Publication Abstracts

Ackerman et al. 1995

Ackerman, A.S., O.B. Toon, and P.V. Hobbs, 1995: Numerical modeling of ship tracks produced by injections of cloud condensation nuclei into marine stratiform clouds. J. Geophys. Res., 100, 7121-7133, doi:10.1029/95JD00026.

Ship tracks are long-lived, linear regions of enhanced reflectivity in low-lying marine clouds that appear in satellite imagery downwind of ships. Ship tracks were first observed as cloud lines in visible satellite imagery (type 1). A second (and more common) type of ship track (type 2), which is masked at visible wavelenghts by natural variability in cloud reflectivity, is seen at near-infrared wavelengths in satellite imagery. A one-dimensional model is used to simulate measurements of both types of ship tracks and to investigate interactions between aerosol and cloud microphysics, radiative transfer, and turbulent mixing in the cloud-topped marine boundary layer that lead to the formation and provide for the persistence of ship tracks. We find that cloud condensation nuclei (CCN) injections can account for many of the observed properties of ship tracks. Higher CCN concentrations produced increased droplet concentrations, which enhance cloud reflectivity by reducing droplet radius and increasing droplet cross-sectional area. The smaller droplets also reduce the drizzle rate, whch can allow cloud water to increase under some conditions, thereby leading to higher cloud reflectivity. However, smaller droplets also evaporate more readily below cloud base. Increased evaportation reduces mixing between the cloud and the subcloud layers during daytime, which causes a decrease in cloud water. The distinction between the two types of ship tracks is suggested to be due to differences in ambient concentrations of CCN that cause variations in turbulent mixing in the boundary layer, through the effect of cloud droplet concentrations on cloud-top longwave radiative cooling. The mode predicts lifetimes of > 1 day and > 2 days for the simulated type 1 and type 2 tracks, respectively. In the atmosphere, processes not treated in the model, such as horizontal dispersion and changes in large-scale atmospheric conditions, may limit ship track lifetimes.

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BibTeX Citation

@article{ac03000u,
  author={Ackerman, A. S. and Toon, O. B. and Hobbs, P. V.},
  title={Numerical modeling of ship tracks produced by injections of cloud condensation nuclei into marine stratiform clouds},
  year={1995},
  journal={J. Geophys. Res.},
  volume={100},
  pages={7121--7133},
  doi={10.1029/95JD00026},
}

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RIS Citation

TY  - JOUR
ID  - ac03000u
AU  - Ackerman, A. S.
AU  - Toon, O. B.
AU  - Hobbs, P. V.
PY  - 1995
TI  - Numerical modeling of ship tracks produced by injections of cloud condensation nuclei into marine stratiform clouds
JA  - J. Geophys. Res.
VL  - 100
SP  - 7121
EP  - 7133
DO  - 10.1029/95JD00026
ER  -

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