Impact of dust particle non-sphericity on climate simulations
Journal article, 2013

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.

MODEL ECHAM5-HAM

INDEPENDENT SPHERES

climate modelling

LIGHT-SCATTERING

dust particles

MINERAL AEROSOL

aerosols

TROPOSPHERIC AEROSOLS

ABSORPTION

OPTICAL-PROPERTIES

SENSITIVITY

radiative transfer

SPHEROIDS

NONSPHERICAL ICE PARTICLE

non-sphericity

Author

P. Raisanen

Finnish Meteorological Institute (FMI)

P. Haapanala

University of Helsinki

C. E. Chung

Gwangju Institute of Science and Technology

Michael Kahnert

Chalmers, Earth and Space Sciences, Global Environmental Measurements and Modelling

R. Makkonen

University of Oslo

University of Helsinki

J. Tonttila

Finnish Meteorological Institute (FMI)

University of Helsinki

T. Nousiainen

University of Helsinki

Quarterly Journal of the Royal Meteorological Society

0035-9009 (ISSN) 1477-870X (eISSN)

Vol. 139 677 2222-2232

Subject Categories

Climate Research

DOI

10.1002/qj.2084

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9/6/2018 2