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Calculation of aerosol radiative forcing in CAM6

W

wbr2023

彬睿王
New Member
Hi!
I wonder how CAM6 calculates the radiative forcing of aerosols. What inputdata of aerosols does it need to calculates the radiative forcing.
Thanks!
 
B

brianpm

Active Member
CAM6 treats aerosols similarly to CAM5, as described in Section 4.8 of the scientific description: https://www2.cesm.ucar.edu/models/cesm1.0/cam/docs/description/cam5_desc.pdf.

There was an update to change from "MAM3" (3 size modes) to "MAM4" (4 size modes) in CAM6: Aerosols - CAM-Chem - wiki.ucar.edu

The aerosols interact with radiation both directly and indirectly through aerosol-cloud interactions. The RRTMG scheme that calculates radiative fluxes in CAM6 uses optical properties as input. Aerosol optical properties for the shortwave and longwave radiative calculation are calculated in $CAMROOT/src/physics/cam/aer_rad_props.F90. The cloud optical properties are altered by the aerosol by changing the drop/ice number and size, and then cloud optical properties are determined in $CAMROOT/src/physics/rrtmg/cloud_rad_props.F90.

The aerosols in the model are driven by emissions, supplied as netCDF files. These emissions are advected by the dynamics, and evolve based on the simple chemistry in CAM6 (specified oxidants), and interact with moist physics.

In general, "aerosol effective radiative forcing" is calculated as the difference in the top-of-atmosphere net radiation between simulations with specified SST/ice using pre-industrial versus present-day aerosol emissions. The forcing can also be calculated with additional diagnostic radiation calls that neglect the aerosol ("clean sky calculations"). For more information see:
- Pincus et al. 2016 GMD - The Radiative Forcing Model Intercomparison Project (RFMIP): experimental protocol for CMIP6
- Ghan 2013: ACP - Technical Note: Estimating aerosol effects on cloud radiative forcing
 
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