New photodissociation module for TM model

1. New photodissociation module for TM model Based on old TM3 code; Completely reprogrammed; Sources: • 56 sets of height-dependent abs. cross sections and quantum yields (xs, qy) (TUV code, Madronich) • Solar spectrum (Atlas3 + Neckel and Labbs) • Explicit T-dependent ozone xs, qy (Bass and Paur, Matsumi) • Landgraf scattering bands selection in combination with: • Full radiative transfer code LIDORt (van Oss) • Parameterisation (Krol and van Weele) • Explicit treatment of aerosol scattering and absorption (own work) • Also valid for twilight conditions (Dahlback and Stamnes) • Easy to expand/adjust with newly published spectral data No, it is not yet ready to use. Now in debugging/testing phase. Implementation in TM will also take time.

2. Relevant phenomena to include • Spectral range 200 - 700 nm (might need expansion) • Absorption by O2, O3 and aerosols • Scattering by air molecules, clouds and aerosols • UV/VIS reflection at the surface • Sun-Earth distance; Solar angle as function of latitude and time • Sphericity of the atmosphere • Orography • Neglect: Absorption by other trace gases Polarisation Raman scattering Refraction, ??

3. Photodissociation module for TM model • Input: • Date/time/grid • meteo fields • ozone masses • aerosol masses • Output: (max. of) 56 photodissociation rates for the chemistry module • Moments of interaction • Each run: read and grid spectral input data; initialise • Each Julian day: update solar zenith angles, S-E distance • Each new meteo: update clouds, surface albedo, ozone xs, qy • Each chemistry time step: update ozone mass, aerosol mass and perform photodissociation rate calculations

4. Methods • absorption: spectral (O2, O3, aerosols) • The complex parameterisation for O2 en O3 absorption (Landgraf en Crutzen) is replaced by spectrally resolved by Lambert-Beer. Included: aerosol absorption, sphericity effects • scattering and reflection per spectral band • Bands of Landgraf en Crutzen (default, more bands optional) • Effect of scattering by clouds and aerosols and surface reflection: • Parameterisation + Look-up table (‘Krol and van Weele’) • Complete LIDORT radiative transfer calculation • Climatological treatment of atmospheric (p, T) effects on molecular properties (height dependent for a standard atmosphere) • Aerosols: default climatological profile, calculated profile optional • absorption spectral; scattering per band

5. Absorption • Absorption-bands O2 (121.4 - 121.9 nm Lyman-Alpha line) (100 - 175 nm Schumann-Runge continuum) 175 - 202 nm Schumann-Runge bands 202 - 241 nm Herzberg continuum • Absorption-bands O3 202 - 240 nm (no name) 240 - 310 nm Hartley band 310 - 400 nm Huggins band 400 - 735 nm Chappuis bands Isaksen-grid: ~ 130 wavelengths (175 - 735 nm; step 2-5 nm)

6. Scattering Same bands as Landgraf and Crutzen band spectral range effective wavelength (subset of absorption grid) 1 202.0 - 241.0 nm 205.1 2 241.0 - 289.9 nm 287.9 3 289.9 - 305.5 nm 302.0 4 305.5 - 313.5 nm 309.0 5 313.5 - 337.5 nm 320.0 6 337.5 - 422.5 nm 370.0 • 422.5 - 735.0 nm 580.0 Possible improvements: More scattering bands; tests are needed Effective wavelength can be made dependent on solar zenith angle (Jochen?)

7. Angles, season Old: • Use longitude-dimension as time dimension for solar angles over the day • Oversampling needed for chemistry time steps > 0.5 hour (?) • Seasonal variations: max(jul) - min(jan) = 6.6% New: • Twilight: • zenith angles <95° • ‘Pseudo-spherical’ approximation following Dahlback and Stamnes • The direct beam is corrected for radiative transfer through layers below the reference level => e.g. shorter polar nights

8. Spectral data • Extraterrestrial spectrum • Atlas3 (< 400 nm) • Neckal and Labbs (> 400 nm) • Absorption cross sections and quantum yields • 56 molecules (source: ‘TUV’ code Madronich) • Interpolation to spectral grid for absorption (#130) • Vertical profiles (#60) of molecular data for standard atmosphere • Spectral interpolation routines available in the module • Ozone: • T dependent absorption cross sections of Bass and Paur • Matsumi et al., 2002 parameterisation for T dependence of quantum yield for reaction O3 + hv => O2 + O(1D);

9. TM Model information => Radiative transfer • Ozone mass => O3 optical depth per TM layer • Aerosol mass => aer. optical depth per TM layer • 0.2095 * pressure level => O2 optical depth per TM layer • Surface albedo (ECMWF) => UV albedo (via classification) • Cloud water + cloud ice => cloud optical depth per TM layer Taucld = (3/2) (lwc dz) / reff + (1+ 2.3 * aspect/length) ) * (iwc dz) reff = 8 mm, aspect = 2.5, length = 250 mm • Cloud cover handling: to be improved by using ‘overhead cloud cover’, currently still cloud cover of TM layer with maximum Taucld

10. TM aerosol information => Radiative transfer Sum over all aerosol types i: Tauaer () = i { 3 * Bi * Qext, eff, i / ( 4 * i * reff, i ) } Look-up table Qext,eff(xeff , veff, mi) with: xeff = 2*  reff /  Look-up table ext,eff(xeff , veff, mi) Aerosol absorption opt. depth: Tauaer,abs () = (1 - ext,eff) Tauaer() Transfer from aerosol module per aerosol type • Burden B (kg/m2) • eff. radius, eff. width (or mode radius+variance) • refr. index (m) and aerosol mass density ()

11. m = [1.33-1.5] – i[0.0-0.04] veff =[0.05 – 0.25] veff= exp(sg*sg) – 1 reff = rg*(1+veff)^2.5

12. Summary • New photodissociation module for TM models is underway • The code will be flexible for the user: • Selection of required rates out of 56 reactions • Possibility to update and add to spectral database • Choice between (look-up table + parameterisation) or accurate LIDORT • Explicit effects of prescribed/calculated aerosols • To do’s: • Parallelisation over the columns is likely needed • Use of overhead cloud cover data not yet implemented • Implementation, debugging, testing phase may still take lots of time • Photodissociation in near-IR (bijv. HO2NO2) not yet included • Schumann-Runge continuum en Lyman-alpha not yet included • Optimalisation of choice of scattering bands needs further testing