D-day 0 C O N T A C T S
Oleg Troshichev
Arctic and Antarctic Research Institute

Title : PC index as a proxy of the solar wind energy incoming into the magnetosphere
PC index has been introduced [Troshichev et al.,1988] as an indicator of the magnetic activity generated in polar caps by the interplanetary electric field EKL (determined according to Kan and Lee [1979]). The PC index is calculated independently for the northern and southern hemispheres by magnetic data from 2 near-pole stations Thule and Vostok (PCN and PCS, correspondingly) with use of the unified procedure, which provides current evaluation of the EKL field irrespective of season, UT and the hemisphere. The PC index was endorsed at the XXII IAGA Scientific Assembly (2013) as a proxy for energy that enters into the magnetosphere during solar wind-magnetosphere coupling. Therein lies the principal distinction of the PC index from AL and Dst indices, which are characteristics of the accumulated energy that is realized in form of magnetospheric disturbances.
The following peculiarities of the PC behavior make it possible to use PC as a ground-based means for the space weather monitoring and the magnetosphere state nowcasting: time evolution of the PC index follows changes in the interplanetary electric field (EKL) with time delay ΔΤ~10-20 min; the PC index growth is a precursor of the storm and substorm development, the PC value exceeding over the threshold level of PC~1.5 mV/m being a necessary condition for the substorm development; the substorm sudden onsets are related to sharp increase of the PC growth rate; the typical delay time (ΔΤ) between the PC leap and substorm onset lies in range from few min to 15 min, being dependent on the PC (EKL) growth rate; the steady (in time lapse > 1hour) exceeding the PC index over the threshold level of ~1,5 mV/m is a necessary condition for the storm development; the run of the geomagnetic field depression (Dst variation) is generally guided by the PC index time evolution, with delay time in range from 30 to 100 minutes; the magnetic storms intensity is linearly related to value of the preceding PC maximum; the specific features of the PC evolution in course of Dst variation give grounds to classify the storm events into categories of classic, pulsed and composite magnetic storms, the classic and pulsed storms being related to such solar drivers as Coronal Mass Ejections (CMEs) and Stream (Corotating) Interaction Regions (SIRs/CIRs), correspondingly; the magnetic disturbances in the auroral zone and magnetic storms are better related to the PC index than to the EKL field; the PC index time evolution is controlled by intensity of field-aligned currents in the Region 1 FAC system.


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