Simulating the cloudy atmospheres of HD 209458 b and HD 189733 b with the 3D Met Office Unified Model

被引:17
作者
Lines, S. [1 ]
Mayne, N. J. [1 ]
Boutle, I. A. [1 ,3 ]
Manners, J. [1 ,3 ]
Lee, G. K. H. [4 ,5 ,6 ]
Helling, Ch. [4 ,5 ]
Drummond, B. [1 ]
Amundsen, D. S. [1 ,7 ,8 ]
Goyal, J. [1 ]
Acreman, D. M. [1 ,2 ]
Tremblin, P. [9 ]
Kerslake, M. [1 ]
机构
[1] Univ Exeter, Coll Engn Math & Phys Sci, Phys & Astron, Exeter EX4 4QL, Devon, England
[2] Univ Exeter, Coll Engn Math & Phys Sci, Comp Sci, Exeter EX4 4QF, Devon, England
[3] Met Off, FitzRoy Rd, Exeter EX1 3PB, Devon, England
[4] Univ St Andrews, Ctr Exoplanet Sci, St Andrews KY16 9SS, Fife, Scotland
[5] Univ St Andrews, Sch Phys & Astron, St Andrews KY16 9SS, Fife, Scotland
[6] Univ Oxford, Dept Phys, Atmospher Ocean & Planetary Phys, Oxford OX1 3PU, England
[7] NASA, Goddard Inst Space Studies, 2880 Broadway, New York, NY 10025 USA
[8] Columbia Univ, Dept Appl Phys & Appl Math, New York, NY 10027 USA
[9] Univ Paris Saclay, Univ Paris Sud, UVSQ, Maison Simulat,CEA,CNRS, F-91191 Gif Sur Yvette, France
基金
欧洲研究理事会;
关键词
planets and satellites: atmospheres; methods: numerical; hydrodynamics; radiative transfer; scattering; planets and satellites: gaseous planets; PARTIAL-DIFFERENTIAL-EQUATIONS; BROWN DWARFS; DUST FORMATION; CHEMICAL-COMPOSITION; PHASE CURVES; EXOPLANET; CIRCULATION; WATER; ABSORPTION; SCATTERING;
D O I
10.1051/0004-6361/201732278
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Aims. To understand and compare the 3D atmospheric structure of HD 209458 b and HD 189733 b, focusing on the formation and distribution of cloud particles, as well as their feedback on the dynamics and thermal profile. Methods. We coupled the 3D Met Office Unified Model (UM), including detailed treatments of atmospheric radiative transfer and dynamics, to a kinetic cloud formation scheme. The resulting model self-consistently solves for the formation of condensation seeds, surface growth and evaporation, gravitational settling and advection, cloud radiative feedback via absorption, and crucially, scattering. We used fluxes directly obtained from the UM to produce synthetic spectral energy distributions and phase curves. Results. Our simulations show extensive cloud formation in both HD 209458 b and HD 189733 b. However, cooler temperatures in the latter result in higher cloud particle number densities. Large particles, reaching 1 mu m in diameter, can form due to high particle growth velocities, and sub-mu m particles are suspended by vertical flows leading to extensive upper-atmosphere cloud cover. A combination of meridional advection and efficient cloud formation in cooler high latitude regions, results in enhanced cloud coverage for latitudes above 30 degrees and leads to a zonally banded structure for all our simulations. The cloud bands extend around the entire planet, for HD 209458 b and HD 189733 b, as the temperatures, even on the day side, remain below the condensation temperature of silicates and oxides. Therefore, the simulated optical phase curve for HD 209458 b shows no "offset", in contrast to observations. Efficient scattering of stellar irradiation by cloud particles results in a local maximum cooling of up to 250 K in the upper atmosphere, and an advection-driven fluctuating cloud opacity causes temporal variability in the thermal emission. The inclusion of this fundamental cloud-atmosphere radiative feedback leads to significant differences with approaches neglecting these physical elements, which have been employed to interpret observations and determine thermal profiles for these planets. This suggests that readers should be cautious of interpretations neglecting such cloud feedback and scattering, and that the subject merits further study.
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页数:27
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