Cloud droplet effective radius
= Cloud droplet effective radius
{title2=$r_e=\langle r^3\rangle/\langle r^2\rangle$}
The ratio of the third to the second radius moment determines projected extinction area per liquid mass. For size-independent extinction efficiency $Q$, the local <particle extinction coefficient> is $3Qw/(4\rho_wr_e)$. It is not generally the mean radius or the mean-volume radius. In <adiabatic cloud droplet moments>, the shape factor gives $r_e=r_v/k^{1/3}$.