**3. Results**

The results are presented in ascending order of set of days. The days in each set are also presented in chronological order. For brevity, the parameters in Table 1 are shortened as follows: polynomials are prefixed by the letter P, followed by the order. For instance, the polynomial of order 3 is represented as P3. That of Savitzky–Golay is prefixed as sgf, followed by the order and window length. For example, the Savitzky– Golay of order 3 with a window length of 30 min is represented as sgf\_3\_30. Figures showing the lightning count and current are also presented. With TEC and DTEC, the stations of the HK SatRef are quite close; hence, similar observations are made by most stations at a given time [14]. Only observations from station HKOH meeting the criteria in Section 2.4 are presented. A plot of TEC and DTEC for a given satellite in a day has six rows. The first row comprises the original and fitted TEC of P3, P5, P6 and P10 while the second row comprises their respective DTEC. The third row also comprises the original and fitted TEC of sgf\_3\_30 to sgf\_3\_120, with the fourth row comprising their respective DTEC. The fifth and last rows follow the same order as the third and

fourth rows for sgf\_6 parameters. All of the subsequent figures presented showing TEC and DTEC in this section follow the same format.
