Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wavenumber ranges in a $\beta \gtrsim 1$ plasma. The $k^{-5/3}$ inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfv\'en speed. At smaller wavelengths $k \rho_i \geq 1$ the electric spectrum is softer and is consistent with the expected dispersion relation of short-wavelength kinetic Alfv\'en waves. Kinetic Alfv\'en waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluid-like nature of the solar wind.Comment: submitted; 4 pages + 3 figure

Initial results from the Helios-1 Search-coil Magnetometer experiment

The Helios search-coil magnetometer experiments provide a unique potential for studies of electromagnetic plasma wave modes in the solar wind between 0.3–1 A.U. because of excellent background noise levels, high time-resolution and high accuracy. Daily average spectral densities (γ √Hz) in the frequency range from 4.7–220 Hz show a pronounced increase as the sun is approached with complex superposed variations. Their values have a range of more than an order of magnitude. The shock of January 6, 1975 provides an interesting example for the use of high time-resolution spectral data. The fine structure and the long term variations in wave fields after the perpendicular shock are discussed. Also two interesting examples of "magnetic holes" are presented.           ARK: https://n2t.net/ark:/88439/y002056 Permalink: https://geophysicsjournal.com/article/116 &nbsp

Spectral features of solar wind turbulent plasma

Spectral properties of a fully compressible solar wind Hall Magnetohydrodynamic plasma are investigated by means of time dependent three dimensional Hall MHD simulations. Our simulations, in agreement with spacecraft data, identify a spectral break in turbulence spectra at characteristic length-scales associated with electromagnetic fluctuations that are smaller than the ion gyroradius. In this regime, our 3D simulations show that turbulent spectral cascades in the presence of a mean magnetic field follow an omnidirectional anisotropic inertial range spectrum close to $k^{-7/3}$. The onset of the spectral break in our simulations can be ascribed to the presence of nonlinear Hall interactions that modify the spectral cascades. Our simulations further show that the underlying charachteristic turbulent fluctuations are spectrally anisotropic, the extent of which depends critically on the local wavenumber. The fluctuations associated with length scales smaller than the ion gyroradius are highly compressible and tend to exhibit a near equipartition in the velocity and magnetic fields. Finally, we find that the orientation of velocity and magnetic field fluctuations critically determine the character of nonlinear interactions that predominantly govern a Hall MHD plasma, like the solar wind.Comment: This paper is accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Aplicación de un modelo de simulación a la evaluación de una zona regable

[ES] La mejora en la gestión del riego en las zonas regables españolas es cada día más necesaria. Para contribuir a esta tarea, se ha elaborado un modelo de simulación que permite el análisis y la evaluación del manejo del agua en la zona regable del Genil – Cabra, en la provincia de Córdoba. Con este modelo y un indicador de funcionamiento se ha logrado hacer una primera evaluación de la zona, tanto por cultivos como espacialmente. El contraste entre el agua aplicada en el riego y la dotación económicamente óptima calculada por el modelo indicó que en el año 1996/97, la zona se regó deficitariamente, aplicándose algo menos de la mitad (45%) de los requerimientos óptimos calculados. El análisis espacial ha posibilitado determinar zonas en donde el aporte de agua por parte del agricultor está más próximo a las necesidades óptimas de los cultivos.Lorite, I.; Mateos, L.; Fereres Castiel, E. (2003). Aplicación de un modelo de simulación a la evaluación de una zona regable. 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Untersuchung von schnellen magnetischen Fluktuationen im solaren Wind zwischen 0.3 AE und 1.0 AE

6 tabs., 35 figs., many refs.SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman