Can I specify U and V wind on a coarser grid in the bulk forcing file?

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I noticed that uwnd in bulk forcing file has dimensions of 'bulk_time', 'eta_u', 'xi_u' and vwnd is on 'bulk_time', 'eta_v', 'xi_v'. For large grid size, a spatially varying wind will result in the bulk forcing file having a very large size. Is it possible to give spatially varying wind on a coarser grid to save space?

I found out that setting the cpp option 'ONLINE' under BULK enables the online interpolation of bulk forcing (spatial and temporal). The time dimension is bulk_time, but what should be the name of lat and lon dimensions? should they be 'bulk_lon' and 'bulk_lat', i.e. u wind speed has dimensions 'bulk_time', bulk_lon', 'bulk_lat' ? If not then what are the correct names of dimensions for the coarser bulk forcing grid?