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 Gravitational Waves, Loving in Einstein et TAY dans Y'becca

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Date d'inscription : 09/11/2005

MessageSujet: Gravitational Waves, Loving in Einstein et TAY dans Y'becca   Ven 6 Oct à 10:29

News | February 11, 2016
Gravitational Waves Detected 100 Years After Einstein's Prediction

Congratulations to the National Science Foundation, Caltech, MIT and the entire LIGO Team!

Background information and a replay of today's news conference
announcing the detection are online at: http://www.caltech.edu/gwave

LIGO opens new window on the universe with observation of gravitational
waves from colliding black holes.

For the first time, scientists have observed ripples in the fabric of spacetime
called gravitational waves, arriving at the earth from a cataclysmic event
in the distant universe. This confirms a major prediction of Albert Einstein's 1915
general theory of relativity and opens an unprecedented new window
onto the cosmos.

Gravitational waves carry information about their dramatic origins
and about the nature of gravity that cannot otherwise be obtained.
Physicists have concluded that the detected gravitational waves
were produced during the final fraction of a second of the merger
of two black holes to produce a single, more massive spinning black hole.
This collision of two black holes had been predicted but never observed.

The gravitational waves were detected on September 14, 2015
at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both
of the twin Laser Interferometer Gravitational-wave Observatory (LIGO)
detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.
The LIGO Observatories are funded by the National Science Foundation (NSF),
and were conceived, built, and are operated by Caltech and MIT.
The discovery, accepted for publication in the journal Physical Review Letters,
was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration
and the Australian Consortium for Interferometric Gravitational Astronomy)
and the Virgo Collaboration using data from the two LIGO detectors.

Based on the observed signals, LIGO scientists estimate that the black holes
for this event were about 29 and 36 times the mass of the sun,
and the event took place 1.3 billion years ago. About 3 times the mass
of the sun was converted into gravitational waves in a fraction
of a second -- with a peak power output about 50 times that
of the whole visible universe. By looking at the time of arrival of the signals
-- the detector in Livingston recorded the event 7 milliseconds before
the detector in Hanford -- scientists can say that the source was located
in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each
other lose energy through the emission of gravitational waves,
causing them to gradually approach each other over billions of years,
and then much more quickly in the final minutes. During the final fraction
of a second, the two black holes collide into each other at nearly
one-half the speed of light and form a single more massive black hole,
converting a portion of the combined black holes' mass to energy,
according to Einstein's formula E=mc2. This energy is emitted
as a final strong burst of gravitational waves. It is these gravitational
waves that LIGO has observed.

LIGO was originally proposed as a means of detecting these gravitational
waves in the 1980s by Rainer Weiss, professor of physics, emeritus,
from MIT; Kip Thorne, Caltech's Richard P. Feynman Professor
of Theoretical Physics, emeritus; and Ronald Drever, professor of physics,
emeritus, also from Caltech.

"With this discovery, we humans are embarking on a marvelous new quest:
the quest to explore the warped side of the universe --
objects and phenomena that are made from warped spacetime.
Colliding black holes and gravitational waves are our first beautiful examples," says Thorne.

"The description of this observation is beautifully described
in the Einstein theory of general relativity formulated 100 years
ago and comprises the first test of the theory in strong gravitation.
It would have been wonderful to watch Einstein's face had we been able
to tell him," says Weiss.

"Caltech thrives on posing fundamental questions and inventing new
instruments to answer them," says Caltech president Thomas Rosenbaum,
the Sonja and William Davidow Presidential Chair and professor of physics. "
LIGO represents an exhilarating example of how this approach can transform
our knowledge of the universe. We are proud to partner with NSF and MIT
and our other scientific collaborators to lead this decades-long effort."

"Our observation of gravitational waves accomplishes an ambitious goal set out
over five decades ago to directly detect this elusive phenomenon
and better understand the universe, and, fittingly, fulfills Einstein's legacy
on the 100th anniversary of his general theory of relativity,"
says Caltech's David H. Reitze, executive director of the LIGO Laboratory.

"This discovery is just the beginning," says Fiona Harrison,
the Benjamin M. Rosen Professor of Physics and holder of the Kent
and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics
and Astronomy. "Over the next years, LIGO will be putting general relativity
to its most stringent tests ever, it will be discovering new sources
of gravitational waves, and we will be using telescopes on the ground
and in space to search for light emitted by these catastrophic events."

The existence of gravitational waves was first demonstrated
in the 1970s and 80s by Joseph Taylor, Jr., and colleagues.
Taylor and Russell Hulse discovered in 1974 a binary system
composed of a pulsar in orbit around a neutron star.
Taylor and Joel M. Weisberg in 1982 found that the orbit
of the pulsar was slowly shrinking over time because of the release
of energy in the form of gravitational waves. For discovering the pulsar
and showing that it would make possible this particular gravitational
wave measurement, Hulse and Taylor were awarded the Nobel Prize
in Physics in 1993.

The new LIGO discovery is the first observation of gravitational waves themselves,
made by measuring the tiny disturbances the waves make to space
and time as they pass through the earth.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC),
a group of more than 1000 scientists from universities around
the United States and in 14 other countries. More than 90 universities
and research institutes in the LSC develop detector technology
and analyze data; approximately 250 students are strong contributing
members of the collaboration. The LSC detector network
includes the LIGO interferometers and the GEO600 detector.
The GEO team includes scientists at the Max Planck Institute
for Gravitational Physics (Albert Einstein Institute, AEI),
Leibniz Universität Hannover, along with partners at the University
of Glasgow, Cardiff University, the University of Birmingham,
other universities in the United Kingdom, and the University
of the Balearic Islands in Spain.

"This detection is the beginning of a new era: The field
of gravitational wave astronomy is now a reality,"
says Gabriela González, LSC spokesperson and professor
of physics and astronomy at Louisiana State University.

The discovery was made possible by the enhanced capabilities
of Advanced LIGO, a major upgrade that increases the sensitivity
of the instruments compared to the first generation LIGO detectors,
enabling a large increase in the volume of the universe probed --
and the discovery of gravitational waves during its first observation run.
The US National Science Foundation leads in financial support
for Advanced LIGO. Funding organizations in Germany (Max Planck Society),
the U.K. (Science and Technology Facilities Council, STFC)
and Australia (Australian Research Council) also have made significant
commitments to the project. Several of the key technologies
that made Advanced LIGO so much more sensitive have been developed
and tested by the German UK GEO collaboration. Significant computer
resources have been contributed by the AEI Hannover Atlas Cluster,
the LIGO Laboratory, Syracuse University, and the University
of Wisconsin-Milwaukee. Several universities designed, built,
and tested key components for Advanced LIGO: The Australian National University,
the University of Adelaide, the University of Florida, Stanford University,
Columbia University of New York, and Louisiana State University.

"In 1992, when LIGO's initial funding was approved, it represented
the biggest investment the NSF had ever made," says France Córdova,
NSF director. "It was a big risk. But the National Science Foundation
is the agency that takes these kinds of risks. We support fundamental science
and engineering at a point in the road to discovery where that path is anything but clear.
We fund trailblazers. It's why the U.S. continues
to be a global leader in advancing knowledge."

"The Advanced LIGO detectors are a tour de force of science
and technology, made possible by a truly exceptional international team
of technicians, engineers, and scientists," says David Shoemaker
of MIT, the project leader for Advanced LIGO. "We are very proud that we finished
this NSF-funded project on time and on budget, and delighted Advanced LIGO
delivered its groundbreaking detection so quickly."

At each observatory, the two-and-a-half-mile (4-km) long L-shaped
LIGO interferometer uses laser light split into two beams that travel back
and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum).
The beams are used to monitor the distance between mirrors precisely positioned
at the ends of the arms. According to Einstein's theory, the distance between
the mirrors will change by an infinitesimal amount when a gravitational
wave passes by the detector. A change in the lengths of the arms smaller
than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.

Independent and widely separated observatories are necessary to determine
the direction of the event causing the gravitational waves,
and also to verify that the signals come from space and are not
from some other local phenomenon.

A network of detectors will significantly help to localize the sources.
The Virgo detector will be the first to join later this year.

The LIGO Laboratory also is working closely with scientists in India
at the Inter-University Centre for Astronomy and Astrophysics,
the Raja Ramanna Centre for Advanced Technology, and the Institute
for Plasma to establish a third Advanced LIGO detector
on the Indian subcontinent. Awaiting approval by the government
of India, it could be operational early in the next decade.
The additional detector will greatly improve the ability
of the global detector network
to localize gravitational-wave sources.

Virgo research is carried out by the Virgo Collaboration,
consisting of more than 250 physicists and engineers belonging
to 19 different European research groups: 6 from Centre National
de la Recherche Scientifique (CNRS) in France;
8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy;
2 in The Netherlands with Nikhef; the Wigner RCP in Hungary;
the POLGRAW group in Poland, and the European Gravitational Observatory (EGO),
the laboratory hosting the Virgo detector near Pisa in Italy.
Y'BECCA, for the observation on Uranus I or Ariel, Jérusalem in Israël and Palestine.

News Media Contact
Kathy Svitil/Caltech
(626) 676-7628
ksvitil@caltech.edu

2016-041

https://www.jpl.nasa.gov/news/news.php?feature=5137


Classroom Activity
Dropping In With Gravitational Waves

The collision of two black holes 1.3 billion years ago (as shown in this animation)
produced gravitational waves that were detected for the first time by researchers
at the Laser Interferometer Gravitational-Wave Observatory (LIGO)
on September 14, 2015. Credit: Caltech

Note: This activity is related to a news event from March 2016.
See "Teachable Moment: Modeling Gravitational Waves."
Materials

Management

The model can be developed in pairs, small groups, larger groups,
or as a whole class demonstration, depending on availability of materials.

The gelatin should be made and set in advance of creating the model.

The pan provides a lot of structural support for the gelatin. Taking
the gelatin out of the pan and inserting a mirror makes the gelatin
more susceptible to rough edges and tears that will affect the model.
You can avoid this by using a clear pan (without textures in the glass
that would affect the path of the laser beam). This way the gelatin can
be kept in the pan. In this case, skip steps 2 and 4 in the "Procedures"
section below, and press the marble into the gelatin after it sets so that
the marble is flush with the surface. This provides more stability
to the gelatin and keeps the edges smooth, reducing the amount
of scattering that the laser beam experiences.

Safety Note:

Lasers are a potential hazard because they can burn the retina
of the eye. Avoid direct eye exposure and take caution when pointing
a laser at a mirror to avoid accidental reflections of a laser beam
into anyone’s eyes.

Background

A century ago, Albert Einstein theorized that when objects move through
space they create waves in spacetime around them.
These gravitational waves move outward, like ripples from
a stone moving across the surface of a pond. Little did he know
that 1.3 billion years earlier, two massive black holes collided.
The collision released massive amounts of energy in a fraction
of a second (about 50 times as much as all of the energy in the visible universe)
and sent gravitational waves in all directions. On September 14, 2015
those waves reached Earth and were detected by researchers
at the Laser Interferometer Gravitational-Wave Observatory (LIGO).

Why Is It Important?

Einstein published the Theory of General Relativity in 1915.
In it, he predicted the existence of gravitational waves, which had never
been directly detected until now. In 1974, physicists discovered
that two neutron stars orbiting each other were getting closer
in a way that matched Einstein’s predictions. But it wasn’t until 2015,
when LIGO’s instruments were upgraded and became more sensitive,
that they were able to detect the presence of actual gravitational waves,
confirming the last important piece of Einstein’s theory.

It’s also important because gravitational waves carry information
about their inception and about the fundamental properties
of gravity that can’t be seen through observations
of the electromagnetic spectrum. Thanks to LIGO’s discovery,
a new field of science has been born: gravitational wave astronomy.

How Did They Do It?

LIGO consists of facilities in Washington and Louisiana.
Each observatory uses a laser beam that is split and sent down 2.5-mile
(4-kilometer) long tubes. The laser beams precisely indicate
the distance between mirrors placed at the ends of each tube.
When a gravitational wave passes by, the mirrors move a tiny amount,
which changes the distance between them. LIGO is so sensitive
that it can detect a change smaller than 1/10,000 the width
of a proton (10-19 meter). Having two observatories placed
a great distance apart allows researchers to approximate
the direction the waves are coming from and confirm
that the signal is coming from space rather than something nearby
(such as a heavy truck or an earthquake).

Update – Oct. 3, 2017: Researchers Kip Thorne and Barry Barish
of Caltech and Rainer Weiss of MIT have been awarded the 2017
Nobel Prize in Physics for their “decisive contributions to the LIGO
detector and the observation of gravitational waves.”

Thorne, Barish and Weiss played key roles in making the LIGO project
a reality through their research, leadership and development
of technology to detect gravitational waves.

In a statement to Caltech, Thorne said the prize also belongs
to the more than 1,000 scientists and engineers
around the world who play a part on LIGO,
the result of a long-term partnership between Caltech,
MIT and the National Science Foundation.

› Read the Caltech press release
Procedures

Prepare the gelatin according to the package directions
and pour it in the baking pan. Be sure enough gelatin fills the pan
that the mirror will be mostly or completely covered
when it’s inserted (step 5).

Place a marble or pebble in one corner of the gelatin,
about one inch from the sides of the pan, and allow it
to sink to the bottom.

Allow the gelatin to completely set.

Once the gelatin is firm, place a flat portable surface
(such as a cutting board or a cookie sheet) on top of the pan,
gently flip the pan and remove the gelatin from the pan.

Press the mirror into the gelatin at a 45-degree angle opposite
the marble. Be sure to put the mirror far enough away from the edges
of the gelatin that the gelatin stays intact.

Pointing through the gelatin from the side closest to the marble,
aim the laser at the mirror and secure it so it doesn’t move
(e.g., by taping it to a book or binder). Use tape or a binder clip to hold down
the laser’s on-button.

Place the Laser Target Card outside the gelatin in the path of the reflected laser.
Secure it so the card is stationary (e.g., by taping it to a book, binder or the side
of the clear baking pan).

With the laser and Laser Target Card steady, drop a second marble on the marble
that is set in the gelatin.

In this model, the gelatin represents spacetime. The collision of the marbles represents
the collision of two black holes. The vibrations in the gelatin represent the gravitational waves,
and the movement of the laser on the marker card indicates
the presence of gravitational waves.

Discussion

For this model, we assume that spacetime extends beyond
the gelatin and that the laser and Laser Target Card are also in spacetime.
Ask students why the model is limited in this way and how it might affect
the model.

Extending the gelatin (spacetime) to encompass the laser and Laser Target Card
would require a much larger container and a greater amount of gelatin.
It would also mean submerging a laser in gelatin long enough for it to set,
and developing a method for turning the laser on while in the gelatin.

Yellow or clear gelatin is used in this model. Ask students to explain why.

Other colors may absorb the laser pointer’s light which
is most commonly green or red.

Assessment

What happens to the laser beam when the marble is dropped
on the second marble? Why?

What are some limitations of this model?

How could this model be improved?

Extensions

Use a mobile device and record a video using the slow motion feature
or the high-frame rate setting. This will allow students to view a slow-motion
playback and see some of the elements of the model and how
they move in response to the collision in more detail.

Add markings (cm, mm, or non-standard units) to the Laser Target Card
and drop the marble from different heights to see how that affects
the motion of the beam on the target.

Explore More

Gravitational waves news, videos and resources
Laser Interferometer Gravitational-Wave Observatory (LIGO) Website

https://www.jpl.nasa.gov/edu/teach/activity/dropping-in-with-gravitational-waves/

AND


Teachable Moments| October 3, 2017
Modeling Gravitational Waves

By Lyle Tavernier


Update – Oct. 3, 2017: Researchers Kip Thorne and Barry Barish of Caltech
and Rainer Weiss of MIT have been awarded the 2017 Nobel Prize in Physics
for their “decisive contributions to the LIGO detector and the observation
of gravitational waves.”

Thorne, Barish and Weiss played key roles in making the LIGO project
a reality through their research, leadership and development of technology
to detect gravitational waves.

In a statement to Caltech, Thorne said the prize also belongs to the more
than 1,000 scientists and engineers around the world who play a part
on LIGO, the result of a long-term partnership between Caltech, MIT
and the National Science Foundation.

› Read the Caltech press release

This story was originally published on March 23, 2016.
In the News

A century ago, Albert Einstein theorized that when objects move
through space they create waves in spacetime around them.
These gravitational waves move outward, like ripples from
a stone moving across the surface of a pond. Little did he know
that 1.3 billion years earlier, two massive black holes collided.
The collision released massive amounts of energy in a fraction
of a second (about 50 times as much as all of the energy
in the visible universe) and sent gravitational waves in all directions.
On September 14, 2015 those waves reached Earth and were detected
by researchers at the Laser Interferometer
Gravitational-Wave Observatory (LIGO).

Why It's Important

Einstein published the Theory of General Relativity in 1915.
In it, he predicted the existence of gravitational waves, which had never
been directly detected until now. In 1974, physicists discovered
that two neutron stars orbiting each other were getting closer
in a way that matched Einstein’s predictions. But it wasn’t until 2015,
when LIGO’s instruments were upgraded and became more sensitive,
that they were able to detect the presence of actual gravitational waves,
confirming the last important piece of Einstein’s theory.

It's also important because gravitational waves carry information
about their inception and about the fundamental properties
of gravity that can’t be seen through observations of the electromagnetic
spectrum. Thanks to LIGO’s discovery, a new field of science has been born:
gravitational wave astronomy.
How They Did It

LIGO consists of facilities in Washington and Louisiana.
Each observatory uses a laser beam that is split and sent down 2.5-mile
(4-kilometer) long tubes. The laser beams precisely indicate
the distance between mirrors placed at the ends of each tube.
When a gravitational wave passes by, the mirrors move a tiny amount,
which changes the distance between them. LIGO is so sensitive
that it can detect a change smaller than 1/10,000 the width
of a proton (10-19 meter). Having two observatories placed
a great distance apart allows researchers to approximate
the direction the waves are coming from and confirm
that the signal is coming from space rather than something nearby
(such as a heavy truck or an earthquake).

each It

Creating a model that demonstrates gravitational waves traveling
through spacetime is as simple as making a gelatin universe!

› See the activity!

Middle school students can develop a model that shows gravitational
waves traveling through spacetime while working toward the following
Next Generation Science Standard:

MS-PS4-2 - Develop and use a model to describe that waves
are reflected, absorbed, or transmitted through various materials.

Explore More

Gravitational waves news, videos and resources
Laser Interferometer Gravitational-Wave Observatory
(LIGO) Website

TAGS: Gravitational Waves, Teachable Moment,
LIGO, Black Holes, Einstein

Lyle Tavernier
ABOUT THE AUTHOR

Lyle Tavernier, Educational Technology Specialist, NASA/JPL Edu

Lyle Tavernier is an educational technology specialist
at NASA's Jet Propulsion Laboratory. When he’s not busy working
in the areas of distance learning and instructional technology,
you might find him running with his dog, cooking or planning
his next trip.

King Crimson - I Talk To The Wind - BBC session (1969) HQ
https://www.youtube.com/watch?v=tJa5sxlvsVg

TAY RAJOUTTE...

Une trombe marine est une colonne d'air mélangé d'eau en rotation,
formant un entonnoir nuageux, sous un nuage convectif au-dessus d'une étendue d'eau1,2.
Ces phénomènes de micro-échelle se forment lorsque les conditions sont très instables
alors que de l'air froid passe au-dessus d'eaux chaudes. Généralement moins intenses
qu'une tornade, elles se dissipent une fois sur la terre. Il en existe deux types :
les trombes d'air froid et les trombes tornadiques2.

Description

Le premier stade consiste en une colonne d'embruns en rotation,
près de la surface de l'eau, pouvant ou non être accompagnée
d'un entonnoir nuageux s'étendant vers le bas à partir d'un nuage
de type cumulus, cumulus bourgeonnant ou cumulonimbus.
L'entonnoir s'allonge vers l'eau lorsque la trombe marine se renforce.
Elle atteint sa maturité quand l'entonnoir touche la surface de l'eau.
La vitesse des vents associés peut dépasser les 100 km/h.
Se produisant pendant la journée, elles peuvent former
des groupes de deux ou plus, durer jusqu'à 20 minutes
et avoir des diamètres d'une vingtaine de mètres.
Elles se déplacent généralement à une vitesse
de l'ordre de 15 à 25 km/h2.
Types
Trombes d'air froid
Conditions de formation des trombes marines
d'air froid, trombes terrestres et « Gustnado »

Le type de trombes marines le plus courant est celui dit
« d'air froid ». Ces trombes se forment quand de l'air frais
se déplace au-dessus d'eaux relativement plus chaudes.
La couche d'air doux juste au-dessus de la surface
de l'eau étant moins dense que l'air froid qui arrive,
il prend un équilibre instable et subit une poussée
d'Archimède vers le haut. L'humidité qu'il contient
se condense en altitude pour former des nuages convectifs
qui peuvent aller du simple cumulus jusqu'au cumulonimbus
et sous lesquels on retrouve des courants ascendants3.

Contrairement aux tornades, ces trombes marines ne sont
cependant pas créées par la concentration d'un mésocyclone
dans le nuage mais prennent naissance dans un tourbillon existant
sous celui-ci2. Ces tourbillons de faible intensité se forment
dans une région où les vents ne subissent pas une variation
de direction et de vitesse importante selon la verticale
mais selon l'axe horizontal. Ainsi, la rencontre de brises
de mer ou de terre de différentes directions, la canalisation
du vent par la côte ou le front de rafale venant d'orages
peuvent initier une zone de convergence locale des vents
à la surface de l'eau. Lorsque cela se produit, il y a création
d'une faible rotation verticale au point de rencontre
et cette rotation peut être étirée par le passage
du courant ascendant d'un nuage convectif en développement.
Ceci donne une rotation intense à très fine échelle appelée micro-échelle
(2 km ou moins) sous le nuage4, le tout se passant généralement
en l'absence de forçage dynamique : pas de front, de courant-jet, etc.

Ces trombes marines mettent en jeu des vents moins rapides
que leurs homologues terrestres et apparaissent habituellement
au printemps ainsi qu'en automne, lorsque le contraste
entre l'air et l'eau est le plus grand5. Des chercheurs ont photographié
des trombes d'eau et effectué des mesures dans le cœur de celles-ci
à l'aide d'instruments embarqués dans des avions. On ne sait cependant
pas clairement si les résultats obtenus sur ces trombes sont transposables
aux tornades, et en particulier à celles qui sont fortes et violentes.
Le courant dans les niveaux inférieurs de la trombe d'eau peut, par exemple,
différer de celui d'une tornade parce qu'un vortex sur l'océan, circulant
sur une surface lisse, est donc soumis à des frottements plus faibles.
Trombes tornadiques
Article détaillé : Tornade.
Basculement d'une rotation horizontale par le courant ascendant
pour former une rotation verticale dans une tornade.

Ce type de trombes est essentiellement identique aux tornades
terrestres et se produisent sous des orages supercellulaires.
Ainsi un cisaillement vertical des vents est transformé
en une rotation verticale par le très fort courant ascendant
sous ce type de nuage6. Elles peuvent atteindre une très forte intensité
et poser un important danger à la navigation, à l'aviation et aux personnes
dans le secteur. Comme elles sont associées à une forte dynamique,
elle ne se dissiperont pas en entrant dans les terres. Elles faibliront cependant
à cause de la friction et de la diminution du nuage associé qui perdra
l'apport thermodynamique que lui procure l'étendue d'eau.

Ce type de trombe marine est assez rare car les conditions nécessaires
d'instabilité pour générer des supercellules se retrouvent en général
sur la terre ferme : fort réchauffement diurne, humidité de surface,
air froid et sec en altitude, déclencheur. On les retrouvera
donc le plus souvent lors d'épisode très bien organisés
d'orages violents associés aux fronts froids très actifs
ou aux systèmes convectifs de méso-échelle passant
de la terre à la mer.
Techniques de prévision

Dans le cas des trombes tornadiques, la prévision se fait
en estimant l'énergie de convection disponible et le cisaillement
des vents dans les bas niveaux de la troposphère.

Pour les autres trombes marines, il existe différentes méthodes
pour estimer le potentiel de développement. L'une de celles-ci
a été développée par un météorologue canadien du nom
de Wade Szilagyi. Il a répertorié un grand nombre d'événements
et les a classé selon la hauteur du sommet des nuages associés
à la trombe par rapport à la différence de température
entre la surface de l'eau et la pression de 850 hPa
(environ 1 500 m d'altitude). La répartition des trombes
dans le graphique montra que l'on pouvait diviser le graphique
en secteurs de potentiel.

L'indice de trombe marine (SWI) qui en résulta va de -10 à +10.
Grosso-modo, une valeur de -10 se retrouve dans le coin inférieur gauche
du graphique, là où la différence de température et la hauteur des sommets
des nuages est faible. Les valeurs de SWI augmentent en se dirigeant
vers le coin supérieur droit. Les valeurs négatives représentent
des conditions défavorables. Plus la valeur positive est grande,
plus le potentiel est élevé7
Trombes hivernales ou de neige
Deux trombes marines hivernales vues sur le lac Champlain
dans l'État de New York le 15 janvier 2009
Article détaillé : Bourrasque de neige.

Un cas particulier de trombe marine en air froid est celui
des trombes de neige. Ces trombes très rares et peu documentées
se produisent lors d'une situation propice aux bourrasques
de neige en aval de plans d'eau en hiver. Lorsque de l'air arctique
ayant des températures bien sous le point de congélation passe
au-dessus d'un lac ou de la mer sans glace, la différence de température
provoque une forte convection8. L'atmosphère devenant rapidement
isotherme ensuite, à cause du niveau très bas de la tropopause,
le sommet des nuages ne dépasse pas celui de gros cumulus.

Cependant les mouvements verticaux sous ces nuages sont très intenses
et la moindre rotation de l'air deviendra un tourbillon important.
Si les vents sont relativement légers et de direction constante
près du courant ascendant, une rotation peut être engendrée
lors de la rencontre d'un point de convergence avec un vent contraire
sur le plan d'eau, comme dans le cas des trombes marines classiques9.
Malgré tout, il y a eu très peu de signalements de trombes hivernales
se formant dans ces conditions, probablement parce que le cisaillement
vertical des vents est en général important en hiver, ce qui empêche
la formation d'une rotation ayant une épaisseur suffisante en changeant
la configuration des vents lorsque l'on s'élève8,9.
Climatologie
Trombe marine vue depuis un avion.

La vaste majorité des trombes marines sont de type d'air froid
et se rencontrent dans les Tropiques mais un certain nombre
se produisent dans les latitudes plus élevées. Elles sont assez courantes
entre autres le long de la côte européenne, des îles Britanniques,
des mers Méditerranée et Baltique. Elles sont particulièrement fréquentes
au large des côtes de la Floride et de ses Keys. Les trombes peuvent se développer
autant sur les eaux salées que les lacs et rivières d'eau douce
puisque l'instabilité atmosphérique et les vents sont les seuls critères
en cause. Ainsi, on rapporte souvent régulièrement des trombes marines
sur les Grands Lacs d'Amérique du Nord10. En général, elles vont se produire
à l'intérieur de 100 kilomètres des côtes.

On relève environ 160 trombes marines par année en Europe, les Pays-Bas
en signalant le plus grand nombre avec 60. Viennent ensuite l'Espagne
avec 30 (en majorité dans la région de Barcelone), l'Italie avec 25,
et la Grande-Bretagne avec 15. Dans l'hémisphère nord, quelques études
climatologiques ont montré une prépondérance de la formation
des trombes d'air froid à l'automne, en particulier en septembre,
alors que des incursions d'air froid passe sur les eaux au maximum
de leur réchauffement5. Cependant, les trombes tornadiques,
moins fréquentes, auront un pic d'activité estival, alors que
les conditions sont plus favorables aux orages supercellulaires,
ainsi que durant la saison des cyclones tropicaux
auxquels elles sont souvent associées.
Effets

La variation de pression et du vent local associé avec les trombes marines
peuvent causer un danger aux embarcations et aux coraux,
cela est particulièrement vrai des trombes tornadiques2,3.
Les trombes en air froid se dissipent généralement rapidement
en touchant terre car elles perdent leur source de chaleur2.

Les trombes tornadiques peuvent persister car les éléments qui
les génèrent se retrouvent dans la masse d'air, elles peuvent
donc causer des dégâts importants sur terre3. Les incidents de trombes marines
ayant causés des dommages sérieux sont assez rares, mais quelques-uns
sont assez célèbres. En 1555, la tornade du Grand Port de Malte
est l'une des plus ancienne confirmation d'une trombe destructrice.
Elle a coulé quatre galères de guerre, de nombreux navires
et fait plusieurs centaines de morts11,12.
En 1851, deux trombes marines tornadiques frappent l'ouest de la Sicile,
dévastant la côte. Le 1er juin 2015, une trombe marime
sur le fleuve Yangtze chavire l’Étoile de l'Orient durant la nuit et fait 442 morts13.

À cause de la pression plus faible à l'intérieur des trombes marines,
elles agissent comme un aspirateur. Elles emportent dans l'air
et les nuages des aérosols riches en plancton, bactéries marines
et virus. Elles interviennent ainsi dans la bioturbation14.
Les plus puissantes peuvent même soulever de petits poissons
ou des batraciens.
Notes et références

↑ (en) « Définition de Waterspout » [archive],
American Meteorological Society, 2006 (consulté le 19 juillet 2008).
↑ a, b, c, d, e et f Service météorologique du Canada,
« Trombes marines » [archive], Vos questions, Environnement Canada,
3 décembre 2004 (consulté le 19 juillet 2008).
↑ a, b et c (en) Bruce B. Smith, « Waterspouts » [archive],
National Weather Service (consulté le 9 avril 2012).
↑ (en) Barry K. Choy et Scott M. Spratt, « Using the WSR-88D
to Predict East Central Florida Waterspouts » [archive] (consulté le 19 juillet 2008).
↑ a et b (en) Wade Szilagyi du Service météorologique du Canada,
« The Great Waterspout Outbreak of 2003 », Mariner's Weather Log,
NOAA, vol. 43, no 3,‎ décembre 2004 (lire en ligne [archive]) .
↑ Service météorologique du Canada, MÉTAVI : L'atmosphère,
le temps et la navigation aérienne, Environnement Canada, janvier 2011,
260 p. (lire en ligne [archive] [PDF]), chap. 13 (« Orages et tornades »), p. 121-135.
↑ Wade Szilagyi, « A Waterspout Forecasting Technique », Pre-prints,
Landshut (Allemagne), 5h European Conference on Severe Storms,‎
12-16 octobre 2009, p. 129-130 (lire en ligne [archive] [PDF]).
↑ a et b (en) Bureau de Burlington au Vermont, « 15 January 2009:
Lake Champlain Sea Smoke, Steam Devils, and Waterspout:
Chapters IV and V » [archive], National Weather Service, 3 février 2009
(consulté le 25 mai 2012).
↑ a et b (en) David Cuthburtson, « A winter waterspout »,
Monthly Weather Review, NOAA,‎ 25 février 1907 (lire en ligne [archive]).
↑ (en) « Fair weather waterspout » [archive],
Environmental Science Resources, Gale Schools, 2001
(consulté le 25 octobre 2006) .
↑ (en) Journal of Meteorology, numéros 285 à 294,
vol. 29, Artetech International, 2004 (lire en ligne [archive]), p. 130.
↑ Loris Miège, Histoire de Malte, vol. 2, Paulin, 1840
(lire en ligne [archive]), p. 148.
↑ « Terrible naufrage d'un navire de croisière en Chine »
[archive], sur francetvinfo.fr, 2 juin 2015 (consulté le 6 juin 2015).
↑ Groupe de trombes (100 mètres de haut environ) [archive]
filmées d’hélicoptère au large d’Avoca Beach
(au nord de Sydney, Australie).

Voir aussi

Sur les autres projets Wikimedia :

Trombe marine, sur Wikimedia Commons

Articles connexes

Trombe terrestre
Tourbillon de poussière
Échelle de Fujita
Échelle de Fujita améliorée


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MessageSujet: Re: Gravitational Waves, Loving in Einstein et TAY dans Y'becca   Ven 6 Oct à 10:30

Ötzi, la momie des glaces
Programme TV » Programme France 5 »

Résumé

Retour sur les investigations menées sur le cadavre d'une momie congelée datant de 5300 ans et qui semble avoir subi d'autres agressions que celles du temps.
Synopsis

Deux montagnards découvrent en 1991, dans les Alpes, un cadavre bien conservé dans la glace. Ses affaires, dont une hache, sont en très bon état également. Cet homme congelé est surnommé «Ötzi». Son extraction des glaces s'opère méticuleusement. Ce n'est qu'en 2007 qu'une équipe de scientifiques basée en Italie entreprend de décongeler le corps afin de l'autopsier. Ses entrailles sont sondées à l'aide d'un endoscope. Son estomac et son crâne sont examinés attentivement. Peu à peu, radios et scanners montrent qu'il a été blessé par une flèche. Son crâne révèle une trace de commotion cérébrale. Son estomac est plein : il a mangé de la viande et des graines moins d'une heure avant de décéder. Enfin, son ADN permet d'en savoir davantage. Peu à peu, un scénario se précise : «Ötzi» était un homme de 40 ans qui aurait été tué par un individu qu'il connaissait.

https://tv-programme.com/otzi-la-momie-des-glaces_documentaire/

-----------------------------

Les premiers hommes de l'Himalaya

Documentaire (histoire) de 52min de 2017
Résumé

En plein coeur de l'Himalaya, au nord du Népal, se cache le Royaume de Lo, où l'archéologue Mark Aldenderfer recherche des traces d'anciennes civilisations.
Synopsis

En plein cœur de l'Himalaya, au nord du Népal, se cache le Royaume de Lo. Pendant des décennies, l'accès à cette région a été interdit aux étrangers. Aujourd'hui, l'archéologue Mark Aldenderfer et son équipe se lancent dans une expédition à la découverte de ce territoire mystérieux. Ils y retrouvent les vestiges d'une civilisation inconnue : des milliers de grottes creusées à flanc de falaise à des dizaines de mètres du sol. Ces grottes referment encore des poteries et des bijoux d'une grande rareté, qui remettent en cause les connaissances actuelles sur la préhistoire de la région. Mais Mark découvre plus qu'un trésor, il réussit également à trouver des traces d'ADN. Cette précieuse matière génétique va révéler qui étaient les premiers habitants de ces hautes montagnes.

https://tv-programme.com/les-premiers-hommes-de-l-himalaya_documentaire/

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MessageSujet: Re: Gravitational Waves, Loving in Einstein et TAY dans Y'becca   Ven 6 Oct à 10:35

News | October 3, 2017
Satellites See Silicon Valley's Quick Drought Recovery.

NASA/university study finds aggressive conservation helped region's aquifer rebound quickly from one of the worst droughts in California history

Underground water reserves in California's Silicon Valley rebounded
quickly from the state's recent severe drought, demonstrating the success
of aggressive conservation measures, according to a new space-based study
by NASA and university scientists.

Using satellite data from COSMO-SkyMed, a constellation of four Italian
Space Agency (Agenzia Spaziale Italiana, or ASI) satellites, a research
team led by Estelle Chaussard at the University at Buffalo in New York,
and including scientists from NASA's Jet Propulsion Laboratory in Pasadena,
California, used a technique called synthetic aperture radar interferometry
to monitor the entire Santa Clara Valley aquifer near San Jose from 2011
to 2017. This type of radar can capture the subtle up-and-down movements
of Earth's surface of just minute fractions of an inch (a few millimeters)
that occur when water levels rise or fall underground. The scientists used
hundreds of radar images obtained under a license from ASI to calculate
how much the land surface elevation changed over time. The measurements show
the aquifer began to rebound in late 2014, when the drought was still going strong,
and that groundwater levels had returned to pre-drought levels by 2017,
thanks to conservation measures that intensified in 2014,
and heavy winter rains in 2016.

During the 2012-15 drought, the Santa Clara Valley Water District
employed an array of conservation measures. These included restricting sprinkler use
and asking customers to take shorter showers and convert lawns and pools
into less-thirsty landscapes. The district also imported water
from outside the region.

Chaussard says the actions may have helped stave off
irreversible damage to the aquifer, which measures about 212 square miles
(550 square kilometers) and lies beneath a highly urbanized area.
She explains when groundwater levels reach a record low,
the porous sands and clays in which the reserves reside can dry up
so much that the clays don't retain water anymore. The new study shows
that thanks to the intensive water management efforts, this did not happen
in the Santa Clara Valley.

Chaussard says the aquifer monitoring method her team used can work anywhere
where there are soft-rock aquifer systems and where synthetic aperture radar
satellite data are available, including in developing nations with few resources
for monitoring.

"We wanted to see if we could use a remote sensing method that doesn't require
ground monitoring to understand how our aquifers are responding to a changing climate
and human activity," she says. "Our study further demonstrates the utility
of synthetic aperture radar interferometry, which scientists also use to measure surface
deformation related to volcanoes and earthquakes, for tracking ground deformation
associated with changes in groundwater levels."

"This study further demonstrates a complementary method, in addition
to traditional ground-based measurements, for water management districts
to monitor ground deformation," added JPL co-author Pietro Milillo. "
The technique marks an improvement over traditional methods because
it allows scientists to gauge changes in ground deformation across
a large region with unprecedented frequency." He said the COSMO-SkyMed satellites
provided information for the aquifer as often as once a day.

Underground stockpiles of water -- housed in layers of porous rock called aquifers
-- are one of the world's most important sources of drinking water.
Some 2.5 billion people across the globe rely on aquifers for water,
and many of these repositories are being drained more quickly than
they can be refilled, according to the United Nations Educational, Scientific
and Cultural Organization.

Yet keeping tabs on these precious reserves is expensive, says Chaussard.

"To monitor aquifers, you need a lot of measurements in both space and time,"
she says. "Sampling water levels at wells may give you a continuous time series,
but only if they are constantly monitored,
and automated monitoring may not be common.
Also, even a high density of wells may not adequately capture basin-wide
spatial patterns of water storage, which is key to understanding processes
at stake."

The methods employed in this study provide a more complete picture of how
an aquifer responds during a drought and how water conservation methods
can have a real and positive impact on sustaining the health and viability
of pumped groundwater aquifers. The satellite radar imagery not only fills
in data gaps between wells, but provides valuable insights into how aquifers
are responding beyond the edges of monitoring well networks
so that water agencies can more effectively manage
their precious resources.

The upcoming NASA-ISRO (Indian Space Research Organisation)
Synthetic Aperture Radar (NISAR) satellite mission, planned for launch in 2021,
will systematically collect radar imagery over nearly every aquifer
in the world, improving our understanding of valuable groundwater resources
and our ability to better manage them. In addition to tracking groundwater
use in urban settings, NISAR will be able to measure surface motion associated
with groundwater pumping and natural recharge in rural communities, in areas
with extensive agriculture, and in regions with extensive vegetation, conditions
that are typically more challenging.

The research was published Sept. 25 in the Journal of Geophysical Research -
Solid Earth. Other participating institutions include the University of California,
Berkeley; Purdue University, West Lafayette, Indiana; and
the Santa Clara Valley Water District.

News Media Contact
Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0474
Alan.buis@jpl.nasa.gov

Charlotte Hsu
University at Buffalo, Buffalo, NY
716-645-4655
chsu22@buffalo.edu

2017-257

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