1.2 - WEATHER SYSTEMS Flashcards by Abbygail Cross

Physical state of the atmosphere at a given time and place.

Weather

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It involves such atmospheric phenomena as temperature, humidity, precipitation (type and amount), air pressure, wind, and cloud cover.

Weather

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simply the movement of warm and cold air across the globe. These movements are known as low-pressure systems and high-pressure systems.

Weather systems

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Low, thick clouds tend to ____ the Earth

cool

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high, thin clouds tend to ____ it

warm

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large bodies of air with fairly uniform temperature and moisture characteristics.

Air Masses

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Air masses acquire their characteristics in _____

source regions

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an extensive region of the earth’s surface where large masses of air having uniform temperature and humidity conditions characteristic of the region originate.

Source Region

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In a source region, ____ or not at all, which allows the air to acquire temperature and moisture characteristics from the region’s land or ocean surface.

air moves slowly

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This form when large bodies of air acquire the temperature and moisture characteristics of the underlying surface.

Air Masses

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Two Surface Types

Maritime air masses
Continental air masses

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form over water and are humid.

Maritime air masses

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form over land and are dry.

Continental air masses

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Air masses is classified by:

latitude zone (arctic, polar, tropical, equatorial)

surface type (maritime, continental)

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The classification system for air masses uses a _____ abbreviation.

two-letter

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The first letter is lowercase and signifies the _______ characteristics.

The second letter is uppercase and refers to the ________ characteristics.

moisture

temperature

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The first letter is lowercase and signifies the moisture characteristics, where:

“c” is for ______
“m” is for _____

continental (dry)

“maritime” (humid)

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The second letter is uppercase and refers to the temperature characteristics:

“A” for _________
“P” for _________
“T’” for _________
“E” for _________

Arctic (or Antarctic)

Polar (somewhat warmer than Arctic)

Tropical

Equatorial

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An “A” air mass is inherently ______, because water in such areas is often frozen.

continental (dry)

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An “E” air mass is inherently _______, because so much of the air at equatorial latitudes is over or near a source of water

maritime

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surface of contact between two unlike air masses.

Front

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TYPES OF FRONTS

cold front.
warm front.
stationary front.
occluded front.
dry line.

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This front is typically associated with intense rain of short duration.

When cold air invades warmer air, the boundary is a

cold front

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This front is typically associated with slow, steady precipitation.

When warm air invades colder air, the boundary is a

warm front

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develops when warm air and cold air meet and the boundary between the two does not move

stationary front

When a cold front overtakes a warm front, the new front is called an

occluded front “Occluded” means closed or shut off

A final type of front—called a

dry line

air motion, dominantly horizontal relative to the Earth’s surface.

Wind

Atmospheric Pressure Systems

High-pressure system Low-pressure system

High-pressure systems keep moisture from rising into the atmosphere and forming clouds. Therefore, they are usually associated with _____

clear skies.

Low-pressure system are rotating masses of warm, moist air. They usually bring ______

storms and high winds.

The _____ of horizontal winds causes air to rise

convergence

The _____ of horizontal winds causes downward motion of the air

divergence

______ the horizontal transport of any atmospheric property by the wind.

advection

There are three (3) forces that control wind speed and direction:

1. Pressure-gradient force 2. Coriolis force 3. Friction force.

_____ is the force that moves air from an area of high pressure to an area of low pressure.

1. Pressure gradient force

An instrument used to measure air pressure.

Barometer

A line drawn on a map connecting points of equal pressure. These are quantitative representations of the changing molecular density of the air over a geographic region.

Isobar

The force created by the Earth’s rotation that causes winds to be deflected to the right in the Northern Hemi-sphere and to the left in the Southern Hemisphere

2. Coriolis force

force opposing the motion of wind, caused by the drag of the Earth’s surface; greatest close to the surface and decreasing with height.

3. Frictional Force

violent or unsteady movement of air or water, or of some other fluid.

Turbulence

River of high-speed air in the upper atmosphere that flows along the polar front.

Polar front jet stream

Band of low pressure, calm winds, and clouds in tropical latitudes where air converges from the Southern and Northern Hemispheres.

Intertropical Convergence Zone (ITCZ)

The primary wind system in the tropics that flows toward the Intertropical Convergence Zone on the equatorial side of the Subtropical High-Pressure System.

Trade winds

Band of easterly winds at high latitudes.

Polar easterlies

winds that generally flow from west to east.

Westerlies Midlatitude

Band of high air pressure, calm winds, and clear skies that exists at about 25° to 30° N and S latitude.

Subtropical High (STH) Pressure System

Core of low-pressure zone associated with the Intertropical Convergence Zone.

Equatorial trough

Zone of high atmospheric pressure at high latitudes.

Polar High

THREE DISTINCT WIND CELLS

Polar cells Ferrel cell Hadley cell

The smallest and weakest cells are the _____, which extend from between 60 and 70 degrees north and south, to the poles.

Polar cells

Ferrel cell, Proposed by _______

William Ferrel (1856).

An air flows poleward and eastward near the surface and equatorward and westward at higher altitudes; this movement is the reverse of the airflow in the Hadley cell.

Ferrel cell

A Large-scale convection loop in the tropical latitudes that connects the Intertropical Convergence Zone (ITCZ) and the Subtropical High (STH).

Hadley cell

Hadley cell, Proposed by _______

George Hadley (1735).

High-speed airflow occurring at high levels in narrow bands within the upper-air westerlies and along certain other global latitude zones.

Jet Stream

The swirling air rises and cools, creating clouds and precipitation.

Cyclone

Air comes in from above and sinks to the ground. High pressure centers generally have fair weather.

Anticyclone

An elongated area of elevated air pressure in the upper atmosphere that is typically associated with sunny skies and calm winds.

High-pressure ridge

An elongated area of depressed air pressure in the upper atmosphere that is typically associated with cloudy skies and rain.

Low-pressure trough

A well-organized low-pressure system in the midlatitudes that contains warm and cold fronts.

Midlatitude cyclone

Three (3) types of traveling cyclones.

1. The Midlatitude Cyclone 2. The Tropical Cyclone 3. The Tornado

These cyclones range from weak disturbances to powerful storms.

The Midlatitude Cyclone

A range from mild disturbances to highly destructive hurricanes, or typhoons.

The Tropical Cyclone

A small, intense cyclone of enormously powerful winds.

The Tornado

pileup of water from waves onshore as a severe storm, particularly a tropical cyclone, makes landfall.

Storm Surge

A _______ is any storm that produces thunder and lightning.

Thunderstorms

persist longer than air-mass thunderstorms and have higher winds. They often produce hail or even tornadoes.

Severe thunderstorms

is a visible electrical discharge from a cloud.

Lightning

This happens when there is an imbalance of charges between a region of the cloud and another surface (usually the ground, a building, another region of the same cloud, or another cloud) that is significant enough to break through air resistance.

Lightning

any strong, heavy snowstorm with wind.

Blizzard

dust that are carried through the atmosphere by strong winds. Mostly occur in dry, open areas.

Dust storm also called sandstorm

1. Minimal Damage

Winds 33-42 m/s (74-95mph) Storm Surge 1.2-1.5 m (4-5 ft)

2. Moderate Damage

Winds 43-49 m/s (96-110mph) Storm Surge 1.82-2.4 m (6-8 ft) (Small trees down, roof damage)

3. Extensive Damage

Winds 50-58 m/s (111-130mph) Storm Surge 2.7-3.6 m (9-12 ft) (Moderate to heavy damage to home, many trees down)

4. Extreme Damage

Winds 59-69 m/s (131-155mph) Storm Surge 3.9-5.4 m (12-18 ft) (Severe damage to all structures)

5. Catastrophic Damage

Winds > 70 m/s (155mph) Storm Surge > 5.5m (18 ft) (Severe damage to all structures)

EF0. Light Damage

39-49 m/s (86-110 mi/hr)

EF1. Moderate Damage

50-60 m/s (111-135 mi/hr)

EF2. Considerable Damage

61-73 m/s (136-165 mi/hr)

EF3. Severe Damage

61-73 m/s (135-165 mi/hr)

EF4. Devastating Damage

74-89 m/s (166-200 mi/hr)

EF5. Incredible Damage

>90 m/s (>200 mi/hr)