The H_α-Spectrum-Spectroheliographic Observations of the Flare Loop Prominence on 1981 April 27

The data such as the H_α-spectrum-spectroheliographic observations, the H_α-chromospheric observations, etc., of a flare loop prominence which occurred on the western soJar limb on 1981 April 27 have been obtained at Yunnan Observatory, Academia Sinica. These data bring to light the general picture of the distribution of the internal motion and the macroscopical motion of the flare loop prominence with time and space in the course of its eruption and ascension:1. The southern leg system of the flare loop had the right-handed motion before the maximum brightness, and after the maximum brightness the two leg systems rotated at the same direction at the angular velocity of about 4×10^-3 arc/see.2. The rotational angular velocity of the two legs decreased with the increase in the height of the legs.3. The rotational direction of the southern leg system was in accordance with that of the main sunspot with N-polarity below it, which shows that there may be some internal relation between the two.4. The two legs rotating at the same direction made the magnetic rope of the top part of the loop keep on tightly twisting so that the kink instability developed abruptly, which may be the principal reason why the loop top part was disintegrated.5. The fact that the H_α-radiation intensity and line width of the loop top part were all greater than those of the two legs shows that its physical quantities such as N₃/N₂, n_e, T, V_t, etc., might be greater than the corresponding ones of the two legs and therefore the loop top part was the most instable place.