M. López-Puertas

Retrieval of mesospheric and lower thermospheric kinetic temperature from measurements of CO2 15 µm Earth Limb Emission under non‐LTE conditions

We present a new algorithm for the retrieval of kinetic temperature in the terrestrial mesosphere and lower thermosphere from measurements of CO2 15 µm earth limb emission. Non-local-thermodynamic-equilibrium (non-LTE) processes are rigorously included in the new algorithm, necessitated by the prospect of satellite-based limb radiance measurements to be made from the TIMED/SABER platform in the near future between 15 km and 120 km tangent altitude. The algorithm requires 20 seconds to retrieve temperature to better than 3 K accuracy on a desktop computer, easily enabling its use in operational processing of satellite data. We conclude this letter with a study of the sensitivity of the retrieved temperatures to parameters used in the non-LTE models, including sensitivity to the rate constant for physical quenching of CO2 bending mode vibrations by atomic oxygen.

Non-LTE Radiative Transfer in the Atmosphere

Molecular spectra basic atmospheric radiative transfer solutions to the radiative transfer equation in LTE solutions to the radiative transfer equation in non-LTE non-LTE modelling of the Earths atmosphere I - CO2 non-LTE modelling of the Earths atmosphere II - other infrared emitters remote sensing of the non-LTE atmosphere cooling and heating rates non-LTE in planetary atmospheres.

Energy transport in the thermosphere during the solar storms of April 2002

The dramatic solar storm events of April 2002 deposited a large amount of energy into the Earths upper atmosphere, substantially altering the thermal structure, the chemical composition, the dynam ...

Observations of infrared radiative cooling in the thermosphere on daily to multiyear timescales from the TIMED/SABER instrument

16 17 Abstract. We present observations of the infrared radiative cooling by carbon dioxide (CO2) and 18 nitric oxide (NO) in Earths thermosphere. These data have been taken over a period of 7 years 19 by the SABER instrument on the NASA TIMED satellite and are the dominant radiative cooling 20 mechanisms for the thermosphere. From the SABER observations we derive vertical profiles of 21 radiative cooling rates (W m -3 ), radiative fluxes (W m -2 ), and radiated power (W). In the period 22 from January 2002 through January 2009 we observe a large decrease in the cooling rates, 23 fluxes, and power consistent with the declining phase of solar cycle 23. The power radiated by 24 NO during 2008 when the Sun exhibited few sunspots was nearly one order of magnitude 25 smaller than the peak power observed shortly after the mission began. Substantial short-term 26 variability in the infrared emissions is also observed throughout the entire mission duration. 27 Radiative cooling rates and radiative fluxes from NO exhibit fundamentally different latitude 28 dependence than do those from CO2, with the NO fluxes and cooling rates being largest at high 29 latitudes and polar regions. The cooling rates are shown to be derived relatively independent of 30 the collisional and radiative processes that drive the departure from local thermodynamic 31 equilibrium (LTE) in the CO2 15 μm and the NO 5.3 μm vibration-rotation bands. The observed 32

Non-local thermodynamic equilibrium in general circulation models of the Martian atmosphere 1. Effects of the local thermodynamic equilibrium approximation on thermal cooling and solar heating

Calculations of CO2 thermal cooling and near-IR solar heating rates under non-local thermodynamic equilibrium (non-LTE) situations have been performed to understand and evaluate the effects of non-LTE on the energy balance of the upper atmosphere of Mars. We find that the 15-μm cooling rates can be in error if LTE is assumed above 80 km. In general, the correct non-LTE values are significantly smaller than the LTE values above about 85 km, but the magnitude and sign of the error depend on the temperature structure and the top altitude of the model and, to a lesser extent, on the collisions with atomic oxygen. A detailed analysis of the relevance of the upper boundary layer and a suggested buffer region are presented for both LTE and non-LTE. Based on general considerations of the thermal profile in the mesosphere and lower thermosphere, recommendations for general circulation models (GCM) are presented as a first guide for minimizing the LTE cooling rates inaccuracies. The error of assuming LTE on the CO2 near-IR solar heating rates is found to be about 20% at 85 km and increases strongly above this altitude. The dependences of this LTE-non-LTE difference on rate coefficients, thermal structure, surface pressure, and solar zenith angle (SZA) are studied. In contrast to the large effect of the SZA on the solar heating rate, we find it is not important for the LTE-non-LTE relative difference, which permits a simple tabulation of the non-LTE effect as a function of pressure only. A table of LTE correction factors for the solar heating rate is included for its potential use as a fast yet accurate operative scheme within GCMs.

On the distribution of CO2 and CO in the mesosphere and lower thermosphere

We have used the Whole Atmosphere Community Climate Model (WACCM) to calculate the distribution of CO2 and CO in the mesosphere and lower thermosphere (MLT), and we have compared the results with observations, mainly from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer and Michelson Interferometer for Passive Atmospheric Sounding satellite-borne instruments. We find that WACCM can reproduce the observed distribution of CO2 in the MLT and the rapid falloff of CO2 above about 80 km. Analysis of the principal terms in the calculated budget of CO2 shows that its global-mean vertical profile is determined mainly by the competition between molecular diffusive separation and eddy mixing by gravity waves. The model underestimates somewhat the mixing ratio of CO2 in the thermosphere compared to that in the observations, but we show that the discrepancy may be eliminated by a reasonable adjustment of the Prandtl number used to calculate the diffusivity due to gravity waves. Simulated CO is also consistent with observations, except that in the standard version of the model, its mixing ratio is uniformly lower than observed above about 100 km. We conclude that WACCM likely underestimates the rate of production of CO in the lower thermosphere from photolysis of CO2 at wavelengths < 121 nm, and we show that this stems from the use of a very large absorption cross section for O2 in the wavelength range 105–121 nm. When a smaller cross section is used, photolysis of CO2 increases by a factor of 2–3 at ~ 95–115 km and, as a result, CO mixing ratios become larger and agree much more closely with observations. We emphasize that the increase in CO2 photolysis implies only minor changes in the vertical profile of CO2 because photolytic loss is a minor term in the budget of CO2 in the MLT.

SABER observations of mesospheric ozone during NH late winter 2002–2009

[1] Observations from the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) satellite show interannual variations of mesospheric ozone in the NH late winter. Ozone in the mid-January to mid-March period is significantly different in 2004, 2006, and 2009 than in other years (2002, 2003, 2005, 2007, 2008). The altitudes of the ozone secondary maximum (∼90―95 km), the minimum (∼80 km) and the tertiary maximum (∼72 km) are all lower by 3―5 km during the three anomalous winters. The ozone anomalies indicate enhanced downward motion and are consistent with other observations of unusual profiles of trace species. The ozone perturbations extend to at least 100 km while temperatures above 90 km are within the range found in the other years.

Non-local thermodynamic equilibrium studies of the 15-μm bands of CO2 for atmospheric remote sensing

A new line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model based on the GENLN2 radiative transfer code is presented. This is capable of high resolution spectral radiance calculations for the upper atmosphere. We describe the non-LTE model implementation and discuss the molecular state vibrational temperature input requirements for studies of the 15-μm ν2 bands of CO2. Monochromatic and band-integrated radiance calculations have been performed for atmospheric limb view tangent heights between 50 and 120 km for non-LTE nighttime and daytime conditions. Two model atmospheres are considered, the U.S. 1976 Standard and a subarctic summer, which show, respectively, mean and large radiance differences from a reference LTE radiance calculation. Non-LTE radiance considerations are shown to be important for the 15-μm CO2 bands for tangent heights greater than 70 km, the magnitude of the divergence from LTE values and diurnal variation being dependent on the band and kinetic temperature profile. We show that the use of the Voigt line shape, rather than the Doppler, is important for tangent heights below 85 km, and that the inclusion of the effect of overlapping lines is a consideration for tangent heights below 75 km. We present calculations of synthetic radiance spectra showing the non-LTE effect for two CO2 temperature sounding channels of instruments aboard the Upper Atmosphere Research Satellite as a demonstration of the model capability.

Middle and upper atmosphere pressure-temperature profiles and the abundances of CO2 and CO in the upper atmosphere from ATMOS/Spacelab 3 observations

Based on a new approach, profiles of kinetic temperature and atmospheric pressure between 20 and 116 km altitude and CO2 and CO volume mixing ratios between 70 and 116 km have been derived from the ∼0.01-cm−1 resolution infrared solar occultation spectra recorded by the atmospheric trace molecular spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission (April 29 to May 6, 1985). The physical model and CO2 profile results have been obtained from simultaneous multiscan least squares fitting of microwindows containing CO2 lines with temperature-dependent and temperature-independent intensities and N2 lines with temperature-independent intensities. The analysis included the retrieval of tangent height separations between spectra in the lower stratosphere, where independent information shows drifts of the sun tracker field of view on the solar disk. The physical model results are compared with climatological profiles, lower thermospheric temperatures computed with the MSISE-90 model, and other data. The CO2 retrievals indicate a nearly constant volume mixing ratio of 320 ± 35 ppmv (parts per million, 10−6, by volume) in the 70-to 90-km altitude region with a rapid decline in the CO2 volume mixing ratio beginning between 90 and 100 km; at 116 km the CO2 volume mixing ratio has declined to about 70 ppmv and is equal to the CO volume mixing ratio, which has been derived from fits to the (1-0) CO vibration-rotation band. The absorption by the v2 + v3 - v2 band of CO2 has been analyzed to quantify nonlocal thermodynamic equilibrium (non-LTE) effects in the upper mesosphere and lower thermosphere. Up to an altitude of 100 km, the results indicate that the vibrational temperature of the v2 state of CO2 is within 5 K of the kinetic temperature. At higher altitudes, non-LTE effects are observable with the vibrational temperature of the v2 state cooler than the kinetic temperature by 40 K (48°S) and 70 K (30°N) at 112 km. Above 112 km, lines of the v2 + v3 - v2 band are too weak to be observed in the ATMOS spectra.

A blind test retrieval experiment for infrared limb emission spectrometry

The functionality and characteristics of six different data processors (i.e., retrieval codes in their actual software and hardware environment) for analysis of high-resolution limb emission infrar ...