Seasonal oscillations in mesospheric temperatures at low-latitudes

Using 3 years of high-quality temperature measurements (2002-2004) recorded from Maui, HI (20.8 degrees N), we have investigated the characteristics of mesospheric seasonal oscillations at low-latitudes. Measurements of the near-infrared OH (6,2) and O-2 (0, 1) nightglow emission layers (centered at similar to 87 and similar to 94 km) independently reveal a distinct semi-annual oscillation (SAO) and annual oscillation (AO) with amplitudes of similar to 3.8 and similar to 2.0 K, respectively. An observed asymmetry in the seasonal variation of the nocturnal mean, previously reported by Taylor et al. [2005. Characterization of the semiannual-oscillation in mesospheric temperatures at low-latitudes. Advances in Space Research 35, doi:10.1016/j.asr.2005.05.111] from this site is shown to be due to a superposed AO of amplitude similar to 50% of the SAO signature. Detailed investigations of the local-time variation of the SAO amplitude and phase combined with TIME-GCM simulations of the seasonal variation of the diurnal tide strongly suggest a large local-time dependence of the amplitude (but not phase) of the observed SAO. These data indicate that the true mean temperature SAO amplitude could be as high as similar to 7 K at this latitude. (c) 2007 Elsevier Ltd. All rights reserved.