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Gravity Map of Earth
dr3vil writes "Interesting results have been published by the GRACE (Gravity Recovery and Climate Experiment) project, of the various gravity anomolies that exist at various places on Earth. The BBC report gives a good overview. Fascinating for me, a resident of California, to see us apparently sandwiched between a high and a low spot. Maybe that helps aids the tectonic flows around here?"
BTW, if you want to know how much gravity differs (and how damn sensitive these sats are), look at this chart:
/ 03 _07_GRACE.html
http://www.csr.utexas.edu/grace/gallery/gravity
And note the range of the legend -60 to +60 mGal.
Because variations in gravity are very small, units for gravity surveys are generally
in milligals (mgal) where 1 mgal is one thousandth of 1cm/s
Thats damn sensitive.
-molo
Using your sig line to advertise for friends is lame.
Looking at the detailed map, it's fair to say that, in the Western Hemisphere, Alaska sucks. Also, Montana seems to suck, and southern Mexico sucks, too. Colombia and Chile, though, really suck.
On the other hand, the Bermuda Triangle totally blows.
Interesting how the map relegates Europe to the fringes... I'm suuuuuuuure it's just because the Prime Meridian happened to cut France in half.
Stressed? Me? Of course not. Stress is what a rubber band feels before it breaks, silly.
If the sub is moving, their is a layer of compressed water on one side, and a layer of slightly less compressed water on the other side (kind of like how radar sees a moving volume). Not to mention any bubbles generated by the spinning prop(s) out back decreasing the density of the water significantly. Question is; can we detect it fast enough to matter? Knowing where a sub was 30min ago is useless.
IIRC, magnetic harmony has already been reached between sub and ocean. I think that was something they did back in the 50's or 60's. Not 100% on that though...
Well, inertially navigated submarines DO have a gravity map of the area they are operating in. At least the one's I was on.
The gravity map values are applied as correction factors to the inertial navigators.
The gyro's are attracted towards denser areas, which causes precession, which is picked up as an incorrect acceleration, and this throws the position of the inertial navigator off.
So we basically aplied a correction signal to keep the gyro's orientated to the correct reference planes in the math model so the 'real' accelerations could be correctly calculated.
Maybe that helps aids the tectonic flows around here? Seems to me that the techtonic flows cause, rather than are caused by gravitational differences. Less mass in one area == less gravity, and so forth.
Tectonic movement is caused by density variations associated with the earth's being heated from within (decay of radioactive elements) and cooled from without. This drives convection currents (think chicken soup). What we see on the surface is the horizontal component of those convective movements. The gravity anomalies associated with these density variations are on the 100km-1000km length scale.
OTOH you can get gravity anomalies due to plain old topography, changes in chemical composition of the crust (e.g. an iron ore body, or uranium deposit) which are associated with both mass and density variations, but have nothing to do with either tectonics. The gravity anomalies associated with these effects are generally of a much shorter wavelength than the anomalies associated with convective (tectonic) forces.
To be fussy, the gravity anolalies are more to do with out-of-equlibrium crust than simple highs and lows. So the East pacific rise (a mid ocean ridge) barely shows up at all, but the ridge over a hotspot at Iceland shows up a mile. In a similar way, the Plateaus of Tibet and S. America, which are currently undergoing gravitational collapse, show up strongly.
On a larger scale (see the Indian ocean), the really large scale anomolies are hypothesised to be the result of deep mantle convection.