Diagnostics of solar wind streams

1. Diagnostics of solar wind streams N.A.Lotova, K.V.Vladimirsky, and V.N.Obridko IZMIRAN

2. Main stages in the solar-wind studies

3. Main stages in the solar-wind studies

4. Main stages in the solar-wind studies

5. Formation of the solar-wind streams, irregularities, and jet structure The analysis was based on three sets of independent experimental data. data on radio scattering on circumsolar plasma obtained with the large radio telescopes of the Lebedev Physical Institute (Pushchino); coronal magnetic field strength and configuration calculated from the J.Wilcox/Stanford Zeeman observations in the photosphere; LASCO/SOHO white-light images of the solar corona

6. Examples of the radial dependenceof radio scattering (R) Routine radio occultation experiments in circumsolar plasma have provided the radial dependences of radio scattering: the scattering angle 2(R) and scintillation index m(R), which allow us to locate the solar-wind transition region on the scale of radial distances from the Sun.

7. Correlation between the supersonic stream velocity and the location of the transition region inner boundary V(Rin) The large distance Rin from the Sun corresponds to the low speed and slow acceleration of the solar wind streams; the small distance, on the contrary, corresponds to the high speed and fast acceleration

8. Radio maps of the solar-wind transition region for the epoch of maximum of cycle 23: 2000-2002 The use of a few occultation sources approaching the Sun simultaneously at different heliolatitudes made it possible to construct radio maps of the transition region. Here, the higher are the stream velocities thecloser to the Sun are Rinand Rout. The radio maps display the jet structure of the flow. They show that the solar wind stream is essentially inhomogeneous and has a significant N-S asymmetry.

9. Comparison of radio maps for the epochs of minimum and maximum solar activity A distinctive feature of the solar wind in the epoch of maximum is the prevalence of low-speed plasma streams. The slowest streams were recorded in 2000 during the first (highest) maximum.

10. Radio maps of the solar wind transition region juxtaposed with the heliolatitudinal velocity patters at large distances from the Sun inferred from the Japanese data (cycle maximum)

11. Radio maps of the solar wind transition region juxtaposed with the heliolatitudinal velocity patters at large distances from the Sun inferred from the Japanese data (cycle minimum)

12. Radio maps for the epoch of maximum and beginning of the declining phase of the solar cycle • Radio maps visualize the stream structure. The map series corroborates the jet structure of the solar wind and the mixed flow regime in the transonic transition region.

13. Comparing the heliolatitudinal structure of the transition region near the Sun with the stream structure at a distance of about 1 a.u., we can see that, with allowance for non-stationary nature of the solar wind, they are quite similar. This suggests that the solar wind propagating from the transition region to 1 a.u. conserves its jet structure formed under the initial conditions at the source surface in the solar corona at R=2.5Rs.Thus, the complicated acceleration processes in the solar wind do not change the initial inhomogenous structure of the stream.

14. Comparison of the isophotes of the white-light corona and the structure of the solar wind transition region Taking into account the non-stationary character of the solar wind, the agreement between the shape of the averaged white-light corona and the structure of the transition region is quite satisfactory.

15. A complex analysis of radio astronomic, optical, and magnetic data on the solar wind structure and sources in the solar corona has revealed some typical features in the formation of the solar wind streams different from the previous epochs: in 2000-2002, the transition region moved farther from the Sun to interplanetary space, and its boundaries were located at ~15-60 Rscompared to ~10-40Rsin the previous epoch; this may be due to the predominance of the low-speed solar solar wind;

16. Rinas a function of the coronal magnetic field intensityBR; data for 1997 • The existence of three different types of the flow manifests itself in several branches of the correlation dependence

17. Rinas a function of the magnetic field intensityBRfor the epoch of solar maximum

18. 2003 2004

19. TABLEStructure of the solar wind streams as inferred from the correlation diagrams Rin=F(BR)

20. Correlation dependences Rin=F(BR) for the epoch of solar maximum: 2000-2002 Evolution of the correlation between Rin=F(BR) and solar activity Rzin the epoch of solar maximum. The typical evolution features are: the change of inclination of the correlation curves with solar activity variations; appearance of the formerly unknown uncorrelated stream component

21. Example of the sources of the uncorrelated slowest component of the solar wind – (E, =42)small, low-altitude magnetic loops interacting with the open field lines of the local coronal holes.

23. Conclusion • The main progress in the study of the solar-wind jet structure was achieved in the diagnostics of the stream components and their sources in the solar corona. The diagnostics is based on the analysis of correlation between the location of the transition region inner boundary Rinand the magnetic field intensity BR on the source surface. The method was developed at IZMIRAN. • Correlation analysis of the relationship Rin=F(BR) between the location of the inner boundary Rinand the source-surface magnetic field has shown that each of the stream components originating from different sources is the slower the higher the solar activity level. There appears a formerly unknown stream component, which displays no correlation dependence Rin=F(BR) at all; these streams are usually the slowest in the general pattern of the solar wind.

24. Conclusion Variations in the solar wind structure with the level of solar activity are associated with: • the change of the predominant type of the streams in the general pattern of the solar wind; • the change of inclination of the dependence Rin=F(BR) in two slow stream components; • the appearance of the formerly absent uncorrelated stream component on the correlation diagram Rin=F(BR) in the epoch of solar maximum; • significant variations in the contribution of the magnetic fields of different scales over the activity cycle. In particular, this manifests itself in intensity variations of the solar global magnetic field, which control the change of the cycle phases and evolution of the solar wind jet structure.