Early Evolution of Coronal Active Regions Observed with the YOHKOH Soft X-Ray Telescope. I. Expansion Velocity

Details Early Evolution of Coronal Active Regions Observed with the YOHKOH Soft X-Ray Telescope. I. Expansion Velocity Early Evolution of Coronal Active Regions Observed with the YOHKOH Soft X-Ray Telescope. I. Expansion Velocity

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...493..970y&link_type=abstract

Astrophysical Journal v.493, p.970

Astronomy and Astrophysics

Astronomy

6

Sun: Corona, Sun: Activity, Sun: X-Rays, Gamma Rays, Sun: Magnetic Fields

Scientific paper

We study the early evolution of active regions in the corona by analyzing 33 emerging flux regions (EFRs) observed with the soft X-ray telescope (SXT) aboard Yohkoh during the period from 1992 February to 1996 May. We examine the time variation of the size (projected area) and the total soft X-ray intensity of the EFRs, and find that the time-averaged apparent velocity of the expansion of most of the EFRs is less than 2 km s-1 during the very early phase (t < 6-14 hr after the birth of the EFRs). The average expansion velocity of 33 EFRs is 1.5 km s-1. This expansion velocity is much lower than the rise velocity of emerging magnetic loop in the upper chromosphere, inferred from H alpha observations of arch filament systems as well as MHD simulation and theory. Some possibilities to account for this discrepancy are discussed.

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