Chapter 2 ECO

Global Air Mass Circulation

• Warm air rises, rising air cools due to expansion, cool air descends

Polar Front

• The polar front is the boundary between the polar cell and the Ferrel cell
• The polar front arises as a result of cold polar air meeting warm tropical air.
• Low pressure

Horse latitudes

• A belt of calm air and sea occurring in both the northern and southern hemispheres between the trade winds and the westerlies.Sub-tropical high
• High air pressure
• Clear weather

Doldrums

• Intertropical Convergence Zone: 0* Equator line; Hadley cells begin at 0*
• Equatorial low
• Lower pressure
• Calm, but with severe hurricanes, typhoons, cyclones

Polar Cells

• Above 60° latitude, the polar cell circulates cold, polar air equatorward. The air from the poles rises at 60° latitude where the polar cell and Ferrel cell meet, and some of this air returns to the poles completing the polar cell
• Winds flow high to low
• Winds above are Polar Easterlies (100% deflection)

Ferrel Cells

• It is characterized by sinking air near 30 degrees and rising air farther poleward
• At the surface, air flowing poleward is deflected to the east by the coriolis force, resulting in westerly surface winds.
• Clockwise circulation
• the low surface pressure at 60° latitude causes air to rise and form clouds. Some of the rising warm air returns to 30° latitude to complete the Ferrel Cell
• Winds are westerlies (86.7% deflection)

Hadley cells

• Convection cell in which air rises at the equator and sinks at medium latitudes, typically about 30° north or south
• Moist air rising at 0*
• Dry air sinking at 30* N or S
• Counterclockwise circulation
• Trade winds (50%)

Coriolis Effect

• The effect on global circulation (air then water) patterns
• ---Caused by the rotation of the earth
• ---Multiple cells (Hadley, Ferrel, Polar)
• ---Deflection of the circulation pattern to the
• Right---Northern hemisphere
• Left---Southern hemisphere
• The Coriolis Effect can be seen in action in the general circulation of the atmosphere. The winds at all latitudes to the north of 0° deflect to the right of their intended path in the Northern Hemisphere. The Coriolis Effect does not impact the wind speed, only the wind direction

Saturation Vapor Pressure

• The maximum amount of water a given volume of air can hold
• Change SVP by changing temp of air mass, usually
• by rising in elevation
• It is variable
• Warm air has a higher SVP (holds more water)

Actual Vapor Pressure

• The current amount of water a given volume of air contains

Relative Humidity

• The amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.
• CALCULATE:
• ACTUAL VAPOR PRESSURE / SATURATION VAPOR PRESSURE X 100%
• Precipitation occurs when RH is 100% (Dew Point)

Precipitation patterns

• Warm, Rising Air---High precipitation
• Cold, Sinking Air---Low precipitation
• A lot of precipitation---60* (forests)
• No/very little precipitation---30* (deserts)

Local Precipitation Patterns

• Rain Shadows: on east-facing slopes
• Increase SVP: warm, little precipitation
• Decrease SVP: cold, more precipitation

El Niño/Southern Oscillation

• Decrease in trade winds
• Less surface water move toward the west
• Warm event
• Decreasing the upwelling of deep, cold ocean water along western coast of S. America
• Warm waters are in central Pacific
• Rains follow the warmer water to the east
• Flood in Peru
• Drought in Indonesia and Australia
• North America
• Dec to Feb --- coastal Alaska, N. Midwest--> warm, less snowfall; southern Cali and S. West--> wet; Texas/East--> wet and cool
• June to Aug--- Intermountain west---> wet

Dew Point

• the atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense and dew can form
• The dew point is the temperature at which air must be cooled for saturation to occur.

Vapor Pressure Deficit

• The difference between SVP and AVP
• the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated.