Explain the hycom grid?

The global hycom grid is rectilinear from j=1 to j=2172, and you can check this by confirming that the minval and maxval of plat(1:4500,j) are identical there. The grid is curvilinear (bi-polar patch) from j=2173 to j=3298. Note that the j=3298 row is a permuted copy of j=3297 (because of the way the tripole grid is implemented in HYCOM), so you can discard j=3298.

Disclaimer

This is a demonstration product from the HYCOM Consortium and is provided as is. HYCOM Consortium does not warrant or suggest that this data is fit for any particular purpose. Further, neither COAPS nor HYCOM consortium guarantees availability, service updates, or timely data delivery.

All hycom data provided is UNCLASSIFIED. DoD DISTRIBUTION A. Approved for Public Release; Distribution Unlimited.