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Introduction to Solar Wind for Heliospheric space weather

Introduction to Solar Wind for Heliospheric space weather

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Introduction to Solar Wind for Heliospheric space weather

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  1. Introduction to Solar Wind for Heliospheric space weather

  2. Heliospheric space weather ・Corotating solar wind structure ・Interplanetary CME

  3. Corotating solar wind structure important itself as well as for CME propagation background

  4. In order to model the solar wind from the solar and coronal observations, it is important to find a universal relation between the global properties of the solar wind and corona.

  5. Properties of the Solar Wind  • Solar Wind Acceleration Theory and Observations

  6. Source surface is imaginary sphere at 2.5 Rs, beyond which solar wind flow becomes radial.

  7. Parker model (1958)

  8. Parker model Velocity (km/s) Heliocentric distance (Rs)

  9. coronal hole source region of fast wind Skylab found fast wind comes from a coronal hole. (1970’)

  10. Fast SW from a cooler coronal hole freezing T (O7+/O8+) at 1.5 Rs after Geiss et al., 1995

  11. 106 Tp 105 lower T <300 km/s Slope –1.33 300 – 400 -1.22 104 adiabatic 400 – 500 -1.033 500 – 600 -0.826 higherT 600 – 700 -0.762 700 – 800 -0.808 after Freeman (1988) non adiabatic R (AU)

  12. Slow (350km/s) Fast (700 km/s) 1 AU Tp T_perp=T_para T_perp>T_para 0.3 AU B after Marsch et al., 82

  13. 250-400 km/s 700-800 km/s 3X104 K 2X105 K ~8 ions/cc ~3 ions/cc How accelerate the fast wind suppressing density and heating temperature.

  14. Solar wind is bimodal. Velocity gradient bimodal

  15. V1 b Vo after Newkirk and Fisk, 1985

  16. after Newkirk and Fisk, 1985 V1 600 b Vo 400 65 75 80 70 65 70 75 80

  17. Problems of Parker model ・ Faster wind from a cooler coronal hole. ・ Hotter wind from a cooler coronal hole.

  18. Hollweg model (1978)introducing wave Heating and acceleration are different mechanisms.

  19. 7 10 wave model Alfven wave heating 6 10 nonlinear saturation → turbulently cascade ▽Pw⇒ acceleration 5 10 Temperature 4 10    → nonlinear saturation → turbulently cascade     → high cyclotron resonant frequencies → heat SW Hollweg, 1978    → wave pressure → accelerate SW Low frequency Alfven waves originate at lower corona 0.001 0.01 0.1 1.0 Heliocentric Distance (AU)

  20. How and where wave pressure work?

  21. wave pressure acceleration deceleration Wave pressure works to deduce gravitational force.  → scale height increases   → density gradient becomes smaller.    → gradual velocity increase

  22. Problems of the initial Alfven wave model

  23. Rapid acceleration Flow speed (km/s) Heliocentric distance (Rs) Grall et al., Nature (1996)

  24. Alfven wave pressure cannot make rapid acceleration. Wave pressure 1000 800 600 Velocity (km/s) 400 200 0 1 20 40 60 80 100 Distance (Rs) after Grall et al., 96

  25. Discovery of the rapid acceleration contradicts Alfven wave model

  26. Coronal temperature • electron temperature • proton temperature • ion temperature

  27. Tion 108 K @ 3 Rs Tp 3–4×106 K @ 3 Rs Te 106 K Esser et al. 1999

  28. electron temperature • proton temperature • ion temperature 106 K 3–4×106 K @ 3 Rs 108 K @ 3 Rs

  29. 7 10 6 10 700-800 km/s 5 10 Temperature Hollweg, 1978 4 10 0.001 0.01 0.1 1.0 Heliocentric Distance (AU)

  30. mass flux problem T: isothermal condition If T increases from 1×106 K to 2×106 K, mass flux increases 100 times larger.

  31. How and where additional input energy work?

  32. deceleration acceleration Thermal E works to increase gravitational force.  → scale height decreases   → density at critical distance decreases.    → acceleration efficiency increases

  33. 1000 800 600 Velocity (km/s) 400 200 -[expansion]+[conduction]±collision-radiation + E flux 0 1 10 100 Rs after Esser et al., 97

  34. Hollweg’s 2nd model (1986, 1988) Low freq. Alfven waves at lower corona →dissipation at the Kolmogorov rate → proton heating →rapid acceleration at the sonic critical point at 2–3 Rs However he thought this might be wrong, because Tp @ r=3 Rs is too high which is “incompatible” with the knowledge that fast wind originates in low temperature corona.

  35. 400 km/s

  36. Techniques for SW velocity measurement in corona • IPS • biased by wave motionnear the Sun • Coronagraph observation and mass flux constant assumption • Motion of structure in coronagraph image • Doppler shift of a spectral line • disk-on observation • Doppler dimming of a spectral line • Decrease of the resonant scattering efficiency by Doppler shift

  37. Axford et al. after Esser et al. (1997)

  38. 0.3-0.9 AU 80o 50o 50o 80o 0.1-0.3 AU

  39. 80o 50o 50o 80o

  40. 14 data sets 14 data sets

  41. The major acceleration of the fast wind finishes near the Sun, but gradual acceleration lasts beyond 0.13 AU. STELab from pCH from eqCH

  42. Large distribution Flow speed (km/s) bias by waves Harmon & Coles (2005) Heliocentric distance (Rs)

  43. 49±44 km/s/AU Comparing the acceleration rate of the fast SW with Helios and Ulysses observations, acceleration rate tends to decrease with a distance from the Sun.

  44. Distance T(R) 0.3-1 AU R-0.808±0.169 Freeman [1988] 1.5-5 AU R-1.02 McComas [2000] <300 km/s Slope –1.33 adiabatic expansion

  45. reconnectionnano/pico flares heating cyclotron damping kHz wave heating ★ after Axford and McKenzie, 93

  46. Parameters which determine SW speed • Energy supply • Efficiency E/particle • Physical properties of CH

  47. 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.

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

  49. CH size vs. V Equatorial CH