Kinematics of the Wind Field. Assignment 9. Due March 19

Purpose: (1) to analyze the kinematics of the wind field as diagnosed by an operational model. (2) examine the evolution of the jet stream over North America over a 48 h period.

Review the information on kinematics in the Djuric text.

There are plenty of resources on the web to visualize different types of fluid flows. Here are a few:

Movie Archive
Flow animations
Shear Flow
3-D Flows
Extra credit- find 1 or more useful animations of fluid motion related to flows observed in the atmosphere

Graphics at 300 mb will be analyzed for the 48 h period beginning at 12z March 12. The following uses GARP to evaluate the kinematics of the wind field using the Eta model forecast.

1. Overlay 300 mb streamlines and 300 mb isotachs (kts) at 10 m/s intervals. It may be helpful to shade the isotachs at 20 m/s intervals. Use the North America domain.
- a. Where are the jets at the initial time in relation to the ridges and troughs?
- b. How did those jets evolve with time relative to the movement of the ridges and troughs and the intensity of the ridges and troughs? Which jets intensified? Which ones weakened?
2. Use the CONUS domain. Overlay isotachs and streamlines at 300 mb.
- a. Identify at the initial time only, at least 1 area of each of the following: (1) stretching of an air parcel, (2) shrinking of an air parcel, (3) strong cyclonic curvature term, (4) strong anticyclonic curvature term, (5) strong cyclonic speed shear, (6) strong anticylonic speed shear,(7) diffluence, (8) confluence.
3. Use the CONUS domain. Overlay the relative vorticity of the wind on the isotachs and streamlines at 300 mb.
- a. Identify at the initial time only, the areas of maximum cyclonic relative vorticity. Explain in the context of the (1) cartesian coordinate frame and (2) natural coordinate frame why the relative vorticity is so large at one of the maxima.
- b. Identify at the initial time only, the areas of maximum anticyclonic relative vorticity. Explain in the context of the (1) cartesian coordinate frame and (2) natural coordinate frame why the relative vorticity is so small at one of the minima.
- c. Provide an explanation for why the peak magnitude of cyclonic relative vorticity is so much stronger than the peak anticylonic relative vorticity.
4. Use the CONUS domain. Overlay the divergence of the wind on the isotachs and streamlines at 300 mb.
- a. Identify at the initial time only, the areas of maximum divergence. Explain in the context of the (1) cartesian coordinate frame and (2) natural coordinate frame why the divergence is so large at one of the maxima.
- b. Identify at the initial time only, the areas of maximum convergence. Explain in the context of the (1) cartesian coordinate frame and (2) natural coordinate frame why the convergence is so large at one of the minima.
- c. Identify at the initial time only, areas where an air parcel would experience areal contraction? areal expansion? Assuming that the tropopause lies immediately above 300 mb, where would you expect rising motion and where would you expect subsidence?
- d. How do areas of maximum divergence or convergence relate spatially to areas of maxima or minima in relative vorticity? In other words, can you find a local maxima in divergence coincident with a local maxima in vorticity?
5. Use the CONUS domain. Overlay the total deformation of the wind on the isotachs and streamlines at 300 mb.
- a. Identify at the initial time only, the areas of maximum total deformation. Explain in the context of the (1) cartesian coordinate frame and (2) natural coordinate frame why the deformation is so large at one of the maxima. (You may want to look at the contributions due to shearing and stretching deformation separately.)

Keep your answers short and focussed. Email responses to me by the due date.