Abstract
In this study, the characteristics and causes of the seasonal variations in plasma bubble occurrence over the Hong Kong area were investigated using the local Global Navigation Satellite System (GNSS) network. Generally, the occurrences of plasma bubbles were larger in the two equinoxes than in the two solstices. Furthermore, two seasonal asymmetries in plasma bubble occurrence were observed: plasma bubble activity was more frequent in the spring equinox than in the autumn equinox (equinoctial asymmetry), and more frequent in the summer solstice than in the winter solstice (solstitial asymmetry). The equinoctial asymmetry could be explained using the Rayleigh–Taylor (R–T) instability mechanism, due to larger R–T growth rates in the spring equinox than in the autumn equinox. However, the R–T growth rate was smaller in the summer solstice than in the winter solstice, suggesting the R–T instability mechanism was inapplicable to the solstitial asymmetry. Our results showed there were more zonally propagating atmospheric gravity waves (GWs) induced by thunderstorm events over the Hong Kong area in the summer solstice than the winter solstice. So, the solstitial asymmetry could be attributed to the seeding mechanism of thunderstorm-driven atmospheric GWs.
Highlights
A plasma bubble is one kind of frequent ionospheric weather event in low-latitude areas
The presence of a plasma bubble can cause severe effects on radio signals of communication and navigation systems, such as the Global Navigation Satellite System (GNSS), when they travel through the ionosphere (e.g., [1,2])
Plasma bubble occurrence was maximum during the high solar activity year of 2014 and minimum during the low solar activity year of 2017, indicating that it was dependent on solar activity
Summary
A plasma bubble is one kind of frequent ionospheric weather event in low-latitude areas. Research shows that plasma bubble occurrence presents seasonal variations and longitudinal variations (e.g., [7,8]). Asymmetric seasonal variations in plasma bubble occurrence in different areas have been reported (e.g., [8]). Two types of physical mechanisms have been employed to account for the seasonal variations and longitudinal variations in plasma bubble occurrence. The growth condition of R–T instability is considered to be the important factor that controls the climatology of plasma bubble occurrence. Hococuwrreevnecre, tohveercathuissearfeoar uthsiengseasonal variationGsNinSSptloatsaml aelebcutrbobnlecoonctceunrtre(TnEcCe)wdaastaradruerliyngin2v0o0l1v–e2d01i2n atnhdeirobstauidneieds.vTerhyismsetaundinygsfouul grehstutltos.address this gapHboywloevoekri,ntgheactatuhsee pfoorttehnetisaelassoonuarlcveasroiaftitohnes sineapsloansmalavbaurbiablteiooncscuinrrepnlcaesmwaasbruarbeblyleinovcocluverdreinnce The monthly plasma bubble occurrence was computed by dividing the number of days with plasma. The seasonal plasma bubble occurrence was obtained by averaging the monthly plasma bubble occurrence of the three months comprising a season
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