Chapter Eight - Test Three

Question 1

What is an Air Mass?

Answer 1

An immense “body” of air (thousands of km2 across, and several km thick) dominated by High Pressure whose: Thermal and moisture properties remain homogenous in any direction within the air mass.

Question 2

When the air mass moves out of its region of origin, it will carry these T and Td characteristics with it

Answer 2

Thermals property: Temperature (T)

Moisture property: Dewpoint (Td)

Question 3

Source Regions

Air masses develop over regions of uniform geography, usually flat
regions of similar composition (i.e. sand, water, ice) that are:

Answer 3

Conducive to the formation of high pressure

Examples: Gulf of Mexico
Deserts of Mexico
Tundra of northern Canada
Atlantic and Pacific Ocean

Question 4

The longer an Air Mass remains stationary over its Source Region, the more likely it will…

Answer 4

acquire the thermal and moisture properties of the surface

Question 5

Classifying Air Masses

Answer 5

Depends on the latitude and nature of the underlying surface.

Question 6

Classifying Air Masses

For latitude, we designate:

Answer 6

arctic, polar or tropical, which determines thermal properties

Question 7

Classifying Air Masses

For surface, we designate:

Answer 7

continental or maritime, which determines moisture properties

Question 8

Air Mass 
      cA
      cP
      cT
      mT
      mP
What about Basic Thermal or Moisture properties?

Answer 8

Basic Thermal,  Moisture Properties
cA	Very cold		Dry (winter only)
cP	Cold			Dry
cT	Hot			Dry	(summer only)
mT	Warm		Moist
mP	Cool			Moist

Question 9

Remember that all four air mass types are characterized by ____

Answer 9

high pressure

Question 10

The typical movement of the four major air

masses is controlled by the:

Answer 10

Jet Stream

Question 11

Continental Polar  (cP) and 
Continental Arctic (cA) Air Masses

Answer 11

Characterized by very cold (cA) or cold (cP) and dry air

Question 12

North American Air Masses are characterized by very cold (cA) or cold (cP) and dry air

Answer 12

Cold : because of the long nights in the high latitudes (i.e. little solar radiation)

lack of water vapor in the air results in maximum, almost continuous radiational cooling

Dry : because the air originates over land and/or frozen ArcticOcean and because cold air holds very little water vapor

Question 13

cA (form over Arctic Basin) and cP (form over northern Canada) air masses originate over flat snow/ice covered areas and generally move south-southeast into the US, responsible:

Answer 13

• coldest air in the winter: “Siberian Express” (Box 8.1)

- Lake Effect snow storms (Box 8.2)

Question 14

Maritime Polar (mP) Air Masses

Answer 14

Originate over the northern Pacific and Atlantic Oceans

Question 15

North American Air Masses are characterized by cool and moist air (mP)

Answer 15

Cool : because it originates over the northern oceans, which are always cool (but never frozen)

Moist: because the air originates over open oceans where water vapor is plentiful

Question 16

Pacific mP Air Masses

Answer 16

Generally move east into the western and central US

- Generally keeps the Pacific Coast states cool (even in summer)
- The moisture gets “squeezed” out by the various mountain ranges in the western states (Fig 15.12)

so that the air mass becomes drier by the time it reaches the central states

Question 17

Atlantic mP Air Masses

Answer 17

Move southwesterly into the US, generally east of the Appalachian Mountains from North Carolina to Maine

- Influence is less frequent, generally in winter and spring
- associated with Nor’easters

Question 18

Maritime Tropical (mT) Air Masses

Answer 18

mT air masses originate over the Atlantic, Gulf of Mexico and Pacific

Question 19

North American Air Masses are characterized by warm and moist air (mT)

Answer 19

Warm: because it originates over the southern oceans (Gulf), which are always warm

Moist: because the air originates over open oceans where water vapor is plentiful

Question 20

Half days in NC are dominated by

Answer 20

Gulf of Mexico (Atlantic) mT Air

Question 21

Gulf of Mexico (Atlantic) mT Air:

Answer 21

during the winter, the mT air mass usually confined to the deep south, however, during the summer it will dominate the weather east of Rocky Mountains.

Question 22

Gulf of Mexico (Atlantic) mT Air is responsible for:

Answer 22

• Oppressively high temperatures and humidity (i.e. High Apparent Temperatures)
• The majority of Precipitation that falls on the eastern half of the U S originates from mT air from the Gulf (Fig 8.9)

It is the air mass found most frequently over North Carolina.

Question 23

Pacific mT Air

Answer 23

Influence is usually confined to the southwest U.S.

-	Associated with “Monsoonal” thunderstorms in Arizona and New Mexico

Question 24

Continental Tropical (cT) Air Masses

Answer 24

cT Air masses generally originate in Mexico and move north into the southwest and south central US

- Occurs only during the summer months
- Responsible for devastating droughts

It is the air mass found LEAST frequently over North Carolina.

Question 25

North American Air Masses are characterized by hot and dry air (cT)

Answer 25

Hot and dry: because it originates over the desert region of northern Mexico which receives strong radiation and contains little water