The solar X-ray spectrum and the density of the upper atmosphere

Abstract

The flux density of solar x-rays arriving in the E region of the ionosphere was measured by means of photon counters in rockets. Flux densities as a function of altitude were obtained in the spectral bands 8A to 20A, 44A to 60A, and 44A to 100A. The data were extrapolated to zero air mass to give the respective flux densities in the three bands outside the atmosphere. To a first approximation, the observations may be fitted to a 700,000 deg K Planckian distribution of solar x-rays with a total flux density of about 0.1 erg cm−2 sec−1 at the earth. A more refined analysis reveals that it is an oversimplification to assign a single temperature to the entire corona. The shortest wavelengths, 8A to 20A, appear to have come from a hotter source, at a temperature between one and two million deg K. From the rate of x-ray absorption between 128 and 110 km and known mass absorption coefficients for air, the atmospheric density was computed to be about one-third the current Rocket Panel average values.