# How to set up the radiation scheme for Palaeo-simulations? – in #9: CCLM

### How to set up the radiation scheme for Palaeo-simulations?

I am trying to use CCLM for downscaling an AGCM simulation during
several time-slices in the last millennium (e.g. LIA , MCA ). I need to adapt the Green
House Gas concentrations to that time. But the ico2_rad option do not
allow me to do so. How should I adapt the model for GHG concentrations in
such simulations.

There are two ways, a quick and a flexible one. For both first determine the equivalent CO2 concentration in ppm and convert it into mixing ratio by dividing by 658157.16

The quick one:

```CASE (10)
! RCP85 scenario (for 1950 <= zyear <= 2150)
!   eff. CO2 (all GreeHouseGases (GHG) considered)
zqco2 = ( – 4.0501145412E+07_ireals               &
+ 7.9386473439E+04_ireals * zyear       &
– 5.8292720579E+01_ireals * zyear*zyear &
+ 1.9002921793E-02_ireals * zyear**3    &
– 2.3202412328E-06_ireals * zyear**4) * 1.519E-06_ireals```

END SELECT zqco2 = …. ! insert your mixing ratio here

The flexible one:
in organize_physics.f90 change

```  IF (ico2_rad.GT.10 )  ico2_rad  = ico2_rad_d
```
to
```  IF (ico2_rad.GT.11 )  ico2_rad  = ico2_rad_d
```

```  zyearmin = 1950
```
to
```IF (ico2_rad < 11) THEN
zyearmin = 1950
ELSE
zyearmin =    ! .... put a year lower than the start year of your simulation period here
```
and change
```CASE (10)
! RCP85 scenario (for 1950 <= zyear <= 2150)
!   eff. CO2 (all GreeHouseGases (GHG) considered)
zqco2 = ( – 4.0501145412E+07_ireals               &
+ 7.9386473439E+04_ireals * zyear       &
– 5.8292720579E+01_ireals * zyear*zyear &
+ 1.9002921793E-02_ireals * zyear**3    &
– 2.3202412328E-06_ireals * zyear**4) * 1.519E-06_ireals```

END SELECT to
```CASE (10)
! RCP85 scenario (for 1950 <= zyear <= 2150)
!   eff. CO2 (all GreeHouseGases (GHG) considered)
zqco2 = ( – 4.0501145412E+07_ireals               &
+ 7.9386473439E+04_ireals * zyear       &
– 5.8292720579E+01_ireals * zyear*zyear &
+ 1.9002921793E-02_ireals * zyear**3    &
– 2.3202412328E-06_ireals * zyear**4) * 1.519E-06_ireals

CASE (11)
!… last millenium
zqco2  =     !… insert your mixing ratio here

ENDSELECT```
In the CCLM namelist PHYCTL set
```ico2_rad=11
```
In the same way you can define several different mixing ratios with additional numbers 12, 13, 14 etc.

I am also running some paleoclimate simulations with the cclm for different time slices starting 6000 years before present. I wanted to know, if I had to define several additional cases for different GHG s concentration for every period of study, what should be the year I have to give to zyearmin for every time slice? in my case the first year of the simulations is called 8240 and it refers to the year 4000 BC.

Thanks.

Your case does not differ much from the case above. ``` zyearmin ``` and ``` zyearmax ``` are only needed, if you fit your GHG concentration with a polygon. These values describe the validity range of the polygon. If you do not need this, you can comment out the following lines in src_radiation.f90:

```    ! Define upper limits of fitted scenarios polynoms to avoid eloping
zyearmin = 1950
IF (ico2_rad < 7) THEN ! SRES fitting
zyearmax = 2100
ELSE                   ! RCP fitting valid until 2150
zyearmax = 2150
ENDIF```

! zyear can be modified, because it is only used for calculation of CO2 trends IF (zyear < zyearmin) THEN zyear = zyearmin ELSEIF (zyear > zyearmax) THEN zyear = zyearmax ENDIF