DIURNAL AND SEMIDIURNAL ATMOSPHERIC VARIATIONS OF UT1/LENGTH OF DAY


Atmospheric tides (both thermal and tidal) cause diurnal and semidiurnal components in the lenght of day or UT1. Most important contributions (diurnal wave S1 and semidiurnal wave S2) have been computed by Brzezinski,Bizouard and Petrov (2002) ["Influence of the atmosphere on Earth Rotation : what new can be learned from the recent atmospheric angular momentum estimates?", Surveys in Geophysics, 23, 33-69, 2002] from NCEP/NCAR Angular Atmospheric Momentum data. Herebelow we present updated estimates for the AAM data spanning the period from 1990 to 2002. Corresponding model is put under the form :

ΔUT1 = Σj aj cos(ARGj) + bj sin(ARGj)
ΔLOD = Σj cj cos(ARGj) + dj sin(ARGj)
where ARGj is integer linear combination of Delaunay arguments, GMST + &$pi; :
ARGj = a1 l + a2 l' + a3 D + a4 F + a5 Ω + a6 (GMST + π).

N.B.: the values here-below should be taken with caution because AAM remain poorly estimated at diurnal scales. 
                  
      l   l'  F   D   Ω  GMST + π      PERIOD     aj       bj        cj        dj       
                                      (hours)    (mus)    (mus)      (mus)    (mus)                
S1    0  -1   0   0   0     1           24.000   -0.3       0.8      -5.1     -1.8
S2    0   0  -2   2  -2     2           12.000    0.0      -0.4       4.6     -0.2


Delaunay arguments 
(IERS Conventions 2000, from Simon et al., 1994, Astron. Astrophys. 282, 663-683):
     
 Mean anomaly of the Moon :
   l = 134°.963 402 51 + 1 717 915 923.2178" t + 31".879 2 t2 + 0".051 635 t3 - 0".000 244 70 t4
 
 Mean anomaly of the Sun  : 
   l'= 357°.529 109 18 +   129 596 581.0481" t - 0".553 2 t2 -  0".000 136 t3 - 0".000 011 49 t4
 
 F = L - Ω  with L mean longitude of the Moon  
   F =  93°.272 090 62 + 1 739 527 262.8478" t - 12".751 2 t2 - 0".001 037 t3 + 0".000 004 17 t4
 
 Mean elongation of the Moon from the Sun :
   D = 297°.850 195 47 + 1 602 961 601.2090" t -  6".370 6 t2 + 0".006 593 t3 - 0".000 031 69 t4

 Mean longitude of the ascending node of the Moon :
   Ω = 125°.044 555 01  - 6 962 890.543 1" t + 7".472 2 t2 + 0".007 702 t3 - 0".000 059 39 t4

where t is measured un Julian Centuries of 36525 days of 86400 seconds of Dynamical Time since J2000.0.          

Rotation angle in arcseconds : Greenwich Mean Sidereal Time + 180°

   GMST + π = (67310.54841 + (876600d0*3600 + 8640184.812866) t 
             + 0.093104 t2 - 6.2 10-6 t3 ) 15 + 648000.0


where t is measured un Julian Centuries of 36525 days of 86400 seconds of Dynamical Time since J2000.0.