High-altitude limb infrared radiance spectra (CO2 15μm and O3 9.6μm bands) registered during CRISTA-1 experiment in November 1994 were interpreted using multiparameter inversion algorithm accounting for the nonlocal thermodynamic equilibrium conditions (non-LTE). Global distributions of temperature in the altitude range 40-120 km were obtained simultaneously with the distributions of CO2 and O3 (40-90 km) and vibrational temperatures of the lower vibrational states of CO2 and O3 molecules. Mean zonal values of temperature agree with CIRA-86 and SMLTM models. The root mean square variability of temperature reaches its maximum of 45 K at 105 km. Mesospheric temperature inversions were detected in 85% of cases during observations. The retrieved CO2 profiles demonstrate that the altitude level, up to which CO2 is well mixed, is considerably lower (70-75km) than predicted by models (85-90 km). Maximal diurnal variations of ozone were observed at 90 km altitude, where the mean value of volume mixing ratio is close to 2 ppmv for daytime and 7 ppmv for nighttime. The altitude levels of the LTE breakdown for the vibrational states of CO2 and O3 molecules and also the magnitude and vertical behavior of the non-LTE effect are in good agreement with numerical models.
An algorithm for the combined retrieval of ozone, NO2, spectral aerosol extinction profiles and different microphysical properties of stratospheric aerosol is described. Principal features of the algorithm are the use of simulated statistical aerosol models as a priori information and optimal parameterization of spectral dependence of aerosol extinction coefficients (by expanding in natural orthogonal basis). The statistical microphysical models of stratospheric aerosols are used for retrieving the aerosol size distribution function. Results of numerical experiments for the study of error budget of this algorithm are given. Data of slant path transmittance spectral measurements by SAGE III (Meteor-3M) have been processed and analyzed. Results of retrieving the different atmospheric parameters are compared with independent measurements.
Algorithms to simulate the statistical microphysical and optical models for aerosol and polar stratospheric cloud (PSC) are described. Examples of such models for stratospheric and tropospheric aerosols and PSC are given. Different ways of applying the statistical aerosol and cloud models are discussed: - optimal parameterization of spectral dependences of aerosol extinction coefficient using the natural orthogonal basis; - multiple regression for estimating the optical parameter from measured one (for example, estimation of scattering coefficients from SAGE III multiwavelength measurements of aerosol extinction coefficients); - retrieval of microphysical properties of stratospheric aerosol and PSC from SAGE III extinction measurements; - lidar sounding.
The overview of different approaches to the problem of remote sensing of the non-LTE atmosphere by satellite instruments working in the infrared region is presented. Special emphasis is made on the approach, which does not require modeling of the processes driving the nonequilibrium populations of the molecular vibrational states. The method of simultaneous retrieval of kinetic temperature, pressure, concentration of atmospheric gases and nonequilibrium populations of the vibrational states of molecules of atmospheric gases (vibrational temperatures) from the high altitude limb infrared radiance measurements in 15 micrometers region is described. The results of the application of this method to the interpretation of the limb radiance spectra measured by the CRISTA instrument are presented. The kinetic temperature profiles derived in the altitude range 40 - 120 km are shown and the features of the thermal structure of this atmospheric region are compared with climatological data. The magnitude of the non-LTE effect for the CO2 vibrational states which give origin to 15 micrometers transitions is analyzed on the basis of retrieved CO2 vibrational temperatures. The vertical distributions of the CO2 volume mixing ratio in the mesosphere and lower thermosphere derived from the CRISTA measurements are presented and compared with model data. The problem of the influence of the amount of a priori information on the retrieval results is discussed on the basis of calculations of the information content by the Shannon approach.
The results of limb radiance calculations in the 9.6 micrometers ozone absorption band are presented for the tangent heights 30 - 110 km. Deviations from local thermodynamic equilibrium (LTE) are taken into account for 20 vibrational transitions forming (nu) 1 and (nu) 3 bands. The monochromatic limb radiance in line contours has been investigated for fundamental and hot bands for LTE and non-LTE. Variations of radiance stipulated by variations of kinetic, vibrational temperatures and ozone concentration have been analyzed. For day- and night-time limb radiance spectra have been calculated for different spectral resolutions. The approach is suggested to retrieve ozone profiles under non-LTE conditions using high-resolution limb spectral measurements (e.g., obtained by space-borne devices of MIPAS type).
Remote sensing methods (space-borne, air-borne, and ground-based) are presently widely used for obtaining information on atmospheric composition and thermal regime. Modern IR remote sensing methods are based on the validity of LTE, which is not true in the upper atmosphere (height of breaking of LTE depends on gas, absorption band and time under consideration). The non-LTE limb radiance has been calculated in the 15-micron CO2 band for tangent heights 50-110 km. The inverse problem has been formulated including the retrieval of vibrational temperature profiles for the lower vibrational states of the CO2 molecule. The method is based on measurements of high-resolution limb radiance spectra. The retrieval accuracy has been investigated depending on measurement error, spectral resolution, and spectral region used.
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