Solar-Wind High-Speed Stream (HSS) Alfvén Wave Fluctuations at High Heliospheric Latitudes: Ulysses Observations During Two Solar-Cycle Minima

We study Alfvén wave fluctuations in solar-wind high-speed streams (HSSs) at high heliolatitudes during the last two solar-cycle minima (SCM). Solar-wind plasma and interplanetary magnetic field (IMF) measured by Ulysses during four 50-day intervals in 1994, 1995, 2007, and 2008 were analyzed using wavelet and Fourier analyses, cross-correlation and kurtosis techniques. Intervals during 1994 and 1995 (2007 and 2008) correspond to the Ulysses polar passes through the southern and northern solar hemispheres, respectively, during the minimum between Cycles 22 and 23 or SCM 22−23 (the minimum between Cycles 23 and 24 or SCM 23−24 ). The solar-wind plasma density [ N_p ], IMF magnitude [ B_0 ], and IMF-component variances are found to be lower during SCM 23−24 than during SCM 22−23 by ≈ 20 – 30