Diagnostics of solar wind streams

N.A.Lotova, K.V.Vladimirsky, and V.N.Obridko

IZMIRAN

Main stages in the solar-wind studiesObject of investigation Authors Years

1 First evidence of the solar-wind streams obtained from the orientation of cometary tails

L.Bierman, S.K.Vsekhsvyatsky et al.

early1950s

2 Discovery of the solar supercorona: near-solar and interplanetary plasma up to ~15Rs. Radioastronomic occultation method

V.V.Vitkevich 1955

3 Radial extension of magnetic irregularities in interplanetary medium.

V.V.Vitkevich,B.N.Panovkin

1957

4 Model of the solar wind flux from the source in the solar corona to the Earth

E.N.Parker 1958

5 The first measurements of proton fluxes on board the “Luna” space mission

K.I.Gringauz 1959

6 In-situ measurements of particle velocities on board the “Mariner-2” and “Mariner-4” space missions

K.U.Snayder, M.Neugebauer

1962

7 Measurements of the solar-wind velocity vector by the radioastronomic scintillation method

V.V.Vitkevich,V.I.Vlasov

1968

8 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

1968

1969

Main stages in the solar-wind studies

Object of investigation Authors Years

9 Discovery of fast solar-wind streams at the magnetic field sector boundaries. ‘Helios” space mission

R.SchwennH.RosenbauerE.M.Neubauer

1970s

10 Coronal holes identified as the source of the high-speed solar wind

Krieger et al. 1973

11 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

1976 1980

12 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.LotovaR.L.Sorochenko,D.F.BlumsN.A.Lotova,K.V.Vladimirsky

1977

1981

1983

13 Mass probing of interplanetary plasma at large distances from the Sun

V.I.Vlasov

Main stages in the solar-wind studies

Object of investigation Authors Years

14 Large-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.KojimaM.Kojima

N.A.Lotova,K.V.Vladimirsky,O.A.Korelov,Ya.V.Pisarenko

1973-1985 Since 1985 Since 1988

15 Correlation study of the solar-wind stream structure and sources in the solar corona. Method of correlation analysis Rin = F(|BR|). The main types of the streams.

N.A.Lotova,K.V.VladimirskyV.N.Obridko

1995

16 Formation mechanisms of the stable solar-wind stream

N.A.Lotova,K.V.Vladimirsky

1986 2003 2005

17 Evolution of the stream sources and components over an activity cycle

N.A.Lotova,V.N.Obridko

1997- 2004

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(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

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 the closer to the Sun are Rin and 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.

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=2.5Rs. 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 2000-2002, the transition region moved farther from the Sun to interplanetary space, and its boundaries were located at ~15-60 Rs compared to ~10-40Rs in the previous epoch;

this may be due to the predominance of the low-speed solar solar wind;

Rin as 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

Rin as a function of the magnetic field intensity BRfor the epoch of solar maximum

2003 2004

TABLEStructure of the solar wind streams as inferred from the

correlation diagrams Rin=F(BR)

N Type of the stream

Magnetic field strength BR

Magnetic field structure Structure of the white-light corona

Symbol

1 Fast stream Strong magnetic field Open field lines Large CH or polar CH

<>

2 Fast stream Strong magnetic field Low loops in very strong magnetic field

Weak diffusion emission

3 Fast stream Weak magnetic field Open field lines Local CH or CH neighborhood, between two streamer lobes

4 Slow stream Weak magnetic field High loops Streamers 5 Slow stream Weak and medium

magnetic fieldMixed Streamer

neighborhood

6 Uncorrelated component: the slowest streams

Weak magnetic field Very low closed loops or a weak streamer

Zone between the streamer and dark region or very weak streamer

Correlation dependences Rin=F(BR) for the epoch of solar maximum: 2000-2002

Evolution of the correlation between Rin=F(BR) and solar activity Rz 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 Rin and 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 Rin 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 Rin=F(BR) at all; these streams are usually the slowest in the general pattern of the solar wind.

ConclusionVariations 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.