20,794 research outputs found
Atmospheric Circulation of Exoplanets
We survey the basic principles of atmospheric dynamics relevant to explaining
existing and future observations of exoplanets, both gas giant and terrestrial.
Given the paucity of data on exoplanet atmospheres, our approach is to
emphasize fundamental principles and insights gained from Solar-System studies
that are likely to be generalizable to exoplanets. We begin by presenting the
hierarchy of basic equations used in atmospheric dynamics, including the
Navier-Stokes, primitive, shallow-water, and two-dimensional nondivergent
models. We then survey key concepts in atmospheric dynamics, including the
importance of planetary rotation, the concept of balance, and scaling arguments
to show how turbulent interactions generally produce large-scale east-west
banding on rotating planets. We next turn to issues specific to giant planets,
including their expected interior and atmospheric thermal structures, the
implications for their wind patterns, and mechanisms to pump their east-west
jets. Hot Jupiter atmospheric dynamics are given particular attention, as these
close-in planets have been the subject of most of the concrete developments in
the study of exoplanetary atmospheres. We then turn to the basic elements of
circulation on terrestrial planets as inferred from Solar-System studies,
including Hadley cells, jet streams, processes that govern the large-scale
horizontal temperature contrasts, and climate, and we discuss how these
insights may apply to terrestrial exoplanets. Although exoplanets surely
possess a greater diversity of circulation regimes than seen on the planets in
our Solar System, our guiding philosophy is that the multi-decade study of
Solar-System planets reviewed here provides a foundation upon which our
understanding of more exotic exoplanetary meteorology must build.Comment: In EXOPLANETS, edited by S. Seager, to be published in the Spring of
2010 in the Space Science Series of the University of Arizona Press (Tucson,
AZ) (refereed; accepted for publication
Dissipative Boussinesq equations
The classical theory of water waves is based on the theory of inviscid flows.
However it is important to include viscous effects in some applications. Two
models are proposed to add dissipative effects in the context of the Boussinesq
equations, which include the effects of weak dispersion and nonlinearity in a
shallow water framework. The dissipative Boussinesq equations are then
integrated numerically.Comment: 40 pages, 15 figures, published in C. R. Mecanique 335 (2007) Other
author's papers can be downloaded at http://www.cmla.ens-cachan.fr/~dutyk
Fairy circle landscapes under the sea
Short-scale interactions yield large-scale vegetation patterns that, in turn,
shape ecosystem function across landscapes. Fairy circles, which are circular
patches bare of vegetation within otherwise continuous landscapes, are
characteristic features of semiarid grasslands. We report the occurrence of
submarine fairy circle seascapes in seagrass meadows and propose a simple model
that reproduces the diversity of seascapes observed in these ecosystems as
emerging from plant interactions within the meadow. These seascapes include two
extreme cases, a continuous meadow and a bare landscape, along with
intermediate states that range from the occurrence of persistent but isolated
fairy circles, or solitons, to seascapes with multiple fairy circles, banded
vegetation, and "leopard skin" patterns consisting of bare seascapes patterns
consisting of bare seascapes dotted with plant patches. The model predicts that
these intermediate seascapes extending across kilometers emerge as a
consequence of local demographic imbalances along with facilitative and
competitive interactions among the plants with a characteristic spatial scale
of 20 to 30 m, consistent with known drivers of seagrass performance. The
model, which can be extended to clonal growth plants in other landscapes
showing fairy rings, reveals that the different seascapes observed hold
diagnostic power as to the proximity of seagrass meadows to extinction points
that can be used to identify ecosystems at risks
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 Survey of Ocean Simulation and Rendering Techniques in Computer Graphics
This paper presents a survey of ocean simulation and rendering methods in
computer graphics. To model and animate the ocean's surface, these methods
mainly rely on two main approaches: on the one hand, those which approximate
ocean dynamics with parametric, spectral or hybrid models and use empirical
laws from oceanographic research. We will see that this type of methods
essentially allows the simulation of ocean scenes in the deep water domain,
without breaking waves. On the other hand, physically-based methods use
Navier-Stokes Equations (NSE) to represent breaking waves and more generally
ocean surface near the shore. We also describe ocean rendering methods in
computer graphics, with a special interest in the simulation of phenomena such
as foam and spray, and light's interaction with the ocean surface
[Report of] Specialist Committee V.4: ocean, wind and wave energy utilization
The committee's mandate was :Concern for structural design of ocean energy utilization devices, such as offshore wind turbines, support structures and fixed or floating wave and tidal energy converters. Attention shall be given to the interaction between the load and the structural response and shall include due consideration of the stochastic nature of the waves, current and wind
Solitary wave collisions for Whitham-Boussinesq systems
This work concerns soliton-type numerical solutions for two
Whitham-Boussinesq-type models. Solitary waves are computed using an iterative
Newton-type and continuation methods with high accuracy. The method allow us to
compute solitary waves with large amplitude and speed close to the singular
limit. These solitary waves are set as initial data and overtaking collisions
are considered for both systems. We show that both system satisfy the geometric
Lax-categorization of two-soliton collision. Numerical evidences indicate that
one of the systems also admits an algebraic Lax-categorization based on the
ratio of the initial solitary wave amplitudes with a different range from the
one predicted by Lax. However, we show that such categorization is not possible
for the second system
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