High-resolution atmospheric angular momentum functions from different ECMWF data classes

Transcription

1 from different ECMWF dt clsses Journees Systèmes de référence stio-temorels Setember 2010, Pris Michel Schindelegger 1, Johnnes Böhm 1, Hrld Schuh 1, Dvid Slstein 2 1 Vienn University of Technology, Vienn, Austri 2 Atmosheric nd Environmentl Reserch. Inc. Lexington, U.S.A. 1

2 GGOS Atmoshere funded by the FWF, the Austrin Science Fund bsed on common dt strem from the ECMWF, four rime quntities re determined in consistent wy: Atmosheric Angulr Momentum Functions Atmosheric Pressure Loding Corrections Atmosheric Grvity Corrections Atmosheric Delys AAM APL AGC htt://ggostm.hg.tuwien.c.t/ 2

3 Erth rottion excittion t dily nd sub-dily eriods, investigted with 2 different sets of AAM functions: 1. 6-hourly AAMF from stndrd ECMWF dt: Atmosheric model nlysis 2. 3-hourly AAMF from the reorgnized ssimiltion system: Atmosheric model (delyed cut-off) cut-off time = ltest ossible rrivl time for observtions nlysis cycles re combined with short-term forecsts in order to dely cut-off time nd mke roducts vilble erlier Time sn: 1 July 2004 to 30 June

4 Amlitude sectr of AAM comonents: inerti tensor due to tmoshere, comonent c 23 reltive ngulr momentum, comonent l 1 6-hourly smling restricts resolution in semi-diurnl bnd good greement in these one-sided sectr 4

5 Conversion to tmosheric excittion: AAM AAMF Convolution of equtoril AAMF with trnsfer function of Brzezinski et l. [2002] in frequency domin tmosheric exc. of olr motion: (σ ) Two-sided sectr: Different signs of eks 6-hourly wind term noisier R( R( w ) ) ressure wind 5

6 Atmosheric excittion: LOD Polr motion mlitude estimtes (nd noise) re smller for 3-hourly AAM eks in olr motion < 2 µs 6

7 Nuttion: The good greement seen in the one-sided sectr emerges in this bnd! Min tmosheric tides: Diurnl tides [h] Semi-diurnl tides [h] π P T S S K R ψ φ

8 By-eye detection of tmosheric tides: LOD Polr motion S1 S2 ψ1 K1 P1 T2 R2 8

9 By-eye detection of tmosheric tides: Nuttion K1 ψ1 Sectrl content round NDFW is π1 P1 S1 φ1 retrogrde seminnul wobble in celestil frme mlified 9

10 Lest squres djustment on tmosheric excittion: Axil excittion modeled s l( t) = ntides j= 1 j rtil tide with frequency ω nd unknown Fourier coefficients nd b j cos( ω t) + b j j sin( ω t) j hse nd men mlitude of tidl wve Equtoril excittion djusted similrly, but rel nd imginry rt treted sertely, yields rel ro-/retrogrde nd imginry ro-/retrogrde mlitudes ro-/retrogrde hses nd men mlitudes of tidl wve 10

11 Lest squres djustment: men mlitudes from 3-hourly AAMF nuttion mlitudes Period [h] equ. rogr. equ. retrogr. xil π P S K ψ φ T S R mlitudes in [µs] (equtoril) nd [µs] (xil) 11

12 Counterction of ressure nd wind terms in 3-hourly AAMF: leds to smll mlitudes = cncelling out when dding ressure term sectrum nd wind term sectrum in frequency domin: equtoril cse: = R + I 2 ( ) ( ) 2 R( I( ) = R( ) = I( ) + R( ) + I( visible in the time evolution of sectrl content: w w ) ) sliding window Fourier trnsform normlized Morlet wvelet trnsform 12

13 Counterction in LOD, S1 nd S2 bnd slit u: S1 sliding window length: 2 S2 13

14 Counterction in olr motion, S1 nd S2 (rogrde) bnd slit u: S1 sliding window length: 2 S2 14

15 Summry, conclusions: Two different ECMWF dt clsses yield different mlitudes nd hses in tmosheric excittion of Erth rottion. However, nuttion mlitudes re in good greement. S2 nd its side lobes show u in the delyed cut-off series. Smll mlitudes in olr motion nd LOD cn be scribed to the counterction of ressure nd wind terms. Outlook: Physicl resoning for counterction. Of more rcticl imortnce: tmosheric forcing of nuttion. 15

16 The End Thnks for your ttention! 16