Study on Seasonal Variations of Plasma Bubble Occurrence over Hong Kong Area Using GNSS Observations

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.

Evaluating Total Electron Content (TEC) Detrending Techniques in Determining Ionospheric Disturbances during Lightning Events in A Low Latitude Region

“…The unit of VTEC and DTEC is Total Electron Content Units (TECU; 1 TECU = 10 16 e/m 2 ). Orders of 3 and 6 and time window lengths 30, 60, 90 and 120 min [13,21,22] were selected for Savitzky-Golay, and orders of 3, 5 [23,24], 6, [1,12,25], and 10 [11] were used for polynomial fitting. The selected parameters for detrending are summarized below in Table 1.…”

A ROTI-Aided Equatorial Plasma Bubbles Detection Method

“…The EPBs can cause the scintillations and huge ionospheric gradients of radio signals, leading to severe effects on navigation and communication systems [3]. As a result, the study on climatology and the forecasting of EPBs has remained an open question among the scientific community during the last two decades [4][5][6][7][8][9][10][11][12][13][14][15][16]. Many measurements, such as in situ satellite data [4,5], ionosonde [6], and airglow imaging [9,16] are applied to investigate the EPBs characteristics.…”

“…Many measurements, such as in situ satellite data [4,5], ionosonde [6], and airglow imaging [9,16] are applied to investigate the EPBs characteristics. In recent years, the Global Navigation Satellite System (GNSS) ionospheric Total Electron Content (TEC) has been an important tool for the study of EPBs due to its high spatial-temporal resolution [10][11][12][13][14][15].…”

“…To study the EPBs using GNSS TEC data, the first step is to extract the EPBs signals in the TEC series. One common method is using a polynomial fitting with a specific window length to fit the TEC series; then the detrended TEC series that might include EPBs signals are obtained by subtracting the fitted TEC series from the observed TEC series [11][12][13][14][15]. However, the detrended TEC series achieved by this method not only contain depletion but also enhancement, which is similar to the feature of the Medium-Scale Travelling Ionospheric Disturbances (MSTIDs).…”

Asymmetric Development of Equatorial Plasma Bubbles Observed at Geomagnetically Conjugate Points Over the Brazilian Sector

“…The threshold of ±1 TECU was chosen to avoid the influence of other disturbances such as medium-and large-scale traveling ionospheric disturbances. Similar methodology has been described by Haase et al (2011), Takahashi et al (2015, Li et al (2020), andTang et al (2020). Figure 1 shows examples of nights with (a and b) and without (c and d) EPBs occurrence.…”