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Impact of dust particle non-sphericity on climate simulations

P. Raisanen ; P. Haapanala ; C. E. Chung ; Michael Kahnert (Institutionen för rymd- och geovetenskap, Global miljömätteknik och modellering) ; R. Makkonen ; J. Tonttila ; T. Nousiainen
Quarterly Journal of the Royal Meteorological Society (0035-9009). Vol. 139 (2013), 677, p. 2222-2232.
[Artikel, refereegranskad vetenskaplig]

Although mineral aerosol (dust) particles are irregular in shape, they are treated as homogeneous spheres in climate model radiative transfer calculations. Here, we test the effect of dust particle non-sphericity in the ECHAM5.5-HAM2 global aerosol-climate model. The short-wave optical properties of the two insoluble dust modes in HAM2 are modelled using an ensemble of spheroids that has been optimized to reproduce the optical properties of dust-like aerosols, thereby providing a significant improvement over spheres. First, the direct radiative effects (DRE) of dust non-sphericity were evaluated diagnostically, by comparing spheroids with both volume-equivalent and volume-to-area (V/A) equivalent spheres. In the volume-equivalent case, the short-wave DRE of insoluble dust at the surface and at the top of the atmosphere (TOA) was slightly smaller (typically by 3-4%) for spheroidal than for spherical dust particles. This rather small difference stems from compensating non-sphericity effects on the dust optical thickness and asymmetry parameter. In the V/A-equivalent case, the difference in optical thickness was virtually eliminated and the DRE at the TOA (surface) was approximate to 20% (approximate to 13%) smaller for spheroids than for spheres, due to a larger asymmetry parameter. Even then, however, the global-mean DRE of non-sphericity was only 0.055 W m(-2) at the TOA and 0.070 W m(-2) at the surface. Subsequently, the effects of dust non-sphericity were tested interactively in simulations in which ECHAM5.5-HAM2 was coupled to a mixed-layer ocean model. Consistent with the rather small radiative effects noted above, the climatic differences from simulations with spherical dust optics were generally negligible.

Nyckelord: aerosols, radiative transfer, climate modelling, dust particles, non-sphericity, NONSPHERICAL ICE PARTICLE, MODEL ECHAM5-HAM, MINERAL AEROSOL, TROPOSPHERIC AEROSOLS, INDEPENDENT SPHERES, OPTICAL-PROPERTIES, LIGHT-SCATTERING, ABSORPTION, SPHEROIDS, SENSITIVITY



Denna post skapades 2014-01-17. Senast ändrad 2014-02-03.
CPL Pubid: 192816

 

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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Global miljömätteknik och modellering (2010-2017)

Ämnesområden

Klimatforskning

Chalmers infrastruktur