Meteorology 2603
Severe and Unusual Weather
Solutions to Problem Set #3

1.  Plot the following data on the graph provided to create a wind hodograph.  Label the altitude of each wind observation next to the point.

2.  For the following storm motions applied to the hodograph that you drew in Problem #1, determine the sense (clockwise or counterclockwise) of rotation in the dominant thunderstorm updraft.  Assume a sufficient amount of CAPE to produce and sustain a strong thunderstorm and BE SURE TO EXPLAIN YOUR REASONING.

a.  Storm is not moving.

If the storm is not moving, then the storm motion vector is simply a point at the center of the hodograph.  The storm-relative winds are shown by the light purple lines, and the horizontal rotation vectors are shown in green.  The dominant updraft will rotate cyclonically because of the degree of parallelism between the blue and green lines, and because the storm-relative winds are reasonbly strong (averaging around 10 m/s) between the ground and 3 km.  In other words, air entering the storm, from the framework of the storm itself, is flowing along the horizontal rotation lines.  When tilted by the updraft, this air will be roughly coincident with the cyclonically-rotating (counterclockwise) vortex, as shown in the MOVIE. Note again that we only consider air flowing into the updraft from the ground (0 km) to 3 km above the ground.

b.  From 135 degrees at 16 m/s.  In this case, the storm-relative winds are nearly perpendicular to the rotation vectors from 0-3 km, and thus the dominant updraft will show little if any evidence of rotation.

c.  From 135 degrees at 30 m/s.  In this case, the storm-relative winds are nearly perpendicular to the rotation vectors at 0 and 1 km, but anti-parallel between 2 and 3 km.  Thus, the dominant updraft is likely to show anticyclonic rotation because the air flowing into it will be coincident with the anticyclonic member of the vortex pair shown in the MOVIE.

d.  From 300 degrees at 15 m/s.  The dominant updraft will definitely be cyclonic owing to the nearly parallel alignment between the storm-relative winds and horizontal rotation vectors from 0 to 3 km.

3.  Which of the storms in Problem #2 would likely contain the updraft having the greatest degree of rotation?  BE SURE TO EXPLAIN YOUR REASONING.

The storm in 2d will contain the most significant rotation because of the nearly parallel alignment between the storm-relative wind vectors and the horizontal rotation vectors, and because the storm-relative wind magnitude from 0-3 km averages well above 10 m/s.

4.  Plot the following data on the graph provided to create a wind hodograph.   Label the altitude of each wind observation next to the point.

5.  For the following storm motions applied to the hodograph that you drew in Problem #4, determine the sense (clockwise or counterclockwise) of updraft rotation.   Assume a sufficient amount of CAPE to produce and sustain a strong thunderstorm and BE SURE TO EXPLAIN YOUR REASONING.

a.  Storm is not moving.  In this case, the storm-relative wind vectors are somewhat parallel to the horizontal rotation vectors, especially at 2 and 3 km.   Thus, the dominant updraft will rotate cyclonically.

b.  From 180 degrees at 25 m/s.  The storm-relative winds are now blowing somewhat anti-parallel to the horizontal rotation vectors, but at a significant angle.  Thus, the updraft will rotate anticyclonically.

c.  From 115 degrees at 23 m/s.  The storm-relative winds are blowing nearly perpendicular to the horizontal rotation vectors, and thus the dominant updraft will have little rotation.  This is characteristic of storms moving on a nearly linear hodograph.

6.  Modify the hodograph in Problem #5, in a qualitative manner, to ensure a dominant right-moving storm, and DISCUSS THE BASIS FOR THIS MODIFICATION.

The modification we make depends upon storm motion, so let's choose the hodograph in 5a.  If we add a curved tail, as shown below, then the storm-relative winds between the ground and 3 km will be blowing almost nearly parallel to the horizontal rotation vectors, and at a speed greater than 10 m/s averaged over the region 0-3 km.   This will ensure a dominant cyclonic updraft and a right-moving storm.