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Extreme-Ultraviolet and X-Ray Spectroscopy of a Solar Flare Loop Observed at High Time Resolution: a Case Study in Chromospheric Evaporation View all abstracts by submitter

Jeffrey Brosius   Submitted: 2004-09-07 10:11

We present EUV and X-ray light curves and Doppler velocity measurements for a GOES class M2 solar flare observed in NOAA Region 9433 on 2001 April 24 at high time resolution with the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) satellite (9.83 s), and the Bragg Crystal Spectrometer (BCS) and Hard X-ray Telescope (HXT) aboard the Yohkoh satellite (9.00 s). Coordinated imagery with SOHO's Extreme-ultraviolet Imaging Telescope (EIT) and the TRACE satellite reveal that the CDS slit was centered on the flare commencement site; coordinated magnetograms from SOHO's Michelson Doppler Imager (MDI) are consistent with this site being the footpoint of a flare loop anchored in positive magnetic field near the outer edge of a sunspot's penumbra. CDS observations include the preflare quiescent phase, two precursors, the flare impulsive and peak phases, and its slow decline. We find that (1) the average wavelengths of O III, O IV, O V, Ne VI, and He II lines measured during the preflare quiescent phase are equal (within the measurement uncertainties) to those measured during the late decline phase, indicating that they can be used as reference standards against which to measure Doppler velocities during the flare; (2) the EUV lines of O III, O IV, O V, and He II exhibit upflow velocities ~ 40 km s-1 during both precursor events, suggestive of small-scale chromospheric evaporation; (3) the Fe XIX EUV intensity rises and stays above its preflare noise level during the second (later) precursor; (4) the maximum upflow velocities measured in Fe XIX with CDS (64 km s-1) and in Ca XIX (65 km s-1) and S XV (78 km s-1) with BCS occur during the flare impulsive phase, and are simultaneous within the instrumental time resolutions; (5) the Fe XIX EUV intensity begins its impulsive rise nearly 90 s later than the rise in intensities of the cooler lines; (6) hard X-ray emission arises nearly 60 s after the cool EUV lines begin their impulsive intensity rise; (7) the EUV lines of O III, O IV, O V, and He II exhibit downflow velocities ~ 40 km s-1 during the flare impulsive phase, suggesting momentum balance between the hot upflowing material and the cool downflowing material. Our observations are consistent with energy transport by nonthermal particle beams in chromospheric evaporation theory.

Authors: Jeffrey W. Brosius and Kenneth J. H. Phillips
Projects: SoHO-EIT,SoHO-MDI,SoHO-CDS,TRACE,Yohkoh-BCS,Yohkoh-HXT

Publication Status: ApJ, 613, 580 (2004 September 20)
Last Modified: 2007-02-28 08:29
Go to main E-Print page  Generalized Regularization Techniques With Constraints For The Analysis Of Solar Bremsstrahlung X-Ray Spectra  Chromospheric Evaporation and Warm Rain During a Solar Flare Observed in High Time Resolution with the Coronal Diagnostic Spectrometer Aboard the Solar and Heliospheric Observatory  Edit Entry  Download Preprint  Delete Entry 

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