A simple question about aerosol radiative forcing

[fkc000@163_com]

Hello there!       I'm trying to estimate the anthropogenic aerosol radiative forcings.       I plan to run these two simulations:              1) one simulation with the present day (2000) emissions of aerosols and precursor;       2) one simulation with the pre-industrial (1850) emissions of aerosols and precursor.       all other forcing kept in present day (2000).       Here's the simple question: which variable in the "*cam.h0*" file should I use in order to calculate aerosol radiative forcing?  FSNT(Net solar flux at top of model) or FSNTOA(Net solar flux at top of atmosphere) or other variables? I suppose the difference of one certain flux variable between these two simulations should be anthropogenic aerosol radiative forcings. If it's wrong, then what's the right way to calculate anthropogenic aerosol radiative forcings?       Thank you in advance!

 

[CESM researcher]

Hello there! I'm trying to estimate the anthropogenic aerosol radiative forcings. I plan to run these two simulations: 1) one simulation with the present day (2000) emissions of aerosols and precursor; 2) one simulation with the pre-industrial (1850) emissions of aerosols and precursor. all other forcing kept in present day (2000). Here's the simple question: which variable in the "*cam.h0*" file should I use in order to calculate aerosol radiative forcing? FSNT(Net solar flux at top of model) or FSNTOA(Net solar flux at top of atmosphere) or other variables? I suppose the difference of one certain flux variable between these two simulations should be anthropogenic aerosol radiative forcings. If it's wrong, then what's the right way to calculate anthropogenic aerosol radiative forcings? Thank you in advance!

Hello, I am using CESM2 once and I want trying to estimate the anthropogenic aerosol radiative forcings,but will not design case.Please give me some guidance， Thank you in advance!

 

[brianpm]

There are several methods to diagnose radiative forcing. My understanding of the current literature is that you should think not only of the instantaneous radiative forcing but also the "rapid adjustments" that occur before slower parts of the system respond. Combining the radiative forcing and the adjustments produces the "effective radiative forcing." The most common way to diagnose effective radiative forcing is to do a pair of simulations with prescribed SST and sea-ice (so called "AMIP" runs, or F-cases in CESM). One is a control run with standard emissions, and the other is identical except it only uses preindustrial emissions. The ERF is then diagnosed as the change in the net top-of-atmosphere radiative flux. This is usually calculated in CESM by:

ERF = RESTOM_2 - RESTOM_1

where the subscript denotes the simulation, and RESTOM is the "residual" Top-Of-Model radiative flux, calculated as:

RESTOM = FSNT - FLNT

where FSNT is the net shortwave flux at top-of-model and FLNT is net longwave flux at top of model.


If one is interested in diagnosing aerosol-cloud interaction, it is useful to also include diagnostic radiation calculations that ignore the aerosol. These produce "clean-sky" fluxes. CESM/CAM supports this by using the namelist parameter called rad_diag_1. Here is an example of specifying diagnostics clean-sky fluxes for CESM2-CAM6:

rad_diag_1             = 'A:Q:H2O', 'N:O2:O2', 'N:CO2:CO2', 'N:ozone:O3', 'N:N2O:N2O', 'N:CH4:CH4', 'N:CFC11:CFC11', 'N:CFC12:CFC12'

I included some details about these topics in a recent paper:
Medeiros, B. (2020). Aquaplanets as a framework for examination of aerosol effects. Journal of Advances in Modeling Earth Systems, 12, e2019MS001874. Error - Cookies Turned Off

There are a lot of useful references there, including a recent review:

Bellouin, N., Quaas, J., Gryspeerdt, E., Kinne, S., Stier, P., Watson‐Parris, D., Boucher, O., Carslaw, K. S., Christensen, M., Daniau, A.‐L., Dufresne, J.‐L., Feingold, G., Fiedler, S., Forster, P., Gettelman, A., Haywood, J. M., Lohmann, U., Malavelle, F., Mauritsen, T., McCoy, D. T., Myhre, G., Mülmenstädt, J., Neubauer, D., Possner, A., Rugenstein, M., Sato, Y., Schulz, M., Schwartz, S. E., Sourdeval, O., Storelvmo, T., Toll, V., Winker, D., & Stevens, B. (2020). Bounding global aerosol radiative forcing of climate change. Reviews of Geophysics, 58, e2019RG000660. Error - Cookies Turned Off