Two velocity structure of the inner solar wind

Measurements of the motion of plasma density irregularities in the inner solar wind are presented. The speeds were estimated using cross-correlation analysis of radio frequency fluctuations the GALILEO spacecraft measured simultaneously at widely spaced ground stations. The radial projections of the correlation baselines on the pattern plane were of the order of several thousand kilometers. For cross-correlation functions calculated with comparatively short averaging times, we find that a pronounced two-velocity configuration is often observed over the range of heliocentric distances 20 R < R < 40 R. The typical mean speed for such observations is about of 300-400 km/s and the difference between the two predominant speeds is about 150-200 km/s . These results may indicate that the density fluctuations are associated with slow magnetosonic waves propagating in opposite directions at the local sound speed in the reference frame moving with the mean solar wind speed. Quite reasonable estimates of the solar wind speed and speed of sound are obtained from this model.