http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3260 An array of magnetometers and Doppler sounders spanning L = 1.56–2.77 was used to examine perturbations in the daytime ionosphere driven by downgoing ULF waves. For frequencies away from the local field line resonance (FLR), the waves caused mostly vertical motions of the F-region plasma with amplitude ∼0.03–0.06 Hz/nT, with a phase delay of 30° to 40° at the ground. At the local resonant frequency and harmonics the amplitude and phase delay increased markedly. We modeled this by considering an admixture of ULF wave modes and oblique magnetic field geometry, and using actual ionospheric parameters. The model results agree well with observations when the downgoing wave mode varies smoothly from pure fast mode away from the resonance to mostly transverse mode at resonance. These results provide new information on the interaction between downgoing ULF waves and the ionospheric plasma. 2012-03-12T07:05:11.059Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1768 The structure of the density discontinuity across the plasmapause is often based on electron and H+ density profiles with the contribution of heavy ions (He+, O+ etc) neglected. Electron and ion density measurements in this region may differ significantly due to the presence of heavy ions and it is important for the intercomparison of different datasets to understand these differences. Dynamics Explorer (DE-1) magnetic field and plasma composition data have been used to compare heavy ion responses across the plasmapause and to calculate the mass loaded ion density (ρ) profiles. To illustrate this we investigate mass loading through radial profile variations in the Alfven velocity (VA). Results show that the gradient in ρ and VA across the plasmapause is modified when mass loading due to multiple heavy ion species is included, particularly in the presence of the O+ torus. Application to ultra-low frequency (ULF) field line resonance is used as an example where the contribution from heavy ions smoothes out the expected ULF wave resonant frequency discontinuity at the plasmapause. 2010-04-27T06:10:31.208Z ]]>