AutoChem | PDF Central | CDACentral

Photolysis Calculations

A key part of the chemical model is the calculation of photolysis rates. In this study they are calculated using full spherical geometry for the direct and ground reflected beams and all orders of multiple scattering done using plane parallel geometry ( Anderson , 1983; Lary and Pyle , 1991 a , b ; Meier et al., 1982; Nicolet et al., 1982) corrected after Becker et al. (2000). The photolysis rate used for each time step is obtained by ten point Gaussian-Legendre integration ( Press et al., 1992). These calculations are updated every day to ensure that the current ozone profile is used to calculate the photolysis rates.

solar-zenith-angle.gif (54036 bytes)plane_parallel.gif (19606 bytes)

For the sake of clarity the schematic above shows the components of the radiation field in a plane parallel atmosphere. However, full spherical geometry is used for the direct and ground reflected beams. 

 

The surface reflectivity usually used in AutoChem comes from TOMS. Daily global fields of reflectivity are available from TOMS.

 

References

Anderson , D., The troposphere-stratosphere radiation-field at twilight - A spherical model, Planet. Space Sci., 31, 15171523,1983.

Becker , G., Grooss, J., McKenna, D., and Muller, R., Stratospheric photolysis frequencies: Impact of an improved numerical solution of the radiative transfer equation, J. Atmos. Chem., 37, 217229, 2000.

Lary , D. and Pyle, J., Diffuse-radiation, twilight, and photochemistry: 1., J. Atmos. Chem., 13, 373392, 1991a.

Lary , D. and Pyle, J., Diffuse-radiation, twilight, and photochemistry: 2., J. Atmos. Chem., 13, 393406, 1991b.

Meier , R., Anderson, D., and Nicolet, M., Radiation-field in the troposphere and stratosphere from 240-1000 nm. 1., General analysis, Planet. Space Sci., 30, 923933, 1982.

Nicolet , M., Meier, R., and Anderson, D., Radiation-field in the troposphere and stratosphere .2. Numerical-analysis, Planet. SpaceSci., 30, 935983, 1982.

Press , W., Teukolsky, S., Vetterling, W., and Flannery, B., NumericalRecipes in Fortran - The Art of Scientific Computing, CambridgeUniv. Press, New York, 2nd edn., 1992.

Contact the Author | 2006 David Lary