Scintillation studies of density microstructure in the solar wind plasma

Interplanetary scintillation observations made with the 74 MHz system at UCSD are used to infer the spatial power spectrum of microscale density fluctuations, and the distribution of microstructure in the solar wind. A technique for estimating the density power spectrum directly from the IPS intensity spectrum is described. The estimation algorithm is applied to a large body of data obtained during 1972--73. Large fluctuations in the shape of the estimated density spectrum are interpreted as bias associated with the passage of high speed streams through the line of sight, rather than changes in the intrinsic shape of the spectrum. When this bias is accounted for, it is found that the density spectrum has a power law slope α approximately equal to 2.8 in the wave-number range .002 less than q less than .01 km-1, and steepens to α approximately equal to 3.2 for q greater than .01 km-1. In light of spacecraft measurements at other wavenumbers, this is consistent with a moderate flattening of the density spectrum in the microscale regime