INTERPRETATION OF THE OBSERVED PLASMA 'TURBULENT' VELOCITIES AS A RESULT OF MAGNETIC RECONNECTION IN SOLAR FLARES

摘要

One of the distinctive features of magnetic reconnection in current sheets, which has been proposed as the primary energy source in solar flares, is the presence of fast plasma outflows, or jets, whose velocities are nearly equal to the Alfven speed and depend mainly on the electron and ion temperatures inside the current sheet. We briefly discuss the outflows that originate during the reconnection process in the high-temperature turbulent current sheet (HTTCS) approximation, both for preflare and " hot" phase conditions. Outflows can give rise to plasma velocity distributions with equal and opposite components along the line of sight, and therefore they can, in this way, create a symmetric, nonthermal broadening in the soft X-ray lines observed during solar flares. A comparison of the nonthermal profiles of the Fe xxv emission lines observed at flare onset with the predictions of the HTTCS model suggests that the observed nonthermal broadenings are consistent with the presence in the flare region of several small-scale or one (or a few) curved, large-scale reconnecting current sheets with internal temperature ≤ 8 x 10~7 K. The velocities of the outflows at the emergence of the reconnecting current sheets are inferred to be ≤ 1100 km s~(-1).