A comparison of lower thermospheric winds derived from range spread and specular meteor trail echoes

Interferometry measurements of range spread meteor trail echoes (RSTEs; also known as nonspecular echoes) have provided new insights into both the irregularity structures in meteor trails and lower-thermospheric winds (LTWs). In this study, we used trail echoes observed with the newly installed Sanya (18.4°N, 109.6°E) 47.5 MHz VHF coherent radar and the Sanya all-sky meteor radar to estimate instantaneous zonal and hourly averaged meridional winds from RSTEs and hourly averaged zonal and meridional winds from large numbers of specular meteor echoes. The mean height variations in both the zonal and meridional winds estimated from the RSTEs were generally consistent with those estimated from specular meteor echoes below 96 km. This gives validity to the technique proposed recently by Oppenheim et al. (2009) and suggests that RSTE measurements made with a small radar can be used to investigate LTWs, whereas this had previously been limited to larger radars such as the Jicamarca radar. However, some observations show significant differences in wind magnitude at individual heights at times. The results of RSTE measurements show the presence of an intense westward wind with a speed near 100 ms^-1. In contrast, the specular meteor zonal winds were generally less than 50 ms ^-1. On the other hand, the meridional drift of RSTEs derived from the meridional Doppler velocity at higher altitudes shows a very poor correlation with the specular meteor meridional wind. Potential causes for the discrepancy in wind estimates obtained from RSTE and specular meteor trail echoes are discussed.