817 research outputs found
A phase-space study of jet formation in planetary-scale fluids
The interaction between planetary waves and an arbitrary zonal flow is
studied from a phase-space viewpoint. Using the Wigner distribution, a
planetary wave Vlasov equation is derived that includes the contribution of the
mean flow to the zonal potential vorticity gradient. This equation is applied
to the problem of planetary wave modulational instability, where it is used to
predict a fastest growing mode of finite wavenumber. A wave-mean flow numerical
model is used to test the analytical predictions, and an intuitive explanation
of modulational instability and jet asymmetry is given via the motion of
planetary wavepackets in phase space.Comment: 10 pages, 10 figure
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
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
Qatar Islamic Archaeology and Heritage Project: End of Season Report : 2011-2012
International audienc
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