The location of Moreton waves in the solar atmosphere

Two explanations for the pattern of Moreton waves observed in the solar atmosphere in H α are considered: a model with a wave-front cloud located in the upper chromosphere and moving radially downward, and a model in which the entire H α absorption line is shifted. It was not possible to obtain the observed brightness curve for the front in the former model for any optical parameters of the cloud: the source function S , optical depth τ , Doppler width Δ λ d , and Doppler shift of the cloud absorption within the H α line Δ λ sh (due to the radial motion of the wave-front cloud). The observed pattern of the wave front can be obtained only if the entire H α absorption line is shifted. On this basis, it is concluded that this wave propagates in the region of formation of the H α absorption, i.e., in the photosphere and lower chromosphere. This conclusion is supported by the fact that Moreton waves are not observed in the upper chromosphere. It is also shown that these waves cannot propagate in the corona, since the time for for the coronal gas to cool to temperatures near 10 000 K exceeds the wave period by an order of magnitude. Moreton waves are also not shocks, since the observed wave-front profiles do not display the discontinuities characteristic of shocks.