Publication Abstracts

Gao et al. 2018

Gao, P., M.S. Marley, and A.S. Ackerman, 2018: Sedimentation efficiency of condensation clouds in substellar atmospheres. Astrophys. J., 855, no. 2, 86, doi:10.3847/1538-4357/aab0a1.

Condensation clouds in substellar atmospheres have been widely inferred from spectra and photometric variability. Up until now, their horizontally averaged vertical distribution and mean particle size have been largely characterized using models, one of which is the eddy diffusion-sedimentation model from Ackerman & Marley (2001) that relies on a sedimentation efficiency parameter, fsed, to determine the vertical extent of clouds in the atmosphere. However, the physical processes controlling the vertical structure of clouds in substellar atmospheres are not well understood. In this work, we derive trends in fsed across a large range of eddy diffusivities (Kzz, gravities, material properties, and cloud formation pathways by fitting cloud distributions calculated by a more detailed cloud microphysics model. We find that fsed is dependent on Kzz but not gravity, when Kzzis held constant. fsed is most sensitive to the nucleation rate of cloud particles, as determined by material properties like surface energy and molecular weight. High surface energy materials form fewer, larger cloud particles, leading to large fsed (>1), and vice versa for materials with low surface energy. For cloud formation via heterogeneous nucleation, fsed is sensitive to the condensation nuclei flux and radius, connecting cloud formation in substellar atmospheres to the objects' formation environments and other atmospheric aerosols. These insights could lead to improved cloud models that help us better understand substellar atmospheres. For example, we demonstrate that fsed could increase with increasing cloud base depth in an atmosphere, shedding light on the nature of the brown dwarf L/T transition.

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BibTeX Citation

  author={Gao, P. and Marley, M. S. and Ackerman, A. S.},
  title={Sedimentation efficiency of condensation clouds in substellar atmospheres},
  journal={Astrophysical Journal},

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RIS Citation

ID  - ga05200z
AU  - Gao, P.
AU  - Marley, M. S.
AU  - Ackerman, A. S.
PY  - 2018
TI  - Sedimentation efficiency of condensation clouds in substellar atmospheres
JA  - Astrophys. J.
JO  - Astrophysical Journal
VL  - 855
IS  - 2
SP  - 86
DO  - 10.3847/1538-4357/aab0a1
ER  -

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