Temporal variation of 2D multi-parameter fields of a post-flare loop system

The 2D Hβ 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 Tex and micro-turbulence velocity Vt) 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 1 h after the maximum of the Hα flare. Our analyses show that the average values of N2 and Vt decrease with time, while Tex is nearly unchanged except for the top part of the PFLs where it is increasing slightly with time. A new evolution property is found in which the regions with the maxima of Tex and N2 move from the middle of the southern leg towards the top part of the PFLs, while the position of Vt maximum shifts from the top part towards the northern leg of the system. This scenario may be a result of successive formation of new loops at higher heights while under continuous cooling. The emission measure (EM), electron density ne and pressure Pe in the PFLs are also estimated.