Longitudinal structure of the equatorial anomaly in the nighttime ionosphere observed by IMAGE/FUV

Abstract

[1] The Far Ultraviolet Imager (FUV) on board the IMAGE satellite provides an instantaneous global view of the OI 135.6-nm nightglow with 2 min time resolution. Because the OI 135.6-nm emission from the nighttime ionosphere is determined by the line-of-sight integrated plasma density, the nightglow images are useful for studying the nighttime low-latitude ionosphere globally. With the IMAGE/FUV 135.6-nm observations from March to June 2002, we have examined the global characteristics of the nighttime equatorial anomaly (EA) by constructing a constant local time map (LT map), in which pixels within an assigned local time range are extracted from the IMAGE/FUV nightglow images obtained over an observation period of 3 days or more and are put together to compose a global distribution map of emission intensities at that local time. These LT maps show that the development of the EA has a significant longitudinal structure, in which peaks and dips of the crest emission intensity and the crest latitude have about 90°longitudinal separation in the longitude range from 0°to 250°. Although there is not enough data over the American sector, this result suggests that the EA longitudinal structure has a prominent zonal component of the wave number 4. The observed longitudinal structure of the nighttime EA could not be fully explained by factors such as the empirical electric field and neutral wind models, the geomagnetic declination angle, or the displacement of the geomagnetic equator from the geographic equator. To explain the observed longitudinal structure of the EA, in particular, the wave number 4 feature, we may need to consider other forcing, for example, nonmigrating tide originated from the lower atmosphere.

A comparison of a model using the FORMOSAT-3/COSMIC data with the IRI model

“…7, a large-scale longitudinal structure, which is similarly reported by many scientists (e.g. Sagawa et al, 2005;Immel et al, 2006;Lin et al, 2007;Kakinami et al, 2011), is clearly seen around the magnetic equator in the F3/C model. According to Kakinami et al (2011), the 4-peak structure of N e at 660 km observed with the DEMETER satellite is the most pronounced in September while a 3-peak structure appears in March and December.…”

“…The International Reference Ionosphere (IRI) has been developed since 1978 (Rawer et al, 1978) and is established as the most standard and reliable ionospheric empirical model. Since a large amount of ionosonde data has been used, IRI derives a relatively accurate electron density (N e ) profile below the F 2 peak.…”

The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE

“…The phase of the SPW defines the longitude where the wave crest occurs. At low and equatorial latitudes the WN4/WN3 patterns of the ionospheric and thermospheric quantities and the related tidal components have been widely studied (Sagawa et al, 2005;Immel et al, 2006;England et al, 2006England et al, , 2010Lühr et al, 2008Lühr et al, , 2012Kil et al, 2007;Häusler and Lühr, 2009;Zhang et al, 2010;Xiong and Lühr, 2013;. These tides originate from the lower atmosphere and can propagate upward to the upper atmosphere, either by direct propagation or through the E region wind dynamo coupling mechanism (e.g.…”

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

“…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].…”