31 March 2016

Improved Representation of Primary Carbonaceous Aerosol Ageing in CAM5 and ACME v1

Primary carbonaceous aerosol ageing in GCMs.


We developed a four-mode verison of Modal Aerosol Module (MAM4) for better representation of microphysical ageing of primary carbonaceous aerosols in the atmosphere. MAM4 significant increases the near-surface black carbon concentrations in the Arctic and improves the agreement with observ


The new MAM4 significantly reduces the model bias of near-surface black carbon concentrations in the Arctic, and has been adopted by the DOE's ACME model and the next version of Community Atmosphere Model verision 6 (CAM6). 




Atmospheric carbonaceous aerosols including primary particular organic matter (POM) and black carbon (BC) exert significant radiative forcing to the Earth’s radiation balance and could perturb the atmospheric temperature, precipitation and general circulation. However, there are still large biases in the simulation of carbonaceous aerosols from global climate models (GCMs). One of the notable biases is the substantial underestimation of near-surface BC concentrations in the Arctic in almost all GCMs. Here in this work, we improve the current three-mode version of the Modal Aerosol Module (MAM3) in the Community Atmospheric Model version 5 (CAM5) and DOE’s Accelerated Climate Modeling for Energy version 1 (ACME v1) by introducing an additional primary carbon mode to explicitly account for the microphysical ageing of primary carbonaceous aerosols in the atmosphere. Compared to MAM3, the new four-mode version of MAM (MAM4) significantly increases the concentrations of POM and BC especially in the remote regions (e.g., Arctic), and improves the model agreement with near-surface BC observations in the Arctic. MAM4 has been adopted by the next version of CAM (CAM6) and ACME v1. This study will have important implications for the coupled climate model simulations of clouds, radiation, surface temperature, and snow melting in the Arctic.

Xiaohong Liu
University of Wyoming