[CF-metadata] Sign convention of upwelling and downwelling fluxes

Jonathan Gregory j.m.gregory at reading.ac.uk
Fri Jul 21 03:41:48 MDT 2017

Dear Martin

The words upwelling and downwelling were chosen specifically with the intention
of indicating the sign convention! Upwelling means positive upwards,
downwelling means positive downwards, in standard names. If that's not clear in
the definitions, we should clarify them.

Best wishes


----- Forwarded message from martin.juckes at stfc.ac.uk -----

> Date: Fri, 21 Jul 2017 08:47:44 +0000
> From: martin.juckes at stfc.ac.uk
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Sign convention of upwelling and downwelling fluxes
> Hello All,
> there are standard names for a number of upwelling and downwelling fluxes, defined clearly as the component of radiation which is travelling upwards or downwards. The sign convention of these fluxes is not specified .. CMIP uses the convention that downwelling is positive down and upwelling is positive upwards, but in the atmospheric literature you can find people using the convention that both are positive upwards. Both approaches make sense, but it leaves us with some ambiguity in the standard names.
> Since 2008 there are a few terms like minus_one_times_surface_upwelling_longwave_flux_in_air which are defined as having the opposite sign convention to terms without "minus_one_times_". But surface_upwelling_longwave_flux_in_air has no explicit sign convention. The inclusion of the minus_one_times terms implies that at least some people thought that the existing standard names should have a specific sign convention ... and I hope, if that is the case, that it can be consistent with CMIP. If so, can we clear up the ambiguity by adding a line in the description of these standard names to say that the sign convention is positive upwards/downwards for upwelling/downwelling fluxes?
> regards,
> Martin
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