The northern tribes of Nigeria; an ethnographical account of the northern provinces of Nigeria together with a report on the 1921 decennial census,

Reprint of the 1925 edMode of access: Internet

Quasi 2-day oscillation of the ionosphere during summer 1992

The relationship between quasi 2-day (QTD) oscillations in the neutral wind near 90 km altitude, and in the critical plasma frequency (ƒoF2) of the ionospheric F region, is investigated for the June–September 1992 period. Wind data are analyzed from MF radar stations at Christmas Island (1.9°N, 202.7°E), Hawaii (20.8°N, 203.5°E), and Saskatoon (52.1°N, 253.4°E) with emphasis on characterizing temporal evolutions of the amplitude and period of the QTD oscillation; four identifiable “events” are found, one each in the months of June, July, August, and September. Evidence for corresponding ±0.5–1.0 MHz QTD oscillations in ƒoF2 is found in data from about half of the 24 ionosonde stations examined. Identification of such concurrent occurrences is complicated by the lack of consistency between QTD “burst” characteristics between station locations (for both wind and ƒoF2) and between the meridional and zonal components of the QTD wind variations. These differences are probably due to the sensitivity of the QTD wind oscillation to the background wind structure, which contains latitude and longitude dependences. Evidence is presented for a zonal wavenumber one (s = 1) longitude dependence for the middle-latitude ƒoF2 oscillation, which contradicts the expected s = 3 dependence of the mesosphere/lower thermosphere (MLT) neutral winds, but which is consistent with the “first type” of QTD oscillation in ƒoF2 at middle latitudes described by Apostolov et al. [1995]. The data presented here are not able to shed light on which of several potential mechanisms lead to the QTD oscillation in ƒoF2Forbes, J. M., R. Guffee, X. Zhang, D. Fritts, D. Riggin, A. Manson, C. Meek, and R. A. Vincen