Ground‐based optical determination of the b2i boundary: A basis for an optical MT‐index

Abstract

[1] The equatorward boundary of the proton aurora corresponds to a transition from strong pitch angle scattering to bounce trapped particles. This transition has been identified as the b2i boundary in Defense Meteorological Satellite Program (DMSP) ion data [Newell et al., 1996]. We use ion data from 29 DMSP overflights of the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) Meridian Scanning Photometer (MSP) located at Gillam, Canada, to develop a simple algorithm to identify the b2i boundary in latitude profiles of proton auroral (486 nm) brightness. Applying this algorithm to a ten year set of Gillam MSP data, we obtain $250,000 identifications of the ''optical b2i,'' the magnetic latitude of which we refer to as b2i à . We intercompare $1600 near-simultaneous optical and in situ b2i à , concluding that the optical b2i à is a reasonable basis for an optical equivalent to the MT-index put forward by Sergeev and Gvozdevsky [1995]. Using $17,000 simultaneous measurements, we demonstrate a strong correlation between the optical b2i à and the inclination of the magnetic field as measured at GOES 8. We develop an empirical model for predicting the GOES 8 inclination, given theuniversal time, dipole tilt, and the optical b2i à , as determined at Gillam. We also show that in terms of information content, the b2i boundary is an optimal boundary upon which to base such an empirical model.

Collective dynamics of bursty particle precipitation initiating in the inner and outer plasma sheet

“…(1) fails to predict the correct isotropic boundary, which can move a considerable distance due to the tail stretching and dipolarization (Donovan et al, 2003;Meurant et al, 2007). However, this model remains a valuable tool for separating the inner (near-Earth) and the tail CPS regions in a typical magnetotail configuration.…”

Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

“…For the protons with energies ranging between a few tens and 100 keV, the boundary between adiabatic and nonadiabatic particle motion occurs near the center of the tail current sheet on the nightside at r ∼ 6 − 9 Re (e.g., Sergeev and Tsyganenko, 1982;Shevchenko et al, 2010;Wang et al, 2012;Yue et al, 2014). Tailward of that boundary a strong current sheet scattering (CSS) provides the nearly isotropic proton angular distributions in the tail plasma sheet (e.g., Ganushkina et al, 2005;Yue et al, 2014) whose precipitation forms an extended isotropic proton precipitation region, the proton auroral oval (Sergeev et al, 1983;Donovan et al, 2003;Meurant et al, 2007). The equatorward boundary at which the ratio of precipitated to trapped fluxes quickly drops down below 1 (called the isotropy boundary, IB) is usually sharply de-fined and well-observed at any particular energy.…”

Meso-scale aurora within the expansion phase bulge

“…9. Proton auroral emission (486 nm) and the location of its equatorward boundary (red diamonds) (Donovan et al, 2003). ary inclination changes: when the geostationary magnetic field configuration becomes more dipolar, the proton emission band moves poleward (Donovan et al, 2003). Thus, it is interesting to compare the GOES B X and B Z variations (two upper panels of Fig.…”

“…In this context, the ground-and space-based optical observations are used to monitor the location of the important magnetospheric regions such as the near-Earth transition region from the dipolar to the stretched magnetic field configuration, or the polar cap boundary (Blanchard et al, 1995;Brittnacher et al, 1999;Donovan et al, 2003). In this paper, we use optical and geostationary data to study the appearance of meso-scale structures (arcs, spirals and streamers) within a poleward (Baker and Wing, 1989).…”