INERTIAL RANGE TURBULENCE OF FAST AND SLOW SOLAR WIND AT 0.72 AU AND SOLAR MINIMUM

We investigate Venus Express (VEX) observations of magnetic field fluctu-ations performed systematically in the solar wind at 0.72 Astronomical Units(AU), between 2007 and 2009, during the deep minimum of the solar cycle 24.The Power Spectral Densities (PSD) of the magnetic field components have beencomputed for the time intervals that satisfy data integrity criteria and have beengrouped according to the type of wind, fast and slow defined for speeds largerand respectively smaller than 450 km/s. The PSDs show higher levels of powerfor the fast than for the slow wind. The spectral slopes estimated for all PSDsin the frequency range 0.005-0.1 Hz exhibit a normal distribution. The averagevalue of the trace of the spectral matrix is −1.60 for fast solar wind and −1.65for slow wind. Compared to the corresponding average slopes at 1 AU, the PSDsare shallower at 0.72 AU for slow wind conditions suggesting a steepening of thesolar wind spectra between Venus and Earth. No significant time variation trendis observed for the spectral behavior of both slow and fast wind.