The principal research objective of SuperDARN is to provide a global-scale view of the configuration and dynamics of plasma convection in the high-latitude ionosphere. The TIGER-PACE combination (see 'cooperation' page) can image simultaneously the two prime drivers of high-latitude convection (IMF coupling on the dayside and substorms on the nightside). This is particularly important in view of the recent wave hypothesis that suggests the response to the nightside storm process is almost instantaneous.
Polar patches are regions of enhanced ionisation, quite irregular in their structure. They form in the cusp region and convect across the polar cap to the nightside. They are observed when the IMF Bz component is negative but details of exactly how they form and decay are still unknown. The TIGER-PACE combination can track polar patches from their souce region on the dayside to their final destruction in the nightside auroral oval.
Sub-Auroral Convection Flows
Sub-Auroral Ion Drift (SAID) events have been described from satellite observations as "latitudinally confined westward plasma flow(s) exceeding 1000m/s and located equatorward of the auroral zone"*. TIGER can image these events in latitude and longitude dimensions and provide information on how they develop and decay, and on how they are related to the auroral oval, substorms and the ionospheric trough. Basic questions about how often SAIDs occur, their relation to enhanced magnetic activity, the structure of the flow patterns, and whether they are sources of atmospheric gravity waves, will be addressed.
Travelling Ionospheric Disturbances (TIDs)
TIDs are coherent, frontal disturbances which travel large distances through
the ionosphere. They are manifestations of Atmospheric Gravity Waves
(AGWs) which are usually classified as small, medium or large scale waves
depending on their wave characteristics.
TIGER will systematically study the generation of medium-scale waves in the auroral region and their propagation towards Australia. The Digisonde-256 operated at Beveridge by La Trobe University measures local ionospheric drift velocities, and has been set up with a special mode in which it can look southward with a relatively narrow beam (see map on 'cooperation' page). It thus monitors local TID activity using standard vertical incidence ionosode measurements and uses the oblique mode to identify TIDs detected by TIGER, as they approach the Australian mainland. Research objectives concerning TIDs:
Magnetic Storm Effects
TIGER is well placed to study the dynamic periods during large magnetic storms
when the aurora surges equatorward. Measuring details of ionospheric
convection during magnetic storms is an important part of the SuperDARN's
study. Recently, Digisonde data from Casey was used to parameterise
ionospheric F region drifts with the IMF and to compare the implied electric
fields with the E region field determined from magnetometer data. A
similar approach using TIGER drift data which covers a much greater area,
provides a more significant comparison and test of our understanding of the
The plasmapause is the outer boundary of the ionosphere-plasmasphere system, and like all boundaries in nature, it is a region where waves are generated, reflected and dissipated. Therefore the plasmapause plays an important role in controlling energy transfer from auroral latitudes to middle and equatorial latitudes. The region can be explored comprehensively by TIGER. SuperDARN radars are able to identify the electromagnetic structure of hydromagnetic resonances in the high-latitude ionosphere, but the occurrence in the region of the plasmapause has not been explored with this technique. Low latitude pulsations are thought to be generated by ULF energy that propagates in the fast wave mode from the magnetopause, through the plasmatrough and across the plasmapause into the inner magnetosphere. Theoretical studies predict wave reflection points so that the fast mode wave is resonant in the magnetospheric cavity. These cavity/waveguide modes couple to localised field line resonances. TIGER will be used:
TIGER can obtain high spatial and time resolution measurements of the following phenomena:
*(Anderson, P.C., W.B. Hanson and R.A. Heelis: The Ionospheric Signatures of Rapid Subauroral Ion Drifts, J. Geophys. Res., 96, 5785-5792, 1991.)
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