bulk flux advice from clivar community

[kate]

I attended a clivar lunch last week in which there was discussion of relative winds vs. absolute winds for use in the bulk flux algorithm. The consensus advice at the end was that for coarse resolution models absolute winds are fine, but for 1/4 degree or finer, relative winds are advised. There was a recent question about it in this forum, so I thought you should know.

Is anyone here using coarser than 1/4 degree? I'm not.

[fLy0516]

Does this advice also suit for ROMS3.5? I use ROMS3.5 BULK_FLUXES with model resolution finer than 1/4 degree,and recently I confused why the timeseries of my model results doesn't show trend and interannual variance although it was forced by monthly forcings. Maybe I should use relative winds instead of absolute winds.

[kate]

The latest ROMS has the WIND_MINUS_CURRENT, which is what I was talking about. Actually, the CLIVAR people now say that one should not use WIND_MINUS_CURRENT with the new JRA55-do forcings because of how they used the satellite-derived winds in the data assimilation.

To get realistic variance, I would use three-hourly winds rather than monthly winds. Monthly winds are going to miss everything on the storm scale and more.

[jivica]

Just to add on top of that, ERA-5 is amazing source of atmo forcing. From 1979 -> recent at 0.25 deg with HOURLY (!) fields. It was couled with ocean and used advanced data assimilation. Even for strong tropical cyclones it gets decent results, think it is better than JRA55 and definitely better then interim.

Cheers
Ivica