Settling rarefaction fan
= Settling rarefaction fan
{title2=$\phi=\tfrac12[1+(z-z_m)/(u_st)]$}
If lower initial concentration $b$ is less than upper concentration $a$, the <entropy solution> expands into a fan with $\phi=[1+(z-z_m)/(u_st)]/2$. Its characteristic speeds range from $u_s(2b-1)$ to $u_s(2a-1)$. The fan can be clipped by a clearing or deposition <shock>.