On the occurrence of F region irregularities over Haikou retrieved from COSMIC GPS radio occultation and ground‐based ionospheric scintillation monitor observations

Abstract

In this paper, the amplitude scintillation index (s4) derived from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) radio occultation (RO) technique and ground‐based Ionospheric Scintillation Monitor (ISM) at Haikou station (geographic latitude: 20.0°N, geographic longitude: 110.3°E, and geomagnetic latitude: 10.02°N) is used to investigate the morphology of F region irregularities in the low latitudes of China. The RO events of tangent point within the range of 10–30°N latitude, 70–160°E longitude, and 150–500 km altitude are adopted to analyze the ionospheric scintillation characteristics. The percentage of ionospheric scintillation occurrence is computed to obtain its diurnal variations, seasonal trends, and the dependence on solar and geomagnetic activities. Based on a statistical analysis of a long‐term period data set (years 2007 to 2013), we found that the ionospheric scintillation occurrence from both techniques show similar variations. After sunset (18 LT), the scintillation occurrence increases rapidly and reaches the maximum 3 h later. Then it decreases rapidly till 04 LT and remains low level during the daytime. The ionospheric scintillation tends to occur more frequently during vernal and autumnal equinoxes, especially in March–April and September–October. The equinoctial asymmetry could be seen clearly from the ground‐based ISM observations. The peak ionospheric scintillation occurrence time varies with seasons. It is reached latest in summer, while in spring it is very close to that in autumn. The nighttime ionospheric scintillation occurrence tends to increase with increasing solar activities. The increasing tendency is more prominent in vernal and autumnal equinoxes than that in summer and winter. In general, the control of geomagnetic activities is apt to inhibit ionospheric scintillation at equinox nighttime. In summer and winter, the geomagnetic activities could either trigger or inhibit the generation of ionospheric irregularities in a much more complicated way. Thus, it can be concluded that the tangent point location does accurately represent the scattering region, at least in an average sense. The RO technique is demonstrated to be a useful tool for remotely sensing the terrestrial ionosphere on a global scale down to the regional scale in terms of scintillation occurrence.

Unseasonal development of post-sunset F-region irregularities over Southeast Asia on 28 July 2014: 1. Forcing from above?

“…Figure 2 shows the locations of the GPS RO event tangent points for which the maximum scintillation levels (i.e., "S4max9sec") were greater than 0.3 between the altitudes of 150 and 400 km in the post-sunset hours (i.e., 19-00 LT) during 27-29 July 2014; the remaining post-sunset RO events are shown in gray. This GPS RO scintillation threshold and these altitude boundaries have been shown to be quite effective in isolating scintillation events caused by EFIs in the post-sunset F layer (e.g., Carter et al 2013;Yu et al 2017). Note that the tangent points between the altitudes of 80 and 600 km are plotted.…”

The Ionospheric Exploration Based on TJU#01 Meteorological Microsatellite Mission: Initial Results

“…In this situation, the fluctuations of SNR and amplitude S4 index are more durable and occurring at higher TP heights between 150 and 400 km, therefore recognized as scintillation caused by F‐region irregularities. These scintillations are more frequently detected in the equatorial areas during nighttime which possibly correspond to the R‐T instability activity (Yeh & Liu, 1982; Yu et al., 2017). As mentioned before, the TP of S4max is regarded as the equivalent location of irregularities.…”

Automatic GNSS Ionospheric Scintillation Detection with Radio Occultation Data Using Machine Learning Algorithm

“…Current research into ionospheric scintillation detection relies heavily on groundbased ionospheric scintillation monitoring (ISM) stations [13,14]. While these stations offer prolonged and continuous monitoring, their limited geographic coverage means they are unable to capture the diverse range of scintillation features present in different regions.…”