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

Main stages in the solar-wind studies Object of investigationAuthorsYears 1First evidence of the solar-wind streams obtained from the orientation of cometary tails L.Bierman, S.K.Vsekhsvyatsky et al. early 1950s 2Discovery of the solar supercorona: near-solar and interplanetary plasma up to ~15R s. Radioastronomic occultation method V.V.Vitkevich1955 3Radial extension of magnetic irregularities in interplanetary medium. V.V.Vitkevich, B.N.Panovkin Model of the solar wind flux from the source in the solar corona to the Earth E.N.Parker1958 5The first measurements of proton fluxes on board the “Luna” space mission K.I.Gringauz1959 6In-situ measurements of particle velocities on board the “Mariner-2” and “Mariner-4” space missions K.U.Snayder, M.Neugebauer Measurements of the solar-wind velocity vector by the radioastronomic scintillation method V.V.Vitkevich, V.I.Vlasov Origin of the irregularities responsible for radio scattering associated with the wave processes in interplanetary plasma N.F.Lotova, A.A.Rukhadze, I.S.Baikov

Main stages in the solar-wind studies Object of investigationAuthorsYears 9Discovery of fast solar-wind streams at the magnetic field sector boundaries. ‘Helios” space mission R.Schwenn H.Rosenbauer E.M.Neubauer 1970s 10Coronal holes identified as the source of the high- speed solar wind Krieger et al The fast and slow solar-wind streams were measured from scintillation observations. The fast solar wind was shown to originate at the poles and the slow wind, in equatorial regions. W.A.Coles, B.J.Rickett Discovery of the solar-wind transonic transition region by radio occultation method on board the “Venera-10” space mission and by scintillation of mazer sources of the water vapour line. Formation of the transition region. Regime of mixed flow solar- wind A.I.Efimov, O.I.Yakovlev, N.A.Lotova R.L.Sorochenko, D.F.Blums N.A.Lotova, K.V.Vladimirsky Mass probing of interplanetary plasma at large distances from the Sun V.I.Vlasov

Main stages in the solar-wind studies Object of investigationAuthorsYears 14Large-scale jet structure of the solar wind: а) radio maps of the solar-wind velocity at large distances from the Sun (by scintillations); б) radio maps of the solar-wind transonic transition region in the vicinity of the Sun. Annual radio maps of the heliolatitude structure of the solar-wind streams T.Какinuma, M.Kojima N.A.Lotova, K.V.Vladimirsky, O.A.Korelov, Ya.V.Pisarenko Since 1985 Since Correlation study of the solar-wind stream structure and sources in the solar corona. Method of correlation analysis Rin = F(|B R |). The main types of the streams. N.A.Lotova, K.V.Vladimirsky V.N.Obridko Formation mechanisms of the stable solar-wind stream N.A.Lotova, K.V.Vladimirsky Evolution of the stream sources and components over an activity cycle N.A.Lotova, V.N.Obridko

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

Examples of the radial dependence of 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.

Correlation between the supersonic stream velocity and the location of the transition region inner boundary V(R in ) The large distance R in 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

Radio maps of the solar-wind transition region for the epoch of maximum of cycle 23: 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 the closer to the Sun are R in and R out. 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.

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.

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)

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)

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.

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=2.5R s. Thus, the complicated acceleration processes in the solar wind do not change the initial inhomogenous structure of the stream.

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.

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 , the transition region moved farther from the Sun to interplanetary space, and its boundaries were located at ~15-60 R s compared to ~10-40R s in the previous epoch;  this may be due to the predominance of the low- speed solar solar wind;

R in as a function of the coronal magnetic field intensity  B R  ; data for 1997 The existence of three different types of the flow manifests itself in several branches of the correlation dependence

R in as a function of the magnetic field intensity  B R  for the epoch of solar maximum

TABLE Structure of the solar wind streams as inferred from the correlation diagrams R in =F(  B R  ) NType of the stream Magnetic field strength  B R  Magnetic field structureStructure of the white-light corona Symbol 1Fast streamStrong magnetic fieldOpen field linesLarge CH or polar CH <> 2Fast streamStrong magnetic fieldLow loops in very strong magnetic field Weak diffusion emission  3Fast streamWeak magnetic fieldOpen field linesLocal CH or CH neighborhood, between two streamer lobes  4Slow streamWeak magnetic fieldHigh loopsStreamers  5Slow streamWeak and medium magnetic field MixedStreamer neighborhood  6Uncorrelated component: the slowest streams Weak magnetic fieldVery low closed loops or a weak streamer Zone between the streamer and dark region or very weak streamer 

Correlation dependences R in =F(  B R  ) for the epoch of solar maximum: Evolution of the correlation between R in =F(  B R  ) and solar activity R z in 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

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.

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 R in and the magnetic field intensity  B R  on the source surface. The method was developed at IZMIRAN.  Correlation analysis of the relationship R in =F(  B R  ) between the location of the inner boundary R in and 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 R in =F(  B R  ) at all; these streams are usually the slowest in the general pattern of the solar wind.

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 R in =F(  B R  ) in two slow stream components; -the appearance of the formerly absent uncorrelated stream component on the correlation diagram R in =F(  B R  ) 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.