Longitudinal structure of the equatorial ionosphere: Time evolution of the four‐peaked EIA structure

Abstract

[1] Longitudinal structure of the equatorial ionosphere during the 24 h local time period is observed by the FORMOSAT-3/COSMIC (F3/C) satellite constellation. By binning the F3/C radio occultation observations during September and October 2006, global ionospheric total electron content (TEC) maps at a constant local time map (local time TEC map, referred as LT map) can be obtained to monitor the development and subsidence of the four-peaked longitudinal structure of the equatorial ionosphere. From LT maps, the four-peaked structure starts to develop at 0800-1000 LT and becomes most prominent at 1200-1600 LT. The longitudinal structure starts to subside after 2200-2400 LT and becomes indiscernible after 0400-0600 LT. In addition to TEC, ionospheric peak altitude also shows a four-peaked longitudinal structure with variation very similar to TEC during daytime. The four-peaked structure of the ionospheric peak altitude is indiscernible at night. With global local time maps of ionospheric TEC and peak altitude, we compare temporal variations of the longitudinal structure with variations of E Â B drift from the empirical model. Our results indicate that the observations are consistent with the hypothesis that the four-peaked longitudinal structure is caused by the equatorial plasma fountain modulated by the E3 nonmigrating tide. Additionally, the four maximum regions show a tendency of moving eastward with propagation velocity of several 10 s m/s.

Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model

“…The amplitude of wave 4 is about 4% in our simulation, which is a degree similar to the total electron content observation by TOPEX (e.g., Figure 8 of Scherliess et al [2008]) but significantly smaller than the electron content integrated over 400-450 km obtained by the FORMOSAT-3/COSMIC observation (e.g., Figure 1 of Lin et al [2007], which shows an amplitude of more than 10%). As for the wave 1 structure, most observations do not show a clear wave 1, except for the plasma density observation at a 400 km height made by the CHAMP satellite (e.g., Figure 1 of Liu and Watanabe [2008]).…”

“…[13] Compared with observations of the F-region plasma density, the wave 4 structure becomes dominant only in the Southern Hemisphere in our simulation, while the wave 4 structure is observed in both hemispheres for a similar situation (September equinox, daytime, moderate solar activity) [Lin et al, 2007;Kil et al, 2008;Liu and Watanabe, 2008;Scherliess et al, 2008]. The amplitude of wave 4 is about 4% in our simulation, which is a degree similar to the total electron content observation by TOPEX (e.g., Figure 8 of Scherliess et al [2008]) but significantly smaller than the electron content integrated over 400-450 km obtained by the FORMOSAT-3/COSMIC observation (e.g., Figure 1 of Lin et al [2007], which shows an amplitude of more than 10%).…”

“…A prominent four-peak longitudinal structure of the equatorial ionization anomaly (EIA) has been discovered by global satellite observations [e.g., Sagawa et al, 2005;England et al, 2006a;Immel et al, 2006;Lin et al, 2007]. In addition, according to modeling works, the longitudinal dependence of tropospheric convection has been shown to be an important source for the excitation of solar nonmigrating (non-Sun-synchronous) tides that propagate upward to the thermosphere, including the diurnal eastward-propagating tide with zonal wave number 3 (DE3), which has four peaks in the local-time fixed frame [e.g., Forbes, 2002, 2003;Miyoshi, 2006].…”

Wavenumber-4 structures observed in the low-latitude ionosphere during low and high solar activity periods using FORMOSAT/COSMIC observations

“…Visually the wave-4 patterns can be observed in 2008, 2009 and 2010. These four peaks are usually located in the Central Pacific (∼ −180 to −120 • longitude), South America (∼ −120 to −60 • longitude), Africa (∼ −20 to 20 • longitude) and Southeast Asia (∼ 80 to 120 • longitude) (Lin et al, 2007c). From 2011 onward these structures are not well defined in comparison with those observed during the low solar activity years.…”

“…The Formosa Satellite 3, also known as Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC or F3/C), is a set of six microsatellites that monitor atmosphere and space weather with instruments of radio occultation observations at altitudes ranging from the troposphere to the ionosphere (Lin et al, 2007c). The satellites have their final orbit at an altitude of 800 km and a GPS receiver is used to obtain the atmospheric and ionospheric measurements through phase and Doppler shifts of radio signals.…”