High-latitude radio observations

Abstract

Observations were made on the ionosphere for nearly a year at 80° 23' N., 19° 31' E. It was found that at local noon the E region was present throughout the winter except on a few days which were magnetically disturbed. The electron-density in this region is at a minimum at midwinter and a maximum at midsummer. The F1 region is observed at noon only during the summer months with maximum electron-density at midsummer. The annual variation of maximum ionization in the F2 region is irregular and not very great, but the electron-density is at a maximum in spring and in late autumn. The diurnal variation of electron-density in the F2 region is more marked in the dark period, with a day to night ratio of 2.3: 1, than in the summer solstice period when the ratio is 1.5: 1. This latter figure which is also the ratio for the E and F1 region is in fair agreement with the ratio of 1.63: 1 deduced theoretically on the assumption that the ionizing power is proportional to the altitude of the sun. In all cases the minimum is near midnight with maxima before and after noon and a subminimum near noon. The effect of magnetic storms is to increase the electron-density in the absorbing region below the E region and, in the summer, to reduce markedly the electron-density in the F2 region. Reflections from the persistent E region persist to very high frequencies especially between 1200 and 1800 G.m.t. An intense E region, with a high reflection coefficient, occurs at all seasons during magnetically quiet conditions, and occurs almost solely between 1400 and 2300 G.m.t. No special conditions in the ionosphere obtain when the aurora is overhead, and absorption is not usually markedly increased under such conditions.