Short-term Forecasting the Magnetic Storm Progression and Intensity by means the PC index
Short-term Forecasting the Magnetic Storm Progression and Intensity by means the PC index
Wednesday, 13 February 2019
Fountain III/IV (Westin Pasadena)
Abstract:
The PC index was introduced as a measure of the magnetic activity generated in the polar caps by interplanetary electric field EKL in course of solar wind – magnetosphere coupling [Troshichev et al., 1988]. At present the PC index is regarded as a proxy for energy that input into the magnetosphere during the solar wind-magnetosphere coupling [Resolutions of XXII IAGA Assembly, 2013]. This judgment is based on the experimental evidences of strong connection between the time evolution of the EKL field and PC-index before the substorm onset, on the one hand, and relationships between the PC growth and development of magnetospheric disturbances (AL and Dst-indices), on the other hand.
Examination of relationships between the interplanetary electric field EKL and PC, AL, Dst/SymH indices for two cycles of solar activity (1997-2017) demonstrates that magnetospheric substorms start when the solar wind energy input into the magnetosphere exceeds the definite threshold level (PC =1.5±0.5 mV/m). Steady overstepping this threshold level (with lapse more than 1 hour) leads to the magnetic storm development (depression of geomagnetic field). The “classic” storms, with pronounced growth phase and distinct maximum of depression, are developed when the PC index growth is stable. If the PC value oscillates (periodically raises and descents), the “pulsed” storms, with long duration and small intensity, are developed. Magnetic storm continues as long as the PC index stays higher the threshold level PC>1.5 mV/m. The storm progression follows the РС behaviour, the maximal depression of magnetic field (storm intensity) being linearly related to the preceding PC index maximum: the higher the PCMAX value, the larger is magnetic storm intensity (DstMIN). Delay times ΔT in response of SymHMIN to the PCMAX occurrence lie in the range from 30 to 180 minutes, being strongly dependent on the PC growth rate. As soon as PC index falls below the threshold level, the magnetic storm starts to decay. The paper presents the magnetic storm short-term forecasting method based on these peculiarities of the PC and SymH relationships.
Examination of relationships between the interplanetary electric field EKL and PC, AL, Dst/SymH indices for two cycles of solar activity (1997-2017) demonstrates that magnetospheric substorms start when the solar wind energy input into the magnetosphere exceeds the definite threshold level (PC =1.5±0.5 mV/m). Steady overstepping this threshold level (with lapse more than 1 hour) leads to the magnetic storm development (depression of geomagnetic field). The “classic” storms, with pronounced growth phase and distinct maximum of depression, are developed when the PC index growth is stable. If the PC value oscillates (periodically raises and descents), the “pulsed” storms, with long duration and small intensity, are developed. Magnetic storm continues as long as the PC index stays higher the threshold level PC>1.5 mV/m. The storm progression follows the РС behaviour, the maximal depression of magnetic field (storm intensity) being linearly related to the preceding PC index maximum: the higher the PCMAX value, the larger is magnetic storm intensity (DstMIN). Delay times ΔT in response of SymHMIN to the PCMAX occurrence lie in the range from 30 to 180 minutes, being strongly dependent on the PC growth rate. As soon as PC index falls below the threshold level, the magnetic storm starts to decay. The paper presents the magnetic storm short-term forecasting method based on these peculiarities of the PC and SymH relationships.