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A New Extension Of The Ackerman & Marley Sedimentation Model For Greater Cloud Diversity

Presentation #207.04 in the session “Extrasolar Planets II”.

Published onJun 18, 2021
A New Extension Of The Ackerman & Marley Sedimentation Model For Greater Cloud Diversity

The observed atmospheric spectrum of exoplanets and brown dwarfs depends critically on the presence and distribution of atmospheric condensates. The Ackerman and Marley (2001) methodology for predicting the vertical distribution of condensate particles is widely used to study radiative transfer in cloudy atmospheres and has recently been re-implemented in an open-source python package VIRGA. The model is founded upon the assumption of a balance between upward turbulent diffusion and downward sedimentation in horizontally uniform cloud decks and relies upon input parameter fsed, the sedimentation efficiency, which until now has been held constant. The relative simplicity of this model renders it useful for retrieval studies due to its rapidly attainable solutions and thus can be computed and compared to data within a manageable timeframe. However, comparisons with more complex microphysical models such as CARMA have highlighted inconsistencies between the two approaches, namely that the cloud parameters needed for radiative transfer produced by VIRGA disagree with those produced by CARMA. In an attempt to address these discrepancies, we have extended the original Ackerman and Marley methodology in VIRGA to allow for non-constant values of fsed, in particular those that vary with altitude. In this contribution, I will discuss how this development effectuates a plethora of alternative cloud profiles that are otherwise unattainable by constant values of fsed and explore whether the ensuing flexibility of VIRGA renders it more agreeable with increasingly complex models and observed data.


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