TO THE POSSIBILITY OF STUDY OF THE EXTERNAL SOLAR WIND THIN STRUCTURE IN DECAMETER RADIO WAVES Marina Olyak Institute of Radio Astronomy, 4 Chervonopraporna, Kharkov, Ukraine

Introduction In the recent years the interest of investigating of outer solar wind thin structure has been increased because of studying of interplanetary turbulence nature on large distances from the Sun. Nowadays in Radio Astronomical institute of the Ukrainian Academy of Sciences the observations of interplanetary scintillations in decameter radio wave are renewed on the basis of the new modern equipment. Such observations allow studying outer areas of interplanetary medium from the Earth.

Problem Formulation Let us assume that monochromatic radiation from the far radio source is distributed in a layer of interplanetary plasma with average electron density N and density fluctuations δN smoothly decreasing along a beam of sight (axis z),.

The following parabolic equation can be written for slowly varying complex amplitude of a field: The decision of the equation can be written down by Feynman path-integral approach (Frehlich, 1987; Kukushkin & Olyak, 1994): Here is the differential in the space of continuous trajectories,,.

Let us designate speed component which is perpendicular to the beam of sight and we shall define the spatial - temporary cross-correlation functions of intensity fluctuations as, and the cross - spectra of scintillations as. Here is a distance between items of supervision (base).

Cross-spectrum of Interplanetary Scintillations The spatial fluctuations spectrum of electron density on the large distances from the Sun can be written as. The calculation of cross-correlation functions and spectra of weak interplanetary scintillations on the basis of a Feynman path-integrals method was considered by Olyak (2004, 2005).

Let us assume that the speed and the vector of base r are parallel. Then we shall receive the following expression for the cross – spectrum of weak interplanetary scintillations in a mode of Feynman path-integrals and Markov approach: Here,,R is a radius - vector of a point on a beam of sight,, =1AU.

This is one of experimental interplanetary scintillations spectra, obtained from Falkovich et al (2006). The theoretical curve corresponds to two- flows model.

For more reliable revealing of presence of various speeds in a flow of a solar wind Lotova & Chashey (1973) offered to carry out observations in two items and to investigate dispersion dependence of phase speed. Let us define a phase of a cross - spectrum as. Also we shall designate speed of a harmonic f of a cross - spectrum

The Falkovich’s observations have shown that at the elongations area of interplanetary medium up to 3 AU and more is the main contributor in observable scintillations. The calculations show that in this case inclination of dispersion curves is determined by both variance of speeds and parameters of turbulent flows. The dispersion dependences of phase speed for different values of power index n and width of solar wind flow are shown in figures.

Investigation of Solar Wind Thin Structure Let us consider the spherically symmetric model of the solar wind. In this case expression for dispersion of relative fluctuations of electron density is following: Here, is a dispersion of relative fluctuations of electron density at a level of the Earth orbit, b ≈ 2.

The diagrams of the normalized temporary scintillations spectrum W(f)=W(0,f) and the dispersion dependence of phase speed V f (f) at r = 100 Km, θ = 0 for the spherically symmetric model of solar wind are given in figures (curves 1). Curves 2 correspond to the two- flows model.

It is supposed that the beam of sight crosses two flows: close to spherically symmetric slow flow with n 1, v 1, b 1 and fast flow with n 2, v 2 and. The spectrum of weak scintillations can be presented as the sum, where W 1,2 were determined above. The parameters v 1,2, n 1,2, b 1,2 of fast and slow flows are chosen so that the difference of temporary spectra W(f) for two models was minimal and was limited by the probable errors of measurements. At the same time, as we can see from the latter figure, the dispersion curves for both models are considerably different.

Conclusion The observation of scintillations on two spatially carried antennas and study of dispersion dependence of phase speed will allow to notice the presence of the accelerated flows on a beam of sight when the measurements on one antenna do not give the unequivocal answer to a question whether the flows of solar wind with various speeds are present at external areas of interplanetary medium. The simultaneous study of temporary spectra and dispersion dependences of phase speed will also allow determining parameters of flows of outer solar wind in decameter radio waves.