A long-term comparison of winds and tides measured at London, Canada (43°N, 81°W) by co-located MF and meteor radars during 1994-1999

Since mid 1994, an MF radar and a meteor VHF radar have been operating continuously at London, Ontario, measuring winds in the upper mesosphere and lower thermosphere. The two radars are essentially co-located, being less than 400 m apart. Comparisons of mean winds and tides have been made by the two systems in the 82-94 km height range from 1994 to 1999. During this time the meteor radar has been subject to at least one major upgrade to enhance performance. In this report we present an advance on an earlier comparison between the MF and meteor VHF radar winds (Hocking and Thayaparan, 1997), but the newer comparison has several advantages over the previous study, allowing it to be more definitive in areas which were previously contentious. Firstly, the study includes new data taken during a time of improved meteor radar performance. Secondly, the comparison includes 5 years of near-simultaneous observations, allowing better estimates of seasonally averaged parameters. Thirdly, we have applied a novel correlation technique to explore the comparison of winds and tides measured by the two radars. With the much larger data sets and higher meteor rate now available, rather better long-term comparisons between the two systems can be made. Strong similarities between the data sets are noted, especially in regard to the zonal winds and the semi-diurnal tide. However, significant differences are also seen with regard to the monthly meridional mean wind and the meridional diurnal tidal amplitudes. We do not have concrete explanations for the differences between the monthly mean meridional winds measured by the two techniques and the reasons for these differences must be the subject of future investigations. (C) 2002 Elsevier Science Ltd. All rights reserved.