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E. Zesta, A. Boudouridis, D. Berube, and M. Moldwin University of California, Los Angeles

Observations of field-line resonances (FLR) in the inner magnetosphere from the MEASURE and SAMBA magnetometer chains. E. Zesta, A. Boudouridis, D. Berube, and M. Moldwin University of California, Los Angeles.

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E. Zesta, A. Boudouridis, D. Berube, and M. Moldwin University of California, Los Angeles

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  1. Observations of field-line resonances (FLR) in the inner magnetosphere from the MEASURE and SAMBA magnetometer chains. E. Zesta, A. Boudouridis, D. Berube, and M. Moldwin University of California, Los Angeles

  2. The plasmasphere is a cold (low energy), dense (tens to thousands per cc) torus of plasma in the inner magnetosphere co-located with the ring current and radiation belts.

  3. Baranksy et al. [1985] Waters et al. [1991] Menk et al. [1999] Berube et al. [2003] • Field-line standing wave period • T = (2/n) ∫ ds/VA [Dungey, 1954]

  4. Cross-Phase method for determining FLR frequencies Phase difference between a closely spaced pair of magnetometers reaches an extreme value at the resonant frequency of the field line halfway between the pair. (Waters 1991; Waters 1994) Automated CP (Berube, Moldwin and Weygand, 2003)

  5. Mass Density Model log10(ρeq) = -0.67*L + 5.1 AMU/cc Berube and Moldwin (JGR 2004)

  6. Plasmaspheric mass composition • Basic: Combine mass density and electron density models to estimate the average composition of the plasmasphere. • Advanced: Case studies where we combine mass and electron density measurements at the same place and time to estimate plasma composition

  7. Mass Composition Model Combine average equatorial mass and electron density models to estimate the average ion mass as a function of L. (Mavg = ρeq/neq) Empirical neq(L) determined by Fung et al. (2001) from database of IMAGE/RPI electron density. Disturbed Dst < -100 nT Overall profile Berube and Moldwin, 2004

  8. Automated FLR determination techniques. The top panel shows the phase difference method while the bottom shows the amplitude ratio method. Both are applied on the horizontal component of the field, BHOR, for the PAC-PNT pair on 21 December 2003. The solid thick lines indicate the FLR frequency resulting from the automated techniques described in the text with the associated errors drawn as thin vertical lines.

  9. Comparison of Fourier and Wavelet FLR determination Figure 2. Fourier based (left) and Wavelet based (right) automated FLR determination techniques for the PAC-PNT pair on 21 December 2003, in the same format as Figure 1.

  10. FLR determination for conjugate pairs FIT-JAX and PAC-PNT

  11. CONCLUSIONS • From our two conjugate pairs we found, surprisingly, that the derived mass density between those two very close L values dropped at a rate that could not be predicted by any of the existing models or from past observations. If this result is general it indicates that our understanding of the inversion of FLRs to determine the equatorial mass density is not complete and existing models could be constrained by our observations.

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