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Radiation Transport of Heliospheric Lyman-alpha from Combined Cassini and Voyager Data SetsHeliospheric neutral hydrogen scatters solar Lyman-alpha radiation from the Sun with '27-day' intensity modulations observed near Earth due to the Sun's rotation combined with Earth's orbital motion. These modulations are increasingly damped in amplitude at larger distances from the Sun due to multiple scattering in the heliosphere, providing a diagnostic of the interplanetary neutral hydrogen density independent of instrument calibration. This paper presents Cassini data from 2003-2004 obtained downwind near Saturn at approximately 10 AU that at times show undamped '27-day' waves in good agreement with the single-scattering models of Pryor et al., 1992. Simultaneous Voyager 1 data from 2003- 2004 obtained upwind at a distance of 88.8-92.6 AU from the Sun show waves damped by a factor of -0.21. The observed degree of damping is interpreted in terms of Monte Carlo multiple-scattering calculations (e.g., Keller et al., 1981) applied to two heliospheric hydrogen two-shock density distributions (discussed in Gangopadhyay et al., 2006) calculated in the frame of the Baranov-Malama model of the solar wind interaction with the two-component (neutral hydrogen and plasma) interstellar wind (Baranov and Malama 1993, Izmodenov et al., 2001, Baranov and Izmodenov, 2006). We conclude that multiple scattering is definitely occurring in the outer heliosphere. Both models compare favorably to the data, using heliospheric neutral H densities at the termination shock of 0.085 cm(exp -3) and 0.095 cm(exp -3). This work generally agrees with earlier discussions of Voyager data in Quemerais et al., 1996 showing the importance of multiple scattering but is based on Voyager data obtained at larger distances from the Sun (with larger damping) simultaneously with Cassini data obtained closer to the Sun.
Document ID
20090007485
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Pryor, W.
(Central Arizona Coll. Coolidge, AZ, United States)
Gangopadhyay, P.
(University of Southern California Los Angeles, CA, United States)
Sandel, B.
(Arizona Univ. Tucson, AZ, United States)
Forrester, T.
(Arizona Univ. Tucson, AZ, United States)
Quemerais, E.
Moebius, E.
(New Hampshire Univ. Durham, NH, United States)
Esposito, L.
(Colorado Univ. Boulder, CO, United States)
Stewart, I.
(Colorado Univ. Boulder, CO, United States)
McClintock, W.
(Colorado Univ. Boulder, CO, United States)
Jouchoux, A.
(Colorado Univ. Boulder, CO, United States)
Colwell, J.
(University of Central Florida Orlando, FL, United States)
Izmodenov, V.
Malama, Y.
Shemansky, D.
(Space Environment Technologies Pacific Palisades, CA, United States)
Ajello, J.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Hansen, C.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Bzowski, M.
Date Acquired
August 24, 2013
Publication Date
July 25, 2008
Publication Information
Publication: Astronomy and Astrophysics
Volume: 491
Subject Category
Space Radiation
Funding Number(s)
CONTRACT_GRANT: RFBR 05-02-22000(PICS)
CONTRACT_GRANT: NNG04GB80G
CONTRACT_GRANT: RFBR 07-02-01101
CONTRACT_GRANT: RFBR 06-02-7255
CONTRACT_GRANT: NNG06GD55G
CONTRACT_GRANT: NNX07AI07G
Distribution Limits
Public
Copyright
Other

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