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 7422.5 - 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 reactionO3 + 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 Tau cld = (3/2) (lwc dz) / r eff + (1+ 2.3 * aspect/length) ) * (iwc dz) r eff = 8 m, aspect = 2.5, length = 250 m Cloud cover handling: to be improved by using overhead cloud cover, currently still cloud cover of TM layer with maximum Tau cld

10. TM aerosol information => Radiative transfer Sum over all aerosol types i: Tau aer ( ) = i { 3 * B i * Q ext, eff, i / ( 4 * i * r eff, i ) } Look-up table Q ext,eff (x eff, v eff, m i )with: x eff = 2* r eff / Look-up table ext,eff (x eff, v eff, m i ) Aerosol absorption opt. depth: Tau aer,abs ( ) = (1 - ext,eff ) Tau aer ( ) 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) – 1reff = 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 dos: –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