Abstract
Abstract Recent observations of the low-latitude F-region ionosphere at times near equinox have shown that it varies with a predominant zonal wavenumber-four pattern in a fixed local-time frame. It has been shown that this pattern corresponds well to the non-migrating diurnal eastward wavenumber-three atmospheric tide (DE3) at E-region altitudes simulated by the Global Scale Wave Model (GSWM). Here we present details of the morphology of the F-region ionosphere from TIMED GUVI with simultaneous observations of the non-migrating diurnal tides at E-region altitudes from TIMED SABER. For the case of equinox (March 2002), the correspondence of the SABER and GUVI observations confirms the relationship previously established using the GSWM simulations. There is also a wavenumber-one signature that is present which may be related to the semi-diurnal westward wavenumber-three, possibly in conjunction with changes in the magnetic field with longitude. During July 2002, when the amplitude of the DE3 maximizes, the amplitude of the wavenumber-four pattern in the F-region ionosphere intensifies. There is also evidence of a strong wavenumber-three pattern in the F-region ionosphere, which can be attributed to the strong diurnal eastward wavenumber-two tide during this period. During January 2003, the amplitude of all non-migrating components observed by SABER are either small or asymmetric and the ionosphere does not display either a wavenumber-three or -four pattern. During both solstice periods, a strong wavenumber-one is seen that is attributed to the offset of the subsolar point and the geomagnetic equator that maximizes at solstice, possibly in conjunction with other geomagnetic effects. During all seasons, significant hemispheric asymmetries in the airglow wavenumber spectra are seen. The combined GUVI and SABER observations presented here demonstrate that the large-scale periodic longitudinal structure of the F-region ionosphere responds significantly to changes in the forcing by non-migrating diurnal tides at E-region altitudes.
Highlights
The plasma density in the low latitude ionosphere is most concentrated in two bands, each around 15◦ from the magnetic equator (Namba and Maeda, 1939; Appleton, 1946)
This feature is referred to as the equatorial ionospheric anomaly (EIA). It is created by the uplift of F-region plasma close to the magnetic equator, followed by the subsequent redistribution of that plasma to lower altitudes, following the magnetic field lines. This uplift is caused by polarization electric fields produced by a combination of tidal winds at E-region altitudes (Tarpley, 1970), which dominate at most local times (LT), and F-region winds, which dominate around sunset (Woodman, 1970; Rishbeth, 1971; Farley et al, 1986)
We have shown that: 1) The wavenumber-four pattern observed in the equatorial F-region ionosphere by GUVI during March is consistent with the driving tidal component (DE3) observed by SABER at E-region altitudes during the same time period
Summary
The plasma density in the low latitude ionosphere is most concentrated in two bands, each around 15◦ from the magnetic equator (Namba and Maeda, 1939; Appleton, 1946). In order to study the morphology of the lowlatitude airglow bands in the absence of external penetrating electric fields, data in each of these seasons are sorted for low to moderate geomagnetic activity (Kp ≤ 4) This is slightly less strict than the sorting of the IMAGE FUV data, or the previous TIMED GUVI analyses discussed in the introduction which sorted for Kp ≤ 3, but is required to allow a sufficient number of observations in each of these time periods to produce plots representative of the monthly mean airglow morphologies. We shall present the residuals from the mean temperatures measured by SABER as a function of latitude and longitude at 110 km altitude (see figure 6 of Forbes et al (2006) and related discussion) For just 30 days of SABER data, it is not possible to separate these out into east and west components, so we shall rely on Fig. 3 for this information
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
