, Volume 148, Issue 1, pp 153-167

Three-dimensional structure of the solar wind: Variation of density with the solar cycle

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Interplanetary Scintillation (IPS) measurements obtained from a large number of compact radio sources (nearly 150 sources) distributed over the heliocentric distance range 15–175 solar radii (R(⊙) and heliographic latitude ∼75° N-75° S have been used to study the global three-dimensional density distribution of the solar wind plasma. Contours of constant electron-density fluctuations (ΔN e) in the heliospheric plasma obtained for both the solar minimum and maximum show a strong solar latitude dependence. During low solar activity, the equatorial density-fluctuation value decreases away from the equator towards higher latitudes and is reduced by ∼2.5 times at the poles; the level of turbulence is reduced by a factor of ∼7; the solar-wind mass flux density at the poles is ∼25% lower than the equatorial value. However, during high solar activity, the average distribution of density fluctuations becomes spherically symmetric. In the ecliptic, the variation of ΔN e with the heliocentric distance follows a power law of the formR −2.2 and it does not show any change with solar activity.