49 research outputs found
TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI): Motivations and protocol version 1.0
This is the final version. Available from European Geosciences Union via the DOI in this record.âŻExoCAM (Wolf and Toon, 2015) is available on GitHub: https://github.com/storyofthewolf/ExoCAM (last access: 8 February 2020). The Met Office Unified Model is available for use under license; see http://www.metoffice.gov.uk/research/modelling-systems/unified-model (Met Office, 2020, last access: 8 February 2020). ROCKE-3D is public domain software and available for download for free from https://simplex.giss.nasa.gov/gcm/ROCKE-3D/ (last access: 8 February 2020, NASA Goddard Institute for Space Studies, 2020a). Annual tutorials for new users take place annually, whose recordings are freely available online at https://www.youtube.com/user/NASAGISStv/playlists?view=50&sort=dd&shelf_id=15 (last access: 8 February 2020b, NASA Goddard Institute for Space Studies, 2020b). LMDG is obtainable upon request from Martin Turbet ([email protected]) and François Forget ([email protected]).Upcoming telescopes such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT), the Thirty Meter Telescope (TMT) or the Giant Magellan Telescope (GMT) may soon be able to characterize, through transmission, emission or reflection spectroscopy, the atmospheres of rocky exoplanets orbiting nearby M dwarfs. One of the most promising candidates is the late M-dwarf system TRAPPIST-1, which has seven known transiting planets for which transit timing variation (TTV) measurements suggest that they are terrestrial in nature, with a possible enrichment in volatiles. Among these seven planets, TRAPPIST-1e seems to be the most promising candidate to have habitable surface conditions, receiving ~ 66 % of the Earth's incident radiation and thus needing only modest greenhouse gas inventories to raise surface temperatures to allow surface liquid water to exist. TRAPPIST-1e is, therefore, one of the prime targets for the JWST atmospheric characterization. In this context, the modeling of its potential atmosphere is an essential step prior to observation. Global climate models (GCMs) offer the most detailed way to simulate planetary atmospheres. However, intrinsic differences exist between GCMs which can lead to different climate prediction and thus observability of gas and/or cloud features in transmission and thermal emission spectra. Such differences should preferably be known prior to observations. In this paper we present a protocol to intercompare planetary GCMs. Four testing cases are considered for TRAPPIST-1e, but the methodology is applicable to other rocky exoplanets in the habitable zone. The four test cases included two land planets composed of modern-Earth and pure-CO2 atmospheres and two aqua planets with the same atmospheric compositions. Currently, there are four participating models (LMDG, ROCKE-3D, ExoCAM, UM); however, this protocol is intended to let other teams participate as well.NASA Planetary Science Division's Internal Scientist Funding ModelEuropean Unionâs Horizon 2020NASA Astrobiology Progra
Impact of Space Weather on Climate and Habitability of Terrestrial Type Exoplanets
The current progress in the detection of terrestrial type exoplanets has
opened a new avenue in the characterization of exoplanetary atmospheres and in
the search for biosignatures of life with the upcoming ground-based and space
missions. To specify the conditions favorable for the origin, development and
sustainment of life as we know it in other worlds, we need to understand the
nature of astrospheric, atmospheric and surface environments of exoplanets in
habitable zones around G-K-M dwarfs including our young Sun. Global environment
is formed by propagated disturbances from the planet-hosting stars in the form
of stellar flares, coronal mass ejections, energetic particles, and winds
collectively known as astrospheric space weather. Its characterization will
help in understanding how an exoplanetary ecosystem interacts with its host
star, as well as in the specification of the physical, chemical and biochemical
conditions that can create favorable and/or detrimental conditions for
planetary climate and habitability along with evolution of planetary internal
dynamics over geological timescales. A key linkage of (astro) physical,
chemical, and geological processes can only be understood in the framework of
interdisciplinary studies with the incorporation of progress in heliophysics,
astrophysics, planetary and Earth sciences. The assessment of the impacts of
host stars on the climate and habitability of terrestrial (exo)planets will
significantly expand the current definition of the habitable zone to the
biogenic zone and provide new observational strategies for searching for
signatures of life. The major goal of this paper is to describe and discuss the
current status and recent progress in this interdisciplinary field and to
provide a new roadmap for the future development of the emerging field of
exoplanetary science and astrobiology.Comment: 206 pages, 24 figures, 1 table; Review paper. International Journal
of Astrobiology (2019
Mineral dust increases the habitability of terrestrial planets but confounds biomarker detection
Identification of habitable planets beyond our solar system is a key goal of current and future space missions. Yet habitability depends not only on the stellar irradiance, but equally on constituent parts of the planetary atmosphere. Here we show, for the first time, that radiatively active mineral dust will have a significant impact on the habitability of Earth-like exoplanets. On tidally-locked planets, dust cools the day-side and warms the night-side, significantly widening the habitable zone. Independent of orbital configuration, we suggest that airborne dust can postpone planetary water loss at the inner edge of the habitable zone, through a feedback involving decreasing ocean coverage and increased dust loading. The inclusion of dust significantly obscures key biomarker gases (e.g. ozone, methane) in simulated transmission spectra, implying an important influence on the interpretation of observations.We demonstrate that future observational and theoretical studies of terrestrial exoplanets must consider the effect of dust
Thermodynamic efficiencies of an idealized global climate model
We employ the heat engine framework to derive a simple method for assessing the strength of irreversible processes in global climate models (GCMs). Using the explicit energy budget of an idealized GCM, we show that the thermodynamic efficiencies based on the net heating rate and frictional work rate provides a measure of physical and numerical irreversibilities present in either open (e.g., the Hadley circulation) or closed (e.g., the general circulation) circulations. In addition, we show that the Carnot efficiency is useful for assessing the maximum possible efficiency attained by closed circulations. Comparison of the work-based efficiency with that based on the net heating rate and the Carnot efficiency provides a gauge of how close to reversible and ideal the circulations are. A series of experiments with the idealized GCM demonstrate the usefulness of our method and show the sensitivity of an essentially reversible model to changes in physical and numerical parameters such as rotation period and resolution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47143/1/382_2005_Article_71.pd
Frequency of extreme Sahelian storms tripled since 1982 in satellite observations
The hydrological cycle is expected to intensify under global
warming, with studies reporting more frequent extreme rain
events in many regions of the world, and predicting increases in future flood frequency. Such early, predominantly mid-latitude observations are essential because of shortcomings within climate models in their depiction of convective rainfall. A globally important group of intense stormsâmesoscale convective systems (MCSs)âposes a particular challenge, because they organize dynamically on spatial scales that cannot be resolved by conventional climate models. Here, we use 35 years of satellite observations from the West African Sahel to reveal a persistent increase in the frequency of the most intense MCSs. Sahelian storms are some of the most powerful on the planet, and rain gauges in this region have recorded a rise in âextremeâ daily rainfall totals. We find that intense MCS frequency is only weakly related to the multidecadal recovery of Sahel annual rainfall, but is highly correlated with global land temperatures. Analysis of trends across Africa reveals that MCS intensification is limited to a narrow band south of the Sahara desert. During this period, wet-season Sahelian temperatures have not risen, ruling out the possibility that rainfall has intensified in response to locally warmer conditions. On the other hand, the meridional temperature gradient spanning the Sahel has increased in recent decades, consistent with anthropogenic forcing driving enhanced Saharan warming. We argue that Saharan warming intensifies convection within Sahelian MCSs through increased wind shear and changes to the Saharan air layer. The meridional gradient is projected to strengthen throughout the twenty-first century, suggesting that the Sahel will experience particularly marked increases in extreme rain. The remarkably rapid intensification of Sahelian MCSs since the 1980s sheds new light on the response of organized tropical convection to global warming, and challenges conventional projections made by general circulation models
Climate simulations for 1880-2003 with GISS modelE
We carry out climate simulations for 1880-2003 with GISS modelE driven by ten
measured or estimated climate forcings. An ensemble of climate model runs is
carried out for each forcing acting individually and for all forcing mechanisms
acting together. We compare side-by-side simulated climate change for each
forcing, all forcings, observations, unforced variability among model ensemble
members, and, if available, observed variability. Discrepancies between
observations and simulations with all forcings are due to model deficiencies,
inaccurate or incomplete forcings, and imperfect observations. Although there
are notable discrepancies between model and observations, the fidelity is
sufficient to encourage use of the model for simulations of future climate
change. By using a fixed well-documented model and accurately defining the
1880-2003 forcings, we aim to provide a benchmark against which the effect of
improvements in the model, climate forcings, and observations can be tested.
Principal model deficiencies include unrealistically weak tropical El Nino-like
variability and a poor distribution of sea ice, with too much sea ice in the
Northern Hemisphere and too little in the Southern Hemisphere. The greatest
uncertainties in the forcings are the temporal and spatial variations of
anthropogenic aerosols and their indirect effects on clouds.Comment: 44 pages; 19 figures; Final text accepted by Climate Dynamic
OSS (Outer Solar System): A fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt
The present OSS mission continues a long and bright tradition by associating
the communities of fundamental physics and planetary sciences in a single
mission with ambitious goals in both domains. OSS is an M-class mission to
explore the Neptune system almost half a century after flyby of the Voyager 2
spacecraft. Several discoveries were made by Voyager 2, including the Great
Dark Spot (which has now disappeared) and Triton's geysers. Voyager 2 revealed
the dynamics of Neptune's atmosphere and found four rings and evidence of ring
arcs above Neptune. Benefiting from a greatly improved instrumentation, it will
result in a striking advance in the study of the farthest planet of the Solar
System. Furthermore, OSS will provide a unique opportunity to visit a selected
Kuiper Belt object subsequent to the passage of the Neptunian system. It will
consolidate the hypothesis of the origin of Triton as a KBO captured by
Neptune, and improve our knowledge on the formation of the Solar system. The
probe will embark instruments allowing precise tracking of the probe during
cruise. It allows to perform the best controlled experiment for testing, in
deep space, the General Relativity, on which is based all the models of Solar
system formation. OSS is proposed as an international cooperation between ESA
and NASA, giving the capability for ESA to launch an M-class mission towards
the farthest planet of the Solar system, and to a Kuiper Belt object. The
proposed mission profile would allow to deliver a 500 kg class spacecraft. The
design of the probe is mainly constrained by the deep space gravity test in
order to minimise the perturbation of the accelerometer measurement.Comment: 43 pages, 10 figures, Accepted to Experimental Astronomy, Special
Issue Cosmic Vision. Revision according to reviewers comment