Thermal evolution of coronal active regions observed with the Yohkoh soft X-ray telescope

We study the thermal evolution of active regions in the corona by analyzing 51 emerging flux regions (EFRs) observed with the soft X-ray telescope aboard Yohkoh. We derive the mean temperature and pressure of active regions as a function time using filter ratio technique, and found that the mean temperature increases with its expansion. We also studied the relationship between the region size and the temperature, and found that the temperature (T) and the pressure (P) of EFRs increase with increasing region size (L); T ∝ L ^0.42 , P ∝ L ^0.25 .