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Ann. Geophys., 20, 1539-1551, 2002
www.ann-geophys.net/20/1539/2002/
© European Geosciences Union 2002
Cusp-latitude Pc3 spectra: band-limited and power-law components
P. V. Ponomarenko1, B. J. Fraser1, F. W. Menk1, S. T. Ables1,*, and R. J. Morris2
1University of Newcastle, Callaghan, NSW, Australia
2Australian Antarctic Division, Kingston, TAS, Australia
*also in: CRC for Satellite Systems, Australia
Correspondence to: P. V. Ponomarenko
(phpp@alinga.newcastle.edu.au)
Abstract. This work attempts to fill a gap in
comparative studies of upstream-generated Pc3–4 waves and broad band ULF
noise observed at cusp latitudes. We performed a statistical analysis of the
spectral properties of three years of cusp-latitude ground magnetometer data,
finding that the average daytime Pc3–4 spectra are characterized by two
principal components: an upstream-related band-limited enhancement (‘signal’)
and a power-law background (‘noise’) with S(f ) a
f -4 . Based on this information we developed an algorithm
allowing for the deconvolution of these two components in the spectral domain.
The frequency of the signal enhancement increases linearly with IMF magnitude
as f [mHz] ~ 4.4 | BIMF
| [nT], and its power maximizes around IMF cone angles qxB
~ 20 and 160° and at 10:30–11:00 MLT. Both spectral components
exhibit similar semiannual variations with equinoctial maxima. The back-ground noise
power grows with increasing southward Bz and remains nearly
constant for northward Bz . Its diurnal variation resembles
that of Pc5 field-line resonance power, with a maximum near 09:00 MLT. Both the
band-limited signal and broad band noise components show
power-law growth with solar wind velocity a V
5.71sw and a V 4.12sw,
respectively. Thus, the effective signal-to-noise ratio increases
with in-creasing Vsw. The observations suggest that the noise
generation is associated with reconnection processes.
Key words. Magnetospheric physics (magnetopause, cusp,
and boundary layers; MHD waves and instabilities; solar wind magnetosphere
interactions)
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