Two-dimensional Distributions and their Evolutions of Physical Quantities for a Post-flare Loop System

The 2D H_β spectral data of the post-flare loop system (PFLs) of August 17, 1989 are obtained and analyzed quantitatively for three different times. Three physical quantities (i.e., the column number density of hydrogen atoms at the second level along the line-of-sight direction N₂,the excitation temperature T_exand micro-turbulence velocity V_t) and their 2D fields are derived during the three times.The time variations of the 2D field are given for the three quantities more than one hour after the maximum of the Hα flare. Our analyses show that the average values of N₂and V_t decrease with time, while T_ex is nearly unchanged except for the top part of the PFLs where it is increasing slightly with time. The distributions of N₂, T_ex and V_t are inhomogeneous and asymmetric in the PFLs, they have a close relation with the position within the PFLs, but a little relation with the height above photosphere.A new evolution property is found in which the regions with the maxima of T_ex and N₂ move from the middle of the southern leg towards the top part of the PFLs, while the position of V_t maximum shifts from the top part towards the northern leg of the system to form a‘siphon’-like phenomenon. This scenario may be a result of successive formation of new loops at higher heights while under continuous cooling.