Topside Ionospheric Structure at Northern Mid-latitudes after Ground Sunset in Summer

Abstract

DURING the period between ground sunset and ionospheric sunset, the solar light is considerably filtered during its passage through the entire atmosphere before reaching still-illuminated ionospheric regions. Most of the ionizing radiation is absorbed before it reaches the illuminated regions, hence only some heating might be caused by the long-wavelength spectrum of the incident radiation. It seems reasonable, however, to expect that topside regions are thermally stable because they have been illuminated for a long period of time.