Effect of the resolution of the O2 Schumann-Runge bands on the photolysis rate coefficients calculations at different altitudes

GUSTAVO G. PALANCAR; RAFAEL P. FERNANDEZ; BEATRIZ M. TOSELLI

Grenoble

Otro; XIII European Research Course on Atmospheres (ERCA 2005); 2005

CNRS - Francia

Light absorption of molecular oxygen plays a decisive role in stratospheric chemistry because it is the first step and the only source for stratospheric ozone and also because it strongly influences the radiative transfer throughout the atmosphere. The TUV model (Madronich, 1993) was used and modified to show how the O2 absorption cross section in the Schumann-Runge (SR) bands can affect the photolysis frequencies (J-values) calculations in the stratosphere. The original parameterized dataset included in the TUV model for molecular oxygen (Kockarts, 1994) was substituted by a high resolution line-byline HITRAN database (Rothman et al., 2003) and the J-values obtained were compared at different altitudes. In order to simulate the spectral lines using the HITRAN database a Voigt profile including an algorithm based on Humlicek (1982) was implemented. A new wavelength grid improving the resolution in the SR bands and in the Lyman-Alpha line was also implemented. All the calculations were performed with an 8-stream discrete ordinate method for different species absorbing at the same wavelength range than the O2 SR bands. The results for HNO3 and N2O are shown for various solar zenith angles (SZA= 14, 30, 60 and 78º) from surface up to 60 km, showing relative differences from 6 to 70 % depending on the altitude. Calculations above 60 km are not reliable due to the fact that the TUV radiative transfer code does not include the occurrence of Non-LTE (Non Local Thermodynamic Equilibrium) processes. A coupling model between a radiative transfer code (RFM) and a differential stiff solver (ODE) is being developed at the moment to take into account Non-LTE processes so that a more extended atmosphere can be studied.