[CF-metadata] relative humidity units

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 3 Jun 2015 14:20:19 +0100

Dear Nan

> >>If one checks the standard names in CF, *relative_humidity* has
> >>canonical units '1'
> >>
> >I can't find any documentation for why this isn't 'percent'. Unlike
> >practical salinity, I think there's general acceptance, within the
> >relevant science disciplines, that relative humidity is a percent. The
> >CF definition doesn't include any text on this subject. Does this happen
> >to be because 'percent' isn't clear enough - whether it's by volume or
> >weight?

Relative humidity is the ratio of partial pressure to saturation vapour
pressure, but that would be the same as any other ratio, wouldn't it, since
it's the same gaseous species in numerator and denominator. Percent is
dimensionally equivalent to 1, and "percent" is allowed by udunits (defined
equal to 0.01) so I don't think it should make a material difference. RH is
not always expressed as percent.

Best wishes

Jonathan
Received on Wed Jun 03 2015 - 07:20:19 BST