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This paper presents the analysis of 3D evolution of solar wind densityturbulence and speed at various levels of solar activity between solar cycles22 and 24. The solar wind data has been obtained from interplanetaryscintillation (IPS) measurements made at the Ooty Radio Telescope. Results showthat (i) on the average, there was a downward trend in density turbulence fromthe maximum of cycle 22 to the deep minimum phase of cycle 23; (2) thescattering diameter of the corona around the Sun shrunk steadily towards theSun, starting from 2003 to the smallest size at the deepest minimum, and itcorresponded to a reduction of ~50% in density turbulence between maximum andminimum phases of cycle 23; (3) The latitudinal distribution of solar windspeed was significantly different between minima of cycles 22 and 23. At theminimum phase of solar cycle 22, when the underlying solar magnetic field wassimple and nearly dipole in nature, the high-speed streams were observed frompoles to ~30 deg. latitudes in both hemispheres. In contrast, in the long-decayphase of cycle 23, the sources of high-speed wind at both poles, in accordancewith the weak polar fields, occupied narrow latitude belts from poles to ~60deg. latitudes. Moreover, in agreement with the large amplitude of heliosphericcurrent sheet, the low-speed wind prevailed the low- and mid-latitude regionsof the heliosphere. (4) At the transition phase between cycles 23 and 24, thehigh levels of density and density turbulence were observed close to theheliospheric equator and the low-speed speed wind extended from equatorial- tomid-latitude regions. Results are consistent with the onset of the currentcycle 24, from middle of 2009 and it has almost reached near to the maximumphase at the northern hemisphere of the Sun, but activity not yet developed inthe southern hemisphere.

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