Simultaneous Measurements of Convection Changes in the High-Latitude Day- and Night-Side Ionosphere With the Halley and TIGER HF Backscatter Radars - Early Results.

M. L. PARKINSON1, M. PINNOCK2, P. L. DYSON1, J. C. DEVLIN3, and P. R. SMITH3
(1) Department of Physics, La Trobe University, Australia.
(2) British Antarctic Survey, UK
(3) Department of Electronic Engineering, La Trobe University, Australia

Measuring the time delay for the large-scale high-latitude ionospheric convection to respond to sudden changes in the interplanetary magnetic field (IMF) is an important part of understanding geospace weather. The actual time delay has a bearing on the role of IMF line draping, fast Alfven mode waves, and the ionospheric drift in communicating convection changes. Recent measurements suggest that the convection response to changes in the By and Bz components of the IMF is practically simultaneous across the dayside ionosphere (<2 min) (e.g., see [1], [2], [3]). By contrast, Cowley and Lockwood [4], supported by some radar and magnetometer studies, have suggested that convection pattern changes propagate with a phase velocity of 5- 10 km s-1 across the polar cap. The Halley SuperDARN HF radar and the recently commissioned Tasman International Geospace Environment Radar (TIGER) are favourably located for making comprehensive measurements of simultaneous day- and night-side convection changes. Halley beam #8 and TIGER beam #4 both point roughly southward down the magnetic meridian and have geomagnetic longitudes diametrically opposite the corrected geomagnetic pole. Coordinated high time resolution (6-sec) discretionary campaigns using these beams have been conducted since December, 1999, and we report a few of the early results, in particular for the geomagnetic storm of February 12, 2000. For example, at about 13:05 UT the IMF component Bz began to change from +13 nT to –6 nT in ~8 mins. The Halley radar subsequently observed enhanced cusp scatter moving equatorward in the pre-noon sector from about 13:18 onward, ~9 mins after the IMF change. TIGER did not observe simultaneous F-region flow bursts near magnetic midnight, probably because of enhanced radio-wave absorption. However, TIGER did observe distinctive E-region scatter from about 13:26, ~8 mins after cusp scatter commenced in the Halley radar. We assume the E-region irregularities were associated with enhanced F-region electric fields. No firm conclusions are made in regards to the time constants at this early stage of the investigation.

[1] Ridley, A. J., L. Gang, C. R. Clauer, and V. O. Papitashvili, J. Geophys. Res., 103, 4023- 4039, 1998.

[2] Ruohoniemi, J. M. and R. A. Greenwald, Geophys. Res. Lett., 25, 2913- 2916, 1998.

[3] Shepherd, S. G., R. A. Greenwald, and J. M. Rhuohoniemi, Geophys. Res. Lett., In Press, 1999.

[4] Cowley, S. W. H., and M. Lockwood, Excitation and decay of solar wind-driven flows in the magnetosphere-ionosphere system, Ann. Geophysicae, 10, 103, 1992.

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