Tidal Signals in AOD1B

Atmospheric Tides

In total 12 tidal frequencies are estimated and removed from the ECMWF surface pressure fields. This includes the main solar tides S1, S2, and S3 as well as the main semi-diurnal lunar tide M2. For each of the four central frequencies two additional side-bands are estimated in order to also account for potential seasonal modulations

Tidal signals are estimated for the period 2007 – 2014, which is the part of the AOD1B reference period where ECMWF operational model data at a spatial resolution of T799 or better has been used. Tidal signals estimated from that period are subtracted from all atmospheric surface pressure grids of the years 2007 and later.

Since interannual variations in atmospheric tides have been found to be less reliable in older years, tidal signals at the 12 selected frequencies have been estimated and removed for each year separately before 2007.

Figure: Surface pressure signals of atmospheric tides for the triplets (P1-S1-K1), (T2-S2-R2, (T3-S3-R3) and (N2-M2-L2) removed from AOD1B as estimated over the period 2007 – 2014. 

Ocean Response to Atmospheric Tides

Periodic changes in atmospheric surface pressure over the oceans pose a time-variable loading to the water column that is not fully compensated isostatically, but excite a periodic motion in the oceans itself that adds to field of lunisolar gravitational ocean tides. The MPIOM simulation used for AOD1B RL06 is forced with atmospheric conditions including atmospheric surface pressure obtained from ECMWF. By doing so, the oceanic response to atmospheric tides is simulated together with the transient non-tidal ocean circulation variability.

All tidal variability from the ocean component of AOD1B has been removed in the same way as for the atmospheric part.

Figure: Ocean tides simulated in response to the atmospheric tides for the triplets (P1-S1-K1), (T2-S2-R2), (T3-S3-R3) and (N2-M2-L2) removed from AOD1B as estimated over the period 2007 – 2014. 


Reference Paper

Dobslaw, H., Bergmann-Wolf, I., Dill, R., Poropat, L., Thomas, M., Dahle, C., Esselborn, S., König, R., Flechtner, F.: A New High-Resolution Model of Non-Tidal Atmosphere and Ocean Mass Variability for De-Aliasing of Satellite Gravity Observations: AOD1B RL06. Geophysical Journal International, in preparation.

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