Daytime longitudinal structures of electron density and temperature in the topside ionosphere observed by the Hinotori and DEMETER satellites

Abstract

[1] Daytime longitudinal structures of the electron density (N e ) and temperature (T e ) in the topside ionosphere observed by Hinotori and DEMETER are examined under various conditions of solar flux, local time, and seasons. Results from both satellites show a similar longitudinal N e structure in the morning from July to October, although the value of N e observed by Hinotori is higher than that of DEMETER owing to higher solar flux. This result implies that the longitudinal structure of N e may appear in any solar cycle. Further, a negative correlation between N e and T e in the longitudinal structures appears in the morning when N e is low, while a positive correlation appears around the magnetic equator when N e is sufficiently enhanced during noontime in the high solar flux. A spectrum analysis performed on the DEMETER data reveals that wave numbers 1-2 for N e and T e are dominant and nondominant. The observed wave numbers 3-4 for N e are dominant during November-May and June-October, while they are dominant for T e during October-June and July-September. Both N e and T e show the largest power of wave number 3 in December and wave number 4 in September. Further, observed annual variations of wave numbers 3-4 for N e and T e also differ from wave numbers 3-4 generated by waves in the lower thermosphere. It can be interpreted as discrepancies between the longitudinal distributions of N e and T e caused by difference in the condition of zonal winds driving E region dynamo and meridional winds modulating the ionospheric plasma structures.

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.…”

“…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. Though the IRI model also shows a longitudinal structure, the longitudinal structure retrieved with the F3/C model is more pronounced than that of the IRI and its seasonal variation agrees with previous studies.…”

Electron Density Comparison Between IRI 2007 and DEMETER Satellite Data in Solar Minimum Year

“…The plasma parameters detected by the ISL have been used in many papers (Onishi et al 2009;Jhuang et al 2010;Kakinami et al 2011;Li et al 2011;Zhao et al 2013). Kakinami et al (2011) studied the daytime longitudinal structures of electron density and temperature in the topside ionosphere observed by the Hinotori and DEMETER satellites, which showed a similar longitudinal N e structure in the morning from July to October, and similar pronounced N e maxima in Southeast Asia, the Pacific Ocean and west of South America in the different solar flux conditions.…”

“…The plasma parameters detected by the ISL have been used in many papers (Onishi et al 2009;Jhuang et al 2010;Kakinami et al 2011;Li et al 2011;Zhao et al 2013). Kakinami et al (2011) studied the daytime longitudinal structures of electron density and temperature in the topside ionosphere observed by the Hinotori and DEMETER satellites, which showed a similar longitudinal N e structure in the morning from July to October, and similar pronounced N e maxima in Southeast Asia, the Pacific Ocean and west of South America in the different solar flux conditions. In addition, Jhuang et al (2010) found a middle latitude enhancement in DEME-TER ISL data in the nighttime from September to April during 2005 -2009, consistent with the ionospheric F2 region observation detected with ionosonde, incoherent scatter radar and the techniques for GPS total electron content (TEC) (Jhuang et al 2010).…”

“…An empirical model like the IRI has to rely on extrapolation to describe the ionosphere during the very low and prolonged minimum. It was found that the empirical ionospheric models overestimated the satellite observations of the upper transition height, the ion temperature and N e in the topside ionosphere (Lühr and Xiong 2010;Kakinami et al 2011;Liu et al 2011aLiu et al , b, 2012. Lühr and Xiong (2010) showed that the International Reference Ionosphere (IRI) 2007 model (Bilitza and Reinisch 2008) overestimated the N e observations of CHAMP and GRACE satellites by 50% in 2008 and more than 60% in 2009, respectively.…”