Investigations of the Structure of the Diurnal Variations of Geomagnetic Field

Changes in solar activity mechanisms generate changes in geomagnetic activity. The structure of geomagnetic activity can be illustrated by classes of the periodic and non-periodic variations of geomagnetic field. This study shows the results of the analysis of the periodic and non-periodic diurnal variations in the geomagnetic field (variations Sq, Sd,) and disturbances of geomagnetic activity (variations of indices Ri, Kp). The analysis was carried out during the months in which extreme solar and geomagnetic storms were recorded, October 2003 and November 2004. An analysis the structure and morphology of diurnal variations was made on the basis of the recorded geomagnetic data (the mean hourly values of geomagnetic field, three-hour indices of geomagnetic activity), at the Geomagnetic Observatory Grocka (GCK) (Serbia).

The Structure of the Big Magnetic Storms

The records of geomagnetic activity during Solar Cycles 22 and 23 (which occurred from 1986 to 2006) indicate several extremely intensive A-class geomagnetic storms. These were storms classified in the category of the Big Magnetic Storms. In a year of maximum solar activity during Solar Cycle 23, or more precisely, during a phase designated as a post-maximum phase in solar activity (PPM – Phase Post maximum), near the autumn equinox, on 29, October 2003, an extremely strong and intensive magnetic storm was recorded. In the first half of November 2004 (7, November 2004) an intensive magnetic storm was recorded (the Class Big Magnetic Storm). The level of geomagnetic field variations which were recorded for the selected Big Magnetic Storms, was ΔDst > 350 nT. For the Big Magnetic Storms the indicated three-hour interval indices geomagnetic activity was Kp = 9. This study presents the spectral composition of the Di – variations which were recorded during magnetic storms in October 2003 and November 2004