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effects. It is therefore plausible that the Bragg scatter events reported in this paper might alsobe linked to the generation of E-region irregularities explained in terms of coherent scattersfrom electron density irregularities generated by the modified two-stream (Farley, 1963;Buneman, 1963) and the gradient-drift (Maeda et al., 1963) plasma instabilities. However thispreliminary interpretation is largely based on previous work discussing SEC/lacuna events,and additional observational parameters (i.e. flow, aspect angle and echo strength) are neededto substantiate this view.ConclusionsWe have shown that interesting E-region Doppler spectral signatures evolve with nearsymmetrical side-peaks during SEC and lacuna conditions, in the vicinity of the southerndayside polar cusp region, at solar cycle minimum. These Bragg scatter events were observedusing both HF and MF radar techniques at two polar stations – although not simultaneously.Our observations are considered in context with independent studies of SEC and lacunaconditions, and studies of Bragg scatter in the E-region. We need to undertake simultaneousHF digisonde and MF radar E-region observations from Davis, Antarctica to confirm that theBragg scatter spectral signatures reported are related. We suggest that these events may berelated to E-region irregularities generated by plasma instability processes. Further research isrequired to unravel the Bragg scatter source region and generation mechanism in order todevelop a theoretical understanding of this interesting high latitude E-region phenomenon.AcknowledgmentsThe Australian Research Council and the Australian Antarctic Science Advisory Committeesupported the installation and operation of the DPS-4 Digisonde at Casey station,Antarctica. We thank Australian National Antarctic Research Expeditions (ANARE)members who contributed to the project, especially Dr. Anthony Breed and Dr. DarrynSchneider who conducted the 1996-1997 summer drift campaign at Casey. We thank JudyWhelan for her assistance with the preparation of the figures.ReferencesBuneman, O., Excitation of field aligned sound waves by electron streams, Phys. Rev. Lett., 10, 285,1963.Cartron, S., and Vila, P., Polar lacuna on ionograms. I: Brief morphology, Ann. Geophys., 12, 355,1994.Farley, D. T., A plasma instability resulting in field-aligned irregularities in the ionosphere, J.Geophys. Res., 68, 6083, 1963.Haldoupis, C., K. Schlegel, and E. Nielsen, Some observations of radio auroral backscatter at 140MHz during E-region electron gas heating, Ann. Geophys., 11, 283, 1993.Maeda, K., T. Tsuda, and H. Maeda, Theoretical interpretation of the equatorial sporadic E layers,Phys. Rev. Lett., 11, 406, 1963.Monselesan, D. P., R. J. Morris, P. L. Dyson, and M. R. Hyde, Polar cap digital ionosondeobservations of E-region Bragg scatter during intense lacuna conditions: implications for drift velocitydetermination, submitted to J. Geophys. Res., (2003).Morris, R. J., D. P. Monselesan, and A. R. Klekociuk, Australian Antarctic research - A new direction,Adv. Space, Res., 16(5), 151, 1995.Piggott, W. R., and K. Rawer, U.R.S.I. Handbook of Ionogram Interpretation and Reduction, Revisionof Chapters 1 to 4, Report UAG-23A, World Data Center A for Solar-Terrestrial Physics, 1978.Schlegel, K., and J. P. St.-Maurice, Anomalous heating of the polar E region by unstable plasmawaves 1. Observations, J. Geophys. Res., 86, 1447, 1981.Tsunoda, R. T., J. K. Olesen, and P. Stauning, Radar evidence for a new low-frequency crossed-fieldplasma instability in the polar mesopause region: A case study, Geophys. Res. Lett., 24, 1215, 1997.125