12,009 research outputs found
Nonuniformity of the Earth's rotation and the motion of the poles
The study of the nonuniformity of the Earth's rotation and the motion of the poles has great practical and theoretical significance. This study makes it possible to determine the coordinates of celestial and terrestrial objects, and to gain information in many domains of earth science. This paper reviews studies of rotation nonuniformity and polar motion, giving attention to astronomical data; the nature of periodic oscillations of the Earth's rotation; the nature of long-period variations of the Earth's rotation rate; and the use of Earth-rotation data in hydrometeorology
Librational response of a deformed 3-layer Titan perturbed by non-keplerian orbit and atmospheric couplings
The analyses of Titan's gravity field obtained by Cassini space mission
suggest the presence of an internal ocean beneath its icy surface. The
characterization of the geophysical parameters of the icy shell and the ocean
is important to constrain the evolution models of Titan. The knowledge of the
librations, that are periodic oscillations around a uniform rotational motion,
can bring piece of information on the interior parameters. The objective of
this paper is to study the librational response in longitude from an analytical
approach for Titan composed of a deep atmosphere, an elastic icy shell, an
internal ocean, and an elastic rocky core perturbed by the gravitational
interactions with Saturn. We start from the librational equations developed for
a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly
the atmospheric torque acting on the surface computed from the Titan IPSL GCM
(Institut Pierre Simon Laplace General Circulation Model) and the periodic
deformations of elastic solid layers due to the tides. We investigate the
librational response for various interior models in order to compare and to
identify the influence of the geophysical parameters and the impact of the
elasticity. The main librations arise at two well-separated forcing frequency
ranges: low forcing frequencies dominated by the Saturnian annual and
semi-annual frequencies, and a high forcing frequency regime dominated by
Titan's orbital frequency around Saturn. We find that internal structure models
including an internal ocean with elastic solid layers lead to the same order of
libration amplitude than the oceanless models, which makes more challenging to
differentiate them by the interpretation of librational motion.Comment: 38 pages, 4 figures. Accepted for publication in Planetary and Space
Scienc
Mars 2000
Twenty years after the Viking Mission, Mars is again being scrutinized in the light of a flood of information from spacecraft missions to Mars, the Hubble Space Telescope, and the SNC meteorites. This review provides an overview of the current understanding of Mars, especially in light of the data being returned from the Mars Global Surveyor Mission. Mars does not now have a global magnetic field, but the presence of crustal anomalies indicates that a global field existed early in Martian history. The topography, geodetic figure, and gravitational field are known to high precision. The northern hemisphere is lower and has a thinner and stronger crust than the southern hemisphere.
The global weather and the thermal structure of the atmosphere have been monitored for more than a year. Surface-atmosphere interaction has been investigated by observations of surface features, polar caps, atmospheric dust, and condensate clouds. The surface has been imaged at very high resolution and spectral measures have been obtained to quantify surface characteristics and geologic processes. Many questions remain unanswered, especially about the earliest period of Mars' history
Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate
Planetary rotation rate is a key parameter in determining atmospheric
circulation and hence the spatial pattern of clouds. Since clouds can exert a
dominant control on planetary radiation balance, rotation rate could be
critical for determining mean planetary climate. Here we investigate this idea
using a three-dimensional general circulation model with a sophisticated cloud
scheme. We find that slowly rotating planets (like Venus) can maintain an
Earth-like climate at nearly twice the stellar flux as rapidly rotating planets
(like Earth). This suggests that many exoplanets previously believed to be too
hot may actually be habitable, depending on their rotation rate. The
explanation for this behavior is that slowly rotating planets have a weak
Coriolis force and long daytime illumination, which promotes strong convergence
and convection in the substellar region. This produces a large area of
optically thick clouds, which greatly increases the planetary albedo. In
contrast, on rapidly rotating planets a much narrower belt of clouds form in
the deep tropics, leading to a relatively low albedo. A particularly striking
example of the importance of rotation rate suggested by our simulations is that
a planet with modern Earth's atmosphere, in Venus' orbit, and with modern
Venus' (slow) rotation rate would be habitable. This would imply that if Venus
went through a runaway greenhouse, it had a higher rotation rate at that time.Comment: 7 pages, 4 figures, accepted at Astrophysical Journal Letter
Teacher's guide book for primary and secondary school
There is an urgent need for collective action to mitigate the consequences of climate change and adapt to unavoidable changes. The complexity of climate change issues can pose educational challenges. Nonetheless, education has a key role to play in ensuring that younger generations have the required knowledge and skills to understand issues surrounding climate change, to avoid despair, to take action, and to be prepared to live in a changing world.
The Office for Climate Education (OCE) was founded in 2018 to promote strong international cooperation between scientific organisations, educational institutions and NGOs. The overall aim of the OCE is to ensure that the younger generations of today and tomorrow are educated about climate change. Teachers have a key role to play in their climate education and it is essential that they receive sufficient support to enable them to implement effective lessons on climate change. The OCE has developed a range of educational resources and professional development modules to support them in teaching about climate change with active pedagogy
Earth's Energy Imbalance and Implications
Improving observations of ocean heat content show that Earth is absorbing
more energy from the sun than it is radiating to space as heat, even during the
recent solar minimum. The inferred planetary energy imbalance, 0.59 \pm 0.15
W/m2 during the 6-year period 2005-2010, confirms the dominant role of the
human-made greenhouse effect in driving global climate change. Observed surface
temperature change and ocean heat gain together constrain the net climate
forcing and ocean mixing rates. We conclude that most climate models mix heat
too efficiently into the deep ocean and as a result underestimate the negative
forcing by human-made aerosols. Aerosol climate forcing today is inferred to be
1.6 \pm 0.3 W/m2, implying substantial aerosol indirect climate forcing via
cloud changes. Continued failure to quantify the specific origins of this large
forcing is untenable, as knowledge of changing aerosol effects is needed to
understand future climate change. We conclude that recent slowdown of ocean
heat uptake was caused by a delayed rebound effect from Mount Pinatubo aerosols
and a deep prolonged solar minimum. Observed sea level rise during the Argo
float era is readily accounted for by ice melt and ocean thermal expansion, but
the ascendency of ice melt leads us to anticipate acceleration of the rate of
sea level rise this decade.Comment: 39 pages, 18 figures; revised version submitted to Atmos. Chem. Phy
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