Three-dimensional Evolution of Solar Wind during Solar Cycles 22-24

We present results on the three-dimensional evolution of solar wind density turbulence and speed at various levels of solar activity between solar cycles 22 and 24. The solar wind data used in this study has been obtained from interplanetary scintillation (IPS) measurements made at the Ooty Radio Telescope, operating at 327 MHz. Comparison of results at corresponding phases of solar cycles reveals that on the average, there is a downward trend in density turbulence from the maximum of cycle 22 to the present phase of cycle 24. In particular, in the present state of reduced solar activity, slow speed dominates the large part of heliosphere and there is a reduction in the supply of mass and energy at the base of the corona and into the heliosphere. Moreover, the latitudinal distribution of solar wind speed has been significantly different during the above period. I will also discuss the results on the radial dependence of solar wind properties (level of turbulence, spatial cut-off scales, etc.) at representative periods of solar cycles 22 to 24.