.Work partially done while the author held an NRC-USAF Resarch Associateship.Supported under a USAF/AFOSR research initiative.The National Optical Astronomy Observatories are operated by the Association of Universities Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation (NSF). Partial support for National Solar Observatory is provided by the United States Air Force under a Memorandum of Understanding with NSF. 相似文献
12.
Tobias Diehl Nicholas Deichmann John Clinton Stephan Husen Toni Kraft Katrin Plenkers Benjamin Edwards Carlo Cauzzi Clotaire Michel Philipp Kästli Stefan Wiemer Florian Haslinger Donat Fäh Urs Kradolfer Jochen Woessner 《Swiss Journal of Geoscience》2013,106(3):543-558
This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2012. During this period, 497 earthquakes and 88 quarry blasts were detected and located in the region under consideration. With a total of only 13 events with ML ≥ 2.5, the seismic activity in the year 2012 was far below the average over the previous 37 years. Most noteworthy were the earthquake sequence of Filisur (GR) in January with two events of ML 3.3 and 3.5, the ML 4.2 and ML 3.5 earthquakes at a depth of 32 km below Zug in February and the ML 3.6 event near Vallorcine in October. The epicentral intensity of the ML 4.2 event close to Zug was IV, with a maximum intensity of V reached in a few areas, probably due to site amplification effects. 相似文献
13.
We analyze the temporal behavior of network bright points (NBPs) searching for low-atmosphere signatures of flares occurring on the magnetic network. We make use of a set of data acquired during coordinated observations between ground-based observatories (NSO/Sacramento Peak) and the MDI instrument on board SOHO. Light curves in chromospheric spectral lines show only small-amplitude temporal variations, without any sudden intensity enhancement that could suggest the presence of a transient phenomenon such as a (micro)flare. Only one NBP shows spikes of downward velocity, of the order of 2–4 km s–1, considered as signals of compression associated with a (micro)flare occurrence. For this same NBP, we also find a peculiar relationship between the magnetic and velocity fields fluctuations, as measured by MDI. Only for this point the B–V fluctuations are well correlated, suggesting the presence of magneto-acoustic waves propagating along the magnetic structure. This correlation is lost during the compression episodes and resumes afterward. An A6 GOES soft X-ray burst is temporally associated with the downward velocity episodes, suggesting that this NBP is the footpoint of a flaring loop. This event has a total thermal energy content of about 1028 erg, and, hence, belongs to the microflare class. 相似文献
14.
We analyze the pre-flare and impulsive phase of an eruptive (two-ribbon) flare at several wavelengths. The total energy (mechanical plus radiative) released by the flare is 8 x 1030 erg, about a factor 6 higher than the free magnetic energy (1.3 1030 erg) estimated from the non-potentiality of the magnetic field configuration in the flare area. During the impulsive phase, we find a very good time coincidence between the hard X-ray light curve and the light curves for 2 small areas ( 4 in size) in the red wing of the H line and in the He-D3 line center. This temporal coincidence is compatible with the interpretation that hard X-ray emission is produced by bremsstrahlung of accelerated electron beams striking these dense areas. For the other regions of the H ribbons we find more gradual light curves, suggesting a different energy transport mechanism such as conduction. 相似文献
15.
L. Van Driel-Gesztelyi B. Schmieder G. Cauzzi N. Mein A. Hofmann N. Nitta H. Kurokawa P. Mein J. Staiger 《Solar physics》1996,163(1):145-170
Ground-based optical observations coordinated with Yohkoh/SXT X-ray observations of an old, disintegrating bipolar active region AR NOAA 7493 (May 1, 1993) provided a multiwavelength data base to study a flaring active region X-ray bright point (XBP) of about 16 hr lifetime, and the activity related to it in different layers of the solar atmosphere. The XBP appeared to be related to a new minor bipole of about 1020 Mx. Superposed on a global evolution of soft X-ray brightness, the XBP displayed changes of brightness, lasting for 1–10 min. During the brightenings the XBP apparently had a spatial structure, which was (tiny) loop-like rather than point-like. The X-ray brightenings were correlated with chromospheric activity: (i) brightenings of underlying chromospheric faculae, and (ii) appearance of strong turbulent velocities in the arch filament system. We propose that the XBP brightenings were due to reconnection of the magnetic field lines (sketched in 3D) between the new bipole and a pre-existing plage field induced by the motion of one of the new pores (v = 0.2 km s–1) towards the plage, and that the XBP itself was a reconnected hot loop between them. 相似文献