[time-nuts] UTC and leap seconds

jimlux 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:
>>    http://www.nasa.gov/topics/earth/features/earth-20100301.html
>> (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:
> ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.266
> ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.267
> Explanations is in:
> ftp://hpiers.obspm.fr/iers/bul/bulb_new/bulletinb.pdf
> 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 
> interest).
>  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 
> interesting.
> 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.

More information about the time-nuts mailing list