Meteorology Test 2 Objectives (Ch. 18 & 19)

Question 1

Describe, in general, how a mercury barometer and an aneroid barometer measure air pressure.

Answer 1

mercury barometer - a tube with one closed end filled with mercury inverted into a dish of mercury. The mercury flows out of the tube until the weight of the column was balanced by the pressure that the atmosphere exerted on the surface of the mercury in the dish. When air pressure increases, the mercury in the tube rises; when it decreases, so does the mercury.
aneroid barometer - uses a partially evacuated metal chamber which is extremely sensitive to variations in air pressure. It changes shape, compressing as the pressure increases and expanding as the pressure decreases. A series of levers transmit the movements of the chamber to a pointer on a dial that is calibrated to read in inches of mercury and/or millibars.

Question 2

State normal sea level atmospheric pressure in lbs/in2, inches of mercury, and millibars.

Answer 2

(14. 7 lbs/in2)
29. 92 inches of mercury
1013. 2 millibars

Question 3

What do isobars represent on a weather map and how can they be used to locate high or low pressure regions and areas of high or low wind speed.

Answer 3

Isobars are lines connecting points of equal pressure. (Differences in pressure create wind. The pressure gradient force drives the winds from higher pressure to lower pressure.)
Closely spaced isobars - steep pressure gradient - air pressure changes rapidly - high winds
Widely spaced isobars - weak pressure gradient - air pressure changes gradually - light winds

Question 4

Interpret wind speed and direction symbols.

Answer 4

The end of the line with the barbs is the end pointing where the winds come from; wind direction is always recorded as where it is coming from NOT where it is going to.
half barb = 5 knots
full barb = 10 knots
flag = 50 knots

Question 5

What is the cause and effect of the Coriolis force?

Answer 5

The cause is the Earth’s rotation. The wind is deflected to the right of its path of motion in the Northern Hemisphere and to the left in the Southern Hemisphere.

Question 6

How does the wind move relative to isobars near the surface and at higher altitudes (geostrophic winds)?

Answer 6

At the surface (below 600 meters/2000 feet), wind move at an angle across the isobars, toward the area of lower pressure (want to go straight, but Coriolis effect deflects it). At higher altitudes, wind moves parallel to the isobars.

Question 7

Given a set of isobars and their pressures, identify an area as a high or low, give its meteorological name, describe its surface air circulation patterns, describe the most likely sky conditions, and describe the air currents (vertical air movement) near its center.

Answer 7

/

Question 8

Name, locate, and describe the dominant high and low pressure areas of the Earth.

Answer 8

Doldrums: low pressure belt around equator; winds light and variable, often calm; lots of rain; ITCZ (Intertropical Convergence Zone)
Horse Latitudes: about 30 degress latitude; air is descending (High pressure), little surface wind; dry (great deserts of the world are located here)
Subpolar Low/Polar Front: warm air from south meets cold air from the north; produces stormy belt-lowpressure
Polar High: a high pressure over the poles -a cold desert

Question 9

Name, locate, and describe the general atmospheric wind patterns of the Earth.

Answer 9

Trade Winds: (NE in North Hemisphere, SE in the Southern) light and steady
Westerlies: come from west; 40 degress latitude; in South, over large stretches of ocean; US in this area
Polar Easterlies: come from east

Question 10

Describe the polar jet stream and its approximate location. Why is it important in describing and predicting the weather?

Answer 10

a rapidly moving river of air; can have wind speeds greater than 100 mph; winter: 4-6 miles altitude, about 30 deg latitude; summer: >6 miles altitude, about 50 deg latitude. It tends to guide low-pressure centers (storms) across North America. Flows west to east. Southern states get more of their stormy weather during winter. During summer, when jet stream is further north, the West Coast has an extended dry season. Cooler air is located to the North of the jet, warmer air to the South of the jet.

Question 11

Compare and contrast the wind, pressures, and weather along the equatorial Pacific under La Nina and El Nino conditions.

Answer 11

El Nino:
Strong equatorial countercurrents(move to east) amass large quantities of warm water that block the upwelling of colder, nutrient-filled water along the west coast of South America. Causes more rain in normally arid regions and lowers pressure in western Americas. Weak trade winds. Weak Peru Current. Pressure increases and dryer than normal in western Pacific (Australia).
La Nina:
Strong equatorial currents (move west) bring warm water to western Pacific, wetter than normal Australia, low pressure; strong trade winds; high pressure and cool water in western Americas; strong Peru Current; dryer than normal; colder northwestern US

Question 12

To what does the Southern Oscillation refer?

Answer 12

the seesaw pattern of atmospheric pressure between the eastern and western Pacific. Each time an El Nino occurs, the barometric pressure drops over large portions of eastern Pacific and rises in western Pacific; as El Nino comes to an end, the pressure difference between those two regions swings back in the opposite direction, triggering a La Nina event.

Question 13

Describe the cause and effect of monsoons, sea and land breezes, and mountain and valley breezes.

Answer 13

monsoon: seasonal reversal of wind direction associated with large continents, especially Asia. In winter, the wind blows from land to sea; in summer, from sea to land.
In coastal areas during warm summer months, the land is heated more intensely during the daylight hours than is the adjacent body of water.
sea breezes: a noon/afternoon breeze which develops as the cooler air over the water (higher pressure) moves toward the warmer land (lower pressure)
land breezes: at night, reverse of sea breeze may take place; land cools more rapidly than sea, so land breeze develops
mountain breezes: at night, air above mountain slopes cools rapidly and drains into warm valley
valley breezes: during the day, air above mountain slopes is heated and rises

Question 14

What are chinook winds? (textbook question)

Answer 14

a wind blowing down the leeward side of a mountain and warming by compression

Question 15

How is an air mass classified? Name the air masses that affect Arkansas’s weather most. What, in general, will the weather be like with the air masses that affect the U.S.?

Answer 15

Classified by where they originate - their source region.
cP; mT
mT - high temperatures, oppressive humidity, precipitation in summer
cP - in winter, brings clear skies and cold temps; early winter lake effect snows; in summer, it can bring a few days of cooler temps
mP - source of moisture for winter heavy rain and snow in western US; can produce a winter nor’easter in New England

Question 16

When and how are “lake effect” snows produced?

Answer 16

Snow showers associated with a cP air mass to which moisture and heat are added from below as the air mass traverses a large and relatively warm lake (such as one of the Great Lakes), rendering the air mass humid and unstable.

Question 17

What, in general, is a front? Draw and/or recognize weather map symbols for a:

• cold front
• warm front
• stationary front
• occluded front

Answer 17

A front is the boundary between two air masses.
cold front - triangles
warm front - semicircles
stationary front - triangles and semicircles on opp. sides
occluded front - triangles and semicircles alternating on one side of line

Question 18

Describe a warm front or a cold front with the aid of a cross-sectional diagram of the front. Include:

• the location of cold and warm air, the slope, and speed of the front
• the location and type of clouds, and characterize any precipitation

Answer 18

see second page of Ch. 19 notes

cold: slope 1:100
avg. speed 20-25 mph
warm: slope 1:200
avg. speed 10-15 mph

Question 19

Describe the atmospheric conditions and weather associated with the passage of a mid-latitude cyclone. Include:

• types of air masses
• types of clouds expected and where
• barometric tendency
• areas of precipitation
• wind directions
• temperature and humidity changes

Answer 19

air masses: cP, mT, mP

pg. 584-585, especially bullets on 585

Question 20

As it relates to the global circulation patterns, where do most mid-latitude cyclones form?

Answer 20

Polar Front (Subpolar Low)

Question 21

What is necessary at higher altitudes in order for a low to persist?

Answer 21

Surface convergence must be matched by divergence aloft.

Question 22

How is a hailstone formed?

Answer 22

successive freezing of layers of water

Question 23

Give a general description of a thunderstorm and describe the two common situations they form in.

Answer 23

A thunderstorm is any storm that produces lightning and thunder; occur in a cumulonimbus cloud; small scale, short-lived systems; produce strong updrafts, gusty surface winds, heavy rain
Air Mass Thunderstorms - occur in mT air masses; scattered; most common in tropics; in US most common in summer in late afternoon and early evening; tend NOT to produce severe weather
Frontal Thunderstorms - occur along fronts, especially along cold fronts; may occur in clusters rather than as isolated storms; can produce severe weather- high winds, hail, flooding, tornadoes

Question 24

What role does latent heat play in the development of a thunderstorm?

Answer 24

All thunderstorms require warm, moist air, which, when lifted, releases sufficient latent heat to provide the buoyancy necessary to maintain its upward flight.

Question 25

Describe, in very general terms, the distribution of thunderstorms in the U.S.

Answer 25

Most common in Florida, SE Gulf states.

Least common in West Coast.

Question 26

Describe some effects of lightning and how to estimate the distance to where lightning strikes.

Answer 26

effects: (it is an electrical discharge of about 100,000,000 volts) causes air to be heated extremely rapidly (>54,000 degrees F) and to expand as a result; extremely rapid expansion of air produces thunder; can cause fires
miles = (number of seconds between lightning and thunder / 5)

Question 27

What weather phenomena have been responsible for most weather related deaths?

Answer 27

floods

Question 28

Give a general description of a tornado that includes some average statistics.

Answer 28

Stronger tornadoes form from supercell thunderstorms that develop a vertical cylinder of rotating air within them called a mesocyclone. The tornado then descends from a rotating wall cloud in the bottom part of the mesocyclone. The main vortex of the tornado may have several small suction vortices. Tornadoes most commonly form in the thunderstorms along the cold front of a mid-latitude cyclone during the spring when the difference in temperature and moisture content between the air masses is greatest.

• there are an avg. of 1,350 tornadoes per year in the U.S.
• most common in April, May, June in the central US
• most move SW to NE and have an average diameter between 500 ft and 2,000 ft
• avg. ground speed = 30 mph
• avg. path on the ground = 6 miles
• damage comes mainly from the high winds; deaths from flying debris

Question 29

What is a tornado over water called?

Answer 29

waterspout

Question 30

What is the difference between a tropical depression, a tropical storm, and a hurricane?

Answer 30

tropical depression: wind speed 74 mph (can be >200mph)

Question 31

Describe some characteristics of a tropical cyclone. Where do they typically form?

• Draw a cross-sectional diagram.
• What are other names for a tropical cyclone?
• What are the three sources of damage?

Answer 31

• avg. diameter = 375 miles; eye diameter = 12.5 miles
• steep pressure gradient; produce lowest naturally recorded pressures in the world
• Typically form over warm ocean near the equator (5-20 degrees), especially in August and September
• cross-sectional diagram on pg. 7 of notes (eye, eyewall, condensation, storm surge, evaporation)
• called typhoons in western Pacific; called cyclones in Indian Ocean
• Sources of damage:
  1. high winds
  2. storm surge
  3. heavy rain

Question 32

Interpret a weather map station model.

• temperature
• dew point
• visibility
• amount of cloud cover
• wind direction
• wind speed
• barometric pressure
• barometric change and tendency
• amount of precipitation

Answer 32

like in class

Question 33

Make simple weather predictions from a weather map.

Answer 33

like in class