SW absorption by CH4 in CAM5

[amatcaos@caos_iisc_ernet_in]

Hi,I was hoping if someone could help regading the shortwave(SW) absorption by CH4 in CAM5. It is knownthat CH4 has a minor SW absortion band 3.3um.Does CAM5 RRTMG package considers this absorption band of CH4?Oxidation of CH4 is an important source of water vapour in the stratosphere. Does CAM5 models this effect? I am doing climate change experiments, so it is very important for me to know about this ?Thank you very muchAngshu  

 

[amatcaos@caos_iisc_ernet_in]

Just to add...In the CAM5 description, section 4.13 I found,"In CAM 5.0, it is assumed that the water vapor (volume mixing ratio)
source is twice the CH4 sink. This approach was also taken by Mote et al. [1993] for middle
atmosphere studies with an earlier version of the CCM. This part of the water budget is of
some importance in climate change studies, because the atmospheric CH4 concentrations have
increased rapidly with time and this increase is projected to continue into the next century (e.g.,
Alcamo et al. [1995]) The representation of stratospheric water vapor in CAM 5.0 is necessar-
ily crude, since there are few levels above the tropopause. However, the model is capable of
capturing the main features of the CH4 and water distributions."

This would mean that in CAM5 changing the CH4 concentration would change the water vapour mixing ratio as well. please confirm this.I would be grateful if someone can point out where in the code this thing is considered.Thanks Angshu  

 

[amatcaos@caos_iisc_ernet_in]

Just to add...In the CAM5 description, section 4.13 I found,"In CAM 5.0, it is assumed that the water vapor (volume mixing ratio)
source is twice the CH4 sink. This approach was also taken by Mote et al. [1993] for middle
atmosphere studies with an earlier version of the CCM. This part of the water budget is of
some importance in climate change studies, because the atmospheric CH4 concentrations have
increased rapidly with time and this increase is projected to continue into the next century (e.g.,
Alcamo et al. [1995]) The representation of stratospheric water vapor in CAM 5.0 is necessar-
ily crude, since there are few levels above the tropopause. However, the model is capable of
capturing the main features of the CH4 and water distributions."

This would mean that in CAM5 changing the CH4 concentration would change the water vapour mixing ratio as well. please confirm this.I would be grateful if someone can point out where in the code this thing is considered.Thanks Angshu  

 

[amatcaos@caos_iisc_ernet_in]

Just to add...In the CAM5 description, section 4.13 I found,"In CAM 5.0, it is assumed that the water vapor (volume mixing ratio)
source is twice the CH4 sink. This approach was also taken by Mote et al. [1993] for middle
atmosphere studies with an earlier version of the CCM. This part of the water budget is of
some importance in climate change studies, because the atmospheric CH4 concentrations have
increased rapidly with time and this increase is projected to continue into the next century (e.g.,
Alcamo et al. [1995]) The representation of stratospheric water vapor in CAM 5.0 is necessar-
ily crude, since there are few levels above the tropopause. However, the model is capable of
capturing the main features of the CH4 and water distributions."

This would mean that in CAM5 changing the CH4 concentration would change the water vapour mixing ratio as well. please confirm this.I would be grateful if someone can point out where in the code this thing is considered.Thanks Angshu