The three-dimensional structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-living feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about turbulence, known to be able of playing a key role in space plasma heating. A ubiquitous presence of a turbulence of Alfvenic type is a well established feature for low-solar-activity polar wind. Does this hold for the new polar flows seen near solar maximum? An answer is given here through a comparative statistical analysis on parameters as total energy, cross helicity, and residual energy, that well describe the Alfvenic character of fluctuations. Our results indicate that the main features of the Alfvenic turbulence observed in low-solar-activity polar wind are quickly recovered in the new polar flows developed shortly after solax maximum.

Alfvenic turbulence in "newborn" polar flows

PIETROPAOLO, Ermanno
2005-01-01

Abstract

The three-dimensional structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-living feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about turbulence, known to be able of playing a key role in space plasma heating. A ubiquitous presence of a turbulence of Alfvenic type is a well established feature for low-solar-activity polar wind. Does this hold for the new polar flows seen near solar maximum? An answer is given here through a comparative statistical analysis on parameters as total energy, cross helicity, and residual energy, that well describe the Alfvenic character of fluctuations. Our results indicate that the main features of the Alfvenic turbulence observed in low-solar-activity polar wind are quickly recovered in the new polar flows developed shortly after solax maximum.
92-9092-903-0
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11697/40052
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