To study the effect of gravity waves/traveling ionospheric disturbances (TIDs) on ionograms with the F2 layer stratification, we reconstructed ionograms using a simple of TIDs model through a ray tracing method. Results show that two typical types of the F2 layer stratification induced by gravity waves/TIDs could be synthesized on ionograms by the simple model of TIDs in this study. Furthermore, we found that vertical and horizontal gradients caused by TIDs could cause different features on ionograms. Results suggested that the vertical gradient induced by gravity waves/TIDs could cause the F2 stratification. The horizontal gradient caused by gravity waves/TIDs might play a significant role in forming spread F on ionograms. Moreover, we found that the smaller wavelength and larger periodical time of TIDs could make it easier to form the F2 layer stratification on ionograms through modeling studies.
Ionospheric nighttime enhancements are manifested in an increase of the electron density at nighttime. This paper studies the latitudinal variation of the specific local time of postmidnight enhancement peaks using ionosondes distributed at low latitudes. To obtain the parameters of the ionosphere, we manually extracted ionograms recorded by ionosondes. Cases show that there are significant latitudinal variations in the observed local time of the postmidnight enhancement peaks. Results show that the lower the geomagnetic latitude, the earlier the enhancement peak occurred in the geomagnetic northern hemisphere. Additionally, the enhancement peaks occurred earlier in the geomagnetic southern hemisphere than that in the geomagnetic northern hemisphere for these present cases. We suggest that the combined effect of the geomagnetic inclination and transequatorial meridional wind might be the main driving force for latitudinal variation of the local time of the occurrence.
The ionospheric responses to the solar eclipse of 15 January 2010 in the equatorial anomaly region have been investigated by three vertical‐incidence and seven oblique‐incidence ionosondes arranged along the meridian from geomagnetic latitudes 18°N to 30°N in eastern China. Though the solar eclipse occurred later in the evening, the eclipse effect on electron density and reflection height of ionospheric F2 layer was clearly observed. The study of the eclipse lag (the time lag between the occurrence of the eclipse maximum obscuration and the occurrence of the maximum depletion of foF2) with latitude indicates it increased with F2 layer altitude. Results suggest also that this eclipse enhanced the prereversal enhancement. An unusual peak occurred after the maximum reduction in foF2 and this was observed by all our ionosondes. The following F2 layer plasma density increase was considered to be caused by the increased westward electric field.
[1] During the total solar eclipse of 22 July 2009, two ground-based high-frequency radio systems were applied to observe the ionospheric variations over Wuhan, China. The ionosonde recorded ionograms every 5 min; the Wuhan Ionospheric Oblique Backscattering Sounding System recorded echo range and Doppler every 1 min. Comparing the observations of the two radio systems, we found that the periodic fluctuation on the top penetration frequency of regular Es (fEs) and on the Doppler velocity of the spread Es appeared and disappeared simultaneously on the eclipse day. Moreover, wavelet analysis results show that the fEs curve and the Doppler velocity of the spread Es contain the same period of ∼35 min. The spread Es occurred owing to the off-vertical reflections from the tilted layer at the Es latitude. Atmospheric gravity waves are considered to be generated during the solar eclipse and propagate upward to deform the Es layer and produce the moving wave-like structures in the layer. The tilted plasma concentration in the moving wave-like structures induced the off-vertical HF radiowave reflections and added the Doppler modulation of also ∼35 min period on the reflected radiowave. Furthermore, the Doppler values of regular Es indicate that the layer at lower altitude was weakly disturbed and the layer at higher altitude was deeply modulated, which is in agreement with the theory that the amplitude of gravity waves increases with height.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.