The power spectra of magnetometer data recorded at low latitudes show a rem
arkable similarity over the latitudinal range, 1.3<L<2.0. Power spectra fro
m magnetometer sites along the east coast of Australia show a similar fine
structure where adjacent power maxima are spaced between 3 and 5 mHz apart.
The H component data also show a superposed feature of the power spectrum
that varies with latitude according to that expected for field line resonan
ce. In order to explain these data, the propagation of fast mode, ULF wave
energy through a one-dimensional model of the magnetosphere is examined. Th
e model features an inner boundary at 1.1 R-E, an input wave spectrum at th
e outer boundary (10 R-E) that varies as 1/f, and a realistic Alfven veloci
ty that depends on the radial coordinate. The model includes a plasmapause,
and in the inner plasmasphere, the Alfven velocity reaches a maximum at L=
1.6 then decreases as the larger plasma density of the upper ionosphere is
approached. The azimuthal wave number and background magnetic field also de
pend on the radial coordinate, and a realistic variation of the field line
resonant frequency is included. This model can reproduce important features
of observed low-latitude ULF power spectra and indicates that the interact
ion between waveguide and field line resonance modes is important in unders
tanding low-latitude data.