Abstract
By using multi-satellite observations of the L1 signal-to-noise ratio (SNR) from the Cyclone Global Navigation Satellite System (CYGNSS) taken in 2017, we present the occurrence of nighttime topside ionospheric irregularities in low-latitude and equatorial regions. The most significant finding of this study is the existence of longitudinal structures with a wavenumber 4 pattern in the topside irregularities. This suggests that lower atmospheric waves, especially a daytime diurnal eastward-propagating zonal wave number-3 nonmigrating tide (DE3), might play an important role in the generation of topside plasma bubbles during the low solar minimum. Observations of scintillation events indicate that the maximum occurrence of nighttime topside ionospheric irregularities occurs on the magnetic equator during the equinoxes. The current work, which could be regarded as an important update of the previous investigations, would be readily for the further global analysis of the topside ionospheric irregularities.
Highlights
Topside ionospheric irregularities observed in low-latitude and equatorial regions, which originate in the unstable bottomside ionosphere, have been observed for many years [1,2,3,4,5]
An example of the observations taken by the Cyclone Global Navigation Satellite System (CYGNSS) satellites on May 29, 2017, is shown in
We focused on the statistical occurrence of topside ionospheric irregularities irregularities using the S4 index calculated from the global positioning system (GPS) signals from the CYGNSS satellites
Summary
Topside ionospheric irregularities observed in low-latitude and equatorial regions, which originate in the unstable bottomside ionosphere, have been observed for many years [1,2,3,4,5]. Plasma bubbles are generated in the bottomside of the equatorial F region and extend vertically to the topside ionosphere. They are caused by the nonlinear plasma process of the generalized Rayleigh-Taylor (R-T) instability [6]. Statistical studies of the occurrence of topside ionospheric irregularities in low-latitude and equatorial region have been conducted over the last few decades. Oya et al [7] found that topside ionospheric irregularities mainly occurred after sunset. Su et al [8] proposed that the occurrence of topside ionospheric irregularities was dependent on geomagnetic and solar activity. The latitudinal, longitudinal, and seasonal characteristics of topside ionospheric irregularities were investigated by Kil and Heelis [9]
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