Multistage substorm expansion: Auroral dynamics in relation to plasma sheet particle injection, precipitation, and plasma convection

• Published in: Journal of Geophysical Research
• Main Authors: Sandholt, Per Even, Farrugia, Charlie J., Lester, Mark, Cowley, Stan, Milan, Steve, Denig, William F., Lybekk, Bjorn, Trondsen, Espen, Vorobjev, Vjacheslav
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2002
• Subjects: Svalbard; Ny-Ålesund; Lovozero; Ny Ålesund
• Online Access: https://scholars.unh.edu/cmerg/257; https://doi.org/10.1029/2001JA900116

We present observations of the auroral expansions during two substorms, focusing on multistage intensifications and the morphology of the poleward boundary, and relate these auroral observations to the local plasma convection and plasma sheet dynamics. The observations are made by meridian scanning photometers and an all-sky camera (ASC) at Ny Ålesund, Svalbard (76° magnetic latitude (MLAT)), an ASC in Lovozero, Russia (64° MLAT), the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain in Svalbard and Scandinavia, the HYDRA instrument on Polar located at the inner edge of the plasma sheet, particle detectors on DMSP F13 and DMSP F14 traversing the ionospheric projection of the plasma sheet, and the CUTLASS Finland HF radar. In each substorm the aurora between 70° and 80° MLAT consisted of two branches separated by ∼5° in MLAT. The higher-latitude branch (at ∼75°–78°MLAT) was subject to a sequence of short-lived (∼1–2 min) intensifications, so-called “poleward boundary intensifications” (PBIs), recurring at ∼3-min intervals. Subsequent to each brightening, auroral forms traveled equatorward at a speed of ∼1.0–1.5 km s−1. On Polar the PBIs are related on a one-to-one basis with injections of electrons in the 5- to 20-keV energy range at the inner edge of the equatorial plasma sheet with predominantly a trapped distribution, delayed by ∼5 min. Electron precipitation within 60°–77° MLAT, corresponding to a large radial extent of the plasma sheet, is documented by DMSP flights in the 1800–2000 magnetic local time (MLT) sector. In discussing the branches of the high-latitude aurora within the context of current understanding of the relation of bursty bulk flows to substorm expansion phase dynamics, we note the following: (1) the initial auroral breakup located at 63°–64° MLAT near the equatorward edge of plasma sheet precipitation, which was followed by (2) two successive brightenings/auroral expansions appearing within 72°–74° MLAT/∼2100 MLT, separated by 14 min, (3) a 20-min-long ...