Turbulence in the Sun's Atmosphere

Abstract

IT is well known that the density gradient in the solar chromosphere is vastly less than what it would be in ordinary gravitational equilibrium. This was a complete enigma until the advent of Milne's theory of selective radiation pressure in the case of ionised calcium. This theory has had many successes but does not seem to admit of generalisation to gases like hydrogen and helium which are present in abundance. It even seems that the radiation pressure is important for Ca⁺ only if enough hydrogen is there initially to prevent excessive ionisation (McCrea, Mon. Not. R.A.S., 89, p. 843; 1929; NATURE, April 6, 1929, p. 527). We have still to explain the presence of these gases.