Abstract
Abstract. A new size-resolved dust scheme based on the numerical method of piecewise log-normal approximation (PLA) was developed and implemented in the fourth generation of the Canadian Atmospheric Global Climate Model with the PLA Aerosol Model (CanAM4-PAM). The total simulated annual global dust emission is 2500 Tg yr−1, and the dust mass load is 19.3 Tg for year 2000. Both are consistent with estimates from other models. Results from simulations are compared with multiple surface measurements near and away from dust source regions, validating the generation, transport and deposition of dust in the model. Most discrepancies between model results and surface measurements are due to unresolved aerosol processes. Biases in long-range transport are also contributing. Radiative properties of dust aerosol are derived from approximated parameters in two size modes using Mie theory. The simulated aerosol optical depth (AOD) is compared with satellite and surface remote sensing measurements and shows general agreement in terms of the dust distribution around sources. The model yields a dust AOD of 0.042 and dust aerosol direct radiative forcing (ADRF) of −1.24 W m−2 respectively, which show good consistency with model estimates from other studies.
Highlights
Mineral dust aerosol is one of the important contributors to global aerosol loading (Textor et al, 2006) and radiative forcing (Kinne et al, 2006; Balkanski et al, 2007), originating from aeolian erosion in arid and semi-arid regions, going through complex atmospheric processes and exerting strong impacts on regional and global climates (e.g., Slingo et al, 2006; McFarlane et al, 2009; Li et al, 2007a,b).Dust aerosols absorb and scatter both solar and terrestrial radiation
The aerosol direct radiative forcing (ADRF) is determined as the difference in net radiative fluxes at the top of atmosphere (TOA) due to scattering and absorption of radiation by aerosol, which is often investigated to quantify the radiative impact of aerosols on the climate.The radiation code is called twice to diagnose the change in net radiative fluxes at TOA that is associated with a change in aerosol concentrations in the model, leaving temperature and other variables constant (Forster et al, 2007)
Since this study focuses on dust aerosol, we extract data from the “dusty” sites in AERONET as defined in Huneeus et al (2011), where the observed monthly mean total aerosol optical depth (AOD) is larger than 0.2 and monthly averaged AE (Angstrom Exponent) is smaller than 0.4 for at least two months in a year
Summary
Mineral dust aerosol is one of the important contributors to global aerosol loading (Textor et al, 2006) and radiative forcing (Kinne et al, 2006; Balkanski et al, 2007), originating from aeolian erosion in arid and semi-arid regions, going through complex atmospheric processes and exerting strong impacts on regional and global climates (e.g., Slingo et al, 2006; McFarlane et al, 2009; Li et al, 2007a,b). Cakmur et al (2006) used several global datasets of aerosol optical depth (AOD), dust surface concentration, deposition as well as particle size distributions, in order to constrain the magnitude of global dust cycle by minimizing the difference between NASA GISS (Goddard Institute for Space Studies) model results and observations, which yields an optimal global, annual emission flux from 1500 to 2600 Tg yr−1. Estimates from other recent models show an extensive range (e.g., Table 3) Both surface measurements and satellite observations provide information about dust aerosol distribution and radiative properties on a global scale. Model results are validated by comparing with surface measurements of the dust size distribution, mass concentration and deposition rates, as shown in Sect.
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