How are air masses classified

LAB MODULE 8: AIR MASSES AND WEATHER SYSTEMS

Note: Please refer to the GETTING STARTED lab module to learn how to maneuver through and answer the lab questions using the Google Earth () component.

Key Terms

You should know and understand the following terms:

Air mass

Cold front

Occluded Front

● Continental (c)

Downburst

Stationary Front

● Maritime (m)

Front

Thunderstorm

● Arctic or Antarctic (A)

Mesocyclones

Tropical Cyclones

● Polar (P)

Microburst

Warm Front

● Tropical (T)

Mid-latitude cyclone

Weather

LAB LEARNING OBJECTIVES

After successfully completing this module, you should be able to the following tasks:

● Identify and describe air masses and their associated moisture and temperature conditions

● Describe fronts and frontal systems

● Identify the evolution and migration of a mid-latitude cyclone in the US

● Identify the mechanisms producing thunderstorms, tornados, and hurricanes

● Interpret maps showing the geographical distributions of severe weather systems

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INTRODUCTION

This lab module explores air masses, fronts and mid-latitude cyclonic weather systems. Topics include the following: continental and maritime air masses; stationary, cold, warm and occluded fronts; and the patterns and processes of mid-latitude cyclones and severe weather storms. The modules start with four opening topics, or vignettes, which are found in the accompanying Google Earth file. These vignettes introduce basic concepts of weather and severe weather systems. Some of the vignettes have animations, videos, or short articles that will provide another perspective or visual explanation for the topic at hand. After reading the vignette and associated links, answer the following questions. Please note that some links might take a while to download based on your Internet speed.

Expand the INTRODUCTION folder and then select Topic 1: Weather.

Read Topic 1: Weather.

Question 1: Briefly describe the likely weather conditions evident in the picture.

A. Sunny and hot

B. Cloudy and raining

C. Warm and humid

D. Hot and hazy

Read Topic 2: Air Masses.

Question 2: The vignette states why there is no mA classification. Additionally, there is no continental equatorial (cE) classification. What is the primary reason that a cE air mass classification does not exist (Hint: it is the opposite reason of mA)?

A. Because equatorial air masses are moist

B. Because continental air masses are moist

C. Because continental air masses originate over land

D. Because there is no land in equatorial regions

Read Topic 3: The Evolution and Weather Conditions of Fronts.

Question 3: Compare the density and speed of cold air (from the cold front) to warm air (from the warm front)

A. Colder air is lighter and travels faster than warm air

B. Colder air is denser and travels faster than warmer air

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C. Warmer air lighter and travels faster than colder air

D. Warmer air is denser and travels faster than colder air

Read Topic 4: Human Interaction: Tornado Alley.

Question 4: Why do areas located between 30°N to 50°N provide favorable conditions for tornado generation?

A. Because this region is flat

B. Because this region is where cold arctic air and warm subtropical air converge

C. Because this region is predominantly agriculture

D. Because precipitation is needed for agriculture in this region

Collapse and uncheck the INTRODUCTION folder.

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GLOBAL PERSPECTIVE

As noted in the vignette, air masses are not randomly distributed across the globe; in fact the geographic origin (source region) of air masses determine each of the six potential air mass types – continental Arctic (cA), continental polar (cP), continental tropical (mT), maritime polar (mP), maritime tropical (mT), and maritime equatorial (mE).

As air masses move around the Earth due to weather conditions, they can gain or lose moisture, or increase or decrease in temperature. For example, a maritime polar (mP) air mass moving across a continent could lose much of its moisture and become a continental polar (cP) air mass.

In this exercise, you will describe the spatial patterns of air masses as they relate to various locations throughout the world.

Verify that Labels (under Borders and Layers) is selected in the Layers panel.

Expand the GLOBAL PERSPECTIVE folder and select the Air Mass folder.

Double-click and select Location A.

Question 5: Identify the principal air mass:

A. mP

B. mT

C. cP

D. cT

Question 6: Identify the air temperature (as very cold, cold, warm, or very warm) and the air humidity (as moist or dry) for the source region of this air mass.

A. Cold and dry

B. Warm and dry

C. Very cold and moist

D. Warm and moist

Double-click and select Location B.

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Question 7: Identify the principal air mass:

A. mP

B. mT

C. cP

D. cT

Question 8: Identify the air temperature (very cold, cold, warm, or very warm) and the air humidity (moist or dry) for the source region of this air mass.

A. Cold and dry

B. Warm and dry

C. Very cold and moist

D. Warm and moist

Double-click and select Location C

Question 9: Identify the principal air mass:

A. mP

B. mT

C. cP

D. cA

Question 10: Identify the air temperature (very cold, cold, warm, or very warm) and the air humidity (moist or dry) for the source region of this air mass.

A. Cold and dry

B. Warm and dry

C. Cold and moist

D. Warm and moist

Double-click and select Location D.

Question 11: Identify the principal air mass:

A. mP

B. mT

C. cA

D. cT

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Question12: Identify the air temperature (very cold, cold, warm, or very warm) and the air humidity (moist or dry) for the source region of this air mass.

A. Cold and dry

B. Warm and dry

C. Very cold and dry

D. Warm and moist

Collapse and uncheck the GLOBAL PERSPECTIVE folder.

FRONTS

Fronts are synoptic scale features, meaning they are usually regional or continental in scale, in the order of several hundred to 1000 km (621 miles) or more in length. Synoptic scale weather maps, known as surface weather analysis, use various symbology from known data (pressure, temperature, cloud cover) to determine weather fronts.

On weather maps, the cold front boundary is designated by a blue line of triangle pips, while warm front boundaries are represented by a red line of half-circle pips. Occluded fronts are shown in purple (red+blue) of alternativing triangle and half-circle pips. In all these cases, the side of the line on which the symbol appears indicates the direction of movement of the frontal zone. For stationary fronts, the direction of movement is static, and thus, is represented by the alternation of blue triangles and red half circles shown in opposing directions.

Expand the FRONTS folder.

Select and double-click Cold front.

This symbol depicts a cold front stretching from northern Minnesota to western Nevada.

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Question 13: In which general direction is the front moving?

A. Northwest

B. Northeast

C. Southwest

D. Southeast

Double-click and select Location E and check Location F.

Question 14: At which location would you expect the air temperature to be warmer?

A. Location E

B. Location F

C. They should be the same temperature

Question 15: Which location would be experiencing thunderstorms?

A. Location E

B. Location F

C. There are thunderstorms at both locations

D. There are not thunderstorms at either location

Uncheck Cold front.

Uncheck Location E.

Double-click and select Warm front.

This symbol depicts a warm front stretching from northern Minnesota to eastern Kentucky.

Check Location G.

Question 16: In which general direction is the front moving?

A. Northwest

B. Northeast

C. Southwest

D. Southeast

Question 17: At which location (F or G) would you expect the air temperature to be warmer?

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A. Location F

B. Location G

C. They should be the same temperature

Question 18: Would there be rainfall at Location G? If so, briefly describe the intensity (how “hard” it is raining) and duration.

A. No rainfall

B. Rainfall, steady drizzle lasting all day

C. Rainfall, intense rain lasting all day

D. Rainfall, thunderstorms lasting a short period

Collapse and uncheck the FRONTS folder.

MID-LATITUDE CYCLONES

Mid-latitude cyclones are organized low pressure systems that have cold and warm fronts. The development of mid-latitude cyclones is part of the process known as cyclogenesis.

Expand the MID-LATITUDE CYCLONES folder.

Click Migration.

This animation shows the development and migration of a mid-latitude cyclone, as well as satellite imagery (Note: The satellite imagery section might take a few minutes to upload).

Now, you will go through the cyclogenesis of a mid-latitude cyclone on Google Earth.

Return to Google Earth.

Double-click and select Day 1

This map shows a typical initial development of a mid-latitude cyclone. The center of the system has the lowest pressure, which is located along the jet stream (blue arrows). The system travels in an easterly direction along the jet stream, with the

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warm front leading, followed by the cold front. The stage of cyclogenesis is the open stage.

Uncheck Day 1.

Select Day 2.

The system continues moving eastward along the jet stream. The cold front is traveling faster than the warm front and the distance between the two fronts is decreasing. With the distance between the fronts becoming smaller, cooler air starts to push the warmer air, and the warmer air begins to move upwards. The stage of cyclogenesis is the mature stage.

Uncheck Day 2.

Select Day 3.

Now, the cold front has caught up with the warm front and forms an occluded front. The warmer air is now aloft (above the surface) and precipitation may occur. This stage of cyclogenesis is the occluded stage.

Question 19: In which direction is the air circulation in a developing mid-latitude cyclone?

A. Upwards

B. Downwards

C. Clockwise

D. Counter clockwise

Question 20: Where is the origin of the cold air mass and warm air mass in these examples?

A. Cold from Canada; warm from Eastern US

B. Cold from Western US; warm from Eastern US

C. Cold from Canada; warm from gulf of Mexico

D. Cold from Western US; warm from Pacific Ocean

Question 21: Why does the cold front move faster than the warm front?

A. Because the cold air is lighter and moves faster.

B. Because the warm air is denser and moves more slowly.

C. Because the cold air is denser and moves faster.

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D. Because the warm air is lighter and moves more slowly.

Question 22: What type of weather do we see during the occluded front?

A. Temperature rising, no rainfall

B. Temperature rising, variable (light to heavy) rainfall

C. Temperature dropping, no rainfall

D. Temperature dropping, variable (light to heavy) rainfall

Question 23: Where does the heaviest rainfall occur - along the cold front or the warm front?

A. Cold front

B. Warm front.

C. Rainfall is equal along both fronts.

D. There is no rainfall along either front.

Collapse and uncheck the MID-LATITUDE CYCLONES folder.

THUNDERSTORMS AND TORNADOS

Thunderstorms

Thunderstorms are formed when parcels of unstable (warm, moist) air are lifted rapidly and vertically from the ground. Lifting mechanisms include convective lifting from the unequal warming of the ground, orographic lifting from air forced over a mountain or similar terrain, or frontal lifting from the leading edge of a cold or warm front. Rapid ascension of unstable air creates strong updrafts (upward moving air) and intense adiabatic cooling (that is, cooling without interacting with the surrounding air). When the updrafts reach the maximum altitude (usually in the troposphere, or over 12 km (40,000 feet) from the Earth’s surface), they change direction and become downdrafts, and precipitate.

Typical thunderstorms have weak updrafts and weak downdrafts. Thunderstorms that produce flash floods have strong updrafts but weak downdrafts. Thunderstorms that produce downbursts (or microbursts) of downward, divergent air have weak updrafts but strong downdrafts. When strong updrafts and down drafts are present severe thunderstorms known as supercells are formed. Associated with these thunderstorms are the anvil shaped cumulonimbus clouds, heavy rains or hail, thunder and lightning, gusts of wind, mesocyclones (strong vertical updrafts that rotate and form a vortex of air), and sometimes tornadoes.

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Expand the THUNDERSTORMS AND TORNADOS folder.

Click Thunderstorms.

Question 24: At what stage(s) does updraft develop?

A. Cumulus stage

B. Developmental stage

C. Mature stage

D. Dissipation stage

Question 25: At what stage(s) does the atmosphere cool and stabilize?

A. Cumulus stage

B. Developmental stage

C. Mature stage

D. Dissipation stage

Tornadoes

Tornadoes form as a result of strong updrafts combined with wind shear (the difference in wind direction and speed with altitude). The combination changes the rotation of air from a horizontal axis to a vertical axis. When the funnel reaches the ground, it has evolved into a tornado.

Click Tornado Formation for the animation of the evolution of a tornado and practice categorizing tornadoes using the Enhanced Fujita Scale.

Question 26: What does an area look like when it is hit by a EF2 tornado?

A. Roofs stripped, mobile homes flipped over, windows broken

B. Large trees uprooted, mobile homes destroyed, roofs ripped off houses

C. Siding stripped, Shingles peeled off roofs, tree branches broken

D. Several damage to shopping centers, cars thrown about

Question 27: What does an area look like when it is hit by a EF4 tornado?

A. Roofs stripped, mobile homes flipped over, windows broken

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B. Large trees uprooted, mobile homes destroyed, roofs ripped off houses

C. Siding stripped, Shingles peeled off roofs, tree branches broken

D. Devastating damage, cars thrown about

Select Tornado Tracks and Icons.

The following tornado data is from the NOAA National Weather Service. Tornados have been classified by the original Fujita Scale (the tornado scale used until 2007); classification ranges from F0 to F5.

Uncheck Tornado Tracks and Icons.

Double-click and expand Tornadoes by F-scale.

Select F0.

F0 are the weakest tornados, and have the least amount of damage. They are also the most common.

Question 28: Which states west of the Mississippi River do not have an F0 tornado recorded?

A. Nevada

B. Utah

C. Washington

D. Every state west of the Mississippi River has had an F0 tornado.

Unselect F0 and then select F1. Note the geographic distribution of tornadoes at this strength.

Repeat F2-F5.

Question 29: How has the frequency and location of tornados changed as the strength increases?

A. The frequency increases and location tends to be in the east half of the US

B. The frequency increases and the location is somewhat random

C. The frequency decreases and location tends to be in the east half of the US

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D. The frequency decreases and the location is somewhat random

Collapse and uncheck Tornadoes by F-scale.

Expand Tornadoes by Month. Select and examine each month.

Question 30: Which couple of months has the most tornadoes?

A. January/February

B. April/May

C. July August

D. August/September

Collapse and uncheck THUNDERSTORMS AND TORNADOS.

TROPICAL CYCLONES

Tropical cyclones have different names, depending on where they develop. In the Atlantic and eastern Pacific Oceans, they are called hurricanes. In the Indian Ocean they are known as cyclones and in the eastern Pacific they are identified as typhoons.

Tropical cyclones are storm systems of low pressure surrounded by a complex spiral of thunderstorms. Unlike mid-latitude cyclones, tropical cyclones do not form in regions with fronts. Rather, hurricanes develop where the atmosphere is relatively homogenous - but with a high pressure aloft to “cap” the low pressure storm. These storm systems rely on energy from warm water to develop, and as such, form in low latitudes.

Expand TROPICAL CYCLONES.

Expand Historical Hurricane Tracks.

Select Legend and then double-click and select Atlantic: 2000-2012 (Note: The imagery might take a few minutes to upload).

Question 31: Explain the general pathway of hurricanes in the Atlantic Ocean.

A. They form in different places, but generally end up off the coast of Africa

B. They travel east across the Atlantic before diverging

C. The pathways are random in direction

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D. They travel west across the Atlantic before diverging

Uncheck Atlantic: 2000-2012.

Double-click and select Eastern North Pacific 2000-2012 (Note: The imagery might take a few minutes to upload).

Question 32: Explain the general pathway of typhoons in the eastern Pacific Ocean.

A. They generally form off the coast of Mexico and head toward Hawai’i

B. They form in different places, but generally end up off the coast of Mexico

C. They travel east across the Pacific before diverging

D. The pathways are random in direction

Collapse and uncheck Historical Hurricane Tracks.

Expand and double-click Hurricane Katrina - 2005. To close the citation, click the X in the top right corner of the window.

Select Katrina Landfall Video. Watch the time lapse of Hurricane Katrina as it hits Louisiana.

Double-click and select Tracks and view the pathway of this hurricane from the Caribbean Sea to North America.

Select Hurricane.

Question 33: Geographically, where was Hurricane Katrina the strongest (an H5 –shown as a red circle)?

A. In the Atlantic Ocean

B. In the Caribbean sea

C. In the Gulf of Mexico

D. New Orleans, LA

Question 34: What happened to the Hurricane once it hit land?

A. It dissipated

B. It continued north at the same strength

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C. It continued north but with decreasing strength

D. It became a tropical storm

Collapse and uncheck Hurricane Katrina.

Double-click and select Hurricane Sandy.

Hurricane Sandy is considered the largest hurricane ever recorded in the Atlantic basin, measuring in at over 1100 miles (1800 km) in diameter.

Question 35: True or False: The storm system that hit New Jersey and the surrounding area on October 29 was a tropical cyclone.

A. True

B. False

Question 36: Explain your answer in the previous question.

A. Tropical cyclones do not travel that far north

B. Tropical cyclones do not occur this last in the year

C. Its inner core was less defined than that required of a tropical cyclone

D. Sustained wind speed, low atmospheric pressure and storm structure are traits of a tropical cyclone.