Kinematics – study of motion without regard to the forces that produce or effect the motion.

The two-dimensional wind field can be thought to be the result of all or some of the following aspects of motion.

Translation -- Constant velocity through the field. Cloud patterns conserve their shape.

Vorticity -- Constant rotational velocity throughout (analogous to solid body rotation). Cloud patterns rotate but do not change their shape.

Divergence – Velocity varies in convergent/divergent patterns. Cloud patterns develop and change shape.

Deformation -- Velocity varies in confluent/diffluent patterns (called Deformation or Hyperbolic Zones) that have zero net divergence. Cloud patterns conserve their area, do not develop, but do change their shape.

Deformation (Hyperbolic Zones)

Background: for a given segment of, say, an upper air chart, define a mean wind obtained by averaging all the winds on that chart. This is called the Mean Wind (given the symbol R in the accompanying reading--sorry, not my fault!). The Relative Wind (V') is related to the actual Wind (V) at a point by the expression:

V = V' + R

The deformation patterns evident in cloud imagery are related to V'. Note that only in the very restrictive circumstance that there is no mean wind, R, is the actual wind representative of V'.

This occurs, though, most nearly for long waves and closed centers, in which the the waves are stationary with respect to the surface of the earth. In those patterns, the mean wind R is often small. (Remember, mean wind, in this context, is the wind averaged over the whole map).

Importance of the Deformation Zones Evident in the Relative Wind Field:

1. Always tell you something about the manner in which the cloud pattern will evolve;

2. Can tell you something about the shape of the respective level's flow pattern if the relative flow pattern is nearly the same as the actual flow pattern;

a. Large wavelength or closed contour pattern—relative flow=actual flow

i. Long waves

ii. Closed highs and lows in mid and upper tropopshere (for example, occluded systems)

b. Short waves/rapidly moving jet streaks etc are usually strongly embeeded in stronger jets so that relative flow does not equal actual flow—other techniques must be used to estimate the actual flow patterns.