http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:12163 Magnetometer data from Davis, Antarctica (74.50 S, 99.80 E CGM-1996) are particularly favourable for examining the spectral characteristics due to geomagnetic field lines resonances near the open-closed field line boundary of the magnetosphere. Field line resonance (FLR) signatures of closed field lines at high latitudes on the dayside magnetosphere show diurnal variations in frequency where maximum power occurs in the Pc5 (1-10 mHz) band. Previous research has suggested that the length of closed field lines threading the ground stations is a major factor that deterntines the FLR frequencies. The general topology of the dayside magnetopause results in longer field lines and therefore lower resonant frequencies on the dawn and dusk flanks and the shortest field lines with corresponding higher resonant frequencies near noon. These features yield an arch-shaped variation in frequency with local magnetic time. We compare eigen-function solutions of ULF wave modes that include the curvature and torsion in the geomagnetic field with data from the Davis magnetometer. Including the curvature and torsion effects provides an explanation for our observation of a dip (or saddle) in the Pc5 arch, observed as a decrease in frequency centred on local magnetic noon, that is often seen in high latitude magnetometer data. 2012-12-05T23:02:33.133Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:12033 The occurrence of Pcl-2 ULF waves in Scott Base and Casey Antarctic magnetometer data has been examined with the objective of determining whether the source region for these waves is located in the Earth's cusp/boundary layer region or the magnetosheath. In particular we explore the hypothesis that some Pcl-2 events are propagated along open field lines which convect over the southern polar cap. For a selected event the location of Scott Base with respect to the open/closed field line boundary was independently determined using DMSP spacecraft particle data and well established particle energy and flux criteria. This event provides evidence that Pcl-2 waves can be seen on the ground well inside the polar cap. The possibility of propagation in the ionospheric waveguide, away from the footpoint of the source, is investigated using numerical modelling and realistic ionospheric parameters. Under the modelled conditions we find a modification of wave ellipticity which excludes this explanation for the polar cap Pcl-2 seen in the event study. 2012-11-19T03:26:42.711Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7819 Coordinated observations from GOES-9, DMSP F-13, and Chokurdakh (CHD) have shown concurrent Pc1-2 band wave activity in the late afternoon sector, close to 16 MLT. The left-hand polarization of the waves in space indicates that these are electromagnetic ion cyclotron (EMIC) waves. In the region of field line conjunction, DMSP also observed 6–30 keV energy ion precipitation. We have examined the propagation of the EMIC waves from the magnetosphere to the ionosphere using both time series analysis and a 2½D magnetohydrodynamic model. Our analysis suggests that the EMIC are generated by interactions with cold plasma within a drainage plume, consistent with theory, and that the waves primarily propagate earthward along geomagnetic field lines at the eastward (outer) edge of the plume. 2011-06-02T06:00:34.848Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:50 A new ground-based diagnostic of reconnection at the magnetopause using ULF waves is presented, and we give an example day in which the dynamics of the open-closed boundary (OCB) are clearly observed. The diagnostic is based on data from two close (similar to 110 km), magnetic azimuthally spaced magnetometer sites (Davis and Zhongshan, Antarctica). During average IMF conditions Davis passes just equatorward of the last closed field lines in the dayside magnetosphere, and cross-phase measurements indicate propagation away from local magnetic noon (LMN) as expected for the Kelvin-Helmholtz Instability (KHI) acting at the magnetopause. During times when IMF B-z < -2 nT intervals of broadband activity appear, with the azimuthal component of propagation directed towards noon. Statistical analysis shows a correlation between the negative magnitude of IMF B-z and cross-phase measurements +/- 2-6 hours from LMN. We conclude that under the right conditions, reconnection signatures can be identified in magnetometer data superimposed on the KHI-like propagation signatures of the last closed field lines. 2010-04-27T05:36:21.123Z ]]>