Tidal and layer structure in the mesosphere and lower thermosphere from TIMED/SABER CO_2 15-μm emission

摘要

The SABER radiometer on the TIMED spacecraft scans the earthlimb continuously in ten channels spanning the spectrum from 1.27 to 15 μm. The signature of the diurnal tide in the equatorial region is apparent throughout the mesosphere in TIMED/SABER data, especially in the CO_2 15-μm radiance profiles. In addition, layer structures are apparent in a large fraction of the both the radiance profiles and the kinetic temperature profiles derived from them. We present results showing tidal and layer features in the variation with local time and latitude of 15-μm radiance and temperature. Temperature inversion layers (TILs) are regions of extreme perturbations in the retrieved temperature profile where the temperature increases rapidly over 3-10 km range by tens of degrees K, sometimes approaching increases of 100 K, and are not represented in any existing atmospheric climatologies. Theories that have been proposed connect them with the amplitude and phase of atmospheric tides, as well as with the interactions and dissipation of atmospheric gravity waves and planetary waves. The radiance local maxima, or "knees," are more mysterious. Their occurrence is rather unpredictable and not well explained by models, although it is known that they are due to vibrational excitation of CO_2 by atomic oxygen and they may have tidal connections. While they may be associated with strong TILs, the most important class occurring at tangent heights in the lower thermosphere between 100 and 115 km appear not to be simply related to local inversion layers. SABER data offers the opportunity to do the first global survey of MLT TILs, determine their spatial extent and persistence time, and develop a global climatology of their occurrence and properties.