ESA Science & Technology - Transition Region Downflows in the Impulsive Phase of Solar Flares

Publication date: 02 May 2005

Authors: Kamio, S., et al.

Journal: ApJ
Volume: 625
Issue: 2
Page: 1027-1035
Year: 2005

Copyright: The American Astronomical Society

We present observations of four flares that occurred during coordinated observations between the Coronal Diagnostic Spectrometer (CDS) on board SOHO and the Domeless Solar Telescope (DST) at Hida Observatory. We studied the evolution of relative Doppler velocities in the flare kernels by using He I (3.5x10⁴ K), O V (2.2x10⁵ K), and Mg IX (1.0x10⁶ K) spectra obtained with high time cadence (42 s) SOHO CDS observations and the Halpha monochromatic images obtained with the DST. We found that the transition region plasma of O V showed strong downward velocities up to 87 km s^-1 simultaneously with the downflows in the lower temperature chromospheric emissions in He I and Halpha during the impulsive phase of all four flares. From these results we suggest that the downflows in the transition region and the chromosphere are a common feature in the impulsive phase of flares. For the Mg IX line we did not detect any significant change in velocity, which suggests that the 10⁶ K plasma was close to the intermediate temperature between the upflowing plasma (10⁷ K) and the downflowing plasma (10⁴-10⁵ K). These are important for understanding the dynamics of the solar atmosphere in response to the sudden energy deposition of a flare.