The Noon and Midnight Sector Response to IMF Changes.
M.PINNOCK
British Antarctic Survey, UK.
We have attempted to test for a simultaneous near-global response in polar convection in response to IMF changing from Bz northward to southward., as shown by [1, 2]. The basis of our test is: if the polar convection is enhanced at all local times (and assuming that nightside reconnection is not) then we expect the nightside polar cap boundary to start moving equatorward immediately the cusp ionosphere responds to the IMF change. Noon magnetograms from Durmont D’Urville and midnight HF radar data from Halley, both in Antarctica, are used in this study. The total B field measured by the Durmont D’Urville magnetometer provides a sensitive indicator of when IMF changes first impact the ionosphere, and obviate the need to deduce accurate timings between spacecraft and the ionosphere. The HF radar data is used to detect the growth phase signature previously documented [3], which we take as a proxy for polar cap boundary motion. Ten events have been studied and the time delay between these two signatures measured. Within the accuracy of the experiment we find a range of time delays from near immediate to 30 minutes or greater. We speculate on the possible physical mechanisms that may give this range of results and also highlight how the Halley/TIGER radar pair will be used to extend this study.
- Ridley et al., Ionospheric convection during non-steady interplanetary magnetic field conditions, JGR, 102, 14563, 1997.
- Ruohoniemi & Greenwald, The response of high-latitude convection to a sudden southward IMF turning, GRL, 25, 2913, 1998.
- Lewis et al., The relationship of HF radar backscatter to the accumulation of open magnetic flux prior to substorm onset, JGR, 103, 22613, 1998.
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