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Rapid Acceleration Model of Solar Wind Distribution Beyond Major Acceleration Region

Explore how solar wind approaches final velocity after rapid acceleration, analyzing IPS data at varying distances from the Sun (0.13-0.9 AU) during 1995-1997 solar minimum phase. Study radial velocity dependence, use two-sphere tomography, compare acceleration rates with Helios and Ulysses; acceleration decreases with distance from the Sun.

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Rapid Acceleration Model of Solar Wind Distribution Beyond Major Acceleration Region

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  1. rapid acceleration Large distribution Flow speed (km/s) bias by waves Harmon & Coles Heliocentric distance (Rs) after Esser et al. (1997)

  2. 400 km/s

  3. Axford et al. SOHO after Esser et al. (1997)

  4. 7±16 km/s/AU @ 0.3 – 1 AU after Schwenn et al. [1978] 1.5 km/s/AU @ 1.5 – 5 AU after McComas et al. [2000]

  5. Axford’s model

  6. after Esser & Habbal

  7. Wang & Sheely model Magnetic field configuration smaller expansion high speed larger expansion low speed RADIAL DISTANCE after Wang and Sheeley, 1990

  8. from flux expansion factor in situ observation after Wang and Sheeley, 1990

  9. in ecliptic plane N60° N30°

  10. after Goldstein et al., 1996

  11. 77 80 83 86 89 <450 450－550 550－650 >650

  12. V estimated from NVA=const. Flux expansion

  13. Feldman’s model

  14. EUV/SOHO Doppler Image

  15. 0.3－0.9 AU 0.1－0.3 AU

  16. 900 600 V 300 △ (km/s) Velocity (km/s) 0 0 30 60 90 Latitude (deg) Resolution test of two-sphere tomography

  17. 20± 9 km/s (expected 20 km/s) 38± 7 km/s (expected 40 km/s)

  18. 0.3－0.9 AU 80o 50o 50o 80o 0.1－0.3 AU

  19. 19±17 km/s Vinner - Vouter

  20. after Breen 2002

  21. Fast solar wind after the rapid acceleration • M. Kojima(1), M. Tokumaru(1), K. Fujiki(1), T. Ohmi(2), • K. Hayashi(3), and M. Yamashita(1) • Solar-Terrestrial Environment Laboratory, Nagoya University • (2) Science and Technology Department, CTI Co., Ltd. • (3) W.W.Hansen Experimental Physics Laboratory, Stanford University

  22. Motivation of this work Elucidate how the rapidly accelerated solar wind approaches asymptotically to the final velocity beyond the major acceleration region.

  23. Data and analysis ・ IPS data at 0.13-0.9 AU obtained at STELab. ・ Observations during the solar minimum phase from 1995 to 1997. Solar wind structure was not complicated. IPS observations were in weak scattering regime.

  24. IPS lines of sight in one solar rotation

  25. Conclusions • We studied the R dependence of the fast solar wind at 0.13-0.9 AU. • Two-sphere tomography was developed. • The analyses were made using the STELab IPS data during 1995 - 1997. • The major acceleration of the fast wind finishes near the Sun, but gradual acceleration lasts beyond 0.13 AU. • Comparing the acceleration rate with Helios and Ulysses observations, shows a tendency in acceleration rate to decrease with a distance from the Sun.

  26. 80o 50o 50o 80o

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