NONLOCAL THERMODYNAMIC-EQUILIBRIUM LIMB RADIANCES FOR THE MIPAS INSTRUMENT ON ENVISAT-1

An evaluation of the effects that the assumption of local thermodynami c equilibrium (LTE) has on the retrieval of pressure, temperature and the five primary target gases (O-3, H2O, CH4, N2O, and HNO3) from spec tra to be taken by Michelson Interferometer for Passive Atmospheric So unding (MIPAS) on the Envisat-1 platform has been conducted. For doing so, non-LTE and LTE limb radiances in the spectral range of 689-2275 cm(-1) (4.15-14.6 mu m) with a resolution of 0.05 cm(-1) at tangent he ights from 10 to 70 km have been computed. These calculations included the most updated non-LTE populations of a large number of vibrational levels of the CO2, O-3, H2O, CH4, N2O and HNO3 molecules which cause the most prominent atmospheric infrared emissions. A discussion of the most important non-LTE effects on the limb radiances as well as on th e retrievals of pressure-temperature and volume mixing ratios of O-3, H2O, CH4, N2O, and HNO3 is presented, together with the most important non-LTE issues that could be studied with the future coming of MIPAS data. (C) 1998 Elsevier Science Ltd. All rights reserved.