Preliminary retrieval of solar wind latitude distribution from Solar Wind Anisotropies/SOHO observations - Université de Versailles Saint-Quentin-en-Yvelines
Article Dans Une Revue Journal of Geophysical Research Space Physics Année : 1998

Preliminary retrieval of solar wind latitude distribution from Solar Wind Anisotropies/SOHO observations

Résumé

The Solar Wind Anisotropies (SWAN) instrument on board the SOHO spacecraft measures Lyman alpha radiation emanating mainly from neutral hydrogen gas in the solar neighborhood. This gas is part of the local interstellar cloud in which the Sun and the hehosphere are immersed. Measurements of Lyman alpha can be used to infer the local cloud characteristics like the velocity and the direction of the flow, gas temperature, and density. The strong interaction between the Sun and the neutral hydrogen gas also makes possible inves.tigations of solar characteristics by Lyman alpha measurements. In this work we will concentrate on deriving the latitudinal distribution of solar-induced ionization from SWAN Lyman alpha maps measured in 1996 at a time of the solar minimum. From the ionization we derive the distribution of the solar wind mass flux. SWAN Lyman alpha data show that the ionization and the mass flux are nearly flat for all solar latitudes except the narrow belt from-20 ø to 20 ø around the solar equator. In this region, ionization and the solar wind mass flux show a definite increase, which can be seen as an intensity depression in the Lyman alpha data from directions near the ecliptic. These results confirm earlier in situ measurements by Ulysses during the present minimum and Lyman alpha measurements by Prognoz satellites 20 years ago. the local cloud, are moving with a velocity of about 25 km/s with respect to each other. If there were no movement, ionization brought by solar UV photons and by the solar wind would carve a large ionization cavity around the Sun. This so-called StrSmgren sphere would reach out to 1000 AU. The movement of the cloud diminishes the influence of the Sun on the cloud so that the actual ionization cavity extends only a few tens of AU from the Sun. Therefore a substantial number of neutral hydrogen atoms reach the immediate neighborhood of the Sun where they are in place to scatter solar Lyman alpha photons. This makes

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insu-04748954 , version 1 (22-10-2024)

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E Kyrölä, T Summanen, W Schmidt, T Mäkinen, Eric Quémerais, et al.. Preliminary retrieval of solar wind latitude distribution from Solar Wind Anisotropies/SOHO observations. Journal of Geophysical Research Space Physics, 1998, 103 (A7), pp.14523 - 14538. ⟨10.1029/97ja03432⟩. ⟨insu-04748954⟩
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