Study of sudden magnetic storm commencement from observations with second time resolution

The article presents the results of a studying detection of the sudden commencement (SC) and main impulse (MI) of a magnetic storm as a function of the geographic coordinates of magnetic observatories and Universal Time, using modern data with second time resolution. The analysis was carried out for two events in which an interplanetary shock wave impacting the magnetosphere was associated with interplanetary coronal mass ejections (CMEs) with sources in different hemispheres of the Sun. The authors propose an approach to determine the time points of SC and MI detection. It is concluded that the SC and MI detection times may differ by several seconds to more than a minute at magnetic observatories located at different geographic latitudes and longitudes. For the studied events, the graphs of SC and MI detection as functions of the geographic coordinates of magnetic observatories and Universal Time revealed trends according to which, on average, the higher station the latitude, the later SC and MI are detected at the station.