= Geostrophic wind with linear drag
{title2=$\mathbf u=[f\hat{\mathbf z}\times\nabla_hp-r\nabla_hp]/[\rho(r^2+f^2)]$}
A steady horizontal parcel with drag acceleration $-r\mathbf u$ obeys $0=-\nabla_hp/\rho-f\hat{\mathbf z}\times\mathbf u-r\mathbf u$. Inverting the horizontal rotation-plus-drag matrix gives the title. For $r>0$, the velocity has a component toward lower pressure and a component along <atmospheric isobars>. For $p_x=0$, $f>0$, $p_y>0$, both $u,v$ are negative. The cross-isobar angle is $\arctan(r/f)$, and the speed is smaller than the corresponding frictionless wind. A vertically resolved turbulent stress is not generally equivalent to one constant $r$.
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