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Chapter 7

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Air mass
A larger body of air (500-1600 miles across in diameter) with relatively uniform temperature and moisture, typically with a homogenous source origin is called?
Cold front
Compared to a warm front, has a much steeper gradient.
Tornadoes
Considered to be the most destructive forces of atmospheric disturbances.
Tornadoes
Tiny storms in diameter usually with the most extreme pressure gradient.
Calm
Unlike tornadoes, the eye of a hurricane is normally...?
The typical air mass in place for New Orleans, LA
mT
Thunderstorms usually dissipate because
The down draft chokes off the updraft.
Exist behind cold fronts
Mid latitude anti-cyclones in the northern hemisphere
Hurricane->Tropical storm->Tropical depression
Ranks tropical cyclones in order of decreasing wind speed.
Vertical tilt with height
Characteristic that distinguishes hurricane from mid latitude cyclones in the northern hemisphere.
Origin of Air Masses
Develops by remaining over a uniform land or sea surface long enough to acquire the temperature/humidity/stability of the surface below.
A
Artic/Antarctic - Antarctica, Artic Ocean and fringes, and Greenland.
[ Very cold, very dry, very stable ]
cP
Continental Polar - High latitude plains of Eurasia and North America.
[ Cold, dry, very stable ]
mP
Maritime Polar - Oceans in vicinity of 50 - 60 degrees N and S latitude.
[ Cold, moist, relatively unstable ]
cT
Continental Tropical - Low-latitude deserts.
[ Hot, very dry, unstable ]
mT
Maritime Tropical - Tropical and subtropical oceans.
[ Warm, moist, of variable stability ]
E
Equatorial - Oceans near the equator.
[ Warm, very moist, unstable ]
Front
Develops between air masses.
Cold Front
forms where an advancing cold air mass meets warmer air.
Warm Front
forms where an advancing warm air mass meets colder air.
Stationary Front
Common boundary when neither air mass displaces the other.
Occluded Front
formed when a cold front overtakes a warm front.
Characteristics of Atmospheric Disturbances
Extremely variable in size, migratory and transient, brief duration, and relatively predictable in weather conditions.
Mid Latitude Disturbances
Principal battleground of tropospheric phenomena: where polar and tropical air masses meet, where most fronts occur, and where weather is most dynamic and changeable from season to season and from day to day.
Tropical Disturbances
same weather day after day, week after week and month after month. Almost the only breaks are provided by transient atmospheric disturbances. Mostly tropical cyclones - known as hurricanes.
Localized Severe Weather
Other parts of the globe. Short-lived. Mostly thunderstorms and tornadoes.
Mid latitude cyclones
Probably most significant of all atmospheric disturbances. Typically has a diameter of 1600 km. Counterclockwise converging circulation. Attracts cool air from the north and warm air from the south.
Mid latitude Anticyclones
Major disturbance in the general flow of the westerlies. Referred to as a 'HIGH' (H). Typically larger than a mid latitude cyclone and generally moves west to east. Clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere.
Easterly Wave
Long but weak migratory, low pressure system that may occur almost anywhere between 5 and 30 degrees latitude.
Tropical Cyclones
Intense, low pressure disturbances that develop in the tropics and occasionally move poleward into the mid latitudes.
Tropical Depression
Has wind speeds less than 33 knots (61 km or 38 mph) but has developed a closed wind circulation pattern.
Tropical Storm
Has winds between 34 and 63 knots (63-117 km or 39-73 mph).
Hurricane
Has winds greater than 64 knots (119 km or 74 mph).
Wind Shear
Refer to significant change in wind direction or wind speed with increasing elevation.
U.S. Midwest
the least likely zone of formation for a large air mass
Low
Tornadoes, although erratic in their pathways, are always characterized by ________ pressure.
Central States
Has the highest incidence of tornadoes
Sinking air
The "eye" of the hurricane is a zone characterized by ________.
Southwest to northeast
The average directional movement of tornadoes is ________.
East to west
The average directional movement of hurricanes is ________.
"tropical cyclone"
The correct designation for a hurricane is as a/an ________.
Thunderstorms
Accompany hurricanes, tornadoes, extratropical cyclones and cold fronts.
60 degrees
As a rule, thunderstorms are unknown poleward of ________ latitude.
Galveston, TX
North America's greatest hurricane disaster took place at ________.
Mid latitude anticyclone
Calm, fair weather is most likely to result from a/an ________.
cP
Of the list below, the coldest air is bound to be associated with a/an ________ air mass.
1 week
Which of the following best represents the length of the life cycle of a typical midlatitude cyclone?
normal slope for a cold front
1:100
Mature
The most active phase of a thunderstorm is called the ________ phase.
Properties of an air mass
Large, relatively uniform, travel as recognizable entity, must modify as it leaves its source region.
Stationary
When neither air mass displaces the adjacent one, their boundary is called a(n) ________ front.
one week
The average hurricane exists, on the average, for about ________.
25-50
A tornado advances at a rate of speed of ________ kilometers per hour.
1:200
The slope of a warm front generally averages about ________.
cold
On the average, ________ fronts move the fastest of all fronts.
westerlies
Extratropical cyclones and anticyclones function as migratory perturbations in the ________.
10
Hurricane formation is very rare within ________ degrees of the Equator.
convective
Thunderstorms are violent ________ storms accompanied by thunder and lightning.
block
Stable anticyclones act as a ________ to moving cyclones.
a few hundred
An easterly wave is on the order of ________ kilometers long.
Anvil Top
A distinguishing feature of thunderstorms.
cold
On a weather map, a symbol consisting of triangles arranged along one side of a line indicates a(n) ________ front.
middle
The global westerly wind zone most heavily impacts the ________ latitudes.
September
The month most likely for a hurricane to occur in the Northern Hemisphere is ________.
The U.S.
Which country is the most likely place on Earth for a tornado to occur?
1,600
An average air mass is on the order of ________ kilometers in diameter.
A wave cyclone
A midlatitude cyclone is also properly termed ________.
cyclones
Upper air divergence is most closely associated with surface ________.
above the ground
In an occluded front, the warm air sector is ________.
Rossby Waves
The movement of middle latitude cyclones is determined by the jet stream and ________.