Establishment and Application of an Interplanetary Disturbance Index Based on the Solar Wind–Magnetosphere Energy Coupling Function and the Spectral Whitening Method

Abstract

We develop a preliminary interplanetary disturbance index ( J ${}_{{\rm{s}}}^{{\rm{W}}}$ ) by applying the spectral whitening method to an energy coupling function with solar wind measurements during the years 1998–2014 as the input, which can be used as an indicator of perturbations in the near-Earth solar wind. The correlation and temporal variation between J ${}_{{\rm{s}}}^{{\rm{W}}}$ and the geomagnetic disturbance index ( J ${}_{{\rm{p}}}^{{\rm{G}}}$ ) constructed from the same method have been analyzed in detail for 167 geomagnetic storms with the minimum D _st index less than or equal to −50 nT. The time delay between J ${}_{{\rm{s}}}^{{\rm{W}}}$ and J ${}_{{\rm{p}}}^{{\rm{G}}}$ is clearly observable and varies for different events, according to which J ${}_{{\rm{s}}}^{{\rm{W}}}$ is shifted backward with respect to J ${}_{{\rm{p}}}^{{\rm{G}}}$ . We obtain a fairly good negative correlation between the shifted J ${}_{{\rm{s}}}^{{\rm{W}}}$ and the J ${}_{{\rm{p}}}^{{\rm{G}}}$ indices for the majority of events, and the significance level for 88% of the events (i.e., 147 events) does not exceed 0.05. A statistical analysis of the shifted J ${}_{{\rm{s}}}^{{\rm{W}}}$ and the J ${}_{{\rm{p}}}^{{\rm{G}}}$ indices for 147 selected events reveals that larger values of J ${}_{{\rm{s}}}^{{\rm{W}}}$ and smaller magnitudes of J ${}_{{\rm{p}}}^{{\rm{G}}}$ are commonly accompanied by enhanced southward magnetic fields, which implies that more solar wind energy is entering the magnetosphere and thus causing strong geomagnetic storms. Furthermore, a linear fit of the two indices suggests that the evolution of J ${}_{{\rm{p}}}^{{\rm{G}}}$ can be predicted about 2 hr in advance based on J ${}_{{\rm{s}}}^{{\rm{W}}}$ , indicating that J ${}_{{\rm{s}}}^{{\rm{W}}}$ can provide early warnings of possible disturbances in the geomagnetic fields, which is crucial for space weather monitoring and operational forecasting.

Keywords

• Solar wind
• Interplanetary magnetic fields
• Solar-terrestrial interactions
• Space weather