Field line resonances in a stretched magnetotail: CANOPUS optical and magnetometer observations

Abstract

Ground‐based observations support the existence of 1–4 mHz field line resonances (FLRs) at auroral latitudes. The low frequencies suggest that many nightside FLRs are excited on stretched magnetic field lines in the inner plasma sheet. Data from the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) magnetometers and photometers on 21 February 1993 indicate a FLR with a peak at 2.4 mHz, and that of 31 January 1997 indicate a peak at 1.3 mHz. In this paper, models of FLRs and models of stretched magnetotail topologies deduced from optical data are compared with the observations. The FLR model is independently constrained by a parametric near‐Earth magnetotail model that allows us to make direct comparisons with the observed FLR frequency. For the two case studies mentioned above, we are able to show that the theoretical FLR spectrum, computed on stretched field lines, is comparable to the low‐frequency experimental observations.