FSNT - FLNT and ERF

[wrunyu]

Hi all,
I'm more confused about the variables in the CESM model output: is FSNT - FLNT equivalent to ERF (Effective Radiative Forcing).I found that the two units are the same, but I don't know if there is a connection.
Looking forward to your reply.

Regards,
Runyu

 

[sacks]

Are these variables from CAM? If so, I'll move this to the atmosphere forum where it should get more attention.

 

[wrunyu]

Are these variables from CAM? If so, I'll move this to the atmosphere forum where it should get more attention.

Hi Bill，

I do have CAM output for my variables. Thanks for your reply.

Regards,
Runyu

 

[brianpm]

Hi Runyu,

Can you elaborate on your question? I'm not sure exactly what you're asking.

FSNT is the net shortwave (visible) radiation at the top of the model, and FLNT is the net longwave (infrared) at the top of the model. Combined they give the net radiative balance of the system; that is, if their difference is non-zero the system is out of balance and would tend to warm/cool to re-establish equilibrium.

 

[wrunyu]

Hi Runyu,

Can you elaborate on your question? I'm not sure exactly what you're asking.

FSNT is the net shortwave (visible) radiation at the top of the model, and FLNT is the net longwave (infrared) at the top of the model. Combined they give the net radiative balance of the system; that is, if their difference is non-zero the system is out of balance and would tend to warm/cool to re-establish equilibrium.

Hi brianpm,​

I learned about a concept:ERF (Effective Radiative Forcing).I would like to know if the CESM model output variable:FSNT - FLNT, is ERF？

Regards,
Runyu

 

[brianpm]

No, FSNT - FLNT is the radiative imbalance at the top of the model. This is related to the radiative forcing, but is not typically called ERF. If the system's imbalance is sustained in some way, this is the radiative forcing, but under typical conditions an imbalance will tend toward zero as the climate system establishes equilibrium by changing temperature.

Usually it is the change in (FSNT - FLNT) associated with a perturbation that is ERF.

One common experiment is to run the global atmosphere-land model (fixed SST and sea-ice) twice: first with aerosols and second with pre-industrial aerosols. Taking (FSNT-FLNT)_present - (FSNT-FLNT)_preindustrial provides the "aerosol ERF" (ERF_aer). See, for example, Pincus et al. 2016: GMD - The Radiative Forcing Model Intercomparison Project (RFMIP): experimental protocol for CMIP6

Other references:
- Forster, P. M., T. Richardson, A. C. Maycock, C. J. Smith, B. H. Samset, G. Myhre, T. Andrews, R. Pincus, and M. Schulz (2016), Recommendations for diagnosing effective radiative forcing from climate models for CMIP6, J. Geophys. Res. Atmos., 121, 12,460–12,475, doi:10.1002/2016JD025320.
- Smith et al. 2020, Effective radiative forcing and adjustments in CMIP6 models
- Tang, T., Shindell, D., Faluvegi, G., Myhre, G., Olivié, D., Voulgarakis, A., et al. (2019). Comparison of effective radiative forcing calculations using multiple methods, drivers, and models. Journal of Geophysical Research: Atmospheres, 124, 4382–4394. https://doi.org/10.1029/2018JD030188

 

[wrunyu]

No, FSNT - FLNT is the radiative imbalance at the top of the model. This is related to the radiative forcing, but is not typically called ERF. If the system's imbalance is sustained in some way, this is the radiative forcing, but under typical conditions an imbalance will tend toward zero as the climate system establishes equilibrium by changing temperature.

Usually it is the change in (FSNT - FLNT) associated with a perturbation that is ERF.

One common experiment is to run the global atmosphere-land model (fixed SST and sea-ice) twice: first with aerosols and second with pre-industrial aerosols. Taking (FSNT-FLNT)_present - (FSNT-FLNT)_preindustrial provides the "aerosol ERF" (ERF_aer). See, for example, Pincus et al. 2016: GMD - The Radiative Forcing Model Intercomparison Project (RFMIP): experimental protocol for CMIP6

Other references:
- Forster, P. M., T. Richardson, A. C. Maycock, C. J. Smith, B. H. Samset, G. Myhre, T. Andrews, R. Pincus, and M. Schulz (2016), Recommendations for diagnosing effective radiative forcing from climate models for CMIP6, J. Geophys. Res. Atmos., 121, 12,460–12,475, doi:10.1002/2016JD025320.
- Smith et al. 2020, Effective radiative forcing and adjustments in CMIP6 models
- Tang, T., Shindell, D., Faluvegi, G., Myhre, G., Olivié, D., Voulgarakis, A., et al. (2019). Comparison of effective radiative forcing calculations using multiple methods, drivers, and models. Journal of Geophysical Research: Atmospheres, 124, 4382–4394. https://doi.org/10.1029/2018JD030188

Hi brianpm,​

I have understood what you are saying. Thank you very much for your reply!

Regards,
Runyu