[ecco-support] Questions about ECCO ocean bottom pressure

[Wang, Ou (US 329B)]

Hello Hongzhi,

V4r4b (and also V4r4) that are hosted by PO.DAAC at https://podaac.jpl.nasa.gov/ECCO have three different ocean pressure variables: OBP, OBPGMAP, and PHIBOT, on native model grid (and two [OBP and OBPGMAP] for lat-lon grid). The description below is for these variables hosted by PO.DAAC. Note that in previous versions of V4r4 files that are not hosted by PO.DAAC, some different name (like OBPNOPAB) has been used and OBP meant something differently.

The variables are grouped into one netDF file for each time record, and the meta data in those netCDF files has detailed information on how to calculate them and the relationship among the three ocean bottom pressure variables. For instance, below is from the meta data about as the comment for OBP:
“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, PHIBOT, 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.”

OBPGMAP-OBP is the spatial mean atmospheric pressure variations over the global ocean.

Best,
Ou Wang

From: ecco-support <ecco-support-bounces at mit.edu> on behalf of Yao, Hongzhi <yao.396 at buckeyemail.osu.edu>
Date: Wednesday, February 15, 2023 at 1:16 PM
To: ecco-support at mit.edu <ecco-support at mit.edu>, podaac at podaac.jpl.nasa.gov <podaac at podaac.jpl.nasa.gov>
Subject: [EXTERNAL] [ecco-support] Questions about ECCO ocean bottom pressure
Hi there,

My name is Hongzhi and I’m a graduate student in the Ohio State University. I’m working on elastic load deformation research and trying to use the ECCO ocean bottom pressure v4r4b. My question is, I noticed that you have the differences between PHIBOT, OBPNOPAB, and OBP, but only OBP is provided in the dataset? Could you also provide the other ocean bottom pressure data? Also I would love to know more details about how you utilize the spatial mean atmospheric pressure variations over the global ocean for the ocean bottom pressure. I couldn’t find the info in the user’s guide, it’ll be great if you can show the details of OBP related calculation.

Thanks,
Hongzhi
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