= Meridional-pressure-gradient geostrophic wind
{title2=$u_g=-p_y/(\rho f),\quad v_g=0$}
With $x$ eastward and $y$ northward, a purely meridional <pressure gradient> gives the velocity in the title. For $f>0$, pressure increasing northward gives westward wind, leaving lower pressure to the wind's left. Reversing the pressure gradient reverses the velocity. At a fixed gradient and density the speed scales as $1/|\sin\phi|$; the formal equatorial divergence signals breakdown of <geostrophic balance>, rather than a real infinite wind.
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