Issues about geopotential anomaly and ssh pressure in Chile

[Lingchao He (River)]

Hi everyone, 

I am confused about the geopotential anomaly and sea surface height pressure data from October to December 2017, as shown in the figures below. For other time periods I have analyzed, they align well with each other, and the bottom pressure is in the range of -5 to 5 hPa. However, for the data from October to December 2017, which I downloaded from this link: https://ncss.hycom.org/thredds/ncss/GLBv0.08/expt_92.9? , there appears to be a time lag between the geopotential anomaly and SSH pressure, causing a bottom pressure anomaly.

Why is there a time lag? Is this a real signal or a data issue? I'm asking because a similar issue in 2016 was caused by missing data, and I used interpolation to fix it. However, I'm unsure what's happening with this dataset. Although lot of the data are missing here too, they miss the same part which should not cause a discrepancy. Please help! Thank you very much!

[Alan Wallcraft]

For expt 93.0 (Jan 2018 onward) the hour;y "sur" fields include SSH and Steric SSH, with the latter being the SSH anomaly associated with density anomalies plus a long term mean SSH.  So SSH-Steric is approximately the bottom pressure anomaly.  This would be a way to check your 3-D calculations.

I suggest looking at snapshots of SSH from the Brazil-Malvinas Confluence for this time period, one thing that throws off diagnostic calculations of SSH and BPA is fronts moving across the shelf slope.

Alan.