FINAL Flashcards
Within a given air mass, humidity and temperature can vary substantially from one region to another at the same elevation.
False - an air mass, by definition, is characterized by relatively uniform temperatures pressures at a given altitude within the air mass.
Source regions are characterized by strong upper level winds that act to drive air masses out of the source region area.
False - if strong upper level winds existed, the air could not remain in a source region long enough to take on the temperature and moisture characteristics of the source region. This is because the upper level winds would drive the incipient air mass out of the area.
Source regions tend to occur in areas where air subsides.
True - if air is subsiding, this means that air is flowing out of the source region, rather than into it from surrounding areas. The air flowing out of the area is therefore relatively uniform in characteristics because it originated in a common area. If air were flowing into an area, then air with widely different temperature and moisture characteristics would come into contact, thereby preventing the development of an air mass.
Source regions typically occur along coasts.
False - Coasts are characterized by the juxtaposition of continental and maritime conditions. Because these are dissimilar conditions, air masses, which are characterized by uniformity over large areas, cannot form there.
. A “cP” air mass is cold and dry.
. True - continental polar air masses form in continental interiors where temperatures become extremely cold in winter (Principle of Continentality; i.e., low heat capacity of the land). And, because the air is cold, it also has a very low level of absolute humidity due to the lack of energy available for evaporation.
mP Pacific air masses often originate over Asia as cP air masses and become unstable as they move over the Pacific Ocean towards North America.
True - as the cP air mass moves over the ocean, the surface layer warms because the ocean is warmer than the Asian land mass over which it originated. So, as the surface layer warms, it becomes unstable–which is one of the reasons that the Pacific Northwest region of the U.S. and Canada experiences so much precipitation. Orographic uplift along the mountainous coast also contributes substantially to the formation of precipitation.
A strong low pressure system over the eastern U.S. can draw moist air (and stormy conditions) into the Northeastern U.S. even though this area lies in the Westerlies.
True - The low pressure system can draw moisture-laden air into the interior of the continent and generate storms. These conditions can produce the infamous storms known as “Nor-Easters”.
Source regions typically occur along coasts.
False - Coasts are characterized by the juxtaposition of continental and maritime conditions. Because these are dissimilar conditions, air masses, which are characterized by uniformity over large areas, cannot form there.
. A “cP” air mass is cold and dry.
. True - continental polar air masses form in continental interiors where temperatures become extremely cold in winter (Principle of Continentality; i.e., low heat capacity of the land). And, because the air is cold, it also has a very low level of absolute humidity due to the lack of energy available for evaporation.
mP Pacific air masses often originate over Asia as cP air masses and become unstable as they move over the Pacific Ocean towards North America.
True - as the cP air mass moves over the ocean, the surface layer warms because the ocean is warmer than the Asian land mass over which it originated. So, as the surface layer warms, it becomes unstable–which is one of the reasons that the Pacific Northwest region of the U.S. and Canada experiences so much precipitation. Orographic uplift along the mountainous coast also contributes substantially to the formation of precipitation.
A strong low pressure system over the eastern U.S. can draw moist air (and stormy conditions) into the Northeastern U.S. even though this area lies in the Westerlies.
True - The low pressure system can draw moisture-laden air into the interior of the continent and generate storms. These conditions can produce the infamous storms known as “Nor-Easters”.
In the wintertime, precipitation in the interior of the U.S. is generated by low pressure, cyclonic storms, whereas during the summertime, it is generated by the flow of air out of the Bermuda High and into the interior of the east coast of the U.S..
True - low pressure systems associated with cyclonic storms draw air in from the coastal areas during the winter, and this supplies moisture for storms. In the summertime, the Bermuda High causes air to flow from over the ocean (where it is warm and moist) and into the interior of the U.S. The summertime heating of the interior also helps to draw moist air into the U.S.
Air masses remain unchanged as they move out of their source regions.
False - They begin to change as soon as they leave the conditions under which they formed in their source region, and the further they move away from their source regions and into areas that differ from them, the more they lose their original characteristics.
cP air masses frequently reach the tropics
False - In virtually all cases, a cP air mass would change into another type of air mass (i.e., it would cease to exist as a cP air mass) by the time it reached the tropics because the temperature and moisture conditions are so different in the tropics.
The Polar Front forms a straight/linear boundary between unlike air masses.
False - it forms a wavy boundary in which the wave migrates to the east. This is because the Polar Front occurs along the northern boundary of the westerly wind belt in which air flows from west to east.
Fronts are named on the basis of which air mass replaces the one that was formerly in the area.
True - In addition, the name of the front indicates what the temperatures will be after the front passes–relative to what they were before passage. Thus, a cold front involves a cold air mass moving into an area and displacing a warm air mass. As a result, temperatures are colder after the front passes.
After the passage of a warm front, temperatures increase.
True - as warm air moves into an area, temperatures increase
Cold fronts have a steeper frontal slope than warm fronts.
True - this is because the cold, dense air that is moving into an area is moving fairly rapidly, causing the warm air to rise rapidly along the frontal boundary. In addition, friction with the ground steepens the frontal boundary.
Weather is usually more intense along a cold front than along a warm front.
True - the more rapid uplift along a cold front causes condensation to occur more rapidly and this causes the weather to be more severe. In addition, the higher wind velocities associated with cold fronts occur because of the steeper pressure gradients associated with such fronts.
An occluded front covers a narrower area than does a cold front.
False - the cold front, for reasons already discussed, has the narrowest boundary.
An occluded front involves only two air masses
False - it involves three air masses–a cold, warm, and cool air mass. See book and notes for details.
Which pair of air masses would produce the most rapid uplift of air along their frontal boundaries based on differences in temperature and moisture?
(cP and mT) - because mT air masses are moist and warm and cP air masses are dry and cold, they represent the greatest difference in density; therefore, they produce the most rapid uplift when they meet. It is these two air masses that produce the most severe weather in the Midlatitudes.
Just prior to, and during, the passage of a cold front, the pressure drops.
True - both as the front approaches, and during the passage of the front, warm air is uplifted, thereby causing the pressure to drop. Also, the condensation that occurs during uplift also causes the pressure to drop as the release of latent heat energy warms the air. Remember that falling pressure is a sign of an impending storm.
As a front approaches, the clouds become lower and, usually, thicker
True - the cloud deck lowers because of the orientation of the frontal boundary which slopes downward toward the surface. The cloud sequence generally changes from high, thin cirrus clouds, to thicker stratus, and then to nimbostratus or cumulonimbus
- The presence of mountains can lead to the formation of a stationary front.
True - If the air masses are shallow (not very thick), the mountains can act as a barrier between them, preventing either from advancing.
Isobars are lines that connect points of equal pressure
True - isobars connect points of equal pressure. Remember, pressure differences cause winds to blow and air masses to move from one region to another.
