The Polar Cap (PC) index combination, PCC: relations to solar wind properties and global magnetic disturbances

Abstract

The non-negative Polar Cap PCC index built from PCN (North) and PCS (South) indices correlates better with the solar wind merging electric field and is more representative for the total energy input from the solar wind to the magnetosphere and for the development of geomagnetic disturbances represented by the Kp index and ring current indices than either of the hemispheric indices. The present work shows that the ring current index, Dst, to a high degree of accuracy can be derived from a source function built from PCC indices. The integration of the PCC-based source function throughout the interval from 1992 to 2018 without attachment to the real Dst indices based on low latitude magnetic observations has generated equivalent Dst values that correlate very well (R = 0.86) with the real Dst index values, which are represented with a mean deviation less than 1 nT and an overall RMS deviation less than 13 nT. The precise correlation between the real and equivalent Dst values has been used to correct the PCC indices for saturation effects at high intensity disturbance conditions where the Dst index may take values beyond À100 nT. The relations between PCC and the ring current indices, Dst and ASY-H have been used, in addition, to derive the precise timing between polar cap convection processes reflected in the polar cap indices and the formation of the partial and total ring current systems. Building the ring current is considered to represent the energy input from the solar wind, which also powers auroral disturbance processes such as substorms and upper atmosphere heating. With current available PC indices, detailed and accurate SYM-H or Dst index values could be derived up to nearly one hour ahead of actual time by integration of the PCC-based source function from any previous quiet state. Thus, the PCC indices enabling accurate estimates of the energy input from the solar wind are powerful tools for space weather monitoring and for solar-terrestrial research.

Transpolar Convection and Magnetospheric Ring Current Relations: Real‐Time Applications of the Polar Cap (PC) Indices

“…The relations between PC indices and the ring current ASY‐H and Dst (or SYM‐H) indices have been investigated previously by Stauning et al. (2008), Stauning (2012), and in a recent study by Stauning (2021). The target in the present study is to examine the validity of the established relations based on post‐event data for their use in real‐time applications.…”

“…(2008) and Stauning (2012). In a recent investigation (Stauning, 2021), the comparison of correlation results was extended to comprise also the plain average, PCA, of PCN and PCS as well as selections of either local winter or summer PC index values (PCW and PCU). Furthermore, the correlation of E M with a PCS (PCD) index version based on using magnetic data from Dome‐C observatory (Chambodut et al., 2009; Di Mauro et al., 2014) was examined.…”

“…Furthermore, the correlation of E M with a PCS (PCD) index version based on using magnetic data from Dome‐C observatory (Chambodut et al., 2009; Di Mauro et al., 2014) was examined. Comparing the correlations between hourly values of E M and PCC, PCN, and PCS values throughout 2009–2018 are presented in Figure 4a here (see Stauning, 2021). In this figure, the PC indices are based on post‐event derivation.…”

“… Display of monthly average coefficients for the correlation between hourly values of E M and PCN (blue line), PCS (red), and PCC (magenta). (a) Post‐event PC indices 2009–2018 (similar to Figure 6 of Stauning [2021]). (b) Simulated real‐time PC indices 2009–2018.…”

“…The PCC indices are derived as the average of positive values of the two hemispherical PC indices disregarding (zero filling) negative values. It has been demonstrated that the PCC indices have a higher degree of correlation with the merging electric fields than either of the individual PC indices or their averages (Stauning, 2012, 2021; Stauning et al., 2008).…”