By Jonathan Amos
Science correspondent, BBC News, Bergen
It is one of the most exquisite views we have ever had of the Earth.
This colourful new map traces the subtle but all pervasive influence the pull of gravity has across the globe.
Known as a geoid, it essentially defines where the level surface is on our planet; it tells us which way is “up” and which way is “down”. It is drawn from delicate measurements made by Europe’s Goce satellite, which flies so low it comes perilously close to falling out of the sky.
Scientists say the data gathered by the spacecraft will have numerous applications. One key beneficiary will be climate studies because the geoid can help researchers understand better how the great mass of ocean water is moving heat around the world.
The new map was presented here in Norway’s second city at a special Earth observation (EO) symposium dedicated to the data being acquired by Goce and other European Space Agency (Esa) missions.
… Imaginary ball
Launched in 2009, the sleek satellite flies pole to pole at an altitude of just 254.9km – the lowest orbit of any research satellite in operation today.
The spacecraft carries three pairs of precision-built platinum blocks inside its gradiometer instrument that sense accelerations which are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth.
This has allowed it to map the almost imperceptible differences in the pull exerted by the mass of the planet from one place to the next – from the great mountain ranges to the deepest ocean trenches.
Two months of observations have now been fashioned into what scientists call the geoid.
…Put a ball on this hypothetical surface and it will not roll – even though it appears to have “slopes”. These slopes can be seen in the colours which mark how the global level diverges from the generalised (an ellipsoid) shape of the Earth.
In the North Atlantic, around Iceland, the level sits about 80m above the surface of the ellipsoid; in the Indian Ocean it sits about 100m below.
The geoid is of paramount interest to oceanographers because it is the shape the world’s seas would adopt if there were no tides, no winds and no currents.
If researchers then subtract the geoid from the actual observed behaviour of the oceans, the scale of these other influences becomes apparent.
This is information critical to climate modellers who try to represent the way the oceans manage the transfer of energy around the planet.
…
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/8767763.stm
//
Oops, I got the color relationships to gravity backwards in my comment above, here is a depiction scaled to gravity strength not elevation
http://en.wikipedia.org/wiki/File:Geoids_sm.jpg
Has there been any peer reviewed papers come out yet that say CO2 is causing heavier than normal gravity?
Any bets on how soon there will be a paper coming out that says short obese people aren’t caused by overeating but because heavy doses of CO2 are causing heavier than normal gravity and it’s pushing people down to the ground?
wink wink
I think it would be at high noon with a solar eclipse…?
—
I’m not certain I understand their description of what I’m looking at. The darkest blue areas are called the lowest because that’s where gravity is the weakest?
That’s more understandable than saying this is how the terrain would have to be in order for you to feel as though you were walking along level ground. BBC’s Bergen concocted an artificial representation of an effect that would be a attributable to the anomaly whereas I think most people would rather just see the representation of the anomaly data directly per your wiki link.
Jim G says: “There is no such thing as centrifugal force.”
Would you accept “Centrifugal Inertial Reaction Force”?
To understand that figure, you need to understand what an ellipsoid and a geoid are.
An ellipsoid is a simple surface that approximates where sea level is (or would be if the continents were completely permeable). It is essentially a squashed sphere- the pole to pole diameter is slightly shorter than the diameter at the equator.
Ellipsoids are very important in mapmaking- every map uses some reference ellipsoid.
A geoid, on the other hand, is a much more complex and accurate representation of where sea level is (or would be). The geoid represents a surface where the gravitational acceleration is everywhere equal; that’s where sea level would be if there were no other effects but gravity. (Geoids aren’t generally used in mapmaking because the math gets too complicated).
What the figure shows is the difference between the simple ellipsoid and the more accurate (and complex) geoid. For example, where the map is colored dark blue, the surface of the geoid is 100 or so meters lower (ie, closer to the center of the earth) than the surface of the ellipsoid. Where the map is colored orange, the surface of the geoid is 100 or so meters higher (ie, further from the center of the earth) than the surface of the ellipsoid.
The difference between the two “oids” is a FUNCTION of the difference in the “strength of gravity” at different places on the earth, but it’s not really a gravity map- because of the shape of the ellipsoid, a spot near the pole and a spot near the equator might have the same strength of gravity, but have different deviations from the ellipsoid.
Forgive me if I have this messed up, but my take is that the levels -100/+80 meters describe corrections needed to an earthlike spheroidal shape to provide equal gravitational acceleration at a particular location and have nothing to do directly with where the surface of the earth/ocean might be.
My earlier concern over the local differences was directed to the use of satellite telemetry for sensing surface elevations/sea levels. The accuracy of this process would depend mightily on correcting for geometry and strengths of the anomalies indicated on this wonderful map – this geometry and these strengths affecting orbit geometry.
It also appears that the center of mass of the earth oscillates with respect to surface “fixes.”
Which of course makes me wonder when the “sea levels are rising” gurus submit for publication and include their telemetry based appraisals, do the publications run their stuff past someone who really understands the issues we’ve been tossing around here? Or maybe just another climate guy who works with same stuff?
It seems this was one of the weightiest of the McKittrick McIintyre discoveries – noone on the “team” was really sharp on statistics. It’s clear that divining relative surface elevations is not simple.
Not too long ago, the Smithsonian service which provides center of mass data to the world was working on resolutions to 3mm. Maybe they’ve got it down to .3mm now.
Help anyone?
Thanks Chris V. Much better than my shot at it.
Mike M:
I looked it up on wikipedia, and we all know how accurate that is, and it referred to centrifugal force as a “ficticious” force which is pretty much what my old physics prof alluded to. Yes, your definition fits the theory of it being an “assumed” force in the opposite direction of the centripetal force, if I understand this correctly.
7. Gravity changes can betray magma movements under volcanoes
This technique would be useful around very active and explosive eruption type of volcanoes like at Kamchatka Peninsula which has a history of sudden undetected eruptions with little warning . I notice this area is shown in orange and yellow colour on the map.
It so happens that there are currently 5 volcanoes in avaiation code yellow or orange . Last year in April /May there were 7 in this danger zone at the same time .
Jim G says:
June 29, 2010 at 10:47 am
Kieth Minto:
Keith Minto:
There is no such thing as centrifugal force, there is a force called cetripetal force caused by rotation at least according to my physics IV professor who threatened me with an F if I used that term again. Gravity, itself, is not a force, per se, but a curvature of space caused by the presence of mass. Where gravity is “stronger” there is more mass and vice versa. The map shows where mass is concentrated and the gravitational differences are apparently miniscule.
So then, is that why my centripetal dollars keep getting drawn towards D.C.?
😉
Cryosat-2 focuses on ice target
The first data from the European spacecraft has been presented at an Earth observation meeting in Norway.
The information clearly shows Cryosat has the required sensitivity to assess the state of Antarctic and Arctic ice, according to its lead scientist.
http://news.bbc.co.uk/1/hi/science_and_environment/10450425.stm
Esa expects to get at least five years of mission life out of the satellite. The spacecraft is mid-way through a six-month commissioning phase. Once this is complete, calibrated and validated data will be delivered to the scientific community.
899 says:
“So then, is that why my centripetal dollars keep getting drawn towards D.C.?”
No, that is a true force! Unlike the oft quoted “gravity is because the earth sucks” Washington DC really does! And it sucks in money from anywhere and anyone it can. When it can’t get anymore it simply has the “privately owned” federal reserve create more out of thin air, an amazing violation of the rule of conservation of matter/energy!
Always thought there was something more Grounded aboot the South Island of new Zealand….now we have the mappy thingo to prove it….
Yes, the blue area around Sri Lanka indicates less gravity than other areas, especially orange/red areas. Another way to think of it is that the greater mass concentration of an area pulls the ocean water towards it, building it up, producing higher altitudes in the geoid. Low gravity areas (Sri Lanka) have water pulled away from it, producing low altitudes.
Dave Wendt said at 10:54 am
It highlights what a meaningless concept Global Mean Sea Level really is.
That summed it up very nicely and points to another fact that some people, including some scientists, do not seam to realize or grasp (at least not openly) and that is – with current technology (or anything in the foreseeable future) we can not calculate the average height of the planets oceans, nor the density, nor the temperature. The same thing holds true for the plants atmosphere, including but not limited to CO2 density. Why? Because we can not measure any of it – accurately. To have any degree of “accuracy” we would have to take our measurement of ALL factors, everywhere – almost simultaneously. And THAT reading on to its own would be meaningless as we have no historical data of comparable accuracy and due to the ever intersecting short, medium, long and extra long weather cycles we would need a couple hundred years history of such data to make any reasonable forecast of….. hmm, sounds like we a multi-million dollar grant.
If gravity has effects on the actual surfaces of the oceans (higher/ lower) as they move around, would it also effect the atmosphere itself, as it moves around? I’m probably not expressing this very well, but I am thinking that the atmosphere’s shape would be more amoeba-like, rather than the ball (ellipsoid) shape we generally assume.
>j ferguson says:
>June 29, 2010 at 4:12 am
>If sea level changes are in mm increments, wouldn’t they be lost in terms of reliable >measureability in the local conditions and “oscillations” discussed above including some >very informative comments?
Scotland is rising at a rate of 3mm per year and England is sinking at a rate of 2mm per year. Whether or not the ocean is falling or rising depends upon where on the island you live.
Agile Aspect says:
June 29, 2010 at 4:32 pm
>j ferguson says:
>June 29, 2010 at 4:12 am
>If sea level changes are in mm increments, wouldn’t they be lost in terms of reliable >measureability in the local conditions and “oscillations” discussed above including some >very informative comments?
Scotland is rising at a rate of 3mm per year and England is sinking at a rate of 2mm per year. Whether or not the ocean is falling or rising depends upon where on the island you live.
All those fat Sassenachs, then?
😉
Jim Barker says:
June 29, 2010 at 4:23 pm
If gravity has effects on the actual surfaces of the oceans (higher/ lower) as they move around, would it also effect the atmosphere itself, as it moves around? I’m probably not expressing this very well, but I am thinking that the atmosphere’s shape would be more amoeba-like, rather than the ball (ellipsoid) shape we generally assume.
Wow! Now there’s a thought: The Earth as ‘amoeba.’
No wonder those space aliens look at us all kinda weird like: “Yo! Dudes! How the heck can you stand to live like that?
“Don’t you get all ‘weirded-out’ sliming from place-to-place?”
🙂
Milwaukee Bob says:
June 29, 2010 at 4:00 pm
Dave Wendt said at 10:54 am
It highlights what a meaningless concept Global Mean Sea Level really is.
That summed it up very nicely and points to another fact that some people, including some scientists, do not seam to realize or grasp (at least not openly) and that is – with current technology (or anything in the foreseeable future) we can not calculate the average height of the planets oceans, nor the density, nor the temperature. The same thing holds true for the plants atmosphere, including but not limited to CO2 density. Why? Because we can not measure any of it – accurately. To have any degree of “accuracy” we would have to take our measurement of ALL factors, everywhere – almost simultaneously. And THAT reading on to its own would be meaningless as we have no historical data of comparable accuracy and due to the ever intersecting short, medium, long and extra long weather cycles we would need a couple hundred years history of such data to make any reasonable forecast of….. hmm, sounds like we a multi-million dollar grant.
Well, you know? Your thoughts just ain’t gonna cut it for the ones who’ve invested BILLIONS OF MOOLAH to get the rest of us to buy into their ‘carbon-come’ scheme.
You see? They’ve got it down flat and simple-like so that the hoi polloi (the commoners) understand the ‘simplicity’ of having to work their miserable lives to the bone and die soon enough so that the new-born get inculcated into the scheme seamlessly.
If you don’t watch out, they’ll send in the carbon-come Stasi to snuff your miserable existence so that you don’t get the chance to poison the well with Real Knowledge®.
The Goce satellite at an altitude of 255k is lower than the Grace satellite pair discussed in Willis’ article http://wattsupwiththat.com/2010/05/23/on-being-the-wrong-size/ . They are at 450-500km and spaced 220km apart and presumably do a similar job to Goce.
My concern with both of these systems, but especially Goce is that they are catching variable amounts of atmosphere on their journey and both rely on an accelerometer to measure gravity. I imagine the atmosphere at that altitude would be variable in density and introduce a spurious signal.
Jim G says:
June 29, 2010 at 3:09 pm
‘899 says:
“So then, is that why my centripetal dollars keep getting drawn towards D.C.?”
No, that is a true force! Unlike the oft quoted “gravity is because the earth sucks” Washington DC really does! And it sucks in money from anywhere and anyone it can. When it can’t get anymore it simply has the “privately owned” federal reserve create more out of thin air, an amazing violation of the rule of conservation of matter/energy!’
I was once told there was only one printed dollar, the rest is done with smoke and mirrors.
Does this explain levitating Bhuddas in India? 🙂
Interesting. The Andes mountains seem to have the opposite effect of the Himalayas. The Himalayas have the same effect as some of the deep ocean trenches. The mid-Atlantic ridge has almost no impact at all. Sri Lanka is the center of a huge anomoly despite being geologically rather dull.
Or maybe that instrument isn’t nearly as astonishingly sensitive as it would need to be to produce such a map reliably.