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The Doppler shifts ofmeteor echoes measured by the SuperDARN HF radar network have been used inseveral studies to observe neutral winds in the upper mesosphere and lowerthermosphere region. In the absence of accurate height information forindividual meteors, it has been necessary to assume a statistical mean meteorlayer where the variations in altitude were not correlated to changes in thehorizontal winds. Observations of spectral width distribution variations made bythe radars allow an independent determination of the systematic error in theheight. We have investigated the dependence of this distribution on a number offactors including the radar geometry, diurnal and seasonal cycles, variations insolar UV irradiance and geomagnetic activity. Changes in the altitude of themean meteor layer observed at different radar ranges provide us with someinsight into the structure of the upper mesosphere and the lower thermospherewithin which the meteors are being ablated. An examination of the spectralwidths, as measured by the CUT-LASS Finland radar, in the days preceding andfollowing a Storm Sudden Commencement in April 1997, illustrates how thespectral properties of the observed region can be affected. The variations inthe widths were consistent with model calculations of the changes to thetemperature profile over this interval. Further refinements in the determinationof the spectral width are outlined for future experiments.  <b>Key words. </b>Meterology andatmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics;instruments and techniques

annales geophysicae

Super Dual Auroral Radar Network observations of fluctuations in the spectral distribution of near range meteor echoes in the upper mesosphere and lower thermosphere