Rates of Occurrence of TIGER HF Radar Echo Parameters Sorted According to the K_p Index and the Interplanetary Magnetic Field - Early Results

M. L. PARKINSON¹, J. C. DEVLIN¹, M. PINNOCK³, P. R. SMITH¹, P. L. DYSON¹, and C. L. WATERS⁴

(1) La Trobe University, Australia
(2) British Antarctic Survey, UK
(3) Johns Hopkins University/Applied Physics Laboratory, USA

The recently commissioned Tasman International Geospace Environment Radar (TIGER) began scientific observations in December, 1999. TIGER is located in a near sea-level wetland on Bruny Island, off the southern tip of Tasmania, Australia. Geographically, it is the most equatorward of any of the SuperDARN radars (43.4° S, 147.2°E), yet the default range gate (180 to 3555 km) covers the interval of corrected geomagnetic latitude (CGM) 57°S to 88°S. This is because the CGM pole is tilted toward the equator near the longitude of TIGER beam #4, which is closely aligned with the magnetic meridian. Thus the radar observes a geomagnetic high-latitude region of the ionosphere subjected to stronger insolation and mid-latitude neutral dynamics than any other radar in the network. Lastly, TIGER has another outstanding feature: the bore sight of the normal 16-beam scan is geographically due south across the Southern Ocean. Most of the first-hop "ground" echoes are backscatter from some of the largest ocean waves on the planet, thus ensuring the viability of the radar for remote sensing of surface winds and sea state. In this paper we present basic occurrence statistics of FITACF parameters derived from all the normal scan beam #4 observations made during December 1999 to February 2000. This interval corresponds to an austral summer, sunspot maximum data set. The F-region ionospheric echoes were predominately due to scatter from the nightside auroral oval. The maximum nighttime scatter rate actually occurred post-midnight, and there was a distinct afternoon minimum. The latitudinal peak exhibited the familiar equatorward expansion and shifting to later local times with increasing K_p index. The E-region scatter observed at short ranges was mostly observed between magnetic midnight and noon. We will consider the major factors determining when scatter from decameter scale irregularities was observed including the availability of suitable propagation modes, the diurnal variation of ionospheric absorption, and the irregularity production mechanisms. The statistical average line-of-sight F-region velocities showed clear evidence for the cross polar cap jet and the dawn convection cell. The location of the greater cusp/cleft was obvious from the maximum spectral widths observed in the pre-noon sector near CGM latitude 78° S. Lastly, a particularly interesting feature was the sharp decrease in cross polar cap velocity and spectral width on the nightside at latitude ~67° S. The relationship between this phenomenon and the location of the plasmapause and main trough is being investigated. Seasonal and IMF variations in all of the parameters will also be compiled.

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