This work involve a series of testing stand-alone versions of radiation codes used in climate models against accurate line-by line radiative transfer codes

We are looking for chemistry-climate-modelling (CCM) groups and line by line modelling groups to sign up.

Please sign up or express an interest by emailing Piers Forster piers@env.leeds.ac.uk

The intercomparison involves 3 stages and a fourth stage for non-LTE models

STAGE ONE: SURVEY

STAGE TWO: Clear sky, instantaneous flux calculations

All calculations should include Rayleigh scattering and oxygen absorption, but have no aerosol or cloud present. Details of other settings appear in file headers. Two input files are provided based on whether model input is required on LAYERS (where heating rates are evaluated) or LEVELS (where fluxes are evaluated). Please indicate on the survey which input type is employed.

Experiments are designed to simulate 1980-2005 Greenhouse gas changes in the stratosphere

A) 1980 Control: LAYERS_A LEVELS_A

B) CO2 from 338 ppm to 380 ppm: LAYERS_B LEVELS_B

C) CH4 from 1600 ppb to 1750 ppb: LAYERS_C LEVELS_C

D) N2O from 300 ppb to 320 ppb: LAYERS_D LEVELS_D

E) CFC11 from 150 ppt to 250 ppt: LAYERS_E LEVELS_E

F) CFC12 from 300 ppt to 550 ppt: LAYERS_F LEVELS_F

G) All well mixed greenhouse gas changes: LAYERS_G LEVELS_G

H) 10% stratospheric ozone depletion, above 150 hPa: LAYERS_H LEVELS_H

I) 10% tropospheric ozone increase, below 150 hPa: LAYERS_I LEVELS_I

J) 10% stratospheric water vapour increase, above 150 hPa: LAYERS_J LEVELS_J

K) 10% tropospheric water vapour increase, below 150 hPa: LAYERS_K LEVELS_K

L) combined stratospheric ozone depletion and WMGHG changes: LAYERS_L LEVELS_L

These next experiments are designed to calculate radiative relaxation times

M) Temperature perturbation in stratosphere: LAYERS_M LEVELS_M

N) Temperature perturbation in troposphere: LAYERS_N LEVELS_N

Output should be in a similar format as the LEVEL files. Vertical profiles from top to bottom of fluxes, with latitude index going form North Pole to South Pole. Any number of header lines can be used, but please begin all header lines with a "*". File should be free format preserving significant figures.

Lat Index,Pressure Index, latitude, Pressure (Pa), Downwards flux (Wm-2), upwards flux (Wm-2), Net flux (Wm-2)

SW flux can be split into direct and diffuse components if available

Four files should be submitted for each experiment. Separate files should be submitted for each solar zenith angle in the shortwave and one longwave file. File names and headers should indicate modelling group and experiment number.

STAGE THREE: Temperature change calculations, assuming fixed dynamical heating

It is optional whether the SW code is included in the adjustment process as changes to SW heating with temperature should be small, please indicate which method was used in your header files.

The adjustment procedure should follow these steps:

i. Calculate control NET (SW +LW daily average) heating rates (Qctrl) for LAYERS, using results from experiment A in STAGE ONE (see LAYER file header for details of this calculation

ii. Calculate perturbed NET (SW +LW daily average) heating rates (Qpert) for LAYERS, using results from chosen experiment (B-K) in STAGE ONE

iii. forward step temperatures above 200 hPa (LAYERS 31-59) by (Qpert-Qctrl). A simple forward time step of 0.5 days is recommended, i.e. only adjust temperatures by one half of the heating rate difference.

iv. repeat ii with new stratospheric temperature profile

v. repeat iii and iv for 100 days/200 steps

Please get in touch if more details are required

Output should be in a similar format as the LAYER files.Fluxes should be produced as for STAGE II. In addition vertical profiles from top to bottom of heating rates and temperature changes, with latitude index going form North Pole to South Pole. Any number of header lines can be used, but please begin all header lines with a "*". File should be free format preserving significant figures.

Lat Index, Pressure Index, Latitude, Pressure (Pa), Initial temperature (K), Final temperature(K), Initial heating rate (K/day), final heating rate (K/day)

One file should be submitted for each experiment. File names and headers should indicate modelling group and experiment number.

STAGE FOUR: Non-LTE intercomparsion

If your model has non-LTE tratment in the 15 um and/or Near IR CO2 bands please provide calculations for four temperture profiles (file: VF_temp_models ) using identical composition model for all 4 cases (file: VF_composition ).

NIR CO2 solar heating for 3 zenith angles and daily averaged should be calculated:

Lat ZEN1 ZEN2 ZEN3 DAY_LENGTH

75S 85.0939 71.7143 51.7162 1.00000

EQ 82.1345 51.8298 21.2567 0.500000

65N 87.7968 85.6834 84.5000 0.185905

75N no calculations for the NIR CO2 bands (polar night)

The daily averaged solar heating rates are given by the Gaussian quadrature:

Q(daily averaged)= 0.23693*Q(ZEN1)+0.47863*Q(ZEN2)+0.28444*Q(ZEN3)*DAY_LENGTH

Output should be given at pressure levels of your model in units Pa (Pressure) and K/day (for 15 um cooling and NIR heating rates):

Index, Pressure, 15 um, NIR(ZEN1), NIR(ZEN2), NIR(ZEN3), NIR(daily av.)

One file should be submitted for each temperature profile. File names and headers should indicate modelling group and temperature profile used (e.g., file: CMAM_NLTE_EQ.out ).

STAGE FIVE: SOLAR VARIABILITY

Heating rate differences between the minimum (min) and maximum (max) phases of the 11-year solar cycle should be calculated by CCM short-wave radiation parameterizations and line-by-line models for prescribed spectral flux and solar induced ozone differences max-min

The spectral solar irradiance and total solar irradiance (TSI) data to be used in this comparison are based on the method described in Lean et al.(1997), Lean (2001) , and Lean et al. (2005) . Spectral data are available between 120.5 and 99975 nm in a spectral resolution ranging from 1 to 50 nm. In addition, the corresponding TSI (spectral integral over all wavelengths) is provided. Solar minimum conditions are represented by the monthly average solar irradiance of September and solar maximum conditions by November 1989.For mean solar conditions average data have been derived from the period 1950 to 2006

Each modeling group is requested to integrate the spectral irradiances to match the spectral intervals of their individual SW radiation codes and to adapt the total solar irradiance to be consistent with the integral over all intervals.

To study the effect of solar induced ozone variations on heating rates experiments with mean solar irradiance and prescribed ozone changes between solar min and max are recommended. The ozone changes have been derived from a 2d-photochemical model (Haigh, 1994).

Other input data required by the radiation schemes should be taken from the 1980 Control simulation (case A of  STAGE TWO: Clear sky, instantaneous flux calculations, see above).

A)   Recommended experiments for CCM radiation codes

i) Impact of solar irradiance changes

• Calculation of solar heating rates for January using solar max irradiance (file SOLMAX )
• Calculation of solar heating rates for January using solar min irradiance (file SOLMIN )

Required output: Total SW heating rates (K/day) for solar min and max cases at all latitudes and LAYERS

ii) Impact of solar induced ozone changes

• Calculation of solar heating rates for January using solar mean irradiance (file SOLMEAN ) and solar minimum ozone derived from file SOLINP_o3
• Calculation of solar heating rates for January using solar mean irradiance (file SOLMEAN and solar maximum ozone derived from file SOLINP_o3

SOLINP_o3 provides ozone changes between solar min and max in % volume mixing ratio at LAYER pressures. By applying these changes to the ozone mixing ratios of the 1980 Control simulation (case A of  STAGE TWO: Clear sky, instantaneous flux calculations) ozone profiles can be derived for solar min (by subtracting half of the SOLINP_O3 changes) and for solar max (by adding half of the SOLINP_O3 changes).

Required output: Total SW heating rates (K/day) for solar min and max cases, at all latitudes and LAYERS

Recommended experiments for line-by-line radiation codes

As reference for the CCM radiation codes, lbl-calculations following the recommendations of section A) should be provided by lbl-models for 3 selected latitudes:

-80oS; (highlatitude summer)

-0° (Tropics)

-45oN; (midlatitude winter)

REFERENCES

Haigh, J. D., The role of stratospheric ozone in modulating the solar radiative forcing of climate, Nature, 370, 544-546, 1994.

Lean, J.L.,G.J. Rottman, H.L. Kyle, T.N. Woods, J.R. Hickey, and L.C.Puga, Detection and parameterization of variations in solar mid and near ultraviolet radiation (200 to 400 nm), J. Geophys. Res., 102, 29939-29956, 1997.

Lean, J.L.,Evolution of the Sun's Spectral Irradiance since the Maunder Minimum, J. Geophys. Res., 27, 2425-2428, 2000.

Lean, J.L., G. Rottman, J. Harder and G Kopp, SORCE contributions to new understanding of global change and solar variability, Solar Phys., 230:27-53, 2005.

Each of the ascii files with solar input data (SOLMAX, SOLMIN, SOLMEAN) is organized as follows:

header  ...

wavelength grid centers ...

wavelength bands width (1 nm bins from 0 to 750 nm, 5 nm bins from 750 to 5000 nm, 10 nm bins from 5000 to 10000 nm, 50 nm bins from 10000 to 100000 nm) ...

Spectral irradiance (mW/m2/nm) for years indicated in the file name

YEAR MONTH    TSI in W/m2

solar flux data ...