Studying the solar wind by simultaneous observations of the interplanetary Lyman alpha background with NOZOMI/UVS and SOHO/SWAN

Details Studying the solar wind by simultaneous observations of the interplanetary Lyman alpha background with NOZOMI/UVS and SOHO/SWAN Studying the solar wind by simultaneous observations of the interplanetary Lyman alpha background with NOZOMI/UVS and SOHO/SWAN

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh21a0499n&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH21A-0499

Physics

2162 Solar Cycle Variations (7536), 2164 Solar Wind Plasma, 7549 Ultraviolet Emissions

Scientific paper

Interplanetary Lyman alpha data have been obtained by the ultraviolet imaging spectrometer (UVS) on board the NOZOMI spacecraft, the first Japanese Mars mission, cruising on Mars transfer orbits since 1999. The interplanetary Lyman alpha emission (121.6 nm) is due to solar photons backscattered by interplanetary hydrogen atoms. UVS has measured this emission over a 3-year period and we can study its temporal and spatial variations. SWAN onboard SOHO, the ESA/NASA cooperative mission, has also been observing the Lyman alpha emission since 1996. By comparing SWAN and UVS data obtained at the same time but at different positions in the heliosphere, we can characterize the spatial distribution pattern of the interplanetary Lyman alpha emission. In this study, we have analyzed data from 1999 and 2000, during the solar maximum period. We have also compared results from the measurements with those from numerical models developed by CNRS France [Lallement R., et al., 1985; Quemerais E., et al., 1993]. According to the comparison of the measurements with model calculation, it is found that an isotropic ionization can more or less reproduce the large scale distribution of interplanetary Lyman alpha emission in the period of solar maximum. The variation of relative intensity of Lyman alpha seen in the model results is almost consistent with that in the observation data. Some discrepancies can be found between the measurements and the calculations, especially in 2000 when the intensity of observational data is 10-20% larger than that from the model in the downwind region and vice versa in the upwind region. We discuss these discrepancies in the light of the hemispheric asymmetry observed by Ulysses and the tomographic analysis of interplanetary scintillation (IPS).

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