Using PC indices to predict violent GIC events threatening power grids

2020

Preprint

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The Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for space weather monitoring and forecasts and for related research. However, this study suggests that the PC index series in the near-real-time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) are invalid and unreliable. Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y-component, B Y , of the interplanetary magnetic field (IMF). However, the IAGA-endorsed handling of SWS effects may generate unfounded PC index changes of up to 4 mV/m at the nightside away from the Cusp. For the real-time PCN and PCS indices, the cubic spline-based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions invalidate the PC index series and prove the IAGA-endorsed derivation methods erroneous. Alternative derivation methods are shown to provide more consistent index reference levels for both final and real-time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability.

Section: Introductionmentioning

confidence: 99%

The Polar Cap (PC) index: invalid index series and a different approach.

2020

Preprint

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“…The PCC index construction, as shall be shown, provides more accurate estimates of the solar wind energy that enters the magnetosphere than available from the individual PC indices or further combinations. A particularly important application is the use of strongly enhanced PC index levels (Stauning, 2013c(Stauning, , 2020a to predict violent substorm events that could threaten important subauroral power grids (Kappenman, 2010).…”

Section: Introductionmentioning

confidence: 99%

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

J. Space Weather Space Clim.

2021

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The non-negative Polar Cap PCC index built from PCN (North) and PCS (South) correlates considerably 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 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 on the 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 have been used to correct the PCC indices for saturation effects at high intensity disturbance conditions where the Dst index may take values beyond -100 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. Thus, the PCC indices measuring accurately the energy input from the solar wind are powerful tools for space weather monitoring and for solar-terrestrial research.

“…A further question of importance is whether the present PC index versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) in their near-real time and final versions are reliable. The present work adds further elements of criticism of the IAGA-endorsed PC index versions to reservations expressed in former publications (Stauning, 2013a(Stauning, , 2013b(Stauning, , 2015(Stauning, , 2018a(Stauning, , 2018b(Stauning, , 2018c(Stauning, , and 2020a(Stauning, , 2020b). It appears that the derivation of scaling parameters rests on inadequate statistical methods.…”

Section: Introductionmentioning

confidence: 67%

Invalid Polar Cap Indices: Erroneous Scaling Parameters

2021

JGR Space Physics

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In the publication Troshichev et al. (2006) (https://doi.org/10.1029/2005JA011402) on the polar cap (PC) indices, PCN and PCS, an error was made by using components of the interplanetary magnetic field (IMF) in their geocentric solar ecliptic (GSE) representation instead of the prescribed geocentric solar magnetospheric (GSM) representation for calculations of index scaling parameters. The mistake has caused a trail of incorrect relations and wrong conclusions extending since 2006 up to now (2020) which should be discontinued, for instance, by issuing a corrigendum note from the authors. The present contribution explains the error and discusses in an extended example its consequences for one of the publications that have referred to the invalid scaling parameter set. Further investigations reported here of the PC index versions recommended by the International Association for Geomagnetism and Aeronomy (IAGA) indicate occurrences of similar problems in the present derivation of index scaling parameters.