Horizontal deformation in atmospheric motion

Horizontal fluid deformation is a basic linear property of motion appearing in two forms: stretching and shearing deformation. The resultant deformation, rate and direction, is found by rotating the coordinates through an angle dependent upon the relative values of the two primitive types of deformation in the initial coordinates. Several methods for measuring horizontal deformation in the wind field are introduced and discussed. These employ arbitrary Cartesian coordinates, the latitude‐longitude grid of the Earth, the local north‐south kinematic directions, and the area outlined between three observation points. The field distribution of deformation for an actual wind field is represented by two methods: (1) by scalar patterns of direction and of rate of deformation, and (2) by a vector method at selected points. The geostrophic deformation is obtained graphically from the geometry of the pressure pattern. The field distribution of deformation is illustrated for several hypothetical pressure patterns simulating common conditions.