## 3 Calculation of Results and Discussion
### Detection of Short-Period Geomagnetic Disturbances, Second-Resolution Data Processing  
Figures 5-7 show the processing results for the raw second data and the data used during the preparation of INTERMAGNET preliminary minute values. The data were obtained on 5 December 2017, by a fluxgate magnetometer FGE-DTU [47], installed at the Paratunka observatory within the scientific cooperation between IKIR FEB RAS and the  
Figure 7: Processing results for H-component variations on 5 December 2017. (**a**) H-component, noisy; (**d**) H-component, cleared; (**b**,**c**,**e**,**f**) results of method application. Deutsches GeoForschungsZentrum GFZ (Helmholtz-Zentrum Potsdam). The magnetometer sensitivity is up to 0.01 nT and the measurement frequency is 2 Hz. A suspended system of sensors is used in the magnetometer. It automatically aligns the Z-axis to a vertical position; however, it causes sensitivity to mechanic impacts on the magnetometer basis, for example, during seismic wave passing or severe shocks near an installation place. There is some noise (oscillations) in the interval under consideration in the records. It is caused by the earthquake that occurred at 09:06:04 UT at a depth of 40 km and about 170 km away from the observatory. The earthquake class was Ks = 10.6 (Figures 5-7, red oval). Noise effects from earthquakes can reach one-hundreds of nT depending on distance, depth, and magnitude. A known and quite frequent problem of the observatories carrying out different kinds of measurements is interference from radio devices, for example, from ionosondes and radars located near magnetometers. At the Paratunka observatory, short packages of noise are observed every 15 minutes in records of FGE-DTU magnetometer. They occur during the ionosphere vertical sounding by automatic ionosonde Parus (Figures 5-7, green box). One more common issue is the mutual influence of closely located magnetometers. For example, magnetometers with coil systems, such as OldD GSM-19 FD or POS-4, create additional magnetic fields around a sensor during current overlapping in coils. Additional fields also occur around the connecting cables and proton magnetometer sensors during the polarization process. An example of the latest effect is illustrated in Figures 5-7, panel (a) Overhauser magnetometer GSM-90 generates noise in FGE-DTU measurements in the form of a meander with the period of 5 s and amplitude of 0.5 nT and more. A detailed description of the noise mentioned above is given in the paper [48]. Standard processing of FGE-DTU records by a magnetologist at the Paratunka observatory includes some operations. The effect from GSM-90 with 5-s cycle is removed by selecting the FGE data out of the time interval when GSM-90 polarization occurs. In this case, the uniform set of values with the frequency of 2 Hz is uniformly gaped with a frequency decrease to 0.4-0.5 Hz. The noise from the ionosonde is regular and occurs at known times, thus, it is removed automatically when a magnetologist has determined sounding parameters and noise duration during sounding. Irregular noise, for example, from earthquakes, is visually identified by a magnetologist from the raw curves. Noised intervals are marked and are not used in further processing [49]. Our algorithms applied in the analysis need the series with uniformly distributed data without gaps. Thus, the gaps were preliminarily filled on a uniform greedy by the nearest neighbor method. Figure 5 shows magnetic field D-component variations (Figure 5a presents raw data, Figure 5d presents data processed by a magnetologist) and the results of method application (Figure 5b,c,e,f; (8), (9) operations were used). The analysis shows evident noise generated by an earthquake and the ionosonde (Figure 5a, red oval and green box). Comparison of the method results obtained for the raw data (Figure 5b,c) and preliminarily processed data (Figure 5e,f), shows a significant impact of noise on the processing results at the times of its occurrences.