3-DIMENSIONAL STRUCTURE OF THE SOLAR-WIND - VARIATION OF DENSITY WITH THE SOLAR-CYCLE

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 similar to 75 degrees N-75 degrees S have been used to study the global three-dimensional density distribution of the solar wind plasma. Contours of constant electron-density fluctuations (Delta N-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 similar to 2.5 times at the poles; the level of turbulence is reduced by a factor of similar to 7; the solar-wind mass flux density at the poles is similar to 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 Delta N-e with the heliocentric distance follows a power law of the form R(-2.2) and it does not show any change with solar activity.