Ulysses paper

Astrophys. J., 507, 984-990, 1998

Abstract:
Ulysses magnetic field and plasma data recorded during 1992 and 1993 as the spacecraft moved through mid helio-latitudes, have been used to identify intervals dominated by Alfvénic fluctuations in the presence of corotating interaction regions. A wavelet frame representation of Elsässer variables was used to calculate the Alfvénicity of the fluctuations as a function of time and frequency, and to describe their occurrence within co-rotating interaction regions which dominated the interval. It was confirmed that, in general, if Alfvén waves are present, then outward propagating waves dominate, but the power in the waves was found to be highly variable in time. A decrease in the power in the Alfvén waves was found for frequencies lower than ~1x10-5 Hz, corresponding to a scale between 0.3 and 0.5 AU. Alfvén waves were typically found to occur during the trailing edge of high speed streams, as expected from previously published studies, but they did not persist for the whole of the trailing edge. They generally occurred within the first half and ended in a sharp cut-off across all frequencies. Alfvénic fluctuations were also identified during some slow speed streams but they did not persist between rotations. No latitudinal dependence of the purity of the fluctuations was found, but they became more persistent at higher latitudes.

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