Summed Field with different longitudes

[JonathanC33]

Hi, I am trying to create a summed field (ocean velocity field summed with 0.02*windage) using ocean parcels and am having issues with how longitude is defined differently in each.

The longitude in the ocean velocity field goes from -180 to 180 and 0-360 for the wind velocity field. Ideally, I'd like to be able to use the fieldset.from_netcdf function to load both in so that I can use the filename_*.npy feature to load in multiple files. Currrently, I have to load in windage velocity fields one at a time using the fieldset.from_data, and then subtract 360 from each in order to get the longitudes to line up.

Is there an easy way to convert the windage fieldset without having to use fieldset.from_data and change it manually for each netcdf file?

[erikvansebille]

Thanks for reporting, @JonathanC33. There unfortunately isn't an easy out-of-the-box solution, I'm afraid. An options you could try is to write a new, custom AdvectionRK4 kernel that uses partilce.lon for the ocean field, but plon for the wind field, where plon is constructed so that it always fits between -180 and 180:

plon = partilce.lon
if particle.lon > 180:
    plon = particle.lon - 360

I've done something similar here when I needed to sample EEZ: https://github.com/OceanParcels/SKIM_dFADtracking/blob/master/fadset_run.py#L19-L23