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Namelist variables related to aerosol activation in MAM4 (for SCAM simulations)


Ramsha Khan
New Member

I am replicating a sensitivity analysis conducted using the Global Model of Aerosol Processes (GLOMAP), with a SCAM6 simulation using the MAM4 aerosol representation. As a first step, I'm trying to match input variables used in the GLOMAP analysis, with namelist variables in SCAM6, which I can subsequently perturb in my analysis. I am having trouble locating relevant namelist variables in CAM for the following GLOMAP variable:

- Oxidation activation diameter: The diameter above which aerosol particles activate into cloud droplets in stratiform clouds

Essentially I'm looking for any input variable or parameter that controls the activation of aerosols into cloud droplets, which I can perturb. I have gone over the MAM model description in the supplementary material for Liu et al (2012), where it states that:

"Water uptake is based on the equilibrium Köhler theory (Ghan and Zaveri, 2007) using the relative humidity and the volume-mean hygroscopicity for each mode to diagnose the wet volume-mean radius of the mode from the dry volume-mean radius,"


" Activation is parameterized in terms of updraft velocity and the properties of all of the aerosol modes (Abdul-Razzak and
Ghan, 2000), with both mass and number transferred to the cloud-borne state."

However, I cannot locate parameters for the hygroscopicity, or those relating to activation (i.e. controlling how particles are converted from the interstitial attachment state to the
cloud-borne state). I intend to use the existing IOPs for the SCAM simulations as outlined in Gettelman et al (2019), and have been going over the namelist settings in the atm_in file for the default ARM-97 case.

I would appreciate any direction to the relevant information, and thanks very much in advance!