# Kinematic boundary condition

From AMS Glossary

## kinematic boundary condition

The condition that the fluid velocity directed perpendicular to a solid boundary must vanish on the boundary itself.

This may be stated mathematically by the expression where

**n**is a unit vector normal to a solid surface and**u**is the fluid velocity vector. In meteorology, this boundary condition is often employed in considering flow near the earth's surface. When the boundary is a fluid surface or interface, this condition applies to the vector difference of velocities across the interface and requires that the interface, although in motion, will at all times consist of the same fluid parcels. In meteorology, such a condition must be applied at fronts and other surfaces of discontinuity.*See also*dynamic boundary condition.