[time-nuts] UTC and leap seconds
jimlux at earthlink.net
Sat Jun 12 13:36:57 UTC 2010
Magnus Danielson wrote:
> On 06/12/2010 02:33 AM, Hal Murray wrote:
>> jimlux at earthlink.net said:
>>> The Chilean earthquake changed the angular rotation rate (or,
>>> probably more
>>> accurately, changed the direction of the axis of rotation as well)
>>> of the earth a small amount, as do most large earthquakes.
>> Has anybody measured that?
>> Is there a good URL on this? (predictions if not data) All I've
>> found so
>> far is a small NASA press release predicting 1.26 microseconds per day:
>> (and a zillion news sources repeating it)
>> 1 microsecond/day is 1 part in 1E11.
> There is one place that keeps track of these things, the IERS. Their
> Bullentin B provides monthly reports of earth rotation observatoins.
> The bulletin for relevant period of time is:
> Explanations is in:
> Clause 3 is of most interest, look at the OMEGA column (appended the
> bulletin b 267 data for a more complete time-series around the date of
> 3 - EARTH ANGULAR VELOCITY : DAILY FINAL VALUES OF LOD, OMEGA AT 0hUTC
> LOD : Excess of the Length of day - 86400 s TAI
> OMEGA : Earth angular velocity
> Description: ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.pdf
> DATE MJD LOD sigma OMEGA sigma
> (0 h UTC) ms ms mas/ms mas/ms
> 2010 2 2 55229 1.8681 0.0026 15.04106685346 0.00000000045
55287 1.3068 0.0018 15.04106695117 0.00000000031
> Yes, we see a dip there... but looking at the two-month data we se a
> regular pattern creating a dip there... and the lack of jump is
> Essentially... I can't see it here.
And I think that's what I heard: it should have changed (permanently)
but that it would be impossible to see without years of data to remove
all the other effects.
My GPS friends (all in the same section as Richard Gross.. the same
section are the folks who do precision measurements of gravity (GRACE
and GRAIL missions), etc.) tell me that once you get down into a certain
range of uncertainty (10cm=ish for GPS), there's a whole lot of factors
that are all of about the same magnitude (tidal movement, atmospheric
delays not due to ionosphere, ionospheric effects, continental drift,
etc.) So making absolute measurements requires lots of data and
painstaking identification of each of the factors and removing it.
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