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

Abstract

Total Electron Content (TEC) from Global Navigation Satellite Systems (GNSS) is used to ascertain the impact of space weather events on navigation and communication systems. TEC is detrended by several methods to show this impact. Information from the detrended TEC may or may not necessarily represent a geophysical parameter. In this study, two commonly used detrending methods, Savitzky–Golay filter and polynomial fitting, are evaluated during thunderstorm events in Hong Kong. A two-step approach of detection and distinguishing is introduced alongside linear correlation in order to determine the best detrending model. Savitzky–Golay filter on order six and with a time window length of 120 min performed the best in detecting lightning events, and had the highest moderate positive correlation of 0.4. That the best time frame was 120 min suggests that the observed disturbances could be travelling ionospheric disturbance (TID), with lightning as the potential source.

Comparative Study of Predominantly Daytime and Nighttime Lightning Occurrences and Their Impact on Ionospheric Disturbances

“…Pseudorandom noise codes (PRN) from the individual satellite-receiver pairs available at the time ROTI lags the lightning are presented to provide extra evidence of ionospheric disturbances. The TEC of the PRN is detrended using the Savitzky-Golay filter of order 6 and window length of 120 min [16]. Detrended TEC (DTEC) is filtered with a bandpass of frequencies between 1 and 2.8 MHz and 4.2 and 8.2 MHz to derive ionospheric gravity (IGW) and ionospheric acoustic (IAW) waves, respectively, from lightning [17,63].…”

“…The network consists of about 17 Vaisala LS8000 sensors that provide the geolocation and source peak currents of lightning in the area [24]. The number of times a current is recorded is positively correlated with lightning activity [25]; a day with a lightning count greater than 10,000 is deemed a "lightning day" [16]. The data span is from 2014 to 2017.…”

“…Thunderstorms/lightning, another troposphere weather event, has also garnered interest in the GNSS scientific community for adopting the advantages of GNSS to gain more insight into its activities. In recent GNSS lightning studies, Osei-Poku et al [16] evaluated common total electron content (TEC) detrending techniques during lightning events. Rahmani et al [17] probed the vertical coupling effect of a thunderstorm on the lower ionosphere.…”

Ionosphere Response to the simultaneous and consecutive occurrence of Geomagnetic Storm and Lightning at various intensities in a Low Latitude Region

“…A day with lightning count greater than 10,000 is deemed as "lightning day." (Osei-Poku et al, 2021). Different intensities of lighting are categorized as follows; Non-lightning (NL): count < 10,000, Moderate Lightning (ML): 10,000 ≤ count < 20,000, Intense Lighting (IL): 20,000 ≤ count < 40,000 and Super Lightning (SL): count ≥ 40,000.…”

“…VTEC was then detrended using Savitzky-Golay order of 6 and window length 120mins (Osei-Poku et al, 2021) to get detrended TEC (DTEC), using Equation (2). DTEC served as the input for spectral analysis.…”