Sunrise Effect on the Field Strength of an If Radio Signal in Relation to the Cosmic Ray Layer of the Ionosphere

Abstract

The daily records of the field strength of an If radio signal on 280 kHz (call sign CB) transmitted from China Day (lat., 9° 11 'N; long., 81° 11 'E) in Ceylon at a distance of about 1800 km from Calcutta (lat., 22° 34'N; long., 88° 24'E) have been examined to explore the role of the cosmic ray layer during sunrise. The results of an analysis of the records obtained during the I-yr period from June 1972 to May 1973, indicate that even in this low latitude the cosmic ray ionization plays an important role during sunrise and that the start of the sunrise in discernible when the ground grazing solar rays strike the 70 km level. The results also indicate that the duration of the sunrise fall of field strength is governed by the subsequent development of ionizations in the C-layer.