SWAN: A study of Solar Wind Anisotropies on SOHO with Lyman alpha sky mapping |
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| Authors: | J L Bertaux E Kyrölä E Quémerais R Pellinen R Lallement W Schmidt M Berthé E Dimarellis J P Goutail C Taulemesse C Bernard G Leppelmeier T Summanen H Hannula H Huomo V Kehlä S Korpela K Leppälä E Strömmer J Torsti K Viherkanto J F Hochedez G Chretiennot R Peyroux and T Holzer |
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| Institution: | (1) Service d'Aéronomie du CNRS, BP. 3, 91371 Verrières-le-Buisson, France;(2) Finnish Meteorological Institute, P.O. Box 503, SF. 00101 Helsinki, Finland;(3) VTT/INS, Technical Research Center of Finland, Espoo and Oulu, Finland;(4) University of Turku, Turku, Finland;(5) High Altitude Observatory, Boulder, Colorado, USA |
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| Abstract: | On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lyman results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1°, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman line and other Lyman emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed. |
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| Keywords: | solar wind interplanetary hydrogen interstellar wind |
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