H_α Observation of the Great Eruptive Loop-Prominence on the Western Limb on April 27 in 1981

We observed a great eruptive loop-prominence on the solar western limb during 0816-0951UT on April 27, 1981, using our Lyot type Ha (6562.8 Å) chromosphric telescope. The telescope has the objective with the diameter of 14cm and focal distance of 140cm, and the passband of filter is 0.75Å, the diameter of solar image is 15.2mm. We added a set of lens to the telescope in order to amplify the solar image to 10cm.After the great x-ray burst (Class X5.5) occurred at 0720 UT, we observed a post-flare loop. Its location was about Φ=15N, λ=150L (MW No:22216 group or SESC No:3049). Our observational results are as followS:1. The loop-like structure appeared before 0816UT, the flare-like bright patch appeared in the outsides of the foot points.2. In the period of 0816-0826.5,0830-0837 and 0839-0908, the northern leg (Leg B) of the loop was thicker than the southern leg (Leg A), and during 0828.5-0830 and 0837.5-0838.5 the leg A was thicker than the leg B.3. The strange structure appeared at the top of the loop at 0829.5 and 0833, which lasted for about one minute.4. A protuberant thing in the shape of a spicule appeared at the loop top at 0836.5, rising and thickening gradually and reached the maximum hight at 0839. A new protbuerant structure appeared once again at the loop top at 0847, which gradually bended itself toward the leg B. We could see the twist structure in the leg B at 0853.5. The foot point A rised and moved gradually towards the south (towards the outside) while the foot point B changed slightly. At about 0855, the foot point A moved more rapidly and the loop-prominence changed obviously: the feet of the loop separated apparently and the hight of the loop also increased apparently while the diameter of the tube of loop at the top decreased slightly at first and then increased steeply.6. On the basis of our measurement, before 0844, the loop-prominence almost riscd at the constant velocity of 8.4 km/sec. The diameter of the tube of the loop at the Lop increased rapidly from 0.74×l0⁴ km at 0816 to 1.27×10⁴ km at 0826. But at 0855 the diameter of the tube at the loop top changed slightly. The loop-prominence rised with the average acceleration of-0.012 km/sec² during 0844-0853, and its ascending velocity decreased down, to 1,8 km/sec at 0853.