Answer Key -- Week 8 Exercise

1) In winter a cP air mass would be very cold and dry, whereas in summer it would be cool and dry. In both instances, such an air mass is usually associated with high pressure and clear skies. Its cool temperatures are often welcome relief in summer.

2) A maritime tropical (mT) air mass is humid because it originates over water and warm because it forms in tropical latitudes. Source areas for mT air masses are the Gulf of Mexico, Caribbean, and adjacent Atlantic Ocean, and the Pacific, west of Mexico. Maritime polar (MP) air masses originate in the North Pacific and off the eastern coast of Canada in the North Atlantic.

3) Warm, moist air (which is usually unstable) is abruptly lifted along the steeply sloping cold front. Cumulonimbus clouds are created, which may bring thunderstorms and occasionally other severe weather such as hail or tornadoes. After the front passes, a sharp temperature drop is experienced as the winds shift to the northwest.

4) An occluded front forms in the late stage of development of a middle-latitude cyclone when the faster-moving cold front catches up to the warm front and the warm (mT) air is forced aloft. The warm, moisture-laden air is wedged out of the picture and eventually the cyclone dissipates. Once there is no warm, moist air being lifted, there is little condensation and latent heat release.

5) As the warm front approaches, winds would blow from the east or southeast and pressure would drop steadily. Cirrus clouds would be sighted first, followed by cirrostratus, altostratus, and finally nimbostratus. Cloud cover would get progressively greater, from a few tenths coverage with cirrus, to completely overcast with the coming of the nimbostratus. Gentle precipitation would begin as the nirnbostratus clouds moved overhead. As the warm front passed, temperatures would rise, precipitation would cease and winds would shift to the south or southwest. Further, the sky clears and the pressure tendency steadies.

Later, with the approach of the cold front, cumulonimbus clouds fill much of the sky and bring the likelihood of heavy precipitation and the possibility of hail and tornado activity. The passage of the front is accompanied by a drop in temperature, clearing skies, a wind shift to the northwest, and rising pressure. Fair weather can probably be expected for the next day or two.

7) Divergence aloft initiates upward air movement, reduced surface pressure, and cyclonic air movement. On the other hand, convergence along the jet stream results in general subsidence of the air column, increased surface pressure, and anticyclonic surface winds.

8) Tornadoes, with diameters of about 0.25 kilometers, and hurricanes, with diameters of about 600 kilometers, are both smaller and more violent than middle-latitude cyclones whose diameters may be 1600 kilometers or more. Thunderstorms, which are characterized by up-and-down air movements rather than the inward spiral of a cyclone, are related in some manner to all three types of these cyclones.

9) Since thunderstorms are produced in towering cumulonimbus clouds, a prime requirement is warm, moist, unstable air.

10) In areas where warm, moist, and unstable air is very common; i.e., the tropics. In the U.S. thunderstorms would be most common during the summer months and likely most prevalent in the southeast near the primary source of mT air.

12) Tornadoes are most often spawned along the cold front of a middle-latitude cyclone in association with severe thunderstorms. During spring, the air masses on either side of the cold front are most likely to have greatly contrasting conditions.

13) Although tornadoes can occur in every month of the year, spring (April-June) is the period of greatest tornado activity.

14) A tornado watch alerts the public to the fact that conditions are right for the formation of tornadoes. A tornado warning is issued when a tornado has actually been sighted in an area or is indicated by radar.

15) With wind speeds between 61 and 115 Ian per hour, a tropical storm has stronger winds than a tropical depression.

16) The most important reason for this rapid demise is the fact that the storms source of warm, moist air is cut off. When an adequate supply of water vapor does not exist, condensation and the release of latent heat must diminish. In addition, because the land is usually cooler than the ocean, the low-level air is chilled rather than warmed. Moreover, the increased surface roughness over land results in a rapid reduction in surface wind speeds. This factor causes the winds to move more directly into the center of the low, thus helping to eliminate the large pressure differences.

17) The three broad categories of hurricane damage are 1) wind damage, 2) storm surge, and 3) inland freshwater flooding. Storm surge is responsible for the greatest percentage of hurricane-related deaths.

18) The most likely cause is the heavy rains and inland flooding that can affect places far from the coast for several days.

19) Since the hurricane is so much larger and lasts not for a fraction of an hour but for days, the destruction it causes is considerably greater than that caused by a tornado.