Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apj...595.1277l&link_type=abstract
The Astrophysical Journal, Volume 595, Issue 2, pp. 1277-1295.
Astronomy and Astrophysics
Astronomy
57
Sun: Activity, Sun: Flares, Sun: Photosphere, Techniques: Polarimetric
Scientific paper
Photospheric vector magnetic field data from the University of Hawai'i Imaging Vector Magnetograph, with good spatial and temporal sampling, are used to study the question of identifying a preflare signature unique to flare events in parameters derived from the magnetic vector field, B. In this first of a series of papers, we present the data analysis procedure and sample results focusing only on three active regions (NOAA Active Regions 8636, 8771, and 0030), three flares (two M class and one X class), and (most importantly) a flare-quiet epoch in a comparable flare-producing region. Quantities such as the distribution of the field morphology, horizontal spatial gradients of the field, vertical current, current helicity, ``twist'' parameter α, and magnetic shear angles are parameterized using their moments and appropriate summations. The time series of the resulting parameterizations are examined one at a time for systematic differences in overall magnitude and evolution between the flare and flare-quiet examples. The variations expected due to atmospheric seeing changes are explicitly included. In this qualitative approach we find (1) no obvious flare-imminent signatures from the plain magnetic field vector and higher moments of its horizontal gradient or from most parameterizations of the vertical current density; (2) counterintuitive but distinct flare-quiet implications from the inclination angle and higher moments of the photospheric excess magnetic energy; (3) flare-specific or flare-productivity signatures, sometimes weak, from the lower moments of the field gradients, kurtosis of the vertical current density, magnetic twist, current helicity density, and magnetic shear angle. The strongest results are, however, that (4) in ensuring a flare-unique signature, numerous candidate parameters (considering both their variation and overall magnitude) are nullified on account of similar behavior in a flare-quiet region, and hence (5) considering parameters one at a time in this qualitative manner is inadequate. To address these limitations, a quantitative statistical approach is presented in Paper II by Leka & Barnes.
Barnes Graham
Leka Kimberly Dawn
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