980 research outputs found

    The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer (article)

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    This is the author accepted manuscript. The final version is available from EDP Sciences for European Southern Observatory (ESO) via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32593In this work we have performed a series of simulations of the atmosphere of GJ 1214b assuming different metallicities using the Met Office Unified Model (UM). The UM is a general circulation model (GCM) that solves the deep, nonhydrostatic equations of motion and uses a flexible and accurate radiative transfer scheme, based on the two-stream and correlated-k approximations, to calculate the heating rates. In this work we consistently couple a well-tested Gibbs energy minimisation scheme to solve for the chemical equilibrium abundances locally in each grid cell for a general set of elemental abundances, further improving the flexibility and accuracy of the model. As the metallicity of the atmosphere is increased we find significant changes in the dynamical and thermal structure, with subsequent implications for the simulated phase curve. The trends that we find are qualitatively consistent with previous works, though with quantitative differences. We investigate in detail the effect of increasing the metallicity by splitting the mechanism into constituents, involving the mean molecular weight, the heat capacity and the opacities. We find the opacity effect to be the dominant mechanism in altering the circulation and thermal structure. This result highlights the importance of accurately computing the opacities and radiative transfer in 3D GCMs.This work is partly supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013 Grant Agreement No. 247060-PEPS and grant No. 320478-TOFU). BD acknowledges funding from the European Research Council (ERC) under the European Unions Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 336792 and thanks the University of Exeter for support through a PhD studentship. DSA acknowledges support from the NASA Astrobiology Program through the Nexus for Exoplanet System Science. NJM and JG’s contributions were in part funded by a Leverhulme Trust Research Project Grant, and in part by a University of Exeter College of Engineering, Mathematics and Physical Sciences studentship. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility. This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure. This work also used the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS and the University of Exeter. Material produced using Met Office Software

    Exploring the climate of Proxima B with the Met Office Unified Model

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    This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.The corrigendum to this article is in ORE at: http://hdl.handle.net/10871/34331We present results of simulations of the climate of the newly discovered planet Proxima Centauri B, performed using the Met Office Unified Model (UM). We examine the responses of both an ‘Earth-like’ atmosphere and simplified nitrogen and trace carbon dioxide atmosphere to the radiation likely received by Proxima Centauri B. Additionally, we explore the effects of orbital eccentricity on the planetary conditions using a range of eccentricities guided by the observational constraints. Overall, our results are in agreement with previous studies in suggesting Proxima Centauri B may well have surface temperatures conducive to the presence of liquid water. Moreover, we have expanded the parameter regime over which the planet may support liquid water to higher values of eccentricity (& 0.1) and lower incident fluxes (881.7 W m−2 ) than previous work. This increased parameter space arises because of the low sensitivity of the planet to changes in stellar flux, a consequence of the stellar spectrum and orbital configuration. However, we also find interesting differences from previous simulations, such as cooler mean surface temperatures for the tidally-locked case. Finally, we have produced high resolution planetary emission and reflectance spectra, and highlight signatures of gases vital to the evolution of complex life on Earth (oxygen, ozone and carbon dioxide).I.B., J.M. and P.E. acknowledge the support of a Met Office Academic Partnership secondment. B.D. thanks the University of Exeter for support through a Ph.D. studentship. N.J.M. and J.G.’s contributions were in part funded by a Leverhulme Trust Research Project Grant, and in part by a University of Exeter College of Engineering, Mathematics and Physical Sciences studentship. We acknowledge use of the MONSooN system, a collaborative facility supplied under the Joint Weather and Climate Research Programme, a strategic partnership between the Met Office and the Natural Environment Research Council. This work also used the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS and the University of Exeter

    The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b

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    We investigate the impact of clouds on the atmosphere of GJ~1214b using the radiatively-coupled, phase-equilibrium cloud model {\sc EddySed} coupled to the {\sc Unified Model} general circulation model. We find that, consistent with previous investigations, high metallicity (100×100\times solar) and clouds with large vertical extents (a sedimentation factor of fsed=0.1f_\mathrm{sed} = 0.1) are required to best match the observations, although metallicities even higher than those investigated here may be required to improve agreement further. We additionally find that in our case which best matches the observations (fsed=0.1f_\mathrm{sed}=0.1), the velocity structures change relative to the clear sky case with the formation of a superrotating jet being suppressed, although further investigation is required to understand the cause of the suppression. The increase in cloud extent with fsedf_\mathrm{sed} results in a cooler planet due to a higher albedo, causing the atmosphere to contract. This also results in a reduced day-night contrast seen in the phase curves, although the introduction of cloud still results in a reduction of the phase offset. We additionally investigate the impact the the {\sc Unified Model}'s pseudo-spherical irradiation scheme on the calculation of heating rates, finding that the introduction of nightside shortwave heating results in slower mid-latitude jets compared to the plane parallel irradiation scheme used in previous works. We also consider the impact of a gamma distribution, as opposed to a log-normal distribution, for the distribution of cloud particle radii and find the impact to be relatively minor.Comment: Accepted to MNRA

    Results from a set of three-dimensional numerical experiments of a hot Jupiter atmosphere.

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    ArticleThis is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.We present highlights from a large set of simulations of a hot Jupiter atmosphere, nominally based on HD 209458b, aimed at exploring both the evolution of the deep atmosphere, and the acceleration of the zonal flow or jet. We find the occurrence of a super-rotating equatorial jet is robust to changes in various parameters, and over long timescales, even in the absence of strong inner or bottom boundary drag. This jet is diminished in one simulation only, where we strongly force the deep atmosphere equator–to–pole temperature gradient over long timescales. Finally, although the eddy momentum fluxes in our atmosphere show similarities with the proposed mechanism for accelerating jets on tidally-locked planets, the picture appears more complex. We present tentative evidence for a jet driven by a combination of eddy momentum transport and mean flow

    The EU and Asia within an evolving global order: what is Europe? Where is Asia?

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    The papers in this special edition are a very small selection from those presented at the EU-NESCA (Network of European Studies Centres in Asia) conference on "the EU and East Asia within an Evolving Global Order: Ideas, Actors and Processes" in November 2008 in Brussels. The conference was the culmination of three years of research activity involving workshops and conferences bringing together scholars from both regions primarily to discuss relations between Europe and Asia, perceptions of Europe in Asia, and the relationship between the European regional project and emerging regional forms in Asia. But although this was the last of the three major conferences organised by the consortium, it in many ways represented a starting point rather than the end; an opportunity to reflect on the conclusions of the first phase of collaboration and point towards new and continuing research agendas for the future

    Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parametrized, phase-equilibrium cloud formation code EDDYSED (article)

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    This is the final version. Available from OUP via the DOI in this recordThe dataset associated with this article is available in ORE: https://doi.org/10.24378/exe.1483We present results from 3D radiative-hydrodynamical simulations of HD 209458b with a fully coupled treatment of clouds using the EDDYSED code, critically, including cloud radiative feedback via absorption and scattering. We demonstrate that the thermal and optical structure of the simulated atmosphere is markedly different, for the majority of our simulations, when including cloud radiative effects, suggesting this important mechanism cannot be neglected. Additionally, we further demonstrate that the cloud structure is sensitive to not only the cloud sedimentation efficiency (termed fsed in EDDYSED), but also the temperature–pressure profile of the deeper atmosphere. We briefly discuss the large difference between the resolved cloud structures of this work, adopting a phase-equilibrium and parametrized cloud model, and our previous work incorporating a cloud microphysical model, although a fairer comparison where, for example, the same list of constituent condensates is included in both treatments is reserved for a future work. Our results underline the importance of further study into the potential condensate size distributions and vertical structures, as both strongly influence the radiative impact of clouds on the atmosphere. Finally, we present synthetic observations from our simulations reporting an improved match, over our previous cloud-free simulations, to the observed transmission, HST WFC3 emission, and 4.5 μm Spitzer phase curve of HD 209458b. Additionally, we find all our cloudy simulations have an apparent albedo consistent with observations.Leverhulme TrustScience and Technology Facilities Council (STFC

    Observable signatures of wind-driven chemistry with a fully consistent three dimensional radiative hydrodynamics model of HD 209458b (article)

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    This is the final version of the article. Available from American Astronomical Society / IOP Publishing via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32579We present a study of the effect of wind-driven advection on the chemical composition of hot Jupiter atmospheres using a fully-consistent 3D hydrodynamics, chemistry and radiative transfer code, the Met Office Unified Model (UM). Chemical modelling of exoplanet atmospheres has primarily been restricted to 1D models that cannot account for 3D dynamical processes. In this work we couple a chemical relaxation scheme to the UM to account for the chemical interconversion of methane and carbon monoxide. This is done consistently with the radiative transfer meaning that departures from chemical equilibrium are included in the heating rates (and emission) and hence complete the feedback between the dynamics, thermal structure and chemical composition. In this letter we simulate the well studied atmosphere of HD 209458b. We find that the combined effect of horizontal and vertical advection leads to an increase in the methane abundance by several orders of magnitude; directly opposite to the trend found in previous works. Our results demonstrate the need to include 3D effects when considering the chemistry of hot Jupiter atmospheres. We calculate transmission and emission spectra, as well as the emission phase curve, from our simulations. We conclude that gas-phase non-equilibrium chemistry is unlikely to explain the model–observation discrepancy in the 4.5 µm Spitzer/IRAC channel. However, we highlight other spectral regions, observable with the James Webb Space Telescope, where signatures of wind-driven chemistry are more prominent.BD and DKS acknowledge funding from the European Research Council (ERC) under the European Unions Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 336792. NJM is part funded by a Leverhulme Trust Research Project Grant. JM and IAB acknowledge the support of a Met Office Academic Partnership secondment. ALC is funded by an STFC studentship. DSA acknowledges support from the NASA Astrobiology Program through the Nexus for Exoplanet System Science. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility. This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure

    Dynamics of sediment flux to a bathyal continental margin section through the Paleocene–Eocene Thermal Maximum

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    The response of the Earth system to greenhouse-gas-driven warming is of critical importance for the future trajectory of our planetary environment. Hyperthermal events – past climate transients with global-scale warming significantly above background climate variability – can provide insights into the nature and magnitude of these responses. The largest hyperthermal of the Cenozoic was the Paleocene–Eocene Thermal Maximum (PETM ∼ 56 Ma). Here we present new high-resolution bulk sediment stable isotope and major element data for the classic PETM section at Zumaia, Spain. With these data we provide a new detailed stratigraphic correlation to other key deep-ocean and terrestrial PETM reference sections. With this new correlation and age model we are able to demonstrate that detrital sediment accumulation rates within the Zumaia continental margin section increased more than 4-fold during the PETM, representing a radical change in regional hydrology that drove dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is that detrital accumulation rates remain high throughout the body of the PETM, and even reach peak values during the recovery phase of the characteristic PETM carbon isotope excursion (CIE). Using a series of Earth system model inversions, driven by the new Zumaia carbon isotope record, we demonstrate that the silicate weathering feedback alone is insufficient to recover the PETM CIE, and that active organic carbon burial is required to match the observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic carbon sequestration coincides with the peak in detrital accumulation rates observed at Zumaia. Based on these results, we hypothesise that orbital-scale variations in subtropical hydro-climates, and their subsequent impact on sediment dynamics, may contribute to the rapid climate and CIE recovery from peak-PETM conditions
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