Wavenumber-4 spectral component extracted from TIMED/SABER observations

The wavenumber spectral components WN₄ at the mesosphere and low thermosphere (MLT) altitudes (70–10 km) and in the latitude range between ±45° are obtained from temperature data (T) observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instruments on board the National Aeronautics and Space Administration (NASA)’s Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) spacecraft during the 11-year solar period from 2002 to 2012. We analyze in detail these spectral components WN_k and obtain the main properties of their vertical profiles and global structures. We report that all of the wavenumber spectral components WN_k occur mainly around 100 km altitude, and that the most prominent component is the wavenumber spectral component WN₄ structure. Comparing these long duration temperature data with results of previous investigations, we have found that the yearly variation of spectral component WN₄ is similar to that of the eastward propagating non-migrating diurnal tide with zonal wavenumber 3 (DE3) at the low latitudes, and to that of the semi-diurnal tide with zonal wavenumber 2 (SE2) at the mid-latitudes: the amplitudes of the A₄ are larger during boreal summer and autumn at the low-latitudes; at the mid-latitudes the amplitudes have a weak peak in March. In addition, the amplitudes of component WN₄ undergo a remarkable short period variation: significant day-to-day variation of the spectral amplitudes A₄ occurs primarily in July and September at the low-latitudes. In summary, we conclude that the non-migrating tides DE3 and SE2 are likely to be the origins, at the low-latitudes and the mid-latitudes in the MLT region, respectively, of the observed wavenumber spectral component WN₄.