Abstract. We present the dust module in the Multiscale Online Non-hydrostatic AtmospheRe CHemistry model (MONARCH) version 2.0, a chemical weather prediction system that can be used for regional and global modeling at a range of resolutions. The representations of dust processes in MONARCH were upgraded with a focus on dust emission (emission parameterizations, entrainment thresholds, considerations of soil moisture and surface cover), lower boundary conditions (roughness, potential dust sources), and dust–radiation interactions. MONARCH now allows modeling of global and regional mineral dust cycles using fundamentally different paradigms, ranging from strongly simplified to physics-based parameterizations. We present a detailed description of these updates along with four global benchmark simulations, which use conceptually different dust emission parameterizations, and we evaluate the simulations against observations of dust optical depth. We determine key dust parameters, such as global annual emission/deposition flux, dust loading, dust optical depth, mass-extinction efficiency, single-scattering albedo, and direct radiative effects. For dust-particle diameters up to 20 µm, the total annual dust emission and deposition fluxes obtained with our four experiments range between about 3500 and 6000 Tg, which largely depend upon differences in the emitted size distribution. Considering ellipsoidal particle shapes and dust refractive indices that account for size-resolved mineralogy, we estimate the global total (longwave and shortwave) dust direct radiative effect (DRE) at the surface to range between about −0.90 and −0.63 W m−2 and at the top of the atmosphere between −0.20 and −0.28 W m−2. Our evaluation demonstrates that MONARCH is able to reproduce key features of the spatiotemporal variability of the global dust cycle with important and insightful differences between the different configurations.
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Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
Abstract. Mineral dust aerosols cool and warm the atmosphere byscattering and absorbing solar (shortwave: SW) and thermal (longwave: LW)radiation. However, significant uncertainties remain in dust radiativeeffects, largely due to differences in the dust size distribution andspectral optical properties simulated in Earth system models. Dust modelstypically underestimate the coarse dust load (more than 2.5 µm indiameter) and assume a spherical shape, which leads to an overestimate ofthe fine dust load (less than 2.5 µm) after the dust emissions in themodels are scaled to match observed dust aerosol optical depth at 550 nm(DAOD550). Here, we improve the simulated dust properties with data setsthat leverage measurements of size-resolved dust concentration, asphericityfactor, and refractive index in a coupled global chemical transport modelwith a radiative transfer module. After the adjustment of size-resolved dustconcentration and spectral optical properties, the global and annual averageof DAOD550 from the simulation increases from 0.023 to 0.029 and fallswithin the range of a semi-observationally based estimate (0.030 ± 0.005). The reduction of fine dust load after the adjustment leads to areduction of the SW cooling at the top of the atmosphere (TOA). To improveagreement against a semi-observationally based estimate of the radiativeeffect efficiency at TOA, we find that a less absorptive SW dust refractiveindex is required for coarser aspherical dust. Thus, only a minor differenceis estimated for the net global dust radiative effect at TOA (−0.08 vs.−0.00 W m−2 on a global scale). Conversely, our sensitivitysimulations reveal that the surface warming is substantially enhanced nearthe strong dust source regions (less cooling to −0.23 from −0.60 W m−2 on a global scale). Thus, less atmospheric radiativeheating is estimated near the major source regions (less heating to 0.15from 0.59 W m−2 on a global scale), because of enhanced LWwarming at the surface by the synergy of coarser size and aspherical shape.
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- NSF-PAR ID:
- 10327830
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 21
- Issue:
- 22
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 16869 to 16891
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-21-16869-2021
