Geology – Chapter 12 – Meteorology

the study of atmospheric phenomena

Current short-term state of the atmosphere. Example weather statement: “It’s raining.”

Long-term variation of weather in a particular area, averaged over 30 years.

Air Mass
A large body of air that takes the characteristics (humidity, temperature) of the area over which it forms.

Air Mass Modification
It is the change in humidity or temperature of an air mass as it moves away from its source region.
Humidity: An air mass becomes more humid if it moves over an ocean, and drier if it moves over land.
Temperature: An air mass becomes warmer if it moves towards the equator, and colder if it moves towards the poles.

Coriolis Effect
Air particles (winds) are deflected and curved because of the rotation of the earth.

Trade Winds
Wind system between 0 degrees (equator) and 30 degrees north or south latitude. Wind blows from the east to the west.

At 0 degrees (equator), air rises, creating clouds and tropical rainforests.

At 30 degrees latitude, air sinks, creating deserts.

Prevailing westerlies
Wind system between 30 – 60 degrees latitude. Wind blows from the west to the east. This wind system blows over most of the U.S. & Canada.

At 30 degrees latitude, air sinks, creating deserts.

At 60 degrees, air rises, creating clouds.

Polar easterlies
Wind system between 60 degrees latitude – 90 degrees (poles). Wind blows from the east to the west.

At 60 degrees, air rises, creating clouds.

At 90 degrees latitude, cold dense air sinks. No clouds.

Jet Streams
*What are they?
What causes them?
Where are they found?
Narrow band of high-speed, high-altitude winds that circle the earth caused by large temperature differences.
Jet streams are found where 2 different types of wind systems with very different temperatures collide:

Polar Jet Stream is found at 60 degrees latitude where the Prevailing Westerlies and Polar Easterlies collide.

Subtropical Jet Stream is found at 30 degrees latitude where the Tradewinds and the Prevailing Westerlies collide.

Boundary between two air masses of different temperatures

Source region
Region over which an air mass forms.
** Example: The source region for a Maritime Tropical air mass might be the Gulf of Mexico.

Humid air mass that forms over oceans

Maritime Tropical (mT)
Humid, warm air mass that forms over a warm ocean like the Gulf of Mexico

Maritime Polar (mP)
Humid, cold air mass that forms over icy, cold oceans such as the North Pacific, Atlantic and Artic Oceans. This type of air mass brings cool air, fog, clouds, & rain to NW United States.

Continental Tropical (cT)
Dry, warm air mass that forms over land in tropical regions like Mexico, Sahara Desert.

Continental Polar (cP)
Dry, cold air mass that forms over cold land, like northern Canada.

Arctic Air Mass (A)
Similar to a cP (Continental Polar) air mass but much colder.

Cold Front
*What type of air mass is pushing?
*What type of clouds?
*Represented by??
Cold, dense air is moving and displaces (pushes)warm air up along a steep front. A narrow band of clouds (cumulonimbus), showers, thunderstorms, or heavy snow may occur. As the storm passes, a drop in temperature occurs.

Blue line with blue triangles pointing in the direction the cold air is moving. (Your lips turn “blue” when you’re cold. Triangles are like “icicles”.)

Warm Front
*What type of clouds?
*Represented by?
Moving warm air displaces (pushes) cold air. The warm air rises in a gentle slope over the cold air.

Many types of clouds are formed at all levels of the troposphere: cirrus, altocumulus, nimbostratus, etc.

This forms a wide band of cloudiness and precipitation.

Red line with red semi-circles pointing the direction the warm air is moving. (Red semi-circles are like hot burners on a stove.)

Occluded Front
Occluded Front
Formed when a Cold Front catches up and passes a Warm Front, forcing the warm air up and running into another cold air mass. The warm air is “occluded” and “shut out” and no longer touches the ground.

Purple line with triangles & semi-circles on SAME side of line, as all 3 air masses are moving in same direction.
Images from:

Stationary Front
Stationary Front
Front that doesn’t move because there isn’t much temperature difference between the 2 colliding air masses.

Varying weather possible: Clear vs. clouds, light or no precipitation vs. thunderstorms, no rain vs. days of rain.

Combo of cold & warm diagrams with short segments of alternating blue triangles & red semicircles pointing in opposite directions

Image from:

High Pressure
pressure system with clockwise and outward winds that bring clear blue skies and dry weahter

It this air pressure system air sinks, so that when it reaches Earth’s surface, it spreads away from the center. this pressure system rotates in a counterclockwise direction

Low Pressure
pressure system with counterclockwise and inward winds that brings cloudiness and stormy weather

A mass of rising warm air that usually bring wet, stormy weather. Some inbalance in temperature, pressure or density causes part of the front to move north as a warm front, this sets up a counterclock wise or cyclonic circulation.

infrared imagery
Detects differences in thermal energy,which are used to map either cloud cover or surface temps. It helps meteorologists to determine the temp. of a cloud.

a system that uses reflected radio waves to detect objects and measure their distance and speed

Doppler effect
Change in wave frequency that occurs in energy, such as sound or light, as the energy moves toward or away from an observer. (Example: pitch of train horn changes as it passes.)

Is used to measure the speed or movement of precipitation.

Measures the “ceiling” of the sky which is the height of the clouds and estimates the amount of sky covered by clouds.

Hygro is like “hydro” or water. It measures humidity (water vapor) in the air.


Measures air pressure.

Measure wind speed. Faster it spins, the faster the wind.

instrument for measuring the relative humidity of the atmosphere

Balloon with sensors to gather upper-level data and “radio” it back to weather station.

Station Model
Use of symbols to record the weather data for a particular site at a particular time.

Lines that connect points of equal or constant values.
(“Iso” is “same”, like an isoceles triangle.)

lines on a map drawn through all points having the same atmospheric pressure

lines that connect points that have the same temperature

short term forecast
the most accurate and detailed forecast, usually 1 to 3 days.

long term forecast
less reliable forecasts that may estimate the weather one to two weeks in the future

digital forecast
forecast that relies on numerical data

analog forecast
involves comparing current weather patterns to patterns that took place in the past