Observations Indicating That ~1 × 10⁷ K Solar Flare Plasmas May Be Produced in Situ from ~1 × 10⁶ K Coronal Plasma

Abstract

We discuss a set of flare observations obtained at a position of 0.10 R_solar above the solar northwest limb. The data were acquired by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO). We derive time-dependent comparisons of physical properties, such as electron temperature and density, between flare plasma and background coronal plasma observed along the same lines of sight. In addition to temperature and density, we discuss emission measures, elemental abundances, nonthermal mass motions (from line widths), and bulk mass motions (from Doppler shifts). The observations appear to indicate that the flaring plasmas (4×10⁶K<=T_e<=1×10⁷K) along the lines of sight were formed by in situ heating and possibly by compression of the ambient coronal material (T_e<=2×10⁶ K).