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Title: A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

Abstract

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements,more » respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.« less

Authors:
;  [1]
  1. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan)
Publication Date:
OSTI Identifier:
22663902
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALTITUDE; AMMONIA; COALESCENCE; COMPARATIVE EVALUATIONS; CONDENSATES; CONDENSATION NUCLEI; CONVECTION; DENSITY; FORECASTING; ICE; JUPITER PLANET; NUCLEATION; SATELLITE ATMOSPHERES; SATELLITES; SIMULATION; SPECTRA; THICKNESS; TRANSMISSION; VELOCITY

Citation Formats

Ohno, Kazumasa, and Okuzumi, Satoshi. A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/261.
Ohno, Kazumasa, & Okuzumi, Satoshi. A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds. United States. doi:10.3847/1538-4357/835/2/261.
Ohno, Kazumasa, and Okuzumi, Satoshi. Wed . "A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds". United States. doi:10.3847/1538-4357/835/2/261.
@article{osti_22663902,
title = {A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds},
author = {Ohno, Kazumasa and Okuzumi, Satoshi},
abstractNote = {A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.},
doi = {10.3847/1538-4357/835/2/261},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
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  • If the aerosol composition and the shape of the aerosol size distribution below cloud are uniform the vertical profile of cloud condensation nuclei concentration can be retrieved entirely from surface measurements, thus providing the potential for long-term measurements of CCN concentrations near cloud base. We have used a combination of aircraft, surface in situ, and surface remote sensing measurements to test various aspects of the retrieval scheme. Our analysis leads us to the following conclusions. If in situ measurements of extinction are used the CCN retrieval works better than expected for the high supersaturations of the in situ CCN measurements.more » The retrieval works better for supersaturations of 0.1% than for 1%, because CCN concentrations at 0.1% are controlled by the same particles that control extinction and backscatter. The retrieval of the vertical profile of the humidification factor is not the major limitation of the CCN retrieval scheme. The performance of the retrieval varies significantly from day to day, particularly at 1% supersaturation. Vertical structure in the aerosol size distribution and composition is the dominant source of error in the CCN retrieval, but this vertical structure is difficult to measure from remote sensing at visible wavelengths.« less
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  • A model of the interaction between incident precipitation and H/sub 2/ atmospheres is described. The local degraded primary and secondary electron density distributions are calculated by using the continuous slowing down approximation. The altitude distribution of the ionization rate and various H And EUV H/sub 2/ emissions are calculated for four different incident electron spectra. A total EUV H/sub 2/ emission efficiency of 10.6 kR/incident erg cm/sup -2/ s/sup -1/ is obtained for a pure H/sub 2/ atmosphere. Comparison with the Voyager Jupiter observations indicates that an incident energy flux of about 8 erg cm/sup -2/ s/sup -1/ was presentmore » at the time of the encounter if the emission is located in an H/sub 2/-dominated region. The local thermospheric heating rate was about 4 ergs cm/sup -2/ s/sup -1/ for Jupiter and of the order of 0.1 erg cm/sup -2/ s/sup -1/ for Saturn. A globally averaged atomic hydrogen production rate of approx.1 x 10/sup 10/ atoms/cm/sup 2/ s/sup -1/ is induced by the Jovian auroral electron precipitation, largely exceeding the solar EUV dissociation rate.« less
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