On Thu, Sep 22, 2011 at 9:11 PM, Howard Staines <span dir="ltr"><<a href="mailto:metris@clear.net.nz">metris@clear.net.nz</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
I understand that rather than using relative humidity, mixing ratio<br>
Is a good predictor for cloud?<br>
<br></blockquote><div><br></div><div>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. </div>
<div><br></div><div> Arlindo</div><div><br></div></div>-- <br>Arlindo da Silva<br><a href="mailto:dasilva@alum.mit.edu">dasilva@alum.mit.edu</a><br>