A study of the white light flare of 1974 September 10

We have made a detailed analysis of the spectral data of the white light flare of 1974 September 10. Using a non-LTE theory we have calculated a semi-empirical atmosphere model and its radiation loss. From the spectra we found (1) a Balmer jump amounting to 11% at the flare maximum, (2) strong and broad Balmer line emission, the width of the higher order terms reaching a minimum between main quantum number 8 and 9, and (3) the continuum emission peaking at about the same time as the microwave emission, a few minutes before the H _α flare maximum. These features may be common to all white light flares. Analysis shows that the heating in the photosphere and lower chromosphere is probably produced by backwarming of the enhanced emission in the upper chromosphere, while the heating of the upper chromosphere is probably due to bombardment by high-energy electron beams.