The scale size of Pc 3-4 pulsations in the outer magnetosphere: Observations from Cluster and multiple ground-based observatories
Abstract
The three-dimensional configuration of the four Cluster satellites can be used, in conjunction with ground observations, to analyze both the propagation and the coherence scale of ULF waves in the outer magnetosphere. We report here on the results of analysis of several events in late 2001 in the Pc 3-4 band (15-100 mHz), both on closed dayside field lines and in the polar cap. We have found poor correlations between transverse wave components at the 4 Cluster spacecraft when they were in the dayside middle magnetosphere, with separation distances of ~1000 - 5000 km. Correlation was considerably better for the field-aligned component, suggesting that compressional waves correlated well but that the transverse wave scale (e.g., of local field line resonances) was quite short. In contrast, all components correlated much better for the same range of separation distances when the satellites were in the polar cap. We interpret this as showing the lack of local resonances, and thus the dominance of the traveling compressional mode, in this region. The rather small correlation distances inferred so far from the dayside passes are consistent with the ionospheric coherence scale sizes determined by Szuberla et al. [GRL 25, 2381, 1998] using multiple ground magnetometers and by Baker et al. [GRL 25, 2347, 1998] using SuperDARN radar observations. Ground-satellite correlations in this frequency range are also usually poor, but again are better between the field-aligned satellite component and ground H components.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....6086E