Abstract
Equatorial plasma bubbles (EPBs) can cause large total electron content (TEC) gradient magnitudes and significant density irregularities. In this paper, depletions and irregularities due to EPBs are identified by using the Global Positioning System (GPS)-TEC time series extracted from nine Global Navigation Satellite System (GNSS) stations over Hong Kong near the equatorial ionization anomaly (EIA) crest region from 2013 to 2019. The correlation analyses between the daily variation in the rate of TEC change index (ROTI) and that of the EPB occurrence rate, depth, and duration are presented. The monthly EPB occurrence rate, depth, duration, and ROTI show strong seasonal variations, with maxima during equinoctial seasons, especially during the moderate-to-high solar activity years of 2013–2016. Furthermore, two seasonal asymmetries can be clearly seen for these parameters from 2013 to 2016. The EPB occurrences rate, depth, and duration vary annually with the solar radio flux at 10.7 cm (F10.7) index. The correlation analyses of the EPB occurrence rate, depth, and duration are found to be much more strongly correlated with the F10.7 index on an annual basis than on a monthly basis. The correlation analysis of monthly variations shows the impacts of solar activity on EPB occurrence, depth, and duration are seasonally dependent, which is significantly greater in the equinoctial seasons and summer than in winter.
Highlights
IntroductionEquatorial plasma bubbles (EPBs) refer to plasma depletions frequently observed in the evening and are the major sources of electron density irregularities in equatorial and low-latitude regions [1,2].The plasma density irregularities within the bubbles can scatter and diffract radio waves, leading to rapid fluctuations in the signal amplitude and phase in a received electromagnetic wave [3].The significant magnitude of total electron content (TEC) gradients associated with the side walls of bubbles or with plasma density irregularities could potentially cause very large Global NavigationSatellite System (GNSS) positioning errors [4,5].Physically, the occurrence of an EPB largely depends on the mechanism for producing initial density perturbations and the conditions affecting the Rayleigh–Taylor (R-T) growth rate [6]
As a Global Positioning System (GPS) satellite–receiver ray path can be impacted by plasma bubbles several times during an observation arc, multiple Equatorial plasma bubbles (EPBs) occurrence events can be observed for a GPS-total electron content (TEC)
The EPB occurrence rate, depth, and duration were highly correlated with the rate of TEC change index (ROTI), with correlation coefficients equal to 0.85, 0.85, and 0.72, respectively
Summary
Equatorial plasma bubbles (EPBs) refer to plasma depletions frequently observed in the evening and are the major sources of electron density irregularities in equatorial and low-latitude regions [1,2].The plasma density irregularities within the bubbles can scatter and diffract radio waves, leading to rapid fluctuations in the signal amplitude and phase in a received electromagnetic wave [3].The significant magnitude of total electron content (TEC) gradients associated with the side walls of bubbles or with plasma density irregularities could potentially cause very large Global NavigationSatellite System (GNSS) positioning errors [4,5].Physically, the occurrence of an EPB largely depends on the mechanism for producing initial density perturbations and the conditions affecting the Rayleigh–Taylor (R-T) growth rate [6]. Equatorial plasma bubbles (EPBs) refer to plasma depletions frequently observed in the evening and are the major sources of electron density irregularities in equatorial and low-latitude regions [1,2]. The significant magnitude of total electron content (TEC) gradients associated with the side walls of bubbles or with plasma density irregularities could potentially cause very large Global Navigation. The occurrence of an EPB largely depends on the mechanism for producing initial density perturbations and the conditions affecting the Rayleigh–Taylor (R-T) growth rate [6]. Through the R-T instability mechanism acting on the steep density gradient of the F region bottom side, equatorial spread. As the lower-density ionosphere moves upward into the higher-density topside ionosphere, a plasma bubble is created.
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