1,045 research outputs found
Atmospheric Circulation of Terrestrial Exoplanets
The investigation of planets around other stars began with the study of gas
giants, but is now extending to the discovery and characterization of
super-Earths and terrestrial planets. Motivated by this observational tide, we
survey the basic dynamical principles governing the atmospheric circulation of
terrestrial exoplanets, and discuss the interaction of their circulation with
the hydrological cycle and global-scale climate feedbacks. Terrestrial
exoplanets occupy a wide range of physical and dynamical conditions, only a
small fraction of which have yet been explored in detail. Our approach is to
lay out the fundamental dynamical principles governing the atmospheric
circulation on terrestrial planets--broadly defined--and show how they can
provide a foundation for understanding the atmospheric behavior of these
worlds. We first survey basic atmospheric dynamics, including the role of
geostrophy, baroclinic instabilities, and jets in the strongly rotating regime
(the "extratropics") and the role of the Hadley circulation, wave adjustment of
the thermal structure, and the tendency toward equatorial superrotation in the
slowly rotating regime (the "tropics"). We then survey key elements of the
hydrological cycle, including the factors that control precipitation, humidity,
and cloudiness. Next, we summarize key mechanisms by which the circulation
affects the global-mean climate, and hence planetary habitability. In
particular, we discuss the runaway greenhouse, transitions to snowball states,
atmospheric collapse, and the links between atmospheric circulation and CO2
weathering rates. We finish by summarizing the key questions and challenges for
this emerging field in the future.Comment: Invited review, in press for the Arizona Space Science Series book
"Comparative Climatology of Terrestrial Planets" (S. Mackwell, M. Bullock,
and J. Harder, editors). 56 pages, 26 figure
A short history of the Science and Mathematics Education Centre at Curtin University
This article is presented in four parts. In the first part, I describe the foundation of the Science and Mathematics Education Centre (SMEC) at Curtin University. In the second part, I explain the development of SMEC’s teaching and research capacity under its three directors. In the third section, I describe how federal government support of SMEC as a national Key Centre for Teaching and Research in School Science and Mathematics provided enhanced postgraduate study opportunities for science and mathematics teachers throughout Australia by offering degree programs through distance education and face-to-face contact, short courses, and seminars. At the same time, research and teaching capacity of the academic staff was enhanced through the internationalisation of the programs being offered. In the final section, I describe current and future developments at SMEC
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
Derek Mahon's Seascapes Mediated through Greece: Antiquity in Modernity, Nature in Abstraction.
The article investigates various approaches to seascape in selected poems of the contemporary Irish poet, Derek Mahon, set against the background of references to Michael Longley, Seamus Heaney or Odysseus Elytis. The sea provides a perspective that cannot be overestimated in trying to get an insight into the communication and the clash between the culture of the South and the North. The two nations have often glimpsed at their reflection in the mirror of the surrounding seas, their history and mentality determined by their geographical position and largely insular experience. Elements such as the isolation from the mainland; the perception of the sea as a personification of the force ruling over life and death, as a threat and a promise; or the focus on some characteristic natural phenomena such as light or surface dominate the seascape imagery both in Greek and Irish literature. The sea often constitutes a border of antagonistic and complementary worlds: dream and reality, light and darkness, male and female, the real world and the underworld – and the vantage point of the poet changes accordingly. Some poems under discussion also explore a series of myths linked with the sea, the best known of which, the Odyssey, has remained a frame of reference for numerous contemporary Greek and Irish poets. Elytis's Cyclades or Longley's Mayo provide us with examples of 'private homelands'. As Longley once observed, “his part of Mayo” reminds him of Ithaca (sandy and remote) and of Greece in general: “I’ve often thought that that part of Ireland . . . looks like Greece. Or Greece looks like a dust-bowl version of Ireland,” which triggers further deliberations on seascape as the common ground for the two countries.
Just as Elytis's Cyclades or Longley's Mayo, Mahon’s Cyclades provide us with examples of 'private homelands'. The focus of this article is Derek Mahon’s seascapes: purely Greek (‘Aphrodite’s Pool’), Irish seen through the prism of the Greek ones (‘Achill’) and purely Irish (‘Recalling Aran’). The level of abstraction in the last category is compared with Odysseus Elytis’s imagery of the Cyclades, while the first poem demystifies a practice which I termed as ‘myth trading’, one of consumerist tourism techniques
Evidence for 9 planets in the HD 10180 system
We re-analyse the HARPS radial velocities of HD 10180 and calculate the
probabilities of models with differing numbers of periodic signals in the data.
We test the significance of the seven signals, corresponding to seven
exoplanets orbiting the star, in the Bayesian framework and perform comparisons
of models with up to nine periodicities. We use posterior samplings and
Bayesian model probabilities in our analyses together with suitable prior
probability densities and prior model probabilities to extract all the
significant signals from the data and to receive reliable uncertainties for the
orbital parameters of the six, possibly seven, known exoplanets in the system.
According to our results, there is evidence for up to nine planets orbiting HD
10180, which would make this this star a record holder in having more planets
in its orbits than there are in the Solar system. We revise the uncertainties
of the previously reported six planets in the system, verify the existence of
the seventh signal, and announce the detection of two additional statistically
significant signals in the data. If of planetary origin, these two additional
signals would correspond to planets with minimum masses of 5.1
and 1.9 M on orbits with 67.55 and
9.655 days periods (denoted using the 99% credibility
intervals), respectively.Comment: 12 pages, 7 figures, accepted for publication in the Astronomy and
Astrophysic
Eliciting risk preferences that predict risky health behaviour: A comparison of two approaches
Information on attitudes to risk could increase understanding of and explain risky health behaviors. We investigate two approaches to eliciting risk preferences in the health domain, a novel “indirect” lottery elicitation approach with health states as outcomes and a “direct” approach where respondents are asked directly about their willingness to take risks. We compare the ability of the two approaches to predict health-related risky behaviors in a general adult population. We also investigate a potential framing effect in the indirect lottery elicitation approach. We find that risk preferences elicited using the direct approach can better predict health-related risky behavior than those elicited using the indirect approach. Moreover, a seemingly innocuous change to the framing of the lottery question results in significantly different risk preference estimates, and conflicting conclusions about the ability of the indicators to predict risky health behaviors
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Martian climate
Valley networks are some of the strongest lines of evidence for extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However, their purported absence on certain ancient terrains, such as Arabia Terra, is at variance with patterns of precipitation as predicted by "warm and wet" climate models. This disagreement has contributed to the development of an alternative "icy highlands" scenario, whereby valley networks were formed by the melting of highland ice sheets. Here, we show through regional mapping that Arabia Terra shows evidence for extensive networks of sinuous ridges. We interpret these ridge features as inverted fluvial channels that formed in the Noachian, before being subject to burial and exhumation. The inverted channels developed on extensive aggrading flood plains. As the inverted channels are both sourced in, and traverse across, Arabia Terra, their formation is inconsistent with discrete, localized sources of water, such as meltwater from highland ice sheets. Our results are instead more consistent with an early Mars that supported widespread precipitation and runoff
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