Physics 137 - Introduction to the Atmosphere and Weather                                                                                    Homework Key - Assignment #15
Revised Fall 1999

15-QT2. Sinking air warms, yet the downdrafts in a thunderstorm are cold. Why?

    Entrainment of dry air, which cools the descending air by the evaporation of rain droplets, results in cooler air than would occur if the temperature in the downdraft were determined by the environmental or dry adiabatic lapse rates.

15-QT3. Explain why squall-line thunderstorms often form ahead of advancing cold fronts but seldom behind them.

    Although an upper-level wave, responsible for the formation of a squall line, may extend both ahead of and behind a cold front, the air behind the front is cold, stable and subsiding while the air ahead of the front is warm and unstable. Thus squall lines form ahead of fronts but seldom behind them.

15-QT6. Suppose while you are on a high mountain ridge a thundercloud passes overhead. What would be the wisest thing to do)stand upright? Lie down? Or crouch? Explain.

    If possible one should get off the ridge. Then one should crouch. Standing, especially on the ridge, increases the probability that one will be struck by lightning while lying down would make it likely that significant electrical current would pass through one's body if a lightning strike should occur nearby.

15-QT9. In the Fujita scale for classifying tornados, into which category would the majority of waterspouts fall?

    Most waterspouts are "fair weather waterspouts" which have peak winds below 45 knots. Hence their Fujita scale classification would be F0.

15-PE1. On a map of the United States, place the surface weather conditions (air masses, fronts, and so on) that are necessary for the formation of most tornadoes.

See figure below for answer.
 

15-PE3. A multivortex-tornado with a rotational wind speed of 125 knots is moving from southwest to northeast at 30 knots. Assume the suction vortices within this tornado have rotational winds of 100 knots: (a) What is the maximum wind speed of this multivortex tornado? (b) If you are facing the approaching tornado, on which side (northeast, northwest, southwest, or southeast) would the strongest winds be found? (c) According to the Fujita scale (Table 15.2, p.423), how would this tornado be classified?

    (a) The maximum wind speed would be 255 knots which would occur (b) on the southeast side of the tornado. (c) Such a tornado would be classified F5 on the Fujita scale.