Magnetic field and plasma data, obtained by the Helios 1 and 2 spacecraft in the solar wind near 0.3 AU during the years 1975 to 1976, have been analyzed by calculating 12 kinds of spectra related to the Els¿sser variables, ΔZ+=ΔV+ΔVA, and ΔZ-=ΔV-ΔVA, where ΔV and ΔVA are the bulk velocity and Alfv¿n velocity fluctuations, respectively. For small amplitude alfv¿n waves the fluctuation variable ΔZ+ simply relates to outward propagation and ΔZ- to an inward sense of propagation, if the ambient magnetic field B0 is directed inward. The frequency range analysed in this paper is 6¿10-6 Hz to 6¿10-3Hz. It is found that (1) the autocorrelation length for ΔZ- is much larger that for ΔZ+ in both the high-speed and low-speed wind. (2) The power spectra of ΔZ-, especially in high-wind speed, are steeper in the low-frequency range and flatten in the high-frequency range. (3) In the low-frequency range, the power spectra for the components of ΔZ+ tend to be isotropic with respect to the three polarization directions, while the spectra of ΔZ- are dominated by the radial component. In the high-frequency domain, the spectra of both ΔXZ+ and ΔZ- are dominated by the transverse component in high-speed wind and are more isotropic in low-speed wind. (4) The spectra related to the residual energy or the cross-correlation in low-speed flows have a power law with the slope near to -5/3.

However, in high-speed flows the corresponding data are widely distributed in a cloud of points with an upper envelope near to the spectrum of ΔZ-. The origin of all these spectra and their importance for the solar wind physics have also been discussed. Several generation mechanisms are suggested as candidates. In the flat part of e- spectrum, the fluctuations may be generated by non-local (in wave number space) interactions with the low-frequency part of the e+ spectrum, or just by parametric decay of the high-frequency part of the e+ spectrum. The steep part of e- (f) may be related to small-scale stream tubes, or be influenced by pressure waves, nonlinear cascading, and the interaction with the outgoing Alfv¿n waves. ¿ American Geophysical Union 1989