TY - JOUR
T1 - Solar wind Alfvénicity during solar cycle 23 and 24
T2 - Perspective for future observations with Parker Solar Probe and Solar Orbiter
AU - D'Amicis, R.
AU - Alielden, K.
AU - Perrone, D.
AU - Bruno, R.
AU - Telloni, D.
AU - Raines, J. M.
AU - Lepri, S. T.
AU - Zhao, L.
N1 - Funding Information:
Acknowledgements. K. A. was partially supported by the COSPAR fellowship program. The authors acknowledge the following people and organizations for data provision: R. Lin (UC Berkeley) and R. P. Lepping (NASA/GSFC) for WIND/3DP and WIND/MFI data, respectively, and G. Gloeckler (University of Maryland) for ACE/SWICS data. Data are available in the NASA-CDAWeb website: https://cdaweb.sci.gsfc.nasa.gov
Publisher Copyright:
© ESO 2021.
PY - 2021/10/1
Y1 - 2021/10/1
N2 - Context. Alfvénic fluctuations are ubiquitous features observed in solar wind, especially in the inner heliosphere. However, strong Alfvénic fluctuations are recovered in the near-Earth solar wind too, mainly in fast streams, but also in some cases in slow wind intervals, as highlighted in recent studies. Aims. The present study focuses on a statistical comparison between different phases of solar cycles 23 and 24 with regard to the Alfvénic content of solar wind fluctuations. Particular attention is devoted to the Alfvénic slow solar wind, in relation to the solar wind composition and other parameters. Methods. Two-dimensional histograms of the solar wind speed versus the normalized cross-helicity have been used to feature the Alfvénic character of solar wind turbulence on each phase of the solar cycles considered. Moreover, we characterize the different phases of solar cycles by also using composition data. Finally, case studies are discussed to better highlight the similarities and differences between the two solar maxima, which more clearly show a predominance of Alfvénic slow solar wind. Results. The statistical analysis highlights similarities between two solar cycles and confirms that the Alfvénic slow wind is more frequently observed during the maximum of solar activity. The two representative time intervals, containing samples of this solar wind regime, show similar characteristics, with a particular reference to the spectral analysis. Conclusions. This study has important implications for future observations by Parker Solar Probe and Solar Orbiter, devoted to the study of the inner heliosphere inside Mercury's orbit. In fact, both missions will operate up to the maximum of solar cycle 25 which is fast approaching. These unprecedented measurements will then provide insights into the origin and evolution of the Alfvénic solar wind close to the region where it is generated and accelerated.
AB - Context. Alfvénic fluctuations are ubiquitous features observed in solar wind, especially in the inner heliosphere. However, strong Alfvénic fluctuations are recovered in the near-Earth solar wind too, mainly in fast streams, but also in some cases in slow wind intervals, as highlighted in recent studies. Aims. The present study focuses on a statistical comparison between different phases of solar cycles 23 and 24 with regard to the Alfvénic content of solar wind fluctuations. Particular attention is devoted to the Alfvénic slow solar wind, in relation to the solar wind composition and other parameters. Methods. Two-dimensional histograms of the solar wind speed versus the normalized cross-helicity have been used to feature the Alfvénic character of solar wind turbulence on each phase of the solar cycles considered. Moreover, we characterize the different phases of solar cycles by also using composition data. Finally, case studies are discussed to better highlight the similarities and differences between the two solar maxima, which more clearly show a predominance of Alfvénic slow solar wind. Results. The statistical analysis highlights similarities between two solar cycles and confirms that the Alfvénic slow wind is more frequently observed during the maximum of solar activity. The two representative time intervals, containing samples of this solar wind regime, show similar characteristics, with a particular reference to the spectral analysis. Conclusions. This study has important implications for future observations by Parker Solar Probe and Solar Orbiter, devoted to the study of the inner heliosphere inside Mercury's orbit. In fact, both missions will operate up to the maximum of solar cycle 25 which is fast approaching. These unprecedented measurements will then provide insights into the origin and evolution of the Alfvénic solar wind close to the region where it is generated and accelerated.
KW - Interplanetary medium
KW - Methods: data analysis
KW - Plasmas
KW - Solar wind
KW - Sun: heliosphere
KW - Turbulence
UR - http://www.scopus.com/inward/record.url?scp=85117735198&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202140600
DO - 10.1051/0004-6361/202140600
M3 - Article
AN - SCOPUS:85117735198
SN - 0004-6361
VL - 654
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A111
ER -