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Elements Of Weather > Ch 8 & 9 > Flashcards

Ch 8 & 9 Flashcards

1
Q

Air Mass

A

large body of air that has relatively uniform temperature and moisture level throughout
around 1000 miles horizontal
types of them are determined by their source region

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2
Q

Source Region

A

region where an air mass is formed

major ones are not found in the middle latitude

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3
Q

Source Regions must meet 2 criteria

A

1) must be an extensive and physically uniform area

2) the region is dominated by stationary or slow-moving anticyclones with their extensive areas of calms or light winds

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4
Q

Regions under the influence of cyclones

A

are not likely to produce air mass because such systems are characterized by converging surface winds

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5
Q

Classification of an air mass

A

depends on the latitude of the source region and the nature of the surface in the area of origin

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6
Q

Latitude of source region

A

indicates the temperature conditions within the air mass

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7
Q

P

A

Polar

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8
Q

A

A

Artic

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9
Q

T

A

Tropical

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10
Q

m

A

maritime

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11
Q

c

A

continential

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12
Q

maritime air masses

A

formed over water

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13
Q

continental air masses

A

formed over land

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14
Q

Main characteristics that define air masses

A

temperature and moisture content

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15
Q

k is added after the air mass symbol when

A

an air mass is colder than the surface over which it is passing

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16
Q

w is added when

A

an air mass is warmer than the underlying surface

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17
Q

cA

A

continental arctic
very cold, very dry
air forms farther north, over the arctic basin and the Greenland ice cap

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18
Q

cP

A

continental polar
cold, dry
originates over the often snow-covered interior regions of Canada and Alaska, poleward of the 50th parallel

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19
Q

mP

A

maritime polar
cool, humid
form over oceans at high latitudes;; two regions important sources for air that influence North America: North Pacific and Northwestern Atlantic

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20
Q

mT

A

maritime tropical
warm, humid
originate over the warm waters of the Gulf of Mexico, the caribbean sea, or the adjacent western atlantic ocean

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21
Q

cT

A

continental tropical
hot, dry
normally remains nearly cloudless because of extremely low humidity;; the prevailing weather is hot with an almost complete lack of rainfall

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22
Q

Lake-effect snow

A

highly localized storms, occurring along the leeward shore of the great lakes

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23
Q

Pacific Maritime Polar Air Masses

A

strong influence on the weather along the western coast; especially in winter

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24
Q

North Atlantic mT air

A

maritime tropical air masses from the Gulf-Caribbean- Atlantic source regions greatly affect the weather of the United States east of the Rocky Mountains

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25
Q

Fronts

A

boundary surfaces that separate air masses of different densities

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26
Q

Types of Fronts

A

1) warm
2) cold
3) stationary
4) occluded
5) drylines

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27
Q

Warm Fronts

A

transition zone where a warm air mass is replacing a cooler air mass;; very gradual slope
red line with red semi circles pointing towards the colder air and in the direction of movement

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28
Q

Warm fronts produce

A

light-to-moderate precipitation over wide area for an extended period;; if overriding air mass is relatively dry, there will be minimal cloud development, and no precipitation

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29
Q

warm fronts in summer

A

very moist air;; if unstable air is lifted sufficiently it will freely rise on its own, producing towering cumulonimbus clouds and thunderstorms

30
Q

Cold Fronts

A

transition zone where a cold air mass is replacing a warmer air mass;; twice as steep as warm fronts;; advance faster than warm fronts
blue line and blue triangles pointing towards the warmer air and in direction of movement;; thunderstorms

31
Q

Stationary Front

A

when a warm or cold front stops moving;; blue and red lines with blue triangles pointing towards warmer air and red semi pointing towards the colder air

32
Q

Occluded Fronts

A

rapidly moving cold front overtakes a warm front, as the cold air wedges the warm front upward, new front forms between the new advancing cold air and the older cool air mass over which the warm front is gliding;; purple line with alternating triangles and semi pointing the direction the front is moving

33
Q

Occluded Frontss

A

mature mid-latitude cyclone;; partially mid-latitude cyclone;; mid-latitude cyclone

34
Q

cold-type occluded front

A

cold air–> warm air–> cool air

35
Q

warm-type occluded front

A

cool air–> warm air–> cold air

36
Q

Drylines

A

boundary that separates a moist air mass from a dry air mass

37
Q

___ fronts are shown by a line with triangular points on one side

A

cold front

38
Q

if cirrus clouds are first appearing, followed later by cirrostratus, and then altostratus a ___ front is approaching

A

warm front

39
Q

The type of front formed when the leading edge of cold air merges with a warm front known as

A

occluded front

40
Q

The surface position of the stationary front does not move or moves very slowly because

A

the winds blow parallel to the front

41
Q

Polar Front

A

weather front located typically in the mid-latitudes that separates arctic and polar air masses from tropical air masses

42
Q

Mid-latitude cyclone

A

cyclonic storm that forms primarily in the middle latitudes;; these storms also contain warm, cold, and occluded fronts;; atmospheric pressure in their center can get as low as 970 millibars

  • -occur most often during the winter season in US b/c of large temp difference between the equator and the north pole
  • -easily identified by comma appearance
43
Q

Polar Front theory (Norwegian Cyclone Model)

A

1) Front develops
2) wave develops
3) cyclonic circulation established
4) occlusion begins

44
Q

Front Develops

A

initially will be a boundary, separating warm air to the south from cold air to the north;; stage set for cyclogenesis (cyclone formation)

45
Q

wave develops

A

wave will form as an upper level disturbance embedded n the jets stream moves over the front;; the front develops a kink where the wave is developing
–precipitation will begin to develop with the heaviest occurrence along the front (dark green)

46
Q

Cyclonic circulation established

A

as wave intensifies both cold and warm fronts become better organized;; resulting flow is a counterclockwise cyclonic circulation that can be seen clearly on the weather map

47
Q

Occlusion begins

A

wave becomes a mature low pressure system, while the cold front, moving faster than the warm front “catches up” with the warm front. As the cold front overtakes the warm front, an occluded front forms
–as occlusion begins the storm often intensifies;; pressure at the storm’s falls, and wind speeds increases. In winter, heavy snowfalls and blizzard-like conditions are possible during this phase

48
Q

Occluded front developed

A

as the cold front continues advancing on the warm front, the occlusion increases and cold air surround the cyclone at low levels
–horizontal temp difference that existed between the two contracting air masses has been eliminated, causing the low pressure system to gradually dissipate

49
Q

Typical movement of mid-latitude cyclone

A

generally moves eastward across the US; requires 2 to 4 days to pass completely over a region

50
Q

A section of mid-latitude cyclone

A

high cirrus clouds (before warm front)

51
Q

B section

A

light precipitation;; as warm front nears, the rate of precipitation increases, temperature rises, winds change from an easterly to a southerly flow

52
Q

C section

A

maritime tropical air mass (warm)

53
Q

D section

A

approach of cold front

54
Q

E

A

once the front passes, the skies clear quickly as cooler air invades the region

55
Q

the lifetime of a mid-latitude cyclone is nearly

A

a few days to 1 week

56
Q

An approaching mid-latitude cyclone would be indicated by a ___ pressure

A

rapidly falling

57
Q

The area enclosed between the cold front and warm front in a a mid-latitude cyclone is called the

A

warm sector

58
Q

Anticyclone

A

large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere
–divergence at the surface is balanced by convergence aloft and general subsidence of the air column

59
Q

Anticyclone weather

A

owing to the gradual subsidence within them, anticyclones produce clear skies and calm conditions

60
Q

Blocking high

A

high pressure area (anticyclone), often aloft, that remains nearly stationary or moves slowly compared to west-to-east motion;; blocks the eastward movement of low pressure areas (cyclones) at its latitude
–can be in place for several days causing the areas affected by them to have the same kind of weather for an extended period of time

61
Q

Montpellier

A

example of blocking highs and flood

62
Q

compared to continental air masses with the same air temp, maritime air masses

A

have higher water vapor content

63
Q

cT air mass is

A

warm and dry

64
Q

when an air mass is warmer than the surface over which it is moving

A

the air becomes more stable

65
Q

the most important properties that should be relatively homogeneous at the same altitude in an air mass are

A

temperature and moisture content

66
Q

Lake-effect snow is associated with the ___ air mass

A

cP

67
Q

An area on the north side of the low-pressure center of a a middle-latitude cyclone usually has this type of front for the longest period of time

A

occluded

68
Q

Cold air –> warm air

A

cold front

69
Q

The type of weather most frequently associated with the front shown on the diagram above cold air–> warm air

A

thunderstorms and other severe weather

70
Q

cool air–> warm air–> cold air

A

warm type occluded front

71
Q

on a weather map, a line with blue triangles on one side and red semicircles on the other represents

A

stationary front

Elements Of Weather (6 decks)

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