response to southward turning of the IMF
Abstract. We document the detailed dynamics of the dayside aurora in the 1200±1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic ®eld (IMF) under negative IMF By conditions. Features not documented in previous work are elucidated by using two meridan scanning pho...
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| Format: | Text |
| Language: | English |
| Published: |
1999
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.371.7092 http://hal.archives-ouvertes.fr/docs/00/31/66/61/PDF/angeo-17-1155-1999.pdf |
| Summary: | Abstract. We document the detailed dynamics of the dayside aurora in the 1200±1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic ®eld (IMF) under negative IMF By 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 AÊ lesund, 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) intensi®cation 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 de¯ection of the X-component at stations located 100±400 km south of the aurora, corresponding to enhanced Sunward return ¯ow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the ®rst 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) |
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