Remote sensing of the active regions on both the front and the far side of the Sun by Nozomi Lyman alpha observation

Details Remote sensing of the active regions on both the front and the far side of the Sun by Nozomi Lyman alpha observation Remote sensing of the active regions on both the front and the far side of the Sun by Nozomi Lyman alpha observation

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh42b0533o&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH42B-0533

Astronomy and Astrophysics

Astrophysics

2100 Interplanetary Physics, 2144 Interstellar Gas, 7500 Solar Physics, Astrophysics, And Astronomy, 7549 Ultraviolet Emissions

Scientific paper

The ultraviolet imaging spectrometer (UVS) on board the Nozomi spacecraft on a transfer orbit to Mars has measured the interplanetary Lyman alpha emission at 121.6 nm on the routine basis over a period of three years since January 1999. There is a flow of interplanetary hydrogen and helium atoms in the heliosphere. This neutral hydrogen and helium flow is called the "interstellar wind". Interplanetary hydrogen atoms induce resonant scattering of solar Lyman alpha emission. One of the most effective factors causing the temporal variations of this interplanetary Lyman alpha emission is enhanced Lyman alpha radiation from the active regions on the Sun. Accordingly, the intensity of the interplanetary Lyman alpha emission changed synchronously with the solar rotation period. Bertaux et al. [2000] showed that excess of illumination from the active regions on the Sun is clearly identified in the interplanetary Lyman alpha map constructed by the SOHO/SWAN data, including excess resulting from active regions on the far side of the Sun. Since CME events from these active regions cause geomagnetic storms on the Earth, earlier detection of the active regions on the far side of the Sun is significantly important for space weather forecast. Particularly, the precise estimation of both the location of the active regions and the scale of activity would be key parameters for space weather forecast. In this study, we have precisely estimated the location of the active regions on both the front and the far side of the Sun by comparing the observed temporal variations of interplanetary Lyman alpha emission with those of the model calculations. The model calculation consists of two parts. The first part is calculation of interplanetary hydrogen density distribution based on Wu and Judge [1979]. The second part is the calculation of the Lyman٬emission intensity due to resonant scattering of solar photons with IPH atoms. We have reproduced observed temporal variations of the interplanetary Lyman alpha emission, and changes in the Lyman alpha flux distribution on the Sun. It is found that the temporal variations of the interplanetary Lyman alpha emission due to the generation, disappearance, growth and decline of the active regions. The methods of the estimation and the transient effect will be discussed.

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