The SABER instrument on TIMED continuously measures certain infrared limb radiance profiles with unprecedented sensitivity. Among these are emissions of CO<sub>2</sub> ν<sub>3</sub> at 4.3 μm, routinely recorded to tangent heights of ~140-150 km, and NO at 5.3 μm, seen to above ~200 km and ~300 km, respectively. We use these infrared channels of SABER and coincident far ultraviolet (FUV) measurements from GUVI on TIMED, to study the geometric storm of April 2002. These all give a consistent measure of auroral energy input into the lower thermosphere at high latitudes. Emission in yet another SABER channel, near 2.0 μm, correlates well with enhanced electron energy deposition. We also have, in the 5.3-μm emissions from the long-lived population of aurorally produced NO, a tracer of how this energy is transported equator-ward and released over an extended period of time, a few days. In this paper, we discuss the global patterns of energy deposition into the expanded auroral oval, its transport to lower latitudes, and its loss as revealed by the NO 5.3-μm emissions.
The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a high-resolution limb sounder on board the European polar platform ENVISAT, scheduled for launch this summer. Three main characteristics converge in MIPAS which make it a very useful instrument for non-LTE studies: its wide spectral coverage (4.15-14.6 micrometers or 680-2275 cm<SUP>-1</SUP>); high spectral resolution (0.03 cm<SUP>-1</SUP>), and high sensitivity; all of this in addition to its global spatial coverage. In this paper we present an overview of the non-LTE studies that have been carried in preparation for the analysis of MIPAS data, including the evaluation of non-LTE effects in the operational processing, focused in the stratosphere, and the retrieval of species that normally emit under non-LTE conditions. The current mission plan for measuring the non-LTE upper atmosphere is described, as well as the general purpose non-LTE retrieval scheme developed for analyzing those measurements.
Atmospheric emissions at 5.3 micrometers will be measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a high-resolution limb sounder on board the European polar platform ENVISAT, scheduled to be launched in 2001. Measured spectra at 5.3 micrometers contain information on important atmospheric quantities such as NO volume mixing ratio, thermospheric temperature, and chemical NO production rates. However, the scientific analysis of this spectral region has to deal with complex non-local thermodynamic equilibrium (non-LTE) effects. A conventional non-LTE retrieval approach using ab initio vibrational temperatures cannot be applied due to rotational and spin-orbit non-LTE of NO in the thermosphere, and the dependence of NO state populations on the NO abundance itself caused by chemical excitations. An innovative non-LTE retrieval method enabling the treatment of vibrational, rotational, and spin non-LTE as well as a dependence of the non-LTE state distribution on the retrieval target quantities has thus been developed for the MIPAS data analysis. The ability of the developed non-LTE inversion tool to retrieve NO abundance profiles, thermospheric temperature profiles, and NO mean production rates by NO<SUB>2</SUB> photolysis in the stratosphere and N+O<SUB>2</SUB> combination in the thermosphere is demonstrated by means of a feasibility study.