Ageostrophic Wind. Assignment 7. Due March 9

Review the information on the ageostrophic wind in the Djuric text.

Model forecast guidance from the Eta model initialized at 00z 2 March will be used, the beginning point of your manual analyses.

Use Garp to access the model forecast sequence.

1. Using the 500 mb height field, describe briefly the evolution of the ridges and troughs forecast by the model from hours 0-72h. How did the major features (ridges/troughs) move and did they amplify or decay?

2. Overlay geopotential height and wind at 500 mb at the analysis time. Identify locations where the flow crosses height contours. Do the following to aid your efforts: change the contour interval to 30 m; plot the wind both as vectors (with barbs) and streamlines. Be sure to investigate the cross-contour flow in at least three different types of curvature: straight flow, cyclonic, anticyclonic. For each case of strong cross-contour flow indicate whether the wind speed of an air parcel will increase or decrease.

3. Now add the geostrophic wind at the initial time. Using your zoomed in areas defined in #2, identify locations where the flow is nearly geostrophic and where it is not. Are there locations where the flow is ageostrophic but parallel to the height contours? Why? What sort of force balance is relevant in those locations?

4. Clear the screen. Start with the height at 500 mb at the initial time again and add the ageostrophic wind. Where/when is the actual wind clearly subgeostrophic? Supergeostrophic? Draw force vectors at a few representative points in regions of straight, cyclonic, and anticyclonic flow.