A complete set of data of a-N importance Ha flare,the firbril structure （0.6"） of which is very clearly started at 1613 UT on May 8,1981 was obtained at Big Bear Solar Observatory.The image processing is made for Ha filtergrams,and the isophotes are drawn then.The fine structure and evolution are obtained with two methods.One is to measure luminosity variation for 50 fixed bright points relative to well-chosen stable brightness feature,which is called fixed point method.The other is to follow the brightest point and to measure its position changes time by time,which is called bright point tracing.The following results are revealed:A.In the bright patches of this flare,the first brightening points and brightest points at the maximum enhancement of radiation are not at same position.The brightening points show systematic displacement.B.Each flare patch,at least,has two kernels with typical size of 2" 3".5.The luminosity of all pixels （0.6"） in the some kernel changes in phase.Different kernels have different luminosity variation patternsC.The light curves of Ha flare and the microwave burst look similar.Ha luminosity gradually enhances during microwave preburst;the flash phase of Ha begins after the main burst of microwave;the Ha luminosity reaches its maximum after the main burst of microwave for several seconds.D.Patch C and patch B are separated for about 50 Mm and they brighten at different time.The brighterning of C is delayed for ten seconds comparing with that of the B.Assume constant a force-free magnetic configuration above active regions,the chromosphere magnetic fields by using Chiu and Hilton method （1977） are extropolated.It is found that patch C and patch B do connect each other by magnetic field lines when the factor is chosen to be 0.418.Further assume the generation and propagation of Alfven waves are from flare source,it is-found that the Alfven traillvng time from flare source to B is 0.3 seconds,while to C is 9.3 seconds,which seems to be the responsible delay time of the brightening of C comparing to B.Same calculation was made for patch A and patch C.However the delay time of the brightening of C comparing with A is not compatible with Alfven travelling time.It might mean that the A and C is not connected with magnetic field lines.
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