[gradsusr] Cloud cover script? alternative to rh

[Arlindo da Silva]

On Thu, Sep 22, 2011 at 9:11 PM, Howard Staines <metris at clear.net.nz> wrote:

> I understand that rather than using relative humidity, mixing ratio
> Is a good predictor for cloud?
>
>
Not really. It is not the amount of water vapor that matters but instead how
close to saturation you are. Because models generally give you the gridbox
mean RH, clouds usually form in grid boxes where the mean RH is less than
100%. This is because in the presence of subgrid variability some areas
inside the grid box may very well exceed saturation.   Most models now give
you estimates of cloud fraction, cloud condensate, sometimes even cloud
optical depth. These parameters, although not always validated by real data,
eliminate the guess work of relating RH to cloud cover, relying instead on
the model parameterizations.

   Arlindo

-- 
Arlindo da Silva
dasilva at alum.mit.edu
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