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The solar cycle evolution of solar wind speed structure was studied for the years from 1973 to 1985 on a basis of interplanetary scintillation observations using a new method for mapping solar wind speed to the source surface. The major minimum‐speed regions are distributed along a neutral line through the whole period of a solar cycle: when solar activity is low, they are distributed on the wavy neutral line along the solar equator; in the active phase they also tend to be distributed along the neutral line, which has a large latitudinal amplitude. The minimum‐speed regions tend to be distributed not only along the neutral line but also at low magnetic intensity regions and/or coronal bright regions which do not correspond to the neutral line. As the polar high‐speed regions extend equatorward around the minimum phase, the latitudinal gradient of speed increases at the boundaries of the low‐speed region, and the width of the low‐speed region decreases. One or two years before the minimum of solar activity, two localized minimum‐speed regions appear on the neutral line, and their locations are longitudinally separated by 180°.

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In early August 1972 several major flares took place in the complex plage region (Mc-Math plage region 11976) and produced pronounced disturbances in the solar wind. This letter reports the spatial structure of these distu?bances as deduced from the interplanetary scintillation (IPS) of several radio sources. The radio observations (69 MHz) were carried out at three 'separa•te locations in central Japan at the meridian passages of radio sources 3C48,