Frequency of radio emission vs. height above the solar surface. The blue solid line shows the dependence according to the Baumbach-Allen formula of the quiet Sun density structure; the green dashed line shows the dependence according to the gravitationally stratified atmosphere with 1 MK temperature; the red dashed lines correspond to the frequencies 29 MHz, 25 MHz, 22 MHz, and 14 MHz, from top to bottom.