The Seasonal and Longitudinal Variations of Nighttime OI 135.6‐nm Emission at Equatorial Ionization Anomaly Crests Observed by the DMSP/SSUSI

Abstract

AbstractNighttime atomic oxygen (OI) 135.6‐nm emission observed by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on board the Defense Meteorological Satellite Program (DMSP) F18 satellite is utilized to investigate the seasonal and longitudinal variations of the equatorial ionization anomaly (EIA) crests at a fixed 20:00 local time (LT) from 1 January 2012 to 31 December 2015. The OI 135.6‐nm emission intensity at the southern and northern EIA crests for each day is considered as a superposition of zonal mean and Zonal Wavenumbers 1–4 components. On the seasonal‐longitudinal variations of the OI 135.6‐nm emission intensity at both EIA crests, the obvious double‐peak structure appears in equinoxes for all 4 years. The longitudinal peaked structures are also prominent in equinoxes, and Peak‐3 structure dominates. The main results are as follows: (1) The zonal mean emission intensity and amplitudes of Wavenumbers 1–4 components at both EIA crests are also evident in equinoxes and have a major semiannual and annual periods, except for amplitude of Wavenumber 4 at the southern EIA crest; the amplitude of Wavenumber 1 component is generally greater than Wavenumbers 2–4; (2) the phases of Wavenumbers 1 and 2 components at both EIA crests have a 1‐year period, and the seasonal variations of the phase of Wavenumber 1 component at both EIA crests are in phase but antiphase in Wavenumber 2; and (3) the phases of Wavenumbers 1 and 2 components between the OI 135.6‐nm emission intensity and the total electron content (TEC) at both EIA crests are almost consistent in April and solstices.