## 3 Calculation of Results and Discussion
### Detection of Short-Period Geomagnetic Disturbances, Second-Resolution Data Processing
Evidently, the anomalies occurred as a result of high noise amplitude. We should note that noise manifestation in the method results is observed only near the signal containing noise, compared, for example, to Fourier methods. The result is provided by wavelet finiteness [29,30]. Figure 6 shows the vertical Z-component variations (Figure 6a presents initial data, Figure 6d presents pre-processed data) and the results of method application (Figure 6b,c,e,f). We can see on the graphs that short (duration is several seconds) noise impact from the ionosonde (Figure 6a, green box) was removed after preliminary processing (Figure 6e,f). Noise from the earthquake at 09:07 UT does not have a visible reflection in the time series (Figure 6a, red oval). However, after the preliminary processing (Figure 6d), a false anomaly appeared due to the removing of part of the data (Figure 6e,f), the correction for the nonorthogonality of H-, D-, and Z-sensors is taken into account in Z-variations. Therefore, data removal in variations H and D causes the gap in the Z record. We should note that the problem of correct and effective filling of the gaps in geomagnetic data is  
topical, does not have indisputably recommended methods at the present time, and is often solved individually for each case. Figure 8: Processing of Paratunka and Magadan observatory geomagnetic data on 21 April 2017 (H-component). (**a**) SWS; (**b**) IMF Bz (GSM); (**c**) H-component PET, noisy; (**f**) H-component PET, cleared; (**i**) H-component MGD, noisy; (**d**,**e**,**g**,**h**,**j**,**k**) results of method application. Red vertical line is the magnetic storm beginning. Figure 9: Processing results for geomagnetic data for the period 11–12 May 2021. (**a**) SWS; (**b**) IMF Bz (GSE); (**c**) DST; (**d**) H-component; (**e,f**) results of method application. The red vertical line is the magnetic storm beginning. Analysis of horizontal component H variations (Figure 7) shows that the considered noise has small amplitude and does not significantly impact method results. Regular interference in the shape of a meander also does not affect the processing results. That allows us to apply the suggested method to analyze geomagnetic data (H-components) in online mode and to obtain results with admissible accuracy in case of short low-amplitude noise. Sudden changes caused by external impact (ionosonde or earthquake effects) of large amplitude should be identified and removed by a magnetologist during the preliminary analysis and processing of raw data, or they should be separately marked in processing results. Estimates showed that if noise amplitude is more than 1-3 nT (depending on regular oscillations caused, for example, by GSM-90 interference), they should be removed to obtain reliable results. Filling long gaps in geomagnetic data, especially when choosing inadequate filling methods, causes significant distortions of natural variation changes and the appearance of false anomalies in results. Figure 8 illustrates the results of method application (operations (8) and (9)) for the beginning of a magnetic storm on 21 April 2017. In operation (8), coefficient values \(U_{1}=1.5\) (threshold \(T_{1,s}\)) and \(U_{2}=2.5\) (threshold \(T_{2,s}\)) were used. The moving time window length corresponded to one hour and was \(l=7200\) counts for the initial data and \(l=2880\) for the preliminarily processed data. The Paratunka observatory data processing results are illustrated in Figure 8d,e (initial data) and Figure 8g,h (data preliminarily processed by  
Figure 10: Results of sequential processing of geomagnetic data for the period 11–12 May 2021, before the storm beginning. a magnetologist). For comparison, Figure 8j,k shows the results of the processing of a raw dataset of the Magadan observatory of IKIR FEB RAS (IAGA code is MGD, 60.05 N, 150.72 E). These data were not preliminarily processed since noise amplitude did not exceed 0.5 nT.