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
//
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Cool, so if the ocean was still enough it would have hills.
So much green and so little red – shouldn’t they use another colour code to remain consistent with climate science ?
kwik says:
June 28, 2010 at 9:41 pm
Could the gravity-variance come from CO2?
Oh man, now ya done gone and done it!
We’ll now be hearing all about ‘Anthropogenic Global Gravity Change’ … 😉
Cool, so if the ocean was still enough it would have hills. That would be great for waterskiing
Policyguy says:
June 28, 2010 at 11:14 pm
Policyguy,
The map is showing the changes in gravity (acceleration) across the surface of the Earth. Gravity is proportional to a body’s mass and distance between it and another mass (ht Sir Isaac Newton, Law of Universal Gravitation) F=G(mass1*mass2)squared.
Our planet does not have a regular surface from a rock density perspective, and the changes in the density of the rocks that make up the lithosphere (top crust, oceanic and continental crust) and lower sections of the earth’s crust (asthenosphere, upper mantle, lower mantle and outer/inner core) identify rock density and as per your second post correctly identifies, areas of tectonic activity.
Areas of the earth’s crust where seafloor is being actively created (seafloor rock generally has a higher density than continental rock) show as anomalous highs (over Iceland and tracking the Atlantic tectonic spreading ridge to the south) as well as over the area of Indonesia/Malaysia/heading towards New Zealand which is also tectonically active with creation of new seafloor.
Density lows can bee seen to correlate with sedimentary basins (sedimentary rocks have lower densities than seafloor rock), the very large one south of India being a classic case. The one under the Great Lakes/Souther Canada is also a sedimentary basin.
This is a gross description of the general process but it gives a rough idea of what it’s all about.
I must be thick because it is not obvious to me what is being shown either. The Himalayan plateau is several thousand metres high but does not show up. The Pacific trench is thousands of metres deep and does not show up. Is this map perhaps showing the difference between the measured heights from sea level and those calculated using gravity measurements? I can see how this would be more valuable than the actual variance in gravity measurement. However if this is the case it would be interesting to see the raw data as well.
In time it will help to see how the map changes, for a variety of reasons. So far I have not read up on the surface resolution – it looks coarse when contoured this way – but I doubt if it reveals much not known already to geophysicists already working with gravity.
In mineral exploration work, the emphasis is often on resolution of gravity differences between points less than a km apart. This airborne instrument is of little help there, but it’s a neat piece of engineering.
It’s a pity that few geologists can agree about the composition of sub-crustal Earth, because that affects the gravity interpretation. Currently, there is no way to measure the sub-crust directly, so in a way the philosophy of this gravity science resembles the selection of CO2 as a warming cause partly because it explains a gap in model predictions. Different investigators will have their beliefs about the sub-crust and their models will reflect this, but it’s not evidence-based.
Richard Hill says: June 28, 2010 at 8:25 pm
It would be good to see the same map in some sort of an “equal area” projection.
You can see global view on my website I recorded some time ago.
http://www.vukcevic.talktalk.net/NFC.htm
tallbloke says: June 28, 2010 at 11:20 pm
It will be interesting to see if any of the motions in the changing geoid correlate with geomagnetic meanderings. That would be indicative that the satellite was capturing the movement of iron rich molten material under the Earth’s crust responsible for most of the changes in the Earth’s Length Of Day (LOD)
That is indeed case in some locations. In my article dealing with the North Atlantic temp anomaly I have maps directly relating to the effect.
http://www.vukcevic.talktalk.net/NATA.htm
tallbloke says: June 28, 2010 at 11:20 pm
It will be interesting to see if any of the motions in the changing geoid correlate with geomagnetic meanderings. That would be indicative that the satellite was capturing the movement of iron rich molten material under the Earth’s crust responsible for most of the changes in the Earth’s Length Of Day (LOD)
That is indeed case in some locations. In my article dealing with the North Atlantic temp anomaly I have maps directly relating to the effect.
http://www.vukcevic.talktalk.net/NATA.htm
pages 3 and 4 then 8 and 9
“5. It is the shape the oceans would take without winds and currents”
and the moon?
tallbloke says: June 28, 2010 at 11:20 pm
It will be interesting to see if any of the motions in the changing geoid correlate with geomagnetic meanderings.
Indian Ocean gravity anomaly does not appear to show magnetic anomaly. Hudson Bay area is only one where two are coincidental.
http://www.ngdc.noaa.gov/geomag/data/mag_maps/browse/Z_map_mf_2005_large.jpeg
Ocean currents do not appear to be greatly affected by gravity anomaly.
http://upload.wikimedia.org/wikipedia/commons/6/67/Ocean_currents_1943_(borderless)3.png
It should be remembered that these anomalies are not particularly large. They are measured in miligals, units of acceleration commonly used in geodetic measurements, equal to 10E-3 Galileo, or 10E-5 meter per second square (10E-5 m/sec2).
Most readers seem to think that this is something static, whereas most of the earth is not solid but molten, and so these gravitational anomalies might change with time. If one compares this map with that of sea level rise, for example http://buythetruth.files.wordpress.com/2008/11/altimetry.jpg?w=375&h=236 there is an interesting correlation. In the northern Indian ocean, sea level rise is zero or negative. Around Indonesia it is very high positive. Off the west coast of USA (California) it is stable or declining slightly. North Atlantic has increasing sea level.
This gravitational map is merely a snapshot. Variations in the gravitational anomalies over time cause variations in sea level. So, as we can see here, it is possible for parts of the Indian ocean to be decreasing in sea level (e.g. around the Maldives), but for rising sea level a thousand miles to the east in Indonesia. The fact that sea level can be rising in one place and decreasing a thousand miles away at the very least (now that we have this gravitational map with reasonable correlation to sea level trends) makes it worth considering whether variations in the gravitational anomalies are a significant factor in sea level trends.
One can imagine that if the gravitational anomalies change significantly over time, then the effects on sea level could in any location outweigh the effects of melting ice etc. Notwithstanding the appalling grandstanding by the Maldives’ president, there is no sea level rise around the Maldives – it has declined since the 1970s, whereas there is noticeable sea level rise around some islands in the southwest Pacific. I can’t help wondering whether that deep blue around the Maldives and the deep orange in the south Pacific are telling us something about the causes of that.
I must admit I don’t quite understand what this is all about.
I make one thing of it so far. If all the fat people migrate to the dark blue areas, they can feel good about themselves. Oh, yes, also, anorexics should stay away from the red bits.
Graham Dick”
““5. It is the shape the oceans would take without winds and currents”
and the moon?”
Good point Graham. Not sure if the Moon’s gravity was removed from the data.
I’m still experimenting with HTML tags..</quote Please bear with me as they seem to have different effects from site to site.. 😉
BuggerDamn!I’m an assembler programmer. Moderators, please remove the above if not funny enough..
@Policyguy: The map is showing the change in height needed to maintain the same potential energy. So comparing two people of the same mass, one goes to Sri Lanka and another to Iceland. Because the gravity is stronger over Sri Lanka (denser/thicker rock) that person would have to move closer to the centre of the earth relative to the person in Iceland (less dense/thinner rock) to have the same potential energy.
So any water at Sri Lanka with higher potential energy than the surrounding water would move away, like a ball rolling, or rivers flowing, downhill, so we would expect deeper water at Iceland (ie water further from the centre of the Earth) than at Sri Lanka.
Excuse my rusty Physics
all Im am worred about is where is my next grant comming from
I don’t understand how balls won’t roll on it’s surface slopes. If the gravity pull on one edge of a ball is higher than on the other edge, the ball will roll.
What about fulcrum balances? Equal weights at each end. Will such balances on a slope be unbalanced? I would think so.
My Gosh! Sir Isaac Newton was WRONG! /sarc
ScientistForTruth says:
June 29, 2010 at 2:03 am
…The fact that sea level can be rising in one place and decreasing a thousand miles away at the very least (now that we have this gravitational map with reasonable correlation to sea level trends) makes it worth considering whether variations in the gravitational anomalies are a significant factor in sea level trends.
Indeed. What would be the effect on sea level if the density of the matter below the crust varies across the oceans? I tend to think it will be fairly negligible. Several milimeters, rather than several Cms.
Baa Humbug says:
June 29, 2010 at 2:11 am
I make one thing of it so far. If all the fat people migrate to the dark blue areas, they can feel good about themselves. Oh, yes, also, anorexics should stay away from the red bits.
Ha ha! I remember throwing away Hal Clement’s ‘Mission of Gravity’ after only ten pages or so. Not because I wasn’t curious about what came next but because it made me feel so, so heavy. The book is set on a planet called Mesklin where the gravity ranges from 3g on the equator to 700g at the poles.
Maybe someone can help me with this. In projecting sea level changes due to the myriad processes that worry the warmists, is it possible that there are too many variables whose coarseness or unknowableness would exceed the likely change values.
(maybe too much in sentence above)
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?
Further to the above. This business with picking signals (sea level changes for example) out of the noise using statistical legerdemain seems to rely on agility in identifying what is and what isn’t signal – not that there may be no signal.
Likely I’m all wet here and this has been sloshed about at great length by the people who understand it better than me.