[ecco-support] [EXTERNAL] ECCOv4r3 OBP units

[Wang, Ou (US 329B)]

Hi Aviv,

ECCO V4r3 OBP files in https://ecco.jpl.nasa.gov/drive/files/Version4/Release3/nctiles_monthly/OBP are in meters. To compare with GRACE data, one would need to remove its area-weighted global ocean mean and also a temporal mean (ideally over the same averaging period GRACE data use to remove its temporal mean). The meta data has since bee improved in ECCO V4r4. Attached below is the updated meta data for the ECCO V4r4 monthly-mean OBP fields (https://podaac.jpl.nasa.gov/dataset/ECCO_L4_OBP_LLC0090GRID_MONTHLY_V4R4) that has detailed description about what exactly the OBP fields are.

"OBP excludes the contribution from global mean atmospheric pressure and is therefore suitable for comparisons with GRACE data products. OBP is calculated as follows. First, we calculate ocean hydrostatic bottom pressure anomaly, PH
IBOT, with PHIBOT = p_b/rhoConst - gH(t), where p_b = model ocean hydrostatic bottom pressure, rhoConst = reference density (1029 kg m-3), g is acceleration due to gravity (9.81 m s-2), and H(t) is model depth at time t. Then, OBP = PHIBOT/g + corrections for i) global mean steric sea level changes related to density changes in the Boussinesq volume-conserving model (Greatbatch correction, see sterGloH) and ii) global mean atmospheric pressure variations. Use OBP for comparisons with ocean bottom pressure data products that have been corrected for global mean atmospheric pressure variations. GRACE data typically ARE corrected for global mean atmospheric pressure variations. In contrast, ocean bottom pressure gauge data typically ARE NOT corrected for global mean atmospheric pressure variations." ;

Best,
Ou Wang


From: ecco-support <ecco-support-bounces at mit.edu> on behalf of aviv solodoch <avivsolo at gmail.com>
Reply-To: "ECCO support list, wider membership" <ecco-support at mit.edu>
Date: Monday, August 22, 2022 at 12:35 PM
To: "ecco-support at mit.edu" <ecco-support at mit.edu>
Subject: [EXTERNAL] [ecco-support] ECCOv4r3 OBP units

Hello
Can you please let me know what are the ECCOv4r3 units for the OBP variable? The ECCO output fields document says it is given in meters, but the actual values at depths of several kms are of order 10s (of meters I guess) rather than similar in value to the depths. Can you please explain what kind of conversion was made here?
Regards,
Aviv Solodoch,
Postdoctoral researcher,
UCLA,
Department of Atmospheric and Oceanic Sciences
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