On the heliographic latitude dependence of the solar wind velocity

Plasma data from Pioneers 6–7 and from a variety of satellites operating near the Earth are used to investigate the heliographic latitude dependence of the solar wind bulk speed near the sunspot maximum. No evidence is found for a latitude effect: the latitudinal gradient, if any, turns out to be 2 km (sec degree)^–1, to be compared with the gradient of 10 km (sec degree)^–1 observed in periods of low or moderate solar activity.