Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh12a..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH12A-02
Physics
[2134] Interplanetary Physics / Interplanetary Magnetic Fields, [2149] Interplanetary Physics / Mhd Waves And Turbulence, [2164] Interplanetary Physics / Solar Wind Plasma, [2199] Interplanetary Physics / General Or Miscellaneous
Scientific paper
In their purest form, Alfvénic fluctuations in the solar wind are transverse fluctuations displaying coupled variations in velocity, V, and magnetic field, B, in which |B| remains nearly constant. Consequently, the fluctuations in the component of V and B corresponding to the direction of the underlying magnetic field vector, Bo, upon which the fluctuations are superimposed are always one-sided relative to base values rather than being equitably distributed about average values. Average values of the direction of B in the presence of large-amplitude Alfvénic fluctuations in the solar wind thus generally do not correspond to the direction of Bo, the quantity needed for comparisons with global models of the heliospheric magnetic field and for determining the parallel and perpendicular components of the fluctuation k-vectors. Here we illustrate the one-sided aspect of the fluctuations in Helios 1 data obtained at 0.36 AU at a time when Bo was directed nearly radially outward from the Sun. Using the Helios data and simulated data sets containing large amplitude Alfvénic fluctuations in which the direction of Bo is known precisely we demonstrate that the orientation of the average magnetic field vector, Bav, does not, in general, correspond to the direction of Bo. Minimum variance analysis of our simulated sets of Alfvénic fluctuations in the solar wind demonstrates that the minimum variance direction corresponds roughly to the direction of Bav, consistent with many previous observational studies, but does not correspond to the direction of propagation of the fluctuations, the group velocity of which is directed along Bo.
Gosling Jack T.
Teh W.
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