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 ________.

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