And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on...

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And The Weather’s Good… AP Env Sci 2011-2011

Transcript of And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on...

Page 1: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

And The Weather’s Good…

AP Env Sci 2011-2011

Page 2: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Weather Basics – and a little more

• Air Takes on the Temperature and Moisture Characteristics of the Surface it is Over.– Does this happen instantaneously? NO– Needs to be Stationary or Slow Moving Air

• Air Mass: – Large body of air (~1600 km across)– Perhaps several kilometers thick– Homogeneous Temperature and Moisture

Content – When the Air Mass moves on, it can carry

Temperature and Moisture properties with it.

Page 3: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Source: NOAA.gov

Air Masses Important for North America

Page 4: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Air Masses: Who’s Who

• cA: Continental Arctic– Source: Arctic basin and Greenland ice cap– Bitterly cold and very dry in winter

• cP: Continental Polar– Source: Interior Canada and Alaska– Very cold and dry in winter, cool and dry in

summer

• mP: Maritime Polar– Source: North Pacific– Mild (cool) and humid entire year

Page 5: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Air Masses: Who’s Who

• mT: Maritime Tropical– Source: Gulf of Mexico, Caribbean, western

Atlantic– Warm and humid entire year

• cT: Continental Tropical– Source: Interior Mexico, Southwestern US– Hot and dry

• Air Mass Weather: entire region is covered by single air mass – can last for days. Conditions set by air mass.

• More interesting weather happens when air masses MEET.

Page 6: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

When Air Masses Meet: Cold Front

• Cold Air Mass meets Warm Air Mass• Cold Air Mass is Moving (fast moving)• “Pushes” Warm Air Up (warm air is less dense)• Result Can Be Violent: Thunderstorms• After: Cooler, Often Drier Conditions

Source: NOAA.gov

Page 7: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

When Air Masses Meet: Warm Front

• Warm Air Mass meets or follows Cold Air Mass• Warm Air Mass is Slower• Warm Air Rises as it Overtakes Cold (warm air is less

dense, air then cools)• Large Area of Moderate Precipitation for a Long

Period• After: Warmer Conditions

Source: NOAA.gov

Page 8: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

When Air Masses Meet: Stationary and Occluded Fronts

• Stationary Front:– Cold and Warm Air Masses Meet with Flow

Parallel to Front– Little or No Movement– Gentle to Moderate Precipitation

• Occluded Front:– Two Cold Air Masses, Warm Air Mass in the

Middle– Warm Air Rises– Precipitation

Page 9: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Know: Symbols Point In Direction The Front is Moving

Source: NOAA.gov

Page 10: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Wind

• ALL wind is caused by horizontal differences in air pressure

• Important points about air pressure:– Gravity on an air mass results in air pressure– Measured in millibars, inches of mercury or

hectopascals (hPa).– Air pressure decreases with altitude– Low pressure produces cloudy, stormy weather– High pressure contains cool, dense air that

descends towards Earth and becomes warmer. Brings fair weather.

• Higher Pressure Difference, More Wind

Page 11: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

What causes the pressure differences?

• Uneven Heating of the Earth’s Surfaces

• Result is sea and land breezes

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm

• Temperature Variation -> Pressure Variation -> Wind

Page 12: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

If Pressure Acted Alone…

• If Earth did not rotate• If there was no friction• Then, air would always flow directly from High

pressure to Low pressure

• In Reality, three factors control wind:– Pressure Differences– Coriolis Effect– Friction

Page 13: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Earth without Rotation…

• http://teachingboxes.org/catalog.jsp?id=TBOXR-000-000-000-039

Page 14: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Rotating Earth – What Does it Do?

• Coriolis Effect: – All free moving objects (wind, planes) are

deflected right of their path of motion in Northern Hemisphere, left of path of motion in Southern Hemisphere

• http://www.youtube.com/watch?v=mcPs_OdQOYU

• http://www.youtube.com/watch?v=1PWjOMrPkrI

• To know: In the Northern Hemisphere, winds spiral clockwise out from high pressure areas and spiral counterclockwise in toward low pressure areas.

Page 15: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Results of the Coriolis Effect

Page 16: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Hadley, Ferrel, and Polar Air Circulation Cells

• Hadley Air Circulation Cells (0-30 degrees)– Hot air near the equator rises. Land area characterized by high

humidity, large high clouds, and heavy rains. (Tropical rain forests)

– Area on land between 0-30 degrees characterized by high temperture and low humidity. (Deserts)

• Ferrel Air Circulation Cells (30-60 degrees)– Some of the air from the falling hadley air cells gets pulled north

by the Westerlies and mixes with Polar cells. Causes defined seasons of winter and summer. (Forests)

• Polar Air Circulation Cells – Cold, dry dense air falls from the troposphere to the ground,

meeting warm air from midlatitudes, returning to the poles and then sinking. Sinking air supresses precipitation. (Tundra and taiga)

Page 17: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Friction

• Most important for air contacting a surface

• Winds aloft – not affected

• At surface, friction slows winds

Page 18: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Some “Local” Winds • Land and Sea Breezes• Mountain and Valley Breezes

– Valley breeze: Sun heats air along slopes more intensely, rises

– At night, mountain breeze• Chinook: warm, dry air descending mountain

– Pulled over mountain by low pressure system– Air is heated by compression as it flows

downward• Katabatic Winds:

– Cold air over ice-covered highland “falls” downhill under influence of gravity

– Antarctica: up to 66 ft/sec

Page 19: And The Weather’s Good… AP Env Sci 2011-2011. Weather Basics – and a little more Air Takes on the Temperature and Moisture Characteristics of the Surface.

Global Winds to Know

Image/Text/Data from the University of Illinois WW2010 Project