Develop a conceptual model of the relationship between synoptic-scale vertical motion and horizontal divergence/convergence.
Improve your understanding of shear and curvature vorticity and their relationship to upper-level vorticity maxima, troughs, jets, and jet streaks.
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Problem 1:
Dines compensation suggests that, on the synoptic scale, rising motion should be accompanied by upper-level divergence and low-level convergence, whereas subsidence should be accompanied by upper-level convergence and low-level divergence. Follow the instructions below to examine if this conceptualization is generally valid.
Start IDV and open the Displays>Favorite Bundles>5110>lab2-omega bundle. This will pull up the latest 24-h forecast loop of 700 mb height and vertical velocity (omega) from the GFS model for the northern Pacific basin. There will also be two cross sections available: vertical velocity (omega, color shaded as at 700 hPa) and divergence (contoured, with negative values dashed, positive values solid, and the zero contour omitted).
Examine the 700-hPa height and vertical velocity loop. Find an area of organized and strong ascent in the mid-latitudes at one forecast time to concentrate on for further analysis.
Position the vertical velocity and divergence cross sections so that they cut through the area of ascent. Be sure to orient them so they are very close together, but also so that the contours can be seen with the vertical velocity color-fill in the back when you rotate the diagram.
Rotate the image and have a close look at the cross section. If it is in a good location, use View>Capture>Image and save the cross section as a jpg image (to do this give it a name ending with .jpg). Do the same for the plan view.
Import your images into Powerpoint and on each identify the ascent maximum. Identify the level(s) of non-divergence in the ascent maximum column.
Turn in your figures electronically, along with answers to the following questions:
Does the divergence change signs with height at least once throughout the cross section?
Do levels of non-divergence roughly correspond to maxima/minima in vertical motion?
In general, does the concept of Dines Compensation apply to your cross sections? Note any supporting or conflicting evidence.
Problem 2:
Upper-level vorticity may be associated with horizontal wind shear, flow curvature, or some combination of the two. Follow the instructions below and identify vorticity maxima where (1) shear vorticity dominates, (2) curvature vorticity dominates, and (3) both terms contribute to the total vorticity.
Using IDV, plot the 0-48 h 80-km NAM forecast of 250 mb height (black contours every 60 m) and absolute vorticity (color fill every 2x10-5 /s) for the continental US (i.e., CONUS). Adjust the contour intervals, maxima, and minima, as well as the color table, as needed. Adjust the map as well.
Identify a forecast hour where there appears to be examples of absolute vorticity maxima associated with (1) shear vorticity, (2) curvature vorticity, and (3) both terms. Save the image and import it into powerpoint.
On your plot, identify the vorticity maxima that are associated with (1) primarily shear vorticity, (2) primarily curvature vorticity, (3) a combination of shear and curvature vorticity.
For the forecast hour of interest, remove the 250 mb height analysis and plot the 250 mb wind speed with black contours every 10 m/s begining at 20 m/s. Print the analysis for the same time used earlier.
Denote on this figure the absolute vorticity noted above.
Turn in your figures electronically, along with answers to the following questions:
For the shear vorticity maxima:
Is there a jet or jet streak associated with the vorticity max?
Is there a short-wave or long-wave trough with pronounced curvature associated with the vorticity maximum?
For the curvature vorticity maxima:
Is there a jet or jet streak associated with the vorticity max?
Is there a short-wave or long-wave trough with pronounced curvature associated with the vorticity maximum?
For the shear/curvature vorticity maxima:
Is there a jet or jet streak associated with the vorticity max?
Is there a short-wave or long-wave trough with pronounced curvature associated with the vorticity maximum?
Based on your answers above, what is the relationship of upper-level vorticity maxima to upper-level troughs, jets, and jet streaks?
