Alexander A. Kutepov

Solution of the non-LTE problem for molecular gas in planetary atmospheres: superiority of accelerated lambda iteration

Abstract A general formulation is given of the multi-level rotation–vibrational non-LTE problem for a mixture of radiating molecular gases in a planetary atmosphere, treating explicitly the coupling of molecular energy levels by collisionally induced energy transfer processes and by band overlap. Various limiting cases of non-LTE effects are discussed. Three techniques—lambda iteration, matrix and accelerated lambda iteration—which are used to solve these problem are discussed and compared. In the case of the CO 2 non-LTE problem in the Earths atmosphere, it is demonstrated that accelerated lambda iteration is far superior to the other algorithms in minimizing computer time and storage and in converging much more rapidly; moreover the convergence rate is insensitive to the initial population estimates and to wide range of variation in the model input parameters. Accelerated lambda iteration therefore makes possible the calculation of much larger and more physically complete atmospheric and molecular models.

Non-local thermodynamic equilibrium in CO2 in the middle atmosphere. I. Input data and populations of the ν3 mode manifold states

Abstract The CO 2 NLTE problem has been extended to account for all vibrational states and transitions included in the HITRAN-92 database of spectroscopic parameters. The set of the rate constants for V-T and V-V collisional processes and the model for pumping the CO 2 states by OH(ν) have been revised. The effect of the vertical kinetic temperature and O mixing ratio profiles on the vibrational temperatures of the ν 3 mode manifold states as well as the dependence of these temperatures on the solar zenith angle have been examined in detail. In the daytime, the lower boundary of the NLTE layer tends to reach the ground when the energy of the ν 3 mode manifold states increases.

Parameterization of the 15 μm CO2 band cooling in the middle atmosphere (15–115 km)

Abstract A new parameterization of the 15 μm CO2 band radiative cooling rate in the middle Earth atmosphere for both LTE (local thermodynamic equilibrium) and non-LTE layers is presented. It includes the parameterization of Akmaev and Shved [(1982) J. atmos. terr. Phys.44, 993] for the 35–70 km layer, which is modified to account for the line overlapping in the band for the 15–35 km layer and for non-LTE effects in the 70–80 km layer. In the non-LTE layer above 80 km a simple recurrence relation between the cooling rates for two neighboring altitude levels is used. For any temperature profile, which has no micro-or meso-scale structure, the absolute error of the parameterization in the 15–80 km layer does not exceed 0.5 K day−1. In the non-LTE 80–115 km layer the error depends on the value of the rate constant for the de-excitation of CO2(0110) by collisions with atomic oxygen O, not exceeding, however, 0.07, 0.4 and 4 K day−1 for values of this constant equal to 5 × 105, 5 × 106 and 5 × 107 s−1 atm−1, respectively.

Radiative cooling of the 30–110 km atmospheric layer

Abstract Near the solstice and equinox, the altitude-latitude distributions of cooling rate in the 15 μm CO 2 and 9.6 μm O 3 bands and in the rotational H 2 O band have been calculated. The atmosphere near 75 km in the vicinity of the equator is heated due to thermal radiation transfer in all seasons. The atmosphere is also heated around the pole near the mesopause in spring, and in autumn it is slightly cooled. Estimates are given of the influence of tropospheric clouds on radiative cooling above 25 km and of additional cooling of the lower thermosphere caused by the propagation of gravity waves and tidal modes. Conclusions have been drawn on the dynamics of the middle atmosphere and its contribution to the thermal regime. The eddy heat conductivity is not the only important global mean sink of energy in the turbulent layer of the lower thermosphere. From spring to autumn in the hemispheric upper mesosphere there are at least two cells of meridional circulation with upward air motion near the equator and the pole. It is possible that the cell of meridional circulation observed near the equinox in the lower thermosphere of the middle and low latitudes is stimulated by air heating due to the dissipation of semi-diurnal tidal energy.

Modelling of non-LTE limb spectra of i.r. ozone bands for the MIPAS space experiment

Abstract A new model for calculating the populations of the ozone vibrational states under non-LTE (Local Thermodynamic Equilibrium) conditions is presented. In the model, 23 vibrational levels of the O3 molecule, as well as three vibrational levels of the O2 molecule and two vibrational levels of the N2 molecule, are considered. The radiative transfer at the break-down of LTE was treated explicitly for 150 000 ro-vibrational transitions. The populations obtained were used to calculate limb radiances in various spectral regions of the 4.8 and 9.6 μm bands. Test retrievals of O3 vertical volume mixing ratio (VMR) profiles with a radiance model disregarding non-LTE were performed in order to assess the potential impact of non-LTE effects on the retrieval of the O3 abundances from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) measurements.

Non-local thermodynamic equilibrium in CO2 in the middle atmosphere. II. Populations in the ν1ν2 mode manifold states

The NLTE problem for the ν1ν2 mode manifold states of CO2 molecules has been solved using the HITRAN-92 database of spectroscopic parameters and new rate constants for V-T and V-V collisional processes. The effect of the vertical kinetic temperature and O mixing ratio profiles on the vibrational temperatures has been investigated in detail, as has the effect of solar pumping. We show that accounting for transitions with the state change of two- and more ν2-quanta during CO2O collisions in the lower thermosphere can increase the vibrational temperature of doubly and triply excited states of the ν2 mode by as much as several tens of degrees Kelvin relative to the one-ν2-quantum transitions commonly used to calculate state populations.

Infrared Radiation in the Mesosphere and Lower Thermosphere: Energetic Effects and Remote Sensing

This paper discusses the formation mechanisms of infrared radiation in the mesosphere and lower thermosphere (MLT), the energetic effects of the radiative absorption/emission processes, and the retrieval of atmospheric parameters from infrared radiation measurements. In the MLT and above, the vibrational levels of the molecules involved in radiative transitions are not in local thermodynamic equilibrium (LTE) with the surrounding medium, and this then requires specific theoretical treatment. The non-LTE models for CO2, O3, and H2O molecules are presented, and the radiative cooling/heating rates estimated for five typical atmospheric scenarios, from polar winter to polar summer, are shown. An optimization strategy for calculating the cooling/heating rates in general circulation models is proposed, and its accuracy is estimated for CO2. The sensitivity of the atmospheric quantities retrieved from infrared observations made from satellites to the non-LTE model parameters is shown.

Non-local thermodynamic equilibrium limb radiances for the mipas instrument on Envisat-1

Abstract An evaluation of the effects that the assumption of local thermodynamic equilibrium (LTE) has on the retrieval of pressure, temperature and the five primary target gases (O 3 , H 2 O, CH 4 , N 2 O, and HNO 3 ) from spectra to be taken by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the Envisat-1 platform has been conducted. For doing so, non-LTE and LTE limb radiances in the spectral range of 680–2275 cm −1 (4.15–14.6 μm) with a resolution of 0.05 cm −1 at tangent heights 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 CO 2 , O 3 , H 2 O, CH 4 , N 2 O and HNO 3 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 the retrievals of pressure-temperature and volume mixing ratios of O 3 , H 2 O, CH 4 , N 2 O, and HNO 3 is presented, together with the most important non-LTE issues that could be studied with the future coming of MIPAS data.

Application of the second-order escape probability approximation to the solution of the NLTE vibration-rotational band radiative transfer problem

Abstract By the approximate solution of the integral equation for the source function in the 01 1 0-00 0 0 band of the 12 C 16 O 2 molecule in the Earths atmosphere a simple recurrence formula has been derived, which relates the values of this function for neighboring levels in the atmosphere. Beginning from the LTE layer, where the source function is equal to the Planck function and going from one level to the next, this formula allows the profile of the source function in the non-LTE layer (above 70km) to be calculated with an error ~ 5% for wide ranges of temperature and quantum survival probability variations.

Validation of the global distribution of CO2 volume mixing ratio in the mesosphere and lower thermosphere from SABER

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite has been measuring the limb radiance in 10 broadband infrared channels over the altitude range from ~ 400 km to the Earth’s surface since 2002. The kinetic temperatures and CO2 volume mixing ratios (VMRs) in the mesosphere and lower thermosphere have been simultaneously retrieved using SABER limb radiances at 15 and 4.3μm under nonlocal thermodynamic equilibrium (non-LTE) conditions. This paper presents results of a validation study of the SABER CO2 VMRs obtained with a two-channel, self-consistent temperature/CO2 retrieval algorithm. Results are based on comparisons with coincident CO2 measurements made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) and simulations using the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM). The SABER CO2 VMRs are in agreement with ACE-FTS observations within reported systematic uncertainties from 65 to 110 km. The annual average SABER CO2 VMR falls off from a well-mixed value above ~80 km. Latitudinal and seasonal variations of CO2 VMRs are substantial. SABER observations and the SD-WACCM simulations are in overall agreement for CO2 seasonal variations, as well as global distributions in the mesosphere and lower thermosphere. Not surprisingly, the CO2 seasonal variation is shown to be driven by the general circulation, converging in the summer polar mesopause region and diverging in the winter polar mesopause region.