In Situ Ocean Bottom Pressure

Both numerical ocean model experiments and new releases of GRACE gravity fields require validation against independent observations. Bottom pressure measurements recorded at the sea-floor provide such an opportunity. We use data from a number of globally distributed in situ OBP recorders from various institutions as compiled by Macrander et al. (2010). In situ records are carefully post-processed in order to remove discontinuities and non-linear drift; to remove effects from re-deployments of sensors after maintenance; and to isolate and remove tidal signals (Pawlowicz et al., 2002). 

From each dataset that is to be validated, data is extracted from four grid points closest to the in situ station and linearly interpolated to the station's actual location. In order to focus on specific frequency bands, we can apply a series of Butterworth low pass filters. Typically, we perform the validation for three frequency bands: 1-3, 3-10 and 10-30 days. The  agreement with the in situ observations is usually expressed in relative explained variance, i.e. the measured variance explained by the numerical model or the GRACE gravity field. 

Displays validation results for the releases 05 and 06 of AOD1B for two frequency bands. Both releases have much higher explained variances for the 3-10 days frequency band than for the 1-3 days band. In the 1-3 days frequency band, both models explain up to 60% of measured variability for many stations and the highest improvement of RL06 compared to the previous release is in the Arctic Ocean and equatorial Pacific. In the 3-10 days frequency band, the relative explained variances are up to 90% and the largest improvements are again in the Arctic and in the southern Atlantic.

References

Dobslaw H, Bergmann-Wolf I, Dill R, Poropat L, Thomas M, Dahle C, Esselborn S, Konig R, Flechtner F (2017) A new high-resolution model of non-tidal atmosphere and ocean mass variability for de-aliasing of satellite gravity observations: AOD1B RL06. Geophys J Int, 2011(1):263-269, DOI 10.1093/gji/ggx302 

Macrander A, Boening C, Boebel O, Schroeter J (2010) Validation of GRACE gravity fields by in-situdata of ocean bottom pressure. In: System Earth via Geodetic-Geophysical Space Techniques, Springer, Berlin 

Pawlowicz R, Beardsley B, Lentz S (2002) Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE. Comput Geosci, 28:929-973, DOI 10.1016/S0098-3004(02)00013-4

Contact

Henryk Dobslaw
Group Leader
Dr. Henryk Dobslaw
Earth System Modelling
Telegrafenberg
Building A 20, Room 316
14473 Potsdam
+49 331 288-1974
Profile