Publication Abstracts

Perlwitz and Miller 2010

Perlwitz, J.P., and R.L. Miller, 2010: Cloud cover increase with increasing aerosol absorptivity - A counterexample to the conventional semi-direct aerosol effect. J. Geophys. Res., 115, D08203, doi:10.1029/2009JD012637.

We re-examine the aerosol semi-direct effect using a general circulation model and four cases of the single scattering albedo of dust aerosols. Contrary to the expected decrease in low cloud cover due to heating by tropospheric aerosols, we find a significant increase with increasing absorptivity of soil dust particles in regions with high dust load, except during Northern Hemisphere winter. The strongest sensitivity of cloud cover to dust absorption is found over land during Northern Hemisphere summer. Here, even medium and high cloud cover increase where the dust load is highest. The cloud cover change is directly linked to the change in relative humidity in the troposphere as a result of contrasting changes in specific humidity and temperature. More absorption by aerosols leads to larger diabatic heating and increased warming of the column, decreasing relative humidity. However, a corresponding increase in the specific humidity exceeds the temperature effect on relative humidity. The net effect is more low cloud cover with increasing aerosol absorption. The higher specific humidity where cloud cover strongly increases is attributed to an enhanced convergence of moisture driven by dust radiative heating. Although in some areas our model exhibits a reduction of low cloud cover due to aerosol heating consistent with the conventional description of the semi-direct effect we conclude that the link between aerosols and clouds is more varied, depending also on changes in the atmospheric circulation and the specific humidity induced by the aerosols. Other absorbing aerosols like black carbon are expected to have a similar effect.

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BibTeX Citation

@article{pe04300u,
  author={Perlwitz, J. P. and Miller, R. L.},
  title={Cloud cover increase with increasing aerosol absorptivity - A counterexample to the conventional semi-direct aerosol effect},
  year={2010},
  journal={Journal of Geophysical Research},
  volume={115},
  pages={D08203},
  doi={10.1029/2009JD012637},
}

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RIS Citation

TY  - JOUR
ID  - pe04300u
AU  - Perlwitz, J. P.
AU  - Miller, R. L.
PY  - 2010
TI  - Cloud cover increase with increasing aerosol absorptivity - A counterexample to the conventional semi-direct aerosol effect
JA  - J. Geophys. Res.
JO  - Journal of Geophysical Research
VL  - 115
SP  - D08203
DO  - 10.1029/2009JD012637
ER  -

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