P.K. Manoharan Radio Astronomy Centre National Centre for Radio Astrophysics

1. THE SOLAR WIND THE SOLAR WIND P.K. Manoharan Radio Astronomy Centre National Centre for Radio Astrophysics Tata Institute of Fundamental Research Ooty 643001, India mano@ncra.tifr.res.in P.K. Manoharan Radio Astronomy Centre National Centre for Radio Astrophysics Tata Institute of Fundamental Research Ooty 643001, India mano@ncra.tifr.res.in Kodai IHY School December 10-22, 2007 Kodai IHY School December 10-22, 2007

2. J. L. Kohl and S. R. Cranmer (eds.), Coronal Holes and Solar Wind Acceleration}, Kluwer Academic Publishers, 1999. • E. Marsch, Living Review in Solar Physics, vol. 3, 2006. • M. K. Bird and P. Edenhofer, Physics of the Inner Heliospher - I, eds. R. Schwenn and E. Marsch, Springer--Verlag, Berlin, 1990.

3. Outline • Introduction – Solar Atmosphere • Solar Wind • formation • acceleration • Interplanetary Magnetic field • magnetic storms • Solar wind measuring techniques • direct (in situ) measurements • remote-sensing techniques • Interplanetary Scintillation • Speed and density turbulence • Quasi-stationary (Steady-state) solar wind • Transients in the solar wind (CIRs and CMEs)

4. Solar Atmosphere • Photosphere • thin layer of low-density gas • allows visible photons to escape into space • currents of rising from beneath cause formation granulation • magnetic fields threading outward • magnetic structures (sunspots, active regions, etc.) • Chromosphere • 3000 – 5000 km thick, above photosphere • 5000 – 5x105 K • Huge convection cells lead to jet-like phenomena • Corona • extends from chromosphere to several R • extremely hot, 3x106 K (causes high state of ionization) • energy transport by magnetic fields (heating!?)

5. X-ray Corona

6. Solar Wind • The concept of continuous flow of solar wind was developed in 1950's • Biermann (1951, 1957) observed comet tails as they passed close to the Sun, and explained the formation of the tail and its deflection by a continuous flux of protons from the Sun. • Parker (1964) postulated the continuous expansion of the solar corona, i.e., the outward streaming coronal gas the 'solar wind'.

7. LASCO Observation – Comets and Coronal Mass Ejections

8. Solar Wind

9. Interplanetary Magnetic Field Radial outflow and solar rotation – frozen-in magnetic field is dragged, Interplanetary Magnetic Field (IMF). Coronal magnetic field and IMF properties are intimately related.

11. SUN Geospace

14. Solar Wind • Supersonic outflow of plasma from the Sun's corona to IP medium • Composed of approximately equal numbers of ions and electrons • Ion component consists predominantly of protons (95%), with a small amount of doubly ionized helium and trace amounts of heavier ions • Embedded in the out flowing solar wind plasma is a weak magnetic field known as the interplanetary magnetic field • Solar wind varies in density, velocity, temperature, and magnetic field properties with • solar cycle • heliographic latitude • heliocentric distance, and • rotational period • Also varies in response to shocks, waves, and turbulence that perturb the interplanetary flow. • Average values of solar wind parameters near the Earth (1 AU) • Velocity 468 km/s • Density = 8.7 protons/cc • magnetic field strength = 6.7 nT

15. Hourly average of solar wind speed. density and thermal speed measured at 1 AU

16. Heliosphere and solar wind studies Exploring Heliosphere in 3-D Determination of overall morphology of the Heliosphere • Acceleration of solar wind • Generation of high speed streams with correct V, N, and T • Coronal propagation of solar energetic particles • CME trajectory • Large-scale variation of solar wind and magnetic field and the behavior of their turbulence levels

18. Formation of the Solar Wind • For a steady state of the spherically symmetric flow of solar wind, • Equation of motion • Equation of continuity • Energy equation • Temperature variation with distance (Parker 1964) • At the base of the corona, E < 0; for b = 0.3, E > 0 ( b<<1 )

19. Supersonic Flow • at the base of the corona, • E is negative • system is stable • gravitation potential decreases as 1/r • thermal energy is governed by T(r), which a weak function of distance, r • for b ~ 0.3, E > 0 at R ~ 10 Rsun • solar wind flows with supersonic speed • gravity aids the nozzle flow (like a rocket jet) • to explain the solar wind speed near the Sun and in the entire heliosphere

20. Thermal and Wave driven • Solar wind driven by thermal conduction • not adequate to explain high-speeds at 1 AU • some other non-thermal processes must play a role • additional energy • work done on the plasma or by heating, or both • spectral broadening suggest substantial increase in turbulence at the low corona (Alfven waves) • model should address heating (ion and electron) and damping/dissipation of waves • at what height energy is added to accelerate solar wind

21. Suzuki, ApJ 2006

22. Large spread Flow speed (km/s) Heliocentric distance (Rs) after Esser et al. (1997)

23. Axford et al.

24. bias by waves Harmon & Coles 2005

25. High-Speed Solar Wind - Coronal Hole Region

26. When a polar coronal hole shrinks to small size at the solar maximum, it becomes the source of slow wind.

27. Origin of slow SW(seCH) Coronal hole origin but ⇒ extra momentum source in lower corona Large NV High To (in seCH) Enhanced Heating in lower corona seCH Strong　B (in seCH)

28. after Kojima et al., 1999

29. after Kojima et al., 1999

30. Flux expansion rateｆ Magnetic field intensity　B

31. Large-scale structure of Solar Wind • Steady-state solar wind (origin & acceleration) • Low-speed solar wind • High-speed solar wind (associated with coronal holes • Disturbed solar wind (due to solar transients generated by interactions, flares, and coronal mass ejections)

32. High- and Low-Speed Solar Wind

33. Solar Wind Measurements Solar wind measuring techniques • Near the orbit of the Earth (~1 AU), the solar wind properties are from in situ measurements • Helios satellite measure up to ~0.3 AU • Ulysses first spacecraft probed the polar region • Scattering techniques provide the three-dimensional view of the heliosphere • various distances • all latitudes • long-term variations and large-scale structure of the solar wind

35. Interplanetary Scintillation Radio source L-O-S Sun Earth

36. Solar rotation and radial outward flow of the solar wind provide the 3-d structure of the solar wind at different view angles Computer Assisted Tomography analysis can remove the line-of-sight integration imposed on the solar wind parameters also provides high spatial resolution

37. Ooty IPS measurements: Density Turbulence and Speed of the Solar Wind in the Inner heliosphere February 25 – March 25, 2005 CR2027

39. Solar Cycle Dependence 1999 1991 2000

40. Quasi-stationary solar windLarge-scale structure and long-term variations Constant level of electron density fluctuations (Ne), observed using the Ooty Radio Telescope, during minimum and maximum of solar activity cycle. Latitudinal variations of solar wind speed, observed using the Ooty Radio Telescope, reveal the changes in the large-scale structure of the coronal magnetic field over the solar activity cycle.

41. Coronal Holes • Significantly lower density and temperature than the typical background corona • Areas of the Sun that are magnetically open to interplanetary space • Configuration is divergent • Observed in X-ray, EUV and radio wavelengths that originate in the corona • Grouped into 3 categories: polar, non-polar (isolated) and transient coronal holes • Sources of high-speed solar wind streams • Give rise to recurrent geomagnetic storms • Important in heliospheric and space weather studies

42. Solar Cycle 23 – Solar Wind Density Distribution Solar Wind Density Turbulence (Ooty)

43. Radial Evolution of CIRs 75 solar radii 100 solar radii expansion 150 solar radii

44. Solar Cycle 23 – Solar wind Speed Distribution

45. Radio Source Sun CME Earth IPS Imaging of interplanetary disturbances (CIRs and CMEs) Shock

46. Radial Evolution of CMEs • LASCO and IPS measurements between Sun and 1 AU • Halo and Partial Halo CMEs • ICME at 1 AU (Wind and ACE data) • Initial Speeds in the range 250 – 2600 km/s

47. June 25, 1992 West Limb CME on June 25, 1992* X3.9 Flare, X-ray LDE Manoharan et al. ApJ., 2000 Type-IV

48. Some example of November 2003 CMES

49. Fast CME on April 2, 2001: Ooty Images

50. CME in the interplanetary medium LASCO Images <30 Rsun Waves Radio Spectrum Ooty Scintillation Images 50 - 250 Rsun