Oceanographers Catch First Wave Of Gravity Mission's Success

David E. Steitz
Headquarters, Washington
(Phone: 202/358-1730) July 21, 2003

Alan Buis Margaret Baguio
JPL Pasadena, Calif. Univ. of Texas (UT), Austin
(Phone: 818/354-0474) (Phone: 512/471-6922)

Vanadis Weber Franz Ossing
German Aerospace Center GeoForschungsZentrum Potsdam
(Phone: 49 (0) 2203/601-3068) Phone: 49 (331) 288-1040)

RELEASE: 03-244

OCEANOGRAPHERS CATCH FIRST WAVE OF GRAVITY MISSION'S SUCCESS

The joint NASA-German Aerospace Center Gravity Recovery
and Climate Experiment (Grace) mission has released its first
science product, the most accurate map yet of Earth's gravity
field. Grace is the newest tool for scientists working to
unlock secrets of ocean circulation and its effects on
climate.

Created from 111 days of selected Grace data, to help
calibrate and validate the mission's instruments, this
preliminary model improves knowledge of the gravity field so
much it is being released to oceanographers now, months in
advance of the scheduled start of routine Grace science
operations. The data are expected to significantly improve
our ability to understand ocean circulation, which strongly
influences weather and climate.

Dr. Byron Tapley, Grace principal investigator at UT's Center
for Space Research, called the new model a feast for
oceanographers. "This initial model represents a major
advancement in our knowledge of Earth's gravity field. "Pre-
Grace models contained such large errors many important
features were obscured. Grace brings the true state of the
oceans into much sharper focus, so we can better see ocean
phenomena that have a strong impact on atmospheric weather
patterns, fisheries and global climate change."

Grace is accomplishing that goal by providing a more precise
definition of Earth's geoid, an imaginary surface defined
only by Earth's gravity field, upon which Earth's ocean
surfaces would lie if not disturbed by other forces such as
ocean currents, winds and tides. The geoid height varies
around the world by up to 200 meters (650 feet).

"I like to think of the geoid as science's equivalent of a
carpenter's level, it tells us where horizontal is," Tapley
said. "Grace will tell us the geoid with centimeter-level
precision."

So why is knowing the geoid height so important? JPL's Dr.
Lee-Lueng Fu, scientist on Topex/Poseidon and Jason project
said, "The ocean's surface, while appearing flat, is actually
covered with hills and valleys caused by currents, winds and
tides, and also by variations in Earth's gravity field.
"Scientists want to separate out these gravitational effects,
so they can improve the accuracy of satellite altimeters like
Jason and Topex/Poseidon, which measure sea surface height,
ocean heat storage and global ocean circulation. This will
give us a better understanding of ocean circulation and how
it affects climate."

Dr. Michael Watkins, Grace project scientist at JPL, put
improvements to Earth's gravity model into perspective.
"Scientists have studied Earth's gravity for more than 30
years, using both satellite and ground measurements that were
of uneven quality. "Using just a few months of our globally
uniform quality Grace data, we've already improved the
accuracy of Earth's gravity model by a factor of between 10
and nearly 100, depending on the size of the gravity feature.
In some locations, errors in geoid height based upon previous
data were as much as 1 meter (3.3 feet). Now, we can reduce
these errors to a centimeter (0.4 inches) in some instances.
That's progress."

Dr. Christoph Reigber, Grace co-principal investigator at
GeoForschungsZentrum Potsdam, said, "As we continue to assess
and refine Grace's instruments and subsystems, we're
confident future monthly gravity solutions will be even
better than the map we're releasing now. "Those solutions
will allow us to investigate processes associated with slow
redistribution of mass inside Earth and on its land, ocean
and ice surfaces. Our initial attempts to identify such small
gravity signals with Grace look very promising."

Grace senses minute variations in gravitational pull from
local changes in Earth's mass by precisely measuring, to a
tenth of the width of a human hair, changes in the separation
of two identical spacecraft following the same orbit
approximately 220 kilometers (137 miles) apart. Grace will
map the variations from month to month, following changes
imposed by the seasons, weather patterns and short-term
climate change.

Grace is a joint partnership between NASA and the German
Aerospace Center. The UT Center for Space Research has
overall mission responsibility. GeoForschungsZentrum Potsdam
is responsible for German mission elements. Science data
processing, distribution, archiving and product verification
are managed under a cooperative arrangement between JPL, UT,
and GeoForschungsZentrum Potsdam. For more information,
visit:

http://www.csr.utexas.edu/grace or http://www.gfz-potsdam.de/grace

Model images are at:

http://photojournal.jpl.nasa.gov/catalog/PIA04652

and

http://www.csr.utexas.edu/grace and http://www.gfz-potsdam.de/grace

-end-

Stupid question:

Does the gravity force only work unidirectional (towards the center of the
earth)
or can outside forces (like the moon or the redistribution of ice/water
masses) also
alter the distribution of mass inside the earth ?

Are there any known effects of the variations of earth distance from the sun
on the distribution of mass inside the earth?

We all know about the "bulge" ocean water suffers from these forces, I've
also
read that moon vulcanism is caused by these grav tides.

Any known effects like this on earth?

Thanks for your feedback
Morenga


David E. Steitz
Headquarters, Washington
(Phone: 202/358-1730) July 21, 2003

Alan Buis Margaret Baguio
JPL Pasadena, Calif. Univ. of Texas (UT), Austin
(Phone: 818/354-0474) (Phone: 512/471-6922)

Vanadis Weber Franz Ossing
German Aerospace Center GeoForschungsZentrum Potsdam
(Phone: 49 (0) 2203/601-3068) Phone: 49 (331) 288-1040)

RELEASE: 03-244

OCEANOGRAPHERS CATCH FIRST WAVE OF GRAVITY MISSION'S SUCCESS

The joint NASA-German Aerospace Center Gravity Recovery
and Climate Experiment (Grace) mission has released its first
science product, the most accurate map yet of Earth's gravity
field. Grace is the newest tool for scientists working to
unlock secrets of ocean circulation and its effects on
climate.

Created from 111 days of selected Grace data, to help
calibrate and validate the mission's instruments, this
preliminary model improves knowledge of the gravity field so
much it is being released to oceanographers now, months in
advance of the scheduled start of routine Grace science
operations. The data are expected to significantly improve
our ability to understand ocean circulation, which strongly
influences weather and climate.

Dr. Byron Tapley, Grace principal investigator at UT's Center
for Space Research, called the new model a feast for
oceanographers. "This initial model represents a major
advancement in our knowledge of Earth's gravity field. "Pre-
Grace models contained such large errors many important
features were obscured. Grace brings the true state of the
oceans into much sharper focus, so we can better see ocean
phenomena that have a strong impact on atmospheric weather
patterns, fisheries and global climate change."

Grace is accomplishing that goal by providing a more precise
definition of Earth's geoid, an imaginary surface defined
only by Earth's gravity field, upon which Earth's ocean
surfaces would lie if not disturbed by other forces such as
ocean currents, winds and tides. The geoid height varies
around the world by up to 200 meters (650 feet).

"I like to think of the geoid as science's equivalent of a
carpenter's level, it tells us where horizontal is," Tapley
said. "Grace will tell us the geoid with centimeter-level
precision."

So why is knowing the geoid height so important? JPL's Dr.
Lee-Lueng Fu, scientist on Topex/Poseidon and Jason project
said, "The ocean's surface, while appearing flat, is actually
covered with hills and valleys caused by currents, winds and
tides, and also by variations in Earth's gravity field.
"Scientists want to separate out these gravitational effects,
so they can improve the accuracy of satellite altimeters like
Jason and Topex/Poseidon, which measure sea surface height,
ocean heat storage and global ocean circulation. This will
give us a better understanding of ocean circulation and how
it affects climate."

Dr. Michael Watkins, Grace project scientist at JPL, put
improvements to Earth's gravity model into perspective.
"Scientists have studied Earth's gravity for more than 30
years, using both satellite and ground measurements that were
of uneven quality. "Using just a few months of our globally
uniform quality Grace data, we've already improved the
accuracy of Earth's gravity model by a factor of between 10
and nearly 100, depending on the size of the gravity feature.
In some locations, errors in geoid height based upon previous
data were as much as 1 meter (3.3 feet). Now, we can reduce
these errors to a centimeter (0.4 inches) in some instances.
That's progress."

Dr. Christoph Reigber, Grace co-principal investigator at
GeoForschungsZentrum Potsdam, said, "As we continue to assess
and refine Grace's instruments and subsystems, we're
confident future monthly gravity solutions will be even
better than the map we're releasing now. "Those solutions
will allow us to investigate processes associated with slow
redistribution of mass inside Earth and on its land, ocean
and ice surfaces. Our initial attempts to identify such small
gravity signals with Grace look very promising."

Grace senses minute variations in gravitational pull from
local changes in Earth's mass by precisely measuring, to a
tenth of the width of a human hair, changes in the separation
of two identical spacecraft following the same orbit
approximately 220 kilometers (137 miles) apart. Grace will
map the variations from month to month, following changes
imposed by the seasons, weather patterns and short-term
climate change.

Grace is a joint partnership between NASA and the German
Aerospace Center. The UT Center for Space Research has
overall mission responsibility. GeoForschungsZentrum Potsdam
is responsible for German mission elements. Science data
processing, distribution, archiving and product verification
are managed under a cooperative arrangement between JPL, UT,
and GeoForschungsZentrum Potsdam. For more information,
visit:

http://www.csr.utexas.edu/grace or http://www.gfz-potsdam.de/grace

Model images are at:

http://photojournal.jpl.nasa.gov/catalog/PIA04652

and

http://www.csr.utexas.edu/grace and http://www.gfz-potsdam.de/grace

-end-

In article ,
Morenga wrote:
Does the gravity force only work unidirectional (towards the center of the
earth)...

Earth's gravity is not directed *precisely* toward its center, because
of complications like its equatorial bulge. But that's not quite what
you really wanted to ask...

or can outside forces (like the moon or the redistribution of ice/water
masses) also
alter the distribution of mass inside the earth ?

Only very, very slightly.

There are tides in the solid Earth as well as in its oceans, because on a
planetary scale there is no such thing as a rigid material. But they are
quite small, and their effect on Earth's mass distribution is minute.

Similarly, redistribution of water (and air) changes Earth's mass
distribution enough to be detectable, but in absolute terms the effect is
extremely small.

Are there any known effects of the variations of earth distance from the sun
on the distribution of mass inside the earth?

Solar tides are a bit stronger when the Earth is closer, but otherwise no.

also read that moon vulcanism is caused by these grav tides.

There is no known vulcanism on the Moon today. Except for meteorite
impacts, the Moon appears to have been a very quiet place, geologically
speaking, for the last couple of billion years.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

"Morenga" writes:

Does the gravity force only work unidirectional (towards the center of
the earth)

No. The gravitational acceleration at any point in space is (in some vague)
sense the "sum" of the gravitational accelrations produced by every object
in the visible universe, and there is no reason why it should always point
"inward." (In fact, for bodies inside their Roche's limit, there are points
where the net gravitational acceleration is "outward," which is why such bodies
may fall apart if the tidal forces exceed that body's tensile strength.)


or can outside forces (like the moon or the redistribution of ice/water
masses) also alter the distribution of mass inside the earth ?

Yes. We have a name for the re-distribution of matter caused by this "force:"
it is called "the lunar-induced tide."


Are there any known effects of the variations of earth distance from the sun
on the distribution of mass inside the earth?

Yes. It is called "the solar-induced tide."


We all know about the "bulge" ocean water suffers from these forces, I've
also read that moon vulcanism is caused by these grav tides.

There is _no_ reliable evidence that volcanism has occurred on the Moon
in aeons. There is evidence for occasional lava upwellings after asteroid
impacts, but that is not the same as volcanism.


Any known effects like this on earth?

The tidal deformation of the body of the Earth is called an "earth tide,"
just as the tidal deformation of the ocean is called an "ocean tide."


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

or can outside forces (like the moon or the redistribution of ice/water
masses) also
alter the distribution of mass inside the earth ?

Only very, very slightly.

But I read that even magma streams beneath the earth's crust are affected by
this.


Similarly, redistribution of water (and air) changes Earth's mass
distribution enough to be detectable, but in absolute terms the effect is
extremely small.

Then why is it that affect the mass of the moon has is big enough to force
the earth's rotatational center away from its gravitational center?
Shouldn't that affect the streams of matter distribution inside a liquid body
such as the inner earth?

Solar tides are a bit stronger when the Earth is closer, but otherwise no.

also read that moon vulcanism is caused by these grav tides.

There is no known vulcanism on the Moon today.


But I did read on multiple occassions about eruptions of hot gases having
been monitored on the moon. Those gases where traced back to pockets
of hot rock having been heated up by grav tidal forces.

I actually have it detailed in a German atronomical journal.

Regards
Morenga

(In fact, for bodies inside their Roche's limit, there are points
where the net gravitational acceleration is "outward," which is why such bodies
may fall apart if the tidal forces exceed that body's tensile strength.)

Now one thing that always fascinated me about this Roche limit is the
question
of what would happen if two bodies of exactly equal mass would cross each
other's
"Roche limit". I mean is the Roche limit different for each pairing or is it
a total
boundary, similar to the "event horizon" of a black hole?

But the bottom line of my questions was actually on wether such a
gravitational
map as that one produced by Grace would even make sense, given that all
these factors constantly change the earth's grav appearance.
Wouldn't they have to keep updating that mapp all the time?


There is _no_ reliable evidence that volcanism has occurred on the Moon
in aeons. There is evidence for occasional lava upwellings after asteroid
impacts, but that is not the same as volcanism.

Well I read of hot gas erruptions and even moon quaked having been measured
w/o any meteorite impacts. An they said these where caused by grav tides
from the earth' influence on the moon.


The tidal deformation of the body of the Earth is called an "earth tide,"
just as the tidal deformation of the ocean is called an "ocean tide."

Now wouldn't all these grav tides suffice to destract the streams of matter
flowing inside the body liquid of the inner earth?

Regards
Morenga

JRS: In article , seen
in news:sci.space.science, Morenga posted at Thu, 31 Jul
2003 04:57:59 :-
(In fact, for bodies inside their Roche's limit, there are points
where the net gravitational acceleration is "outward," which is why such bodies
may fall apart if the tidal forces exceed that body's tensile strength.)

Now one thing that always fascinated me about this Roche limit is the
question
of what would happen if two bodies of exactly equal mass would cross each
other's
"Roche limit".


You must also consider the relative densities - see my gravity3.htm.
Only if the equal masses have equal densities will they enter each
other's Roche Limits simultaneously.

The arithmetic will be different, since the closer parts of each body
will be significantly nearer than the centres of gravity.

Each body will be affected by the tide of everything else; the effect of
Body A on Body B will not immediately be much affected by part of the
surface of A becoming detached.

The calculation for fluid bodies will be much worse than in the small-
orbiter case; and that looked hard enough in Roche's paper. But I
expect that brute force computation can give a result nowadays.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

You must also consider the relative densities - see my gravity3.htm.

URL for that one?

Only if the equal masses have equal densities will they enter each
other's Roche Limits simultaneously.

Do black holes have Roche limits?
What if two black holes of equal mass approach each other?
Could they rip each other appart? And how so as nothing is
supposedly allowed to leave the "event horizon" once it enters.

Each body will be affected by the tide of everything else; the effect of
Body A on Body B will not immediately be much affected by part of the
surface of A becoming detached.
The calculation for fluid bodies will be much worse than in the small-
orbiter case; and that looked hard enough in Roche's paper. But I
expect that brute force computation can give a result nowadays.

How does the grav field look like if two fluid bodies (like gas giants)
would approach each other? I mean they would not tear each other
appart but rather "flow" towards each other, right?

Maybe even forming a 3rd body at their new unified center of gravity?

Also is there a computer (PD) program for multiple stellar body grav
simulations?

Greetings
Morenga

You must also consider the relative densities - see my gravity3.htm.

URL for that one?

Only if the equal masses have equal densities will they enter each
other's Roche Limits simultaneously.

Do black holes have Roche limits?
What if two black holes of equal mass approach each other?
Could they rip each other appart? And how so as nothing is
supposedly allowed to leave the "event horizon" once it enters.

Each body will be affected by the tide of everything else; the effect of
Body A on Body B will not immediately be much affected by part of the
surface of A becoming detached.
The calculation for fluid bodies will be much worse than in the small-
orbiter case; and that looked hard enough in Roche's paper. But I
expect that brute force computation can give a result nowadays.

How does the grav field look like if two fluid bodies (like gas giants)
would approach each other? I mean they would not tear each other
appart but rather "flow" towards each other, right?

Maybe even forming a 3rd body at their new unified center of gravity?

Also is there a computer (PD) program for multiple stellar body grav
simulations?

Greetings
Morenga

JRS: In article , seen
in news:sci.space.science, Morenga posted at Fri, 1 Aug
2003 17:08:46 :-

You must also consider the relative densities - see my gravity3.htm.

URL for that one?

If you cannot readily locate the page from the information provided,
then ...

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.