Pc1–Pc2 waves and energetic particle precipitation during and after magnetic storms: Superposed epoch analysis and case studies

Abstract

Magnetic pulsations in the Pc1–Pc2 frequency range (0.1–5 Hz) are often observed on the ground and in the Earth's magnetosphere during the aftermath of geomagnetic storms. Numerous studies have suggested that they may play a role in reducing the fluxes of energetic ions in the ring current; more recent studies suggest they may interact parasitically with radiation belt electrons as well. We report here on observations during 2005 from search coil magnetometers and riometers installed at three Antarctic stations, Halley (−61.84° magnetic latitude, MLAT), South Pole (−74.18° MLAT), and McMurdo (−79.96° MLAT), and from energetic ion detectors on the NOAA Polar‐orbiting Operational Environment Satellites (POES). A superposed epoch analysis based on 13 magnetic storms between April and September 2005 as well as case studies confirm several earlier studies that show that narrowband Pc1–Pc2 waves are rarely if ever observed on the ground during the main and early recovery phases of magnetic storms. However, intense broadband Pi1–Pi2 ULF noise, accompanied by strong riometer absorption signatures, does occur during these times. As storm recovery progresses, the occurrence of Pc1–Pc2 waves increases, at first in the daytime and especially afternoon sectors but at essentially all local times later in the recovery phase (typically by days 3 or 4). During the early storm recovery phase the propagation of Pc1–Pc2 waves through the ionospheric waveguide to higher latitudes was more severely attenuated. These observations are consistent with suggestions that Pc1–Pc2 waves occurring during the early recovery phase of magnetic storms are generated in association with plasmaspheric plumes in the noon‐to‐dusk sector, and these observations provide additional evidence that the propagation of waves to ground stations is inhibited during the early phases of such storms. Analysis of 30‐ to 250‐keV proton data from four POES satellites during the 24–27 August and 18–19 July 2005 storm intervals showed that the location of the inner edge of the ring current matched well with the plasmapause model of O'Brien and Moldwin (2003). However, the POES data showed no evidence of the consequences of electromagnetic ion cyclotron waves (localized proton precipitation) during main and early recovery phase. During later stages of the recovery phase, when such precipitation was observed, it was coincident with intense wave events at Halley, and it occurred at L shells near or up to 1 RE outside the modeled plasmapause but well equatorward of the isotropy boundary.

Temporal and spatial characteristics of Pc1 waves observed by ST5

“…Most events had frequencies between 0.2 and 1.4 Hz. The distribution of frequencies observed by ST5 is qualitatively similar to that shown in Figure 8 of Engebretson et al [2008], which grouped frequencies observed at Halley, Antarctica ( L = 4.56), according to UT and day after magnetic storm onset. Figure 9 (middle) shows the distribution of wave frequencies as a function of amplitude (from 5 to 110 nT); these show no evident correlation.…”

“…Pc1–2 wave activity has also been suggested as a possible prompt loss mechanism for relativistic electrons during the main phase of such storms [ Thorne et al , 2005]. However, although the few published satellite studies of Pc1–2 waves during storms report their occurrence during both main and recovery phases, such waves are consistently absent in ground data during the main and early recovery phases [e.g., Bräysy et al , 1998; Engebretson et al , 2008].…”

The Upgraded CARISMA Magnetometer Array in the THEMIS Era

“…At present there is a peculiarity that most MeV electron loss in the radiation belts occurs during main phase, yet on the ground EMIC power typically only appears during the recovery phase (e.g. Engebretson et al 2008;Bortnik et al 2008 and references therein). Whether this is due to internal reflection of EMIC waves in the magnetosphere (e.g.…”

Limitation of energetic ring current ion spectra

“…In fact, there is still much current interest in ion pitch angle scattering by EMIC waves in the context of ring current dynamics. This is evidenced by the substantial literature that relates EMIC waves to ion precipitation resulting in ring current decay [e.g., Cornwall et al, 1970;Erlandson and Ukhorskiy, 2001;Summers, 2005;Fraser et al, 2006;Jordanova et al, 2007;Yahnin and Yahnina, 2007;Engebretson et al, 2008;Sakaguchi et al, 2008;Spasojevic et al, 2011;Xiao et al, 2012;Yuan et al, 2014]. In the present work, we treat EMIC wave-ion interactions as linear or quasi-linear, in common with most previous studies.…”