Magnetic Fluctuations in the Magnetosheath: Cluster Data and the K-Filtering Method

Details Magnetic Fluctuations in the Magnetosheath: Cluster Data and the K-Filtering Method Magnetic Fluctuations in the Magnetosheath: Cluster Data and the K-Filtering Method

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm21b0216s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM21B-0216

Physics

2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence, 2728 Magnetosheath, 2752 Mhd Waves And Instabilities, 7863 Turbulence

Scientific paper

Magnetic turbulence in the magnetosheath certainly plays an important role in the transfers between the solar wind and the magnetosphere. A few theoretical models exist for interpreting the role of the magnetic fluctuations in these transfers, but experimental constraints are now available which can help to decide between them and allow for new advances. The k-filtering technique has been designed for analysing the spatial structure of the electromagnetic field from multi-point measurements: for each temporal frequency it can provide a 3-D spectrum in the wave-vector space. Taking advantage of short CLUSTER separations (100 km ), we have applied this method to the magnetic Cluster-STAFF data and present the results obtained in the frequency range about 0.3 - 3 Hz, in the magnetosheath close to the magnetopause. This frequency range allows to focus on wavelengths that are most generally larger than the spacecraft separation, avoiding the so-called spatial aliasing effect. We can exhibit the first direct determination of the field energy distribution in the (omega, k) space for this frequency range. Moreover, we show that the energy maxima distribution in (omega, k) domain is in a good agreement with the prediction of the linear theoretical wave dispersions. Besides this identification of the nature of turbulence from the point of view of the wave dispersion, a study of the polarization is also initiated for each energy peak. As the existing theories for magnetosheath turbulence rely on assumptions as bi-dimensionality or weak/or strong wave-wave interactions, we show how the k-filtering method allows yielding valuable constraints to all these theoretical issues.

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