Open AccessSolar and geomagnetic trends of equatorial evening and nighttime F region vertical ion drifts
Author(s) -
Oyekola O. S.,
Oluwafemi C. O.
Publication year - 2008
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008ja013315
Subject(s) - solstice , earth's magnetic field , noon , evening , morning , ionosphere , atmospheric sciences , solar maximum , magnetic dip , solar minimum , solar cycle , environmental science , physics , solar wind , geophysics , latitude , astronomy , magnetic field , quantum mechanics
F region vertical ion drifts were inferred from the evening and nighttime ionosonde data for two magnetic equatorial stations in West Africa: Ouagadougou (geographic: 12°N, 1.5°W; 5.9°N dip) and Ibadan (geographic: 7.9°N, 3.9°E; 6°S dip). We examine and discuss the short‐term patterns of behavior of ionospheric variability over Ouagadougou for 1986–1987 years of low solar activity ( F 10.7 = 80) and 1988–1989 years of high solar activity ( F 10.7 = 180) for quiet time, while that of Ibadan is for undisturbed ( Kp ≤ 3.0) and disturbed ( Kp > 3.0) geomagnetic conditions during the 1958 International Geophysical Year (IGY) period, corresponding to high solar flux conditions ( F 10.7 = 208). Our results indicate that the evening and nighttime ion drift exhibits strong variations with the phase of the solar cycle but only small variations with geomagnetic activity. The characteristic values of evening prereversal velocity enhancements (PRE) vary between about 2–14 m/s and 12–22 m/s and 17–42 m/s and 18–40 m/s for low and high solar flux, unperturbed and perturbed conditions, in that order. The solar minimum evening reversal times are strongly season dependent, while the morning reversal times are season independent except during December solstice, which occurs earliest. During solar maximum, reversal times near dawn and dusk are essentially season independent except during June solstice season, which occurs late. The average occurrence time (1900 LT) of PRE is strongly independent of solar and magnetic variations apart from June solstice of high solar activity periods.