The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

• Published in: Annales Geophysicae
• Main Authors: P. E. Sandholt, C. J. Farrugia, B. Lybekk
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 1999
• Subjects: Science; Q; Physics; QC1-999; Geophysics. Cosmic physics; QC801-809; Svalbard; Ny-Ålesund; Lockwood; Cowley; Ny Ålesund
• Online Access: https://doi.org/10.1007/s00585-999-1155-5; https://doaj.org/article/88c56a50fba8425f996af726876bda63

We document the detailed dynamics of the dayside aurora in the \sim1200-1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF B y conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5 ° MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71 ° 75 ° MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ~100 km equatorward shift of its equatorward boundary, at ~75 ° MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5-6 min, and (3) east-west expansion of the higher-latitude aurora (at ~77 ° 78 ° MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100-400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection. Key words. Mangetospheric physics (magnetopause · cusp and boundary layers; solar wind-magnetosphere interactions; auroral phenomena)