Origin of low cross-helicity regions in the inner solar wind

Journal Article · Wed May 01 04:00:00 EDT 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA00144· OSTI ID:5261858

Bruno, R; Bavassano, B ^[1]

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1. Consiglio Nazionale delle Ricerche, Frascati (Italy)

Part of the present understanding of the phenomena governing the radial evolution of the solar wind MHD turbulence can be summarized in the following scenario: outward propagating Alfven waves are generated near the Sun and, in addition, more waves of the same type, with mixed sense of propagation, are freshly generated at interplanetary stream shears, through plasma instabilities. The nonlinear interaction between outward propagating (majority modes) and inward propagating (minority modes) Alfven waves is then crucial for the dynamical evolution of the MHD turbulence, which is reflected in the radial dependence of the normalized cross-helicity ({sigma}{sub c}). The evolution of this parameter toward lower values, with increasing heliocentric distance, is interpreted as a continuous production of minority modes. However, since the same effect on {sigma}{sub c} can be obtained simply by decreasing the presence of the outward modes alone, the authors have separated the inward from the outward contribution by using Elsaesser variables ({und z}{sup {plus minus}}) and investigated the possibility that this phenomenon could be statistically related to the presence of nonpropagating field and/or density fluctuations able to reduce the {und v},{und b} correlation of the majority modes. The results support this point of view and show that while fluctuations of field intensity produce a depletion of the outward modes, fluctuations in density reinforce the inward modes. These observations pose new theoretical problems for any model which attributes to local generation and as a consequence to e{sup {minus}} modes, a role that they do not seem to have in the evolution of the large-scale solar wind turbulence.

• OSTI ID: 5261858
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 96:A5; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INSTABILITY
INTERPLANETARY SPACE
MAGNETOHYDRODYNAMICS
MATHEMATICAL MODELS
MECHANICS
NONLINEAR PROBLEMS
ORIGIN
PLASMA DENSITY
PLASMA INSTABILITY
SHEAR
SOLAR ACTIVITY
SOLAR WIND
SPACE
TURBULENCE
WAVE PROPAGATION