Pressure coordinate
= Pressure coordinate
{title2=$p$}
An atmospheric vertical coordinate using <pressure> instead of geometric height. Under <hydrostatic balance>, <pressure> decreases upward and <geopotential> obeys $\partial_p\Phi=-1/\rho$. With the <ideal gas law>, $\partial_{\ln p}\Phi=-RT$. Horizontal <gradients> taken at fixed $p$ lie on an <isobaric surface>. A <log-pressure coordinate> is a useful related coordinate with the opposite upward sign.