Occurrence probability and amplitude of equatorial ionospheric irregularities associated with plasma bubbles during low and moderate solar activities (2008–2012)

Abstract

We present a statistical analysis of the occurrence probability of equatorial spread F irregularities measured by the Communication/Navigation Outage Forecasting System satellite during 2008-2012. We use different criteria (plasma density perturbations, ΔN, and relative density perturbations, ΔN/N 0 ) to identify the occurrence of ionospheric irregularities. The purpose of this study is to determine whether the occurrence probability of irregularities is the same for different criteria, whether the patterns of irregularity occurrence vary with solar activity and with local time, and how the patterns of irregularity occurrence are correlated with ionospheric scintillation. It is found that the occurrence probability of irregularities and its variation with local time are significantly different when different identification criteria are used. The occurrence probability based on plasma density perturbations is high in the evening sector and becomes much lower after midnight. In contrast, the occurrence probability based on relative density perturbations is low in the evening sector but becomes very high after midnight in the June solstice. We have also compared the occurrence of ionospheric irregularities with scintillation. The occurrence pattern of the S4 index and its variation with local time are in good agreement with the irregularity occurrence based on plasma density perturbations but are significantly different from those based on relative density perturbations. This study reveals that the occurrence pattern of equatorial ionospheric irregularities varies with local time and that only the occurrence probability of irregularities based on plasma density perturbations is consistent with the occurrence of scintillation at all local times.

Effects of the postsunset vertical plasma drift on the generation of equatorial spread F

“…When the background plasma density is high, especially in the evening sector during the periods of high solar radio flux, the global distributions of ESF occurrence based on the two definitions are similar. Significant difference in the global distributions occurs when the background plasma density is low, for example, in the postmidnight sector near June solstice at deep solar minimum (Huang et al 2014). The global distribution of ESF occurrence based on ΔN with C/NOFS data at moderate solar activity is quite similar to that based on σ with ROCSAT-1 data (Kil et al 2009).…”

“…Kil et al (2009), also using ROCSAT-1 data, used 100-s data (~700 km along the satellite track) instead of 10-s data, and the background ion density (N 0i ) was represented by an 11-point smoothing curve. In the study of Huang et al (2014), the ion density data were measured by the Planar Langmuir Probe (PLP) onboard the C/NOFS satellite. The original PLP measurement was made at 512 Hz.…”

“…The original PLP measurement was made at 512 Hz. The ion density data used by Huang et al (2014) were the 1-s averages over the 512 samples per second. In other words, the ion density data in the study of Huang et al (2014) had temporal resolution of 1 s. The σ value is calculated over 10 data points (10 s).…”

“…The ion density data used by Huang et al (2014) were the 1-s averages over the 512 samples per second. In other words, the ion density data in the study of Huang et al (2014) had temporal resolution of 1 s. The σ value is calculated over 10 data points (10 s). Each N i is the ion density at the ith data point, and each N 0i is the average value over 60 s (corresponding to4 20 km along the satellite track) centered at the ith data point.…”

“…In the studies of Huang et al (2014) and Huang and Hairston (2015) using C/NOFS data, the method for the calculations of ΔN is the same as that for σ.…”