Temperature Distributions and Energy Scaling Law of Solar Coronal Loops Obtained with Yohkoh

Abstract

Abstract We derived the temperature distributions along the 16 steady loops observed with the Yohkoh Soft X-ray Telescope. We have found that the temperature and emission measure (pressure) are the highest around the loop top, and decrease towards the footpoints. Some of the loops have a plateau in the temperature distribution at around the loop top (“trapezoidal” temperature distribution). The other loops, on the other hand, have a sharp peak in the temperature distributions (“triangular” temperature distribution). This triangular temperature distribution suggests that the energy input is concentrated at the peak. We have estimated the thermal conductive fluxes downward to the footpoints from the gradients of the temperature distributions. The flux ranges from 1 × 107 to 2 × 108 [erg s−1 cm−2]. We derived the total energy loss LT, which is the sum of the conductive and radiative losses: LT = 2 × 107−3 × 108 [erg s−1 cm−2]. We discovered a good correlation between the total energy loss and the gas pressure Pg for the steady loops: LT = 1.2 × 107p0.99 ± 0.12g. The correlation is consistent with the theoretical energy scaling law for the steady loops: LT = 4.0–5.1 × 103 · (pg · Tm1/2 ), where Tm is the maximum temperature (Tm ∼ 6 × 106 [K] for all the loops analyzed here).