Greco, A.; Matthaeus, W.H.; D'Amicis, R.; Servidio, S.; <div class="autor_fcen" id="2615">Dmitruk, P.</div>
Fecha de publicación: 2012.
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The formation of coherent structures in turbulence is a signature of a developing cascade and therefore might be observable by analyzing inner heliospheric solar wind turbulence. To test this idea, data from the Helios 2 mission, for six streams of solar wind at different heliocentric distances and of different velocities, were subjected to statistical analysis using the partial variance of increments (PVI) approach. We see a clear increase of the PVI distribution function versus solar wind age for higher PVI cutoff, indicating development of non-Gaussian coherent structures. The plausibility of this interpretation is confirmed by a similar behavior observed in two-dimensional magnetohydrodynamics simulation data at corresponding dimensionless nonlinear times. © 2012. The American Astronomical Society. All rights reserved.
Afiliación de los autores: Dmitruk, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
magnetohydrodynamics (MHD); solar wind; turbulence.
Repositorio: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
Matthaeus, W.H.; Servidio, S.; <div class="autor_fcen" id="2615">Dmitruk, P.</div>; Carbone, V.; Oughton, S.; Wan, M.; Osman, K.T.
Correlation anisotropy emerges dynamically in magnetohydrodynamics (MHD), producing stronger gradients across the large-scale mean magnetic field than along it. This occurs both globally and locally, and has significant implications in space and astrophysical plasmas, including particle scattering and transport, and theories of turbulence. Properties of local correlation anisotropy are further documented here by showing through numerical experiments that the effect is intensified in more localized estimates of the mean field. The mathematical formulation of this property shows that local anisotropy mixes second-order with higher order correlations. Sensitivity of local statistical estimates to higher order correlations can be understood in connection with the stochastic coordinate system inherent in such formulations. We demonstrate this in specific cases, and illustrate the connection to higher order statistics by showing the sensitivity of local anisotropy to phase randomization, after which the global measure of anisotropy is recovered at all scales of averaging. This establishes that anisotropy of the local structure function is not a measure of anisotropy of the energy spectrum. Evidently, the local enhancement of correlation anisotropy is of substantial fundamental interest and must be understood in terms of higher order correlations, specifically fourth-order and above. © 2012. The American Astronomical Society. All rights reserved.
interplanetary medium; magnetic fields; magnetohydrodynamics (MHD); methods: data analysis; solar wind; turbulence.