Publication Date:
2016-05-14
Description:
This paper examines a number of sources of ionospheric variability and demonstrates that they have relationships in common which are currently not recognised. The paper initially deals with medium to large scale travelling ionospheric disturbances. Following sections deal with non-TID ionospheric variations which are often repetitious from day to day. The latter include the temporary rise in F2 height associated with sunset in equatorial latitudes resulting from strong upward drift in ionisation driven by an ExB force. The following fall in height is often referred to as the pre-midnight collapse and is accompanied by a temporary increase in foF2 as a result of ionospheric compression. An entirely different repetitious phenomenon reported recently from middle latitudes in the southern hemisphere consists of strong morning and afternoon peaks in foF2 which define a mid-day bite-out and occur at the equinoxes. This behaviour has been speculated to be tidal in origin. All the sources of ionospheric variability listed above exhibit similar relationships associated with a temporary expansion and upward lift of the ionospheric profile and a fall involving a compression of the ionospheric profile producing a peak in foF2 at the time of maximum compression. Such ionospheric compression/decompression is followed by a period in which the ionospheric profile recovers. Such relationships in travelling ionospheric disturbances (TIDs) have been noted previously. The present paper establishes for the first time that relationships hitherto seen as occurring only with TIDs are also present in association with other drivers of ionospheric variability.
Print ISSN:
0048-6604
Electronic ISSN:
1944-799X
Topics:
Geosciences
,
Physics
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