Conjugate F‐Region Enhancement Related to the South Atlantic Magnetic Anomaly

Abstract

Airborne ionospheric measurements have been made during solar minimum years (1963‐1965) off the east coast of the United States from Boston to Puerto Rico, the area conjugate to the western slope of the South Atlantic magnetic anomaly. Vertical incidence ionosonde soundings were made on 17 flights under both day and night conditions, and were compared with ground‐based observations along the 75° W meridian. On several late afternoon and night flights, higher values of foF2 were observed over the North Atlantic Ocean compared with the same local time values observed by the ground stations. During the daytime, no such enhancements were found. To determine the east‐west extent of this anomaly, an additional analysis was made using published true‐height profile data (from White Sands, New Mexico, as well as from the east coast chain), which revealed that the east coast exhibits a significant enhancement of F‐region ionization when compared to White Sands and manifests seasonal and diurnal variations. Earlier reported measurements in the southern conjugate region indicated that there is an effect of dumping of trapped electrons, which is most pronounced in the F layer on the western slope of the magnetic anomaly between L = 1.75 and 3 during December and January. No significant D‐ or E‐region effects have been observed in both hemispheres as yet. Circumstantial evidence indicates that there are F‐region ionospheric effects in the Northern Hemisphere due to energetic electrons backscattered from the southern dumping region.