Solar wind‐magnetosphere energy coupling efficiency and partitioning: HILDCAAs and preceding CIR storms during solar cycle 23

Abstract

A quantitative study on the energetics of the solar wind-magnetosphere-ionosphere system during High-Intensity, Long-Duration, Continuous AE Activity (HILDCAA) events for solar cycle 23 (from 1995 through 2008) is presented. For all HILDCAAs, the average energy transferred to the magnetospheric/ionospheric system was~6.3 × 10 16 J, and the ram kinetic energy of the incident solar wind was~7.1 × 10 18 J. For individual HILDCAA events the coupling efficiency, defined as the ratio of the solar wind energy input to the solar wind kinetic energy, varied between 0.3% and 2.8%, with an average value of~0.9%. The solar wind coupling efficiency for corotating interaction region (CIR)-driven storms prior to the HILDCAA events was found to vary from~1% to 5%, with an average value of~2%. Both of these values are lower than the > 5% coupling efficiency noted for interplanetary coronal mass ejection (and sheath)-driven magnetic storms. During HILDCAAs,~67% of the solar wind energy input went into Joule heating,~22% into auroral precipitation, and~11% into the ring current energy. The CIR-storm Joule heating (~49%) was noticeably less than that during HILDCAAs, while the ring current energies were comparable for the two. Joule dissipation was higher for HILDCAAs that followed CIR-storms (88%) than for isolated HILDCAAs (~60%). Possible physical interpretations for the statistical results obtained in this paper are discussed.

Cross-correlation and cross-wavelet analyses of the solar wind IMF Bz and auroral electrojet index AE coupling during HILDCAAs

“…Such particle precipitation prevents the decay of the ring current, which delays the Dst (disturbance storm time) recovery. Comparing the intensity of energy that enters into inner magnetosphere during the HILDCAAs and during geomagnetic storms, showed that the HILDCAA events can be more "geoeffective" than some geomagnetic storms, since HILDCAA events generally continue for longer durations (Hajra et al, 2014a).…”

“…During the HILDCAAs, ∼ 6.3 × 10 16 J of kinetic energy is transferred from the solar wind to the magnetosphereionosphere system (Hajra et al, 2014a). It was observed that the major part of the energy is dissipated as Joule heating (67 %), and the rest is dissipated as the auroral precipitation (∼ 22 %) and the ring current energy (∼ 11 %).…”

Study of interplanetary parameters, polar cap potential, and polar cap index during quiet event and high intensity long duration continuous AE activities (HILDCAAs)

“…As the solar cycle approaches descending phase, increment takes place in the number of HILDCAA events and they persist for longer period of time. Moreover, AE index measures a higher auroral activity during this phase which maybe the result of long-term fast streams, originated from coronal holes, present in solar wind [Hajra et al, 2013[Hajra et al, , 2014. The component of Interplanetary magnetic field's is expected to have a zero value but is found to have an average of −0.70 nT which indicates that during HILDCAA events, southward is the preferred direction (see HILDCAA* events between 1998 and 2007 and their related interplanetary magnetic field and plasma values, https://arxiv.org/abs/1612.03887).…”

High-intensity, long-duration, continuous AE activity events associated with Alfvénic fluctuations in 2003

“…In Alfvén waves within HSSs, the negative interplanetary magnetic field (IMF) B z component fluctuations induce continuous auroral zone activity, the so-called high-intensity long-duration continuous AE activity (HILDCAA, Tsurutani and González, 1987;Tsurutani et al, 2004;Guarnieri, 2013;Hajra et al, 2013Hajra et al, , 2014aSouza et al, 2016;Prestes et al, 2017). The yearly AE index average can be higher in the solar descending phase and minimum activity due to HSS/CIR events (HSS + CIR and their combination), than during the solar maximum activity, when the geomagnetic activity is usually caused by fast interplanetary coronal mass ejections (ICMEs; Tsurutani and González, 1987;Tsurutani and Ho, 1999;Tsurutani et al, 1995Tsurutani et al, , 2006Guarnieri, 2013;Ojeda-González et al, 2017b).…”