Improved Dust Representation and Impacts on Dust Transport and Radiative Effect in CAM5

Abstract

Dust transport and spatial distribution are poorly represented in current global climate models (GCMs) including the Community Atmosphere Model version 5 (CAM5). Particularly, models lack explicit representation of super‐coarse dust, which may have important implications for dust radiative forcing and impacts on biogeochemistry. A nine‐mode version of the modal aerosol model (MAM9) has been developed to address these issues. In this new aerosol scheme, four dust modes have been designed to treat dust particles of sizes up to 20 μm. The MAM9‐simulated results are compared with those from the default four‐mode version of MAM (MAM4) and also with the in situ surface measurements of dust concentration and deposition flux, satellite‐retrieved dust extinction profile, and in situ vertical measurements of dust concentrations from the NASA Atmosphere Tomography Mission (ATom). Overall, MAM9 improves the dust representation in remote regions while maintaining reasonably good results near the dust source regions. In addition, MAM9 reduces the fine dust burden and increases the coarse dust burden globally. The increased coarse dust burden has slightly increased the dust direct radiative effect by 0.01 W m−2 while it enhanced dust indirect radiative effect by 0.36 W m−2, globally.

Important Ice Processes Are Missed by the Community Earth System Model in Southern Ocean Mixed‐Phase Clouds: Bridging SOCRATES Observations to Model Developments

“…However, ice nucleation parameterizations in current GCMs are often derived based on measurements of dust aerosols and ice nucleating particles (INPs) over the Northern Hemisphere (NH) (DeMott et al., 2010, 2015; Meyers et al., 1992; Niemand et al., 2012). Dust aerosols have limited presence over the SO, with the averaged dust mixing ratio lower than 0.5 μg m −3 in the boundary layer, compared with that over the NH dust source and outflow regions which can be higher than 100 μg m −3 (Ke et al., 2022; M. Wu et al., 2020). This leads to a limited amount of dust INPs over SO.…”

Larger Dust Cooling Effect Estimated From Regionally Dependent Refractive Indices

“…With respect to the effect of dust PSD on DRE, it is worth noting that the coarser dust exhibits a weaker scattering capacity and a stronger absorbing capacity. This leads to a progressive weakening of the SW cooling when coarse dust particles, up to 20 μm in Kok et al (2017) and Ke et al (2022) and over 20 μm in Di Biagio et al (2020), are introduced, in contrast to dust particles below 10 μm in AeroCom (Aerosol Comparisons between Observations and Models) (Huneeus et al, 2011). In this study, we update the original AS83 PSD scheme to the BFT22 scheme, resulting in increases in the coarse and giant dust fraction and loading in the atmosphere, which significantly reduces the SW cooling by a global mean of 0.22 W m 2 .…”

“…Furthermore, these models utilize generic CRI values across various dust source regions, with an intermodel variability of the imaginary part by up to an order of magnitude (Adebiyi, Huang, et al., 2023; Balkanski et al., 2007). Although recent studies better constrained the dust PSD based on observations and concluded that dust tends to contribute to warming (Adebiyi & Kok, 2020; Di Biagio et al., 2020; Ke et al., 2022; Kok et al., 2017), the variations in dust DRE due to CRI uncertainties are still large (Huneeus et al., 2011; Kinne et al., 2006; Li et al., 2021). As a result, whether dust aerosols warm or cool the climate system still remains elusive.…”

The Saharan dust plume: Current knowledge on the impact on health, human activities, and the ecosystem, with comments on research gaps

“…Dust transport and spatial distribution are also poorly represented in current global climate models including the Community Atmosphere Model version 5 (CAM5). (Ke et al, 2022) are developing aerosol models to address these issues.…”