EAGER: A New Look at the Middle Atmosphere through the Eyes of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry)

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The investigators will study various Infrared (IR) emission mechanisms in the Mesosphere and Lower Thermosphere (MLT), which may be responsible for a largely unexplained enhanced IR feature at ~90 km. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), one of four instruments on board of NASA's Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) mission, is a 10-channel broadband limb-scanning infrared radiometer covering the spectral range from 1.27 to 17 microns. SABER has already provided a decade worth of information about kinetic temperature, pressure, ozone, carbon dioxide, water vapor and atomic oxygen. The interpretation of these results, which are strongly affected by the quality of models of the IR emissions in the MLT, have crucial importance for understanding the physics and chemistry of this region. An IR limb emission feature that resembles a layer-like enhancement has been present since the beginnings of the satellite operations in SABER's 4.3 micron channel. This feature is localized at an altitude region that corresponds to tangent heights between 85-95 km and has a distinct spatial and temporal variability. Although the enhanced limb radiances are present at all latitudes and seasons, they appear to be stronger at the polar summer MLT. Preliminary analysis of observations from other spacecraft reveal similar features although those instruments operate significantly different, which indicate this is, at least in part, a real phenomena. This enhancement is not predicted by our current IR emission models in the MLT, in particular when compared to similar effects observed in additional channels. Due to a lack of understanding of its origins, this effect has been ignored for a decade and, as a result, is generally unknown by the aeronomy and space science communities. The investigators will study a number of radically different as well as interdisciplinary approaches, among them non-equilibrium chemistry of molecular, atomic and ionic compounds of MLT and their possible interactions with dust and ice particles, various potential mechanism of energy transfer from photolysis and chemical reaction products to molecular vibrations, non-LTE molecular emission, absorption, transformation and multiple scattering of radiation in various spectral regions, etc The investigation will address a feature that may alter the understanding of the CO2 characteristics in the MLT. As such, the results may have high impact on atmospheric chemistry and climate. Additionally, this study will provide a more robust analysis of IR radiances that can be later expanded to other space missions.