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What coronal parameters determine solar wind speed?

What coronal parameters determine solar wind speed?. M. Kojima, M. Tokumaru, K. Fujiki, H. Itoh and T. Murakami Solar-Terrestrial Environment Laboratory, Nagoya University K. Hakamada Department of Natural Science and Mathematics, Chubu University.

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What coronal parameters determine solar wind speed?

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  1. What coronal parameters determine solar wind speed? M. Kojima, M. Tokumaru, K. Fujiki, H. Itoh and T. Murakami Solar-Terrestrial Environment Laboratory, Nagoya University K. Hakamada Department of Natural Science and Mathematics, Chubu University

  2. In order to model the solar wind acceleration it is important to find a universal relation between the global properties of the solar wind and corona holes. However most coronal holes are at high latitudes where spacecraft cannot access, with the exception of the Ulysses. In this study we identify the relation between the wind velocity and the coronal magnetic conditionusing the IPS tomographic measurements, which can derive an unbiased solar wind velocity map over all latitudinal ranges,.

  3. Freq.327 MHz Aperture2000 m2

  4. Four-station system for IPS 102km 126km 98km 109km 131km

  5. Radio source ☆ Earth Interplanetary scintillation measures an integration of the solar wind speed V and density turbulent level △Ne distributed along a line of sight.

  6. The IPS los integrations provide us with perspective views of 3D SW structures at various different view angles using both the solar rotation and solar wind outward motion. Computer Assisted Tomography analysis This technique can retrieve not only unbiased solar wind parameters but also provides high spatial resolution.

  7. 1996 CT Analysis

  8. Nolte et al. (1976) the velocity depends on the coronal holescale size. • Wang and Sheeley (1990) the flux expansion rate is inversely proportional to the solar wind speed. • Fisk et al. (1999) reconnection of emerging magnetic fields in supergranules supplies Poynting flux to accelerate the solar wind.

  9. CH size vs. V

  10. potential field neutral line ? ? after Kojima et al., 1999

  11. after Kojima et al., 1999

  12. dependence on polar coronal hole scale size Oct. 1999 1991 2000

  13. CH size vs. V Polar CH Equatorial CH polarCH

  14. CH size B 10Gsmall expansion B weakmedium expansion B weaksmall expansion B 20Glarge expansion

  15. We investigate the relation between the solar wind velocity • and the coronal magnetic condition for various kinds of • coronal holes, which have different properties of magnetic • field intensity B and flux expansion ratef. • We make correlation analysis between the velocity V and • the inverse of an expansion rate 1/f, • photospheric magnetic field intensity B, and • the ratio between these two parameters B/f.

  16. V-map on the source surface from IPS tomography Potential magnetic field lines Coronal holes on the photosphere HeI, open B region Data fromthe National Solar Observatory (NSO) at Kitt Peak

  17. Analysis 1 Data period: 1995-1996

  18. Although the polar coronal hole extended to lower latitudes than 60 degrees, we examine the coronal hole area at latitudes higher than 60 degrees because the boundary region has a complex structure. If there is a extension from a polar coronal hole toward the equator beyond a latitude of 40 degrees, it is treated as an independent mid-latitude coronal hole.

  19. Flux expansion rate weak B strong B after Hirano et al. (2004)

  20. Magnetic field energy large expansion small expansion after Hirano et al. (2004)

  21. Flux expansion + B energy after Hirano et al. (2004)

  22. Analysis 3 Data period: 1990-2001 • 1. CR1830 : Jun. 11.4556, 1990. • 2. CR1844 : Jun. 28.2611, 1991. • 3. CR1855 : Apr. 23.4361, 1992 • 4. CR1870 : Jun. 6.4778, 1993. • 5. CR1887 : Sep. 12.9590, 1994. • 6. CR1898 : Jul. 10.0910, 1995. • 7. CR1901 : Sep. 29.8104, 1995. • 8. CR1909 : May 5.2840, 1996. • 9. CR1925 : Jul. 15.5059, 1997. • 10. CR1939 : Aug. 1.3214, 1998. • 11. CR1950 : May 28.5213, 1999. • 12. CR1964 : Jun. 13.3296, 2000. • 13. CR1976 : May 6.7222, 2001.

  23. Mesh size:

  24. Solarminimum phase

  25. V=236.7×B/f +473.4

  26. Solar maximum phase

  27. Bp≦１５G (High Latitude) Bp＞１５G (Low Latitude) V=163.6×B/f +419.9 V=143.1×B/f +376.5

  28. CH size fast slower slower slow Physical meaning of the parameter B/f • Energy supply ー B • Efficiency ー Flux expansion f What is the role of the coronal hole size in determining the solar wind speed ?

  29. Flux expansion + B energy after Hirano (2004)

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