Quiz #5 Study Questions
Chapter 10, pp. 257-275
Chapter 6, pp. 133-145
Turn in Monday, April 10 by start of class.
Answers should be on a separate sheet of paper and legible.
This is worth up to 5 points extra credit towards Quiz #4
Questions 1-7 refer to Chapter 10. Questions 8-10 refer to Chapter 6.
- Which region of the United States has the highest number of thunderstorms throughout the year? What regions have the lowest number of thunderstorms throughout the year? Why is this so?
- The southeastern United States (and Florida in particular) have the most thunderstorms per year. The Pacific coast and the northeastern United States have the fewest thunderstorms. Warm moist air from the Gulf of Mexico fuels thunderstorms in the southeast. Air from the Pacific and Atlantic ocean is generally cooler, and does not contain as much water vapor. The key difference is the temperature of the ocean surface over the Gulf of Mexico (warmer) versus the Pacific and Atlantic (cooler).
- Explain the current popular theory of charge separation within a thunderstorm cloud? Sketch the resulting distribution of charge within a thunderstorm cloud.
- The basis of the popular charge separation theory is that COLLISIONS take place between heavier, warmer graupel particles and lighter, cooler ice crystals within the updraft region of a thunderstorm cloud (temperature less than -15C). Under these conditions, negative charge accumulates on the warmer, heavier graupel particlesfalling through the middle and lower regions of the cloud. Positive charge accumulates on the colder, lighter ice crystals which are transported to the top of the cloud.
- Explain the steps that lead up to a cloud-to-ground lightning discharge. Why is it not a good idea to stand under a tree during a thunderstorm?
- charge separation leads to strong electric field between the cloud (negative) and the surface (positive)
- the strong electric field leads to ionization of air molecules, air's electrical resistance breaks down
- current begins to descend from cloud in a series of segments called stepped leaders
- positive charge builds on surface objects and extends upwards, i.e. positive streamers
- when a stepped leader and positive streamer meet, current flows through the ionized channel. The return stroke travels up this channel. Air becomes superheated, resulting in the flash of light we see and the thunder we hear
- subsequent currents from the cloud flow quickly down the same channel of air (i.e. dart leaders), resulting in multiple return strokes. We see this as the flickering lightning stroke.
- Where and at what time of year do most tornadoes occur in the United States? At what time of year do the most violent tornadoes typically occur?
- Most tornadoes occur in the Great Plains region known as "Tornado Alley" which extend from Texas up through Nebraska. Most tornadoes occur in spring and summer when warm moist air from the Gulf of Mexico encounters cooler drier air from the north. The most violent tornadoes occur in April when temperature contrasts between air masses and wind shear is most pronounced.
- According to the Fujita scale of tornado intensity, what is the classification of the strongest tornado? What are the typical wind speeds in this class of tornadoes? Under these conditions, what is the most likely cause of personal injury and death?
- Based on damage assessment at the ground, the strongest class of tornadoes is F5, with winds of 261-318 mph (227-276 knots). It is possible to have tornadic winds that exceed this range, but these will most often be present above the surface.
- What is a supercell thunderstorm? What is there about a supercell thunderstorm that favors the formation of tornadoes (you can answer this with one word).
- A supercell is a massive rotating sever thunderstorm which consists of one main updraft and downdraft. The rotating updraft region 5 - 10 kilometers across within a supercell is called a mesocyclone. This is what can produce tornadoes, because it is the primary source of rotation for the eventual tornado. I was looking for either "mesocyclone" or "rotation" as an answer here.
- Describe the steps in the formation of a tornado from a mesocyclone.
- We start with the rotating mesocyclone in the updraft region of the supercell thunderstorm. From the base of the supercell descends the dark, slowly rotating wall cloud. The funnel cloud appears from the base of the wall cloud and when it contacts the surface, we have a tornado.
- Two columns of air hold the same number of air molecules, and thus exert the same pressure on the surface (see Figure 6.2). One column has a high temperature and one column has a low temperature. Which column is taller? Why?
- The warmer column of air is taller; the colder column of air is shorter. The gas law tells us that the density and temperature of a gas at constant pressure are related such that warmer air is less dense, colder air is more dense. Thus the warmer air column must occupy a greater volume (i.e. it is taller).
- What information is plotted on a surface map (Figure 6.8a), and what does it tell a meteorolgist? What information is plotted on a 500-millibar map (Figure 6.5b), and what does it tell a meteorologist?
- A surface map plots surface pressure, showing high and low pressure centers and isobars. The spcing of the isobars tells us the strength of the pressure gradient that drives wind. Tightly spaced isobars indicate a strong pressure gradient, and thus strong winds. An upper-air (500 millibar) map indicates the height of the 500 millibar pressure surface. It also shows lines of constant temperature (isotherms). This information is used to determine the pressure gradient and winds in the upper atmosphere, which help meteorologists forecast changes in surface pressure (see discussion related to Figure 6.2 in text).
- Describe how the pressure gradient force and the Coriolis force influence winds.
- Pressure gradient force directs air from high pressure to low pressure
- Moving air is delfected to the right in the Northern Hemisphere due to the effect of the earth's rotation - this is called the Coriolis force. This deflection increases with increasing wind speed and latitude. The Coriolis effect is zero at the equator. In the Southern Hemisphere, the Coriolis force deflects moving air masses to the left, relative to its direction of motion (opposite of Northern Hemisphere).
Additional review questions (not to be handed in): p. 276: #14, 17, 24; p. 155: #3, 6, 9, 11, 14, 15