We describe simultaneous interplanetary scintillation (IPS) measurements for the solar distance range 70-185 R⊙ made using the Ooty Radio Telescope and the Solar Terrestrial Environment Laboratory three-antenna system during the first half of the current solar cycle 22. These measurements have been used to establish the spectral characteristics of the electron density fluctuations in the solar wind, and we study the relation of these to the plasma flow speed. At times of low activity, for high-speed streams (Vsw ≈ 600 km s-1) the spectra (sensitive to the IPS temporal frequency range 1-10 Hz) are steep, with a power law exponent α ≈ 3.8. During high levels of activity for high-speed streams, the spectra are less steep with α ≈ 3.4. In the low-speed wind (Fgw ≈ 400 km s -1) the spectra are clearly flatter, α ≈ 2.9, and nearly invariant with solar activity. The average shape of the spectrum obtained from this study is consistent with results obtained via other techniques. By combining the present estimates with earlier spacecraft data, it is possible to consider the shape of the density fluctuation spectrum in the frequency range 10-5-101 Hz. It is shown that the spectrum has different slopes in different spectral domains and is well described by a three-component model as proposed by Coles and Harmon . Moreover, the high-frequency components of the spectra in the low- and high-speed streams involve different spatial frequency ranges.
ASJC Scopus subject areas
- Space and Planetary Science