Solar Atmospheric Heating by Hydromagnetic Waves

Previous estimates of solar atmospheric heating by hydromagnetic waves (due to Joule loss and viscosity) showed negligible heating. A new mechanism is described, involving neutral atoms, which leads to absorption (and heating) many orders of magnitude greater than previously believed. If hydromagnetic waves are present they must cause strong heating effects. The formation of such waves from granules is described, their absorption at low levels, and partial reflection being discussed in some detail. A very rough order-of-magnitude estimate of energy flow is obtained. The region in which heating effects are important is restricted to the transition zone between lightly ionized and fully ionized gas. The energy absorbed in this region is estimated as $$\sim\,{10}^{5}\,\text{erg}\,\text{cm}^{-2}.\,\text{sec}^{-1}$$ . Numerous particles with energies ~ 100 EV are released in this region and these may account for the quiet (non-spot) corona. The mechanism is likely to be important in connection with sunspot heating and flares and perhaps also interstellar hydromagnetic waves and cosmic ray generation.