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Motivations Physical problem Modeling of line-mixing

Line Shape Studies for Atmospheric Spectra: Modeling and consequences for Remote Sensing Fabrizio Niro niro@fci.unibo.it. Motivations Physical problem Modeling of line-mixing Model for CO2 and application for Earth atmosphere Overview of previous line mixing results (N2O, CH4, NH3)

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Motivations Physical problem Modeling of line-mixing

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  1. Line Shape Studies for Atmospheric Spectra:Modeling and consequences for Remote SensingFabrizio Nironiro@fci.unibo.it Motivations Physical problem Modeling of line-mixing Model for CO2 and application for Earth atmosphere Overview of previous line mixing results (N2O, CH4, NH3) Conclusion

  2. Collaborations CO2 study Theory: J.-M. Hartmann, C. Boulet IR Spectra: P.-M. Flaud, C. Broadebeck Atmospheric spectra: T. von Clarmann, F. Hase, K. Jucks, C. Camy-Peyret, S. Payan CH4, NH3, N2O previous studies J.-M. Hartmann, C. Boulet, D. Pieroni, S. Hadded, H. Aroui, P.-M. Flaud, C. Broadebeck, F. Thibault, T. Gabard, J.-P. Champion, T. Fouchet, P. Drossart, D.C. Benner, A. Pine, M. Tonkov et al.

  3. Introduction and Motivations The line-shape modeling of special signature (Q branches, multiplets, far wings) is still the major source of systhematic uncertainty in the modeling of IR spectra of many molecules (e.g. H2O, CO2, CH4, N2O, NH3) The consequences for atmospheric sounding of different planets are very important, a precise modeling of those spectral intervals is mandatory since: • Q branches are the most intenses signature, usually used for retrieve VMR • Line wings and continuum absorption are importants for p-T sounding (very sensitive to p), furthermore they can hide low abundance signature (heavy molecules, clouds aerosol) Theoretical approach are needed to model the IR spectra of many molecules important for remote sensing of Earth (CO2, N2O, CH4) or other planets such as Venus, Jupiter (CH4, NH3)

  4. Physical problem of line-mixing Collisions active molecule-perturber Widening of individual line (L) (Lorentz profile) When line profiles overlap 1-2 < L Collisions transfer of population (Intensity) |>  |k> (Line-mixing) collisional transfer E = |1 - 2 | 2 1 Always foundin Q branch multiplets and Line Wings Transfer intensity from weak Abs  High Abs Sub-Lorentzian shape in line wings In the far-wings the effect of finite duration of collision can be significant

  5. Absorption Coefficient calculation under Impact Approximation Used approximations • Low density: binary collisions • Impact approximation: c· << 1  W()  W W(Relaxation matrix): All the effect of collisions • Detailed Balance • Sum rule

  6. Construction of W matrix (Real part)Statistical and semi-classical models Statistical model: Exponential Gap Law (EGL) • The probability for a molecule to make a collisional transition depend only on the energy gap: • E: Energy gap of lower levels • A and B fitted parameters • Model fails in predict mixing in manifolds at low pressure (e.g. CH4: Pieroni et al., J. cHem. Phys., Vol. 110, 7717-7732, 1999) Semi-classical model • Kl-k (state to state rotational cross section) determined from semi-empirical calculation • A(l,k) fitted parameters dependent on (l,k) coupling • In the case of lack of accurate potential energy surface the semi-classical approach is intractable  use of dynamical model (IOS,ECS)

  7. Construction of W matrix (Real part)The Energy Corrected Sudden (ECS) approach • Based on IOS approximation : neglecting the rotation of molecule during the choc • Based on a decoupling of spectroscopy and dynamic of the problem • The ECS corrections to the IOS allow to take into account the rotation of molecule (via L) and the detailed balance principle (via J>), the Wlk elements are then: • The basic rates QL are related to the basic cross sections for downward transition to ground state: • QL can be calculated for very simple systhème (CO2-gaz rare) • For many application QL are represented with mathematical law (e.g. Exp. Power) using a small set of adjustable parameters

  8. ECS approach for modeling CO2 P-Q-R mixingLaboratory spectra • Starting from a previous work on CO2 Q branch the ECS model has been extended to take into account the mixing (inter and intra branch) of all P-Q-R line in each vibrational band via construction of a global matrix W • Forcing the W matrix to the detailed balance and sum rule principles allow to correct respresent the sub-lorentzian behaviour in far wings

  9. Laboratory spectraQ branch of 2 band (CO2 – N2) Low pressures Experiment No mixing Line-mixing 300 K, 100 atm Absorption (cm-1/atm) (Obs-Cal)/Obs  (cm-1)

  10. Central and wings regions of 2 band (CO2 – N2) 300 K, 100 atm Absorption (cm-1/atm) (Obs-Cal)/Obs  (cm-1)

  11. Central and wings regions of 2 band (CO2 – N2) Low Temperature 250 K, 160 atm Absorption (cm-1/atm) (Obs-Cal)/Obs  (cm-1)

  12. Wings regions of  3 band (CO2 – N2) Experiment No mixing Line-Mixing Absorption (cm-1 /amagat2) (Obs-Cal)/Obs  (cm-1)

  13. Remaining problem: Finite duration of collision Wings regions of  3 band (CO2 – CO2) 193 K 296 K Experiment No mixing Line-Mixing ECS Absorption (cm-1 /amagat2)  (cm-1)  (cm-1)

  14. ECS approach for modeling CO2 P-Q-R mixingApplications to the Earth atmosphere • CO2 major absorber in the IR spectrum of Earth atmosphère • The W matrix was built for a 79% N2 + 21% O2 mixture • The model was compared to a large series of spectra representing a wide range of geometries (Nadir, Limb, Zenith) and tecniques (emission, transmission), giving a stringent test of our approach

  15. Atmospheric limb emission spectra from ballon (SAO) Line mixing effects in CO2 Q branches Radiance (mW/m2cm-1sr) Radiance (mW/m2cm-1sr) Experiment No mixing Line mixing Experiment No mixing Line-mixing  (cm-1)  (cm-1)

  16. SPECTRES HIS (air-borne)Wings of CO2 2 band Radiance normalised to NESR Radiance and Residuals (mW/m2cm-1sr) Experiment No mixing Line-mixing  (cm-1) Tjemkes, et al., JQSRT 77, 433, (2003)

  17. MIPAS (on ENVISAT) emission spectra Effect in trough between lines and in the wings of 2 band Experiment No mixing Line-Mixing Geometry = Limb from satellite (ENVISAT) Height of the instrument = 800 km Tangent altitude = 8.4 km Radiance and Residuals (mW/m2cm-1sr)  (cm-1)

  18. MIPAS emission spectra Importance of CO2 line-wings modeling for clouds detection Radiance (mW/m2cm-1sr)  (cm-1)

  19. Emission Limb spectra from ballon FIRS (SAO) Validation of the model in the left side wing of 2 band Geometry: Limb from ballon. Instrument’s height = 37 km. Tangente altitude = 10 km Experiment Lorentz Line-Mixing Radiance and Residuals (mW/m2cm-1sr)  (cm-1)

  20. Transmission ground-based spectra FTIR (IMK) Importance of CO2 Q branch and far wings modeling for minor constituent retrieval 5% d’Abs du to CCl4 Geometry = Zenith from the ground Elevation solar angle = 14° Transmission 3 band CCl4 No mixing Line-Mixing Residuals  (cm-1)

  21. Ground-based transmission spectra FTIR (IMK) Far wings of the  3 band region Induced absorption of N2 Experiment No mixing Line-Mixing Transmission and Residuals  (cm-1)

  22. Some more examples of line-shape problem for remote sensing application (N2O, CH4, NH3)Overview of results concerning laboratory and atmospheric spectra

  23. ECS modeling of line-mixing on N2O Q branchesSamples of laboratory and atmospheric results Experiment No mixing Line-Mixing Laboratory spectra Q branch of n2 band N2O - N2 mixture Atmospheric transmission spectra Q branch of n2 band of N2O Hartmann et al, J. Chem Phys. 110, 4, (1999)

  24. Line mixing effects in the CH4 spectrumAtmospheric transmission Limb spectra from ballon (LPMA) Experiment No mixing Line-Mixing  (cm-1) Pieroni et al, J.Q.S.R.T. 68, (2001)

  25. Line-mixing effect in n4 band of CH4 Jupiter ISO emission spectra Experiment No mixing Line-Mixing

  26. ECS model applied to NH3 line-mixingLaboratory spectra in the regions of 2 band Experiment No mixing Line-Mixing Hadded et al, J. Chem. Phys. 116, (2002)

  27. Conclusion • The impact models (ECS, semi-classical) show to correctly represent the line-mixing effects for Q branch as for P, R lines and wings of CO2, CH4, NH3, N2O molecules • The breakdown of impact approximation is evident only for some particular regions (wings of 3 band for CO2-CO2 collisions), but this assumption remains sufficient for most of the atmospheric applications • The applications of these studies in remote sensing of planetary atmosphere are various and important, allowing better precision in retrieve p-T profile as weak IR signature (clouds aerosol, heavy molecules).

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