Summary
- The primary purpose of a hodograph is to reveal vertical wind shear
- Vertical wind shear is a description of how the velocity of the horizontal wind changes with height. We determine the vertical wind shear by taking the vector difference between the horizontal wind at two levels
- The hodograph is based on wind vectors, rather than wind barbs. To create a hodograph, wind vectors are plotted on a polar coordinate chart. Then their endpoints are connected
- The total magnitude of vertical wind shear over a particular depth is an important factor in anticipating possible storm structure and evolution. Estimating total vertical wind shear is done by combining the lengths of all the shear vectors over a particular depth (the net length of the hodograph)
- You can determine the direction of the mean wind shear vector (but not the magnitude) by drawing a line from the point that plots the surface wind to the point plotting the 6-km (20-kft)wind
- Calculating the mean wind shear vector is simply a matter of averaging the x and y components of each of the single layer wind shear vectors
- In addition to the magnitude of the shear, we are also concerned with whether the hodograph is relatively straight or curved. While similarly shaped hodographs may affect convective storm evolution in similar ways, their implications for larger-scale processes and for convective potential may differ substantially
- Because the storm moves through its environment, the wind it experiences is often very different from the ground-relative winds. Storm-relative winds can also be calculated on a hodograph
In this module, we have learned how to calculate several different shear parameters and we have started to see a little of how these parameters are applied. To learn more about how shear affects convective storms, see the module Principles of Convection III: Shear and Convective Storms.