Homework Questions for Chapter 14 - Thunderstorms and Tornadoes

Consult Syllabus for Due Date

Questions 1 and 2 will be turned in for a grade.

Follow the Problem solving steps discussed in class

1. We've learned that if a parcel of air is warmer, or positively buoyant relative to its surrounding environment, it will rise. A measure of the amount of energy available to create such vertical motions is called the convective available potential energy (CAPE). CAPE can be visualized on a thermodynamic diagram and represents the area between the sounding and parcel path wherever the parcel is warmer than the environment This area is often called positive area. Here is a schematic example.

CAPE can be computed from the following equation:

where g is the acceleration due to gravity, Te is the environmental temperature at a given level, Tp is the parcel temperature at a given level, and Dz is an increment in height.  The sum is over all of the rectangular boxes containing the positive area.  Again, see the schematic example for a visual.

Once the CAPE is known, a parcels vertical velocity in the updraft of a thunderstorm can be estimated by the following equation:

(a)  What are the units of CAPE?

(b)  Using the U.S. Standard Atmosphere and the sounding below:

1. What is the environmental temperature at the height levels given in the sounding below?
2. What is the value of CAPE for the sounding given below?
3. What is the maximum vertical velocity expected with the sounding given below?

HINT:  Make sure all temperature values are in K, also make sure that g is a positive number!

 Z (meters) Tparcel (Celsius) 0 14.0 500 11.5 1000 9.0 1500 6.5 2000 4.0 2500 1.0 3000 -1.8 3500 -5.0 4000 -8.2 4500 -11.5 5000 -15.0 5500 -19.0 6000 -23.0 6500 -27.0 7000 -31.5 7500 -36.5

2.  Given a circular tornado that has a relative vorticity value of 1 s-1 and a diameter of 100m.  If the tornado is moving northward at 25 ms-1, what is the ground relative wind speed on the east and west sides of the tornado?  What damage intensity values (EF-scale) would you expect to see on the east and west sides of the tornado?

EXTRA CREDIT:  Microbursts are generally subdivided into "wet" and "dry" events.  Wet microbursts are accompanied by heavy precipitation while dry microbursts are accompanied by little or no precipitation.  Speculate as to what are the important processes that generate wet and dry microbursts.  Where would you commonly observe wet and dry microbursts within the U.S.?