Short-term tidal variations in UT1: compliance between modeling and observation

Transcription

1 IAU 2009 JD 6 Tme & Astronomy Short-term tdal varatons n UT1: complance between modelng and observaton S. Englch, H. Schuh, R. Weber

2 Short-term (tdal) varatons n UT1 2 Durnal and sub-durnal varatons Ocean tdes effect up to 80 μs Atmospherc tdes effect ca. 1 μs Lunsolar torque on traxal Earth effect ca. 4 μs Varatons up to 35 days Sold Earth tdes effect up to 2 ms Ocean tdes effect ca. 0.2 ms AAM, OAM

3 Outlne 3 VLBI/GNSS solutons for UT1/LOD determnaton Durnal and sub-durnal varatons Estmaton of ocean tdal terms Comparson to the 2003 model + model for sem-durnal spn lbraton Varatons up to 35 days Estmaton of zonal tdal terms Comparson to the 2003 model and to a combned model suggested by R. Gross

4 VLBI/GNSS solutons for UT1/LOD determnaton 4 Observaton data VLBI all sessons sutable for EOP determnaton GNSS GPS and GLONASS of 120 IGS network stes Tme span (25 years) 8 months of 2008 Reference frames EOP ITRF2005, ICRF Ext. 2 nutaton fxed to IAU2000A + dx, dy from C04 1h and 5h UT1 IGS05, CODE orbts nutaton fxed to IAU2000A 1h LOD Software OCCAM Gauss-Markov model Bernese GPS Software

5 Ocean tdal terms 5 Ampltude estmaton: least squares adjustment Removal of low-frequency sgnal wth 05 C04 seres UT1/LOD varatons as pseudo-observatons 70 terms (+ 6 zero terms wth no sgnal expected) rato of nseparable terms constraned wth rato of tdal potental VLBI δut1: n δut1 = A = 1 sn( ξ ) + B cos( ξ ) GPS δlod: δlod = n = 1 A 'cos( ξ ) + B 'sn( ξ ) δut1 [ d] perod Amp( UT1) = Amp( LOD) & retard phase by 90 2π

6 Major tdal terms w.r.t model 6 Model has stll defcences n both tdal bands

7 Major tdal terms w.r.t model 7 Model has stll defcences n both tdal bands Confrmed by GNSS observatons

8 Major tdal terms w.r.t model 8 Account for the effect of the lunsolar torque on the traxal Earth (Brzeznsk and Captane, 2002)

9 Qualty/nose level check - zero terms 9 3-fold formal error seems reasonable

10 Conclusons part I 10 The 2003 model for the durnal and sub-durnal UT1 varatons does not completely remove all sgnal n these bands. Sgnfcant resdual ampltudes reman, whch should be consdered when studyng varatons wth longer perods n order to avod alasng effects (especally f the samplng nterval exceeds 12h). It would be benefcal to nclude a model for the effect of the traxalty of the Earth on UT1 n the next Conventons.

11 Zonal tdal terms (< 35 d) 11 Ampltude estmaton: least squares adjustment VLBI δut1: δut1 = C = 1 41 terms (+ 1 zero term) Removal of largest known effects / low frequences: Atmospherc nfluence: from Atmospherc Angular Momentum Data (NCEP, 6 h) Durnal and sub-durnal ocean tdes: reduced wth the before estmated VLBI-model Flterng of sgnal >35 d n sn( ξ ) + D cos( ξ )

12 Terms are calculated wth respect to Model of Conventons 2003 not qute clear how t s composed Combnaton of models suggested by R. Gross Yoder et al. (1981) elastc body tde model Wahr and Bergen (1986) nelastc body tde model Kantha et al. (1998) ocean tde model

13 Resdual ampltudes of major terms 13 major terms Mqm Msqm Mtm Mstm Mf Mf Msf Mm Msm Tdal wave Perod(d)

14 Resdual ampltudes of all terms 14 major terms sde terms Mqm Msqm Mtm Mstm Mf Mf Msf Mm Msm Tdal wave Perod(d)

15 Resdual ampltudes of all+zero terms 15 major terms sde terms zero term 3-fold formal error Mqm Msqm Mtm Mstm Mf Mf Msf Mm Msm Tdal wave Perod(d)

16 Terms whch dffer by 1 cycle n 18.6 y constraned 16 major terms sde terms zero term 3-fold formal error Mqm Msqm Mtm Mstm Mf Mf Msf Mm Msm Tdal wave Perod(d)

17 Phasor plot 17 The man part of the resdual sgnal n the fortnghtly tdal band s due to the cosne or the out-of-phase part respectvely.

18 Conclusons part II 18 The comparson of observed UT1 varatons <35 d wth the correspondng terms of the 2003 model for the zonal tdes revealed rather large dscrepances (>40 μs) n the fortnghtly tdal band, n partcular n the out-of-phase parts. The combnaton of models proposed by R. Gross accounts for most of the fortnghtly tdal sgnal and reduces the resdual ampltudes almost below the 3-sgma level. The model could be updated, especally concernng the ocean tdal contrbuton and represented more clearly, preferably n two parts (sold Earth tdes, ocean tdes).

19 Thank you!