PC index as a proxy of the solar wind energy that entered into the magnetosphere: 3. Development of magnetic storms

Abstract

Relationships between the 30-min smoothed PC and SymH indices in course of 430 magnetic storms observed in period of 1998–2015 have been examined. The storms were classified, by features of the PC evolution, as classic, pulsed and composite magnetic storms. It is shown these storm types are related, correspondingly, to such solar drivers as Interplanetary Coronal Mass Ejections (ICME), Stream Interaction Regions (SIR), and their joint action. Results of the statistical analysis demonstrate that depression of geomagnetic field (“Dst variation”) starts to develop as soon as PC index steadily excess the threshold level ∼1.5 mV/m, like to case of magnetic substorms. SymH index in course of magnetic storms (during 48 h preceding and succeeding the maximal depression of geomagnetic field) generally follows the time evolution of the PC index with typical delay time of ΔT ∼ 1 ± 0.5 h. The storm intensity (SymHMIN) is linearly related to maximal value of the foregoing PC index (PCMAX) observed ∼0.5÷2 h before the moment of maximal depression. The conclusion is made that the PC index can be successfully used for nowcasting the magnetic storm development.