@Article{EcherFraCosHajBol:2022:UlObDu,
               author = "Echer, Ezequiel and Franco, Adriane Marques de Souza and Costa 
                         J{\'u}nior, Edio da and Hajra, Rajkumar and Bolzan, 
                         Maur{\'{\i}}cio Jos{\'e} Alves",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)}",
                title = "Solar-Wind High-Speed Stream (HSS) Alfv{\'e}n Wave Fluctuations 
                         at High Heliospheric Latitudes: Ulysses Observations During Two 
                         Solar-Cycle Minima",
              journal = "Solar Physics",
                 year = "2022",
               volume = "297",
               number = "11",
                pages = "e143",
                month = "Nov.",
             keywords = "Alfv{\'e}n waves, Coronal holes, Magnetic fields, interplanetary, 
                         Solar cycle, Solar wind.",
             abstract = "We study Alfv{\'e}n 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 SCM22\−23 (the minimum between 
                         Cycles 23 and 24 or SCM23\−24). The solar-wind plasma 
                         density [Np], IMF magnitude [B], and IMF-component variances are 
                         found to be lower during SCM23\−24 than during 
                         SCM22\−23 by \≈ 20 30%. The cross-correlation 
                         between the plasma velocity and IMF vector components, an 
                         indicative of Alfv{\'e}nicity, is smaller during SCM23\−24 
                         than during SCM22\−23. The Alfv{\'e}n wave periodicity 
                         exhibits a large range, from \≈ 8 hours to 10 days, with 
                         peak occurrences near 1 5 days during both minima. The statistical 
                         kurtosis analysis shows that the IMF distributions are mostly 
                         sub-Gaussian. Further, the Fourier power law analysis reveals a 
                         higher spectral power of transverse IMF components Bt and Bn than 
                         the radial field-aligned component Br. The power spectrum shows a 
                         spectral break near 10\−4 Hz, with its high-frequency 
                         portion following a \−1.7 power law dependence (Kolmogorov 
                         spectrum), while the low-frequency portion shows an \≈ 
                         \− 1.0 power law index dependence. This low-frequency index 
                         is slightly higher during SCM22\−23 (\−0.65 to 
                         \−0.87) than during SCM23\−24 (\−0.49 to 
                         \−0.78). We conclude that while the Alfv{\'e}nicity of the 
                         high-latitude HSSs does not vary substantially between the two 
                         minima, the amplitude of the Alfv{\'e}n wave fluctuations is 
                         reduced during SCM23\−24 compared to SCM22\−23.",
                  doi = "10.1007/s11207-022-02070-w",
                  url = "http://dx.doi.org/10.1007/s11207-022-02070-w",
                 issn = "0038-0938 and 1573-093X",
             language = "en",
        urlaccessdate = "30 abr. 2024"
}