Hydrogen Atmospheres in the Absence of Thermodynamic Equilibrium. IV. The Solar Chromosphere

Abstract

A discussion of the observational data shows that in the range 0<z<2.5 x 10⁸ cm. the electron concentration in the lower chromosphere may be expressed as N_e=5x 10¹¹ exp(-6 x 10^-9z) per cc., where z cm. is the height measured from a level 500 km. above the base of the chromosphere. It is shown that above the 500-km. level hydrogen atoms are almost completely ionized, and that with hydrostatic equilibrium the observed density gradient corresponds to a temperature of 2.7 X 10⁴ °K . This is in good agreement with the temperature derived by Redman from line profile measurement, so that the lower chromosphere appears to be effectively in thermal and hydrostatic equilibrium. Estimates of lower accuracy are given for the electron concentrations at some higher levels in the chromosphere. A discussion is given of the mechanism of absorption of Hα radiation by a chromosphere whose temperature is well above that of the photosphere.