Chapter Nine - Test Three

Question 1

Polar Front Theory (Norwegian Cyclone Model)

Answer 1

Was developed during WWI by Norwegian scientists and characterizes the life cycle of mid-latitude cyclones in association with the polar Front

Question 2

Polar Front:

Answer 2

A semi-permanent, semi-continuous boundary that separates tropical air masses (cT, mT) from polar air masses (cP, mP)

Question 3

Mid-latitude cyclones (low-pressure systems) typically:

Answer 3

• form between 25ºand 50º N latitude
• have diameters up to 1000 km
• move from west to east
• life cycle lasts about a week

Question 4

Mid-latitude cyclones all produce counterclockwise, converging circulation, resulting in:

Answer 4

• Rising motion resulting in clouds and precipitation

Most mid-latitudes cyclones have fronts extending from them.

Question 5

The “Storm of the Century” (Mid-latitude cyclone) impacted the east coast during March, 1993:

Answer 5

• record snowfall
• record low pressures
• severe thunderstorms and tornadoes

Question 6

Fronts

Answer 6

Relatively narrow boundaries characterized by low pressure that mark the transition zone between air masses of differing densities: thermal properties [T], moisture properties [Td]

Question 7

Four Major Front Types:

Answer 7

Warm Front
Cold Front
Stationary Front
Occluded Front

Question 8

Criteria used to identify fronts on a surface weather map include:

Answer 8

1) sharp temperature (T) difference over short distance
2) sharp dewpoint (Td) difference over short distance
3) shifts in wind direction
4) shifts in pressure
pressure will fall as a front approaches
pressure will be lowest as front passes
pressure will rise as front departs
5) cloud and precipitation patterns

Question 9

Review Sample Station Plot and Keys

Answer 9

Review Sample Station Plot and Keys

Question 10

Warm Fronts

Answer 10

Denoted by red semicircles that point in direction of movement, toward colder air

The warm moist, less-dense mT air gently overruns the colder, more dense air cP (or mP), slowly displacing it.

Question 11

Warm Front typical characteristics:

Answer 11

Slow movement: speeds 15-20 mph
Gradual slopes: rise: run of 1:200
Stratiform cloud sequence: 1.Ci 2.Cs 3.As 4.Ns
1 being the greatest

Ns produces light to moderate, continuous rain that called: Overrunning precipitation

Question 12

Characteristics behind a Warm Front:

Answer 12

• Pressure rising
• Winds from SW
• No precipitation
• Skies clearing
• T, Td higher

Question 13

Characteristics ahead of a Warm Front:

Answer 13

• Pressure falling
• Winds from se
• Clouds increase - Lgt., cont. prec. - T, Td lower

Question 14

Cold Fronts

Answer 14

Denoted by blue triangles that point in
direction of movement, toward warmer air (Fig. 9.6)

The cold, dense cP air literally “plows” through the warmer, less dense mT air lifting it rapidly.

Question 15

Typical Characteristics of a Cold Front:

Answer 15

Fast movement: Speeds 20-35 mph Steep slopes: ratios rise: run of 1:100
Convective cloud sequence: Cu greater thn Cb
Cbs produces intense, though short-lived:
Showers and thunderstorms

Question 16

Characteristics behind a Cold Front:

Answer 16

• Pressure rising
• Skies clearing
• Winds from nw
• T, Td low

Question 17

Characteristics ahead of a Cold Front:

Answer 17

• Pressure falling
• Winds from sw
• T, Td high
• Clouds increasing
• Convective prec.

Question 18

Stationary Fronts

Answer 18

Denoted by alternating red semicircles, which point toward colder air and blue triangles, which point toward warmer air.

Question 19

Typical Characteristics of Stationary Fronts:

Answer 19

• Essentially no movement because:

The wind flow is parallel to the front, and in opposite directions.

Question 20

Occluded Fronts (Cold type)

Answer 20

Denoted by semicircles and triangles, which point toward the direction of movement (and toward warmer air)

Since cold fronts typically move faster than warm fronts, they 	often “catch up” and overtake the warm front, lifting them off the 	surface.  (Fig. 9.8)

Question 21

Life Cycle of a Mid-Latitude Cyclone

Answer 21

Figure 9.10 illustrates the six stages of development and dissipation of a mid-latitude cyclone along the polar front.

Question 22

Life Cycle of a Mid-Latitude Cyclone

Formation: The Clash of Two Air Masses

Answer 22

Often a “wave” or “kink” will form along a frontal boundary separating two air masses (typically, cP and mT ). Under favorable conditions, a low pressure area will begin to form through a process called: Cyclongenesis

Question 23

Life Cycle of a Mid-Latitude Cyclone

Development of Cyclonic Flow

Answer 23

Pressure continues to fall, resulting in a closed counterclockwise circulation that advects warm air north and cold air south generating fronts through: Frontogenesis

Question 24

Life Cycle of a Mid-Latitude Cyclone

Occlusion: The Beginning of the End

Answer 24

Cold fronts move faster than warm fronts, as a result an occluded front will form and grow in length. After a day or two, the warm sector is displaced and cold air surrounds the entire cyclone, thus:
eliminating the temperature (density) gradient that provided the source of energy for cyclone development.

Question 25

Traveling Cyclones

Air masses tend to form in certain areas (source regions). Cyclones too have favored areas of formation:

Answer 25

Leeside of mountains
	-  Alberta Clipper
	-  Colorado Low
Coastal areas
	- Nor’ easters (storm of the century)
	-  Hatteras Low

Question 26

Traveling Cyclones’ patterns of movement

Answer 26

Once developed, these cyclones tend to move in a westerly direction, following the Jet stream