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Introduction to Meteorology: Air Masses and Fronts
As you read the following assignment, click on the hyperlinked words and/or phrases to find answers to
the questions presented. URL’s are also listed in numerical order at the end of the investigation.
INTRODUCTION
Students tend to remember places on the earth that are
unique, or special, in some way. The Equator, 0o latitude is a
neat place where the insolation 1is the most direct and the
climate is hot and humid all year round. The North Pole, 90o
N and the South Pole, 90o S are interesting places also,
frozen and remote and dark for half the year. But when it
comes to weather, these places are actually boring when
compared to the latitude where you live, the mid latitudes2
where some of the most interesting and unique weather in the
world happens!
North Pole
CLIMATE vs. WEATHER
People who haven’t learned Earth Science yet sometimes get
confused between the terms climate3 and weather4.
1.
2.
3.
4.
Define “climate”?
Define “weather”
What is the difference between climate and weather?
Where in the world are the “mid- latitudes”?
South Pole
THE ATMOSPHERE
What makes the mid-latitudes so special? To understand that we need to back up a bit.
The earth is comprised of three parts, or spheres. The Hydrosphere5, the Lithosphere6 and the
Atmosphere7. The atmosphere is then separated into several distinct layers8 based on the altitude,
temperature, air pressure and water vapor
concentration of each layer.
5. Define “Hydrosphere”, “Lithosphere”
and “Atmosphere”
6. Which layer of the atmosphere is
closest to the earth’s surface?
7. Which layer of the atmosphere does
all weather happen in?
8. Approximately how far above the earth’s surface does the troposphere extend up to?
9. Approximately how think is the stratosphere?
WEATHER
Weather is the state of condition of the lowest layer of the atmosphere at a given place at a given time.
Weather is described in terms of cloud coverage, temperature, dew-point temperature, air pressure,
visibility, wind direction and speed, humidity and precipitation.9 But weather is different in different
places. In fact, we can drive through torrential
rains in one area and two miles down the road
find ourselves in a location that is sunny and
dry. If all places on earth are surrounded by the
same atmospheric layers and combination of
gasses10, how can different areas have such
different weather?
The general atmospheric conditions of a
location over a period of time, or climate, is
determined by the tilt of the earth’s axis and the
resulting angle of the insolation that area
receives and the distance between that location
and the sun at predictable times of year. This is
what causes the poles to be cold and the equator to be hot. Other areas in between 0o and 90o have
differing climate trends based on their location and angle in relation to the sun.
10. When is it called when the dew point temperature falls below freezing?
11. Define Temperature.
12. Length can be expressed in inches or centimeters. Weight can be expressed in pounds or grams.
What are the two units in which air pressure can be expressed?
13. What is the difference between “humidity” and “relative humidity”?
14. What are the two main gasses found in the atmosphere? These gasses make up what percentage of
the air?
15. What are “trace gasses”? Give an example of a “trace gas” in our atmosphere.
AIR MASSES
The air that is located over a certain place (called a
“source region”) takes on the characteristics of that
region. For example, air sitting over the oceans will
naturally become increasingly moist as water
evaporates and enters the air. Air over the
continents will be much drier. Air hanging out over
the poles will be cold. Air located at the equator
will be warm.
Even though we can’t see air, we give names to
sections of air based on the characteristics that the
air picks up from it’s source region. We call these
uniform bodies of air “Air Masses.” There are five
categories of air masses11 which describe their
characteristic humidity and temperature.
Regions of air mass formation for North America12
The characteristics of an air mass are important for a number of reasons. First, if we know where an air
mass is coming from, we can anticipate what kind of weather it will be bring with it when it arrives. If an
air mass is coming in from over the oceans we can expect higher humidity, probably rain depending on
how long that air mass was over the water and how much water vapor it collected. Second, different air
masses are, well, different. Cold air masses are dense and faster moving. Warmer air masses are slow
moving and less dense. What this means is that when different air masses meet, they don’t just blend into
one another. When different air masses meet, they clash in a variety of ways and create some very
interesting weather!
16. Name and describe the 5 types of air masses.
17. Where in the Northern Hemisphere do Polar and Artic air masses originate? What general
direction do they travel towards?
18. Where in the Northern Hemisphere do Tropical air masses originate? What general compass
direction do they travel towards?
19. Give the approximate latitudes where air masses meet. Name four major cities located in those
latitudes.
FRONTS
We all know that air doesn’t just sit still. It moves in both local breezes and larger global patterns called
convection currents (or Hadley Cells13) created by the uneven heating and cooling of the earth’s surface.
The place where two or more different air masses meet is called a Front. There are four kinds of fronts
and each creates different weather.
Cold Front14- A front formed where a cold, dry air mass replaces a warm, moist air mass.
Warm Front15- A front formed where an advancing warm, moist air mass follows and replaces a
retreating cold, dry, polar air mass.
Occulded Front16.- A front formed when a moist, warm air mass is caught between two cold, dry air
masses.
Stationary Front17- A stationary Front is a transition zone in the atmosphere where there is little
movement of opposing air masses and winds blow towards the front from opposite directions.
20. What weather changes can be expected at each frontal zone?
21. What are the weather map symbols for the each of the four fronts?
22. Which front causes the development of “towering cumulus and cumulonimbus clouds”?
23. What are the two types of occluded fronts?
24. Where are “warm-type occluded fronts” common?
25. What is a “mid-latitude cyclone”?
Web Sites Linked:
1
http://www.uwsp.edu/geo/faculty/ritter/glossary/h_k/insolation.html
2
http://www.bom.gov.au/climate/glossary/mid_latitudes.shtml
3
http://www.cpc.ncep.noaa.gov/products/outreach/glossary.htm
4
http://www.doc.mmu.ac.uk/aric/eae/Atmosphere/Older/Weather.html
5
http://www.hyperdictionary.com/dictionary/hydrosphere
6
http://www.hyperdictionary.com/dictionary/lithosphere
7
http://nsidc.org/arcticmet/glossary/atmosphere.html
8
http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html
9
http://www.uswx.com/us/wx/ny/11779/
10
http://www.doc.mmu.ac.uk/aric/eae/Atmosphere/Older/Atmospheric_Gases.html
11
http://www.usatoday.com/weather/tg/wamsorce/wamsorce.htm
12
http://www.glacier.rice.edu/weather/3_weatherbasics.html#anchor606049
13
http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Easterly_Waves/Trade_Winds/Trade_Winds.html
14
http://www.physicalgeography.net/fundamentals/7r.html
15
http://www.physicalgeography.net/fundamentals/7r.html
16
http://www.physicalgeography.net/fundamentals/7r.html
17
http://www.physicalgeography.net/fundamentals/7r.html
“The World Wide Web: An Educator’s Best Friend”
SOLO4-004 –Chris Visco
Online Investigation Assignment #1
Introduction to Meteorology: Air Masses & Fronts