u & v in ROMS grids

[Yunli]

I was just having difficulty in understanding the u- and v-component in ROMS. To be more specific, does u or v lie in an exact horizontal plane or locally tangential to an S-coordinate surface?

Any help on answering this question will be appreciated.

[kate]

u and v are in the horizontal plane. The only rotation done on them is to make them align with the i,j directions rather than strictly east and north, respectively. They are orthogonal to the vertical omega velocity.