Tidal impact on the ESPC products

[Sherry F]

Hi there,

I have some questions about the new ESPC product. I used to download surf_el, u, and v from HYCOM and combine them with the TPXO product to force the boundaries of my model.

However, with the new ESPC product, the downloaded SSH data appears quite strange. Barton et al. (2021) suggested that the new ESPC product integrates tidal velocities, but there is no further clarification on how the tides were incorporated into the data.

The attached image shows HYCOM data plotted at the same location for two products. The data before the vertical dashed line is from GOFS 3.1 93.0, and the data after the dashed line is from the ESPC product. It looks like the tidal pattern is included in the new ESPC ssh, but the amplitude was not fully incorporate. 

Thank you in advance for addressing my questions.

Best regards,
Sherry

[Alan Wallcraft]

ESPC-D-V02 includes tidal forcing, so it has tides, but it is not assimilating tides and so the tides are not as accurate as TPXO, see Tidal Analysis of ESPC-D-V02.  In order to improve the S2 tide, it also includes atmospheric pressure forcing which also has an effect on SSH.

If you want to add your own tides, it is probably best to start with daily means, which are at http://data.hycom.org/datasets/ESPC-D-V02/data/daily_netcdf/

If you are only using SSH, then Steric SSH, which is based on the vertically averaged density anomaly, removes the tides and atmospheric pressure contributions.  See Clarifying the Distinction between Steric and Baroclinic Sea Surface Height  for the limitations of this approach.

Alan.