Core ion interactions with BB ELF, lower hybrid, and Alfvén waves in the high‐latitude topside ionosphere

Abstract

[1] We present simultaneous observations of ion distribution functions and plasma waves in the high-latitude topside ionosphere (500-1000 km) near local midnight during substorm activation. Using a new instrument, the Suprathermal Ion Imager (SII), we are able to explore two-dimensional ion distribution functions with unprecedented resolution in time (93 s À1 ) and energy, focusing on the lowest-energy core (<1 eV) population and suprathermal extensions thereof. The GEODESIC sounding rocket flew through regions containing broadband extremely low frequency (BB ELF) waves, large-amplitude Alfvén waves, and lower-hybrid solitary structures (LHSS), all of which have been shown previously to correlate with ion heating. However, GEODESIC detected heating only in association with LHSS. Ion distributions in and near LHSS showed acceleration in the direction transverse toB 0 (TAI) with temperatures as high as 5-10 eV, appearing in regions 65 ± 25 m across. TAI were centered on much smaller structures ($20 m across) of depleted plasma density and enhanced perpendicular electric fields from 0.1 to 10 kHz, consistent with observations from previous rocket flights. Also in agreement with previous findings, we find two distinct ion populations inside LHSS. The dominant population is composed of unheated, isotropic ''core'' Maxwellian ions having temperatures comparable to the surrounding ambient plasma, while roughly 10% of the plasma density corresponds to the TAI at pitch angles of 90 ± 5°. We argue that the TAI associated with LHSS is consistent with bulk heating of the core ions, and we describe two scenarios that can lead to the observed two-temperature distributions. The BB ELF wave emissions were correlated with LHSS heating at short scales and anticorrelated with auroral electron precipitation at large scales. The GEODESIC instruments observed no large-scale ion heating in association with BB ELF waves. Similarly, no ion heating was detected in the presence of large-amplitude, short perpendicular wavelength Alfvén waves.

Lower-hybrid (LH) oscillitons evolved from ion-acoustic (IA)/ion-cyclotron (IC) solitary waves: effect of electron inertia

“…Notice that this requirement is not only applicable to regions where ξ T = T e0 /T i0 > 1 (or, equivalently, T e0 > T i0 ), but also to those where T e0 < T i0 . Table 1 lists some plasma parameters in auroral regions where T e0 > T i0 , calculated from measurements by the GEODESIC rocket (Burchill et al, 2004), the Freja satellite , and the FAST satellite (Ergun, 1999), respectively. By contrast, in most magnetosphic plasmas (especially encountering some extreme situations like, e.g., substorms), ξ T lies between 1/12 and 1/3, as reported by, e.g., AMPTE/IRM and Cluster observations in the Earth's central plasma sheet, the sheet boundary layers, and magnetosheath (Baumjohann, 1993;Phan et al, 1994;Lavraud, 2009).…”

“…Table 1. Some typical plasma parameters in auroral plasmas measured by the Geodesic rocket (Burchill et al, 2004), the Freja satellite , and the FAST satellite (Ergun, 1999 Appendix A…”

“…They are associated with the lower-hybrid (LH) mode, accompanied by density depletions. The MARIE sounding rocket made the first definitive observations of the LH cavities (LaBelle et al, 1986), and the waveforms have been exhibited by many implemented space projects, such as, the FREJA satellite Eriksson et al, 1994;Pécseli et al, 1996;Høymork et al, 2001), the Alaska-93 sounding rocket (Delory, 1996), the AMICIST sounding rocket (Pinçn et al, 1997), the Polar satellite (Cattell et al, , 1999, the FAST satellite Pottelette et al, 1999), the GEODESIC sounding rocket (Knudsen et al, 2003;Burchill et al, 2004), and the Viking and Cluster satellites (Tjulin et al, 2003(Tjulin et al, , 2004. Schuck et al (2003) made a detailed review on related observations and simulations.…”

On the correlation between Broad-Band ELF wave power and ion fluxes in the cusp

“…Wahlund et al, 1998;Knudsen et al, 1998;Kintner et al, 2000;Lund et al, 2000;Lynch et al, 2002;Hamrin et al, 2002;Bogdanova et al, 2004;Burchill et al, 2004;Backrud et al, 2005;Tam et al, 2005). The term BB-ELF has been used to refer to different frequency ranges by different authors, but generally it covers a frequency range from below the ion cyclotron frequency to above the ion plasma frequency.…”

The CASSIOPE/e-POP Suprathermal Electron Imager (SEI)

“…Using data from the GEODESIC sounding rocket, Burchill et al (2004) used the SII to resolve strongly heated ion populations confined within filamentary density cavities only 20 m in diameter, and to track ion flow velocity variations within a 3 Hz shear Alfvén wave. Burchill et al (2010) In this paper we provide a technical description of the e-POP SEI instrument in Sect.…”