A large‐scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999

Abstract

Using a comprehensive data set and model calculations, we have investigated a prominent large‐scale traveling ionospheric disturbance (LSTID) observed in Japan (∼37°–16° MLAT) on 15 September 1999, during a recovery phase of sequential storms. The LSTID was detected at 2300–2400 LT (1400–1500 UT) as an enhancement of the 630‐nm airglow intensity (50→350 R), a decrease in the F layer virtual height (at 2 MHz, 360→200 km), an enhancement of foF2 (6→8 MHz), and an enhancement of GPS total electron content (∼1.0 × 1016 m−2). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of ∼400–450 m/s. From a comparison with the Sheffield University Plasmasphere‐Ionosphere Model (SUPIM) we conclude that an enhancement (250–300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800–1100 UT (4–6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed.