GLOBAL ATMOSPHERIC CIRCULATION, MOISTURE, & CLOUDS

CLOUD FORMATION

1. MOIST AIR IS LIFTED:

warm & humid air near ground

2. AIR RISES INTO LOWER PRESSURE

parcel expands as surrounding pressure decreases

3. AIR COOLS ADIABATICALLY

temperature falls during parcel expansion

4. RELATIVE HUMIDITY INCREASES

cooler air holds less vapor before saturation

5. AIR REACHES DEW POINT

relative humidity = 100%

6. CONDENSATION BEGINS

vapour forms tiny droplets

OROGRAPHIC LIFTING

AIR IS FORCED UP MOUNTIAN

CONVECTIONAL LIFTING

SUN HEATS EARTHS SURFACE

CONVERGENT LIFTING

AIR FLOWS TOGETHER NEAR EARTHS SURFACE

FRONTAL LIFTING

2 AIR MASSES MEET AT FRONT

RELATIVE HUMIDITY

AMOUNT of VAPOR in air compared to HOW MUCH it could hold at temperature

RELATIVE HUMIDITY DECREASES

WARM AIR holds MORE VAPOR

RELATIVE HUMIDITY INCREASES

COOL AIR holds LESS VAPOR

ATMOSPHERIC STABILITY

if AIR pushed upward will RISE OR SINK

RISING AIR

UNSTABLE ATMOSPHERE

• Rising air stays WARMER & LESS DENSE

SINKING AIR

STABLE ATMOSPHERE

• Rising air becomes COOLER & DENSER

LAPSE RATE

Air temperature CHANGES as ALTITUDE INCREASES

ADIABATIC COOLING

RISING air cools from EXPANSION as air PRESSURE DECREASES

DRY ADIABATIC LAPSE RATE

• UNSATURATED AIR

• RELATIVE HUMIDITY: BELOW 100%

• COOLS FASTER

MOIST ADIABATIC LAPSE RATE

• SATURATED AIR

• RELATIVE HUMIDITY: 100%

• CONDENSATION RELEASES LATENT HEAT

• COOLS SLOWER

HADLEY CELL FUNCTION

• MOVES: HEAT AWAY from Equator TOWARS Subtropics

• CREATES: DRY SUBTROPICAL REGIONS

HADLEY CELL WIND PATTERN

TRADE WINDS

Equator 0° to 30°( N/S)

• AIR RISES: 0°

• AIR SINKS: 30

FERREL CELL FUNCTION

• CONNECTS: SUBTROPICAL to POLAR CIRCULATIONS

• WHY: MIDLATITUDE weather systems TRAVEL EAST to WEST

FERREL CELL WIND PATTERN

WESTERLIES

30° to 60° (N/S)

• AIR RISES: 60°

• AIR SINKS: 30°

POLAR CELL FUNCTION

• MOVES: HEAT BETWEEN SUBPOLAR REGIONS & POLES

POLAR CELL WIND PATTERN

POLAR EASTERLIES

60° to 90° (N/S)

• AIR RISES: 60°

• AIR SINKS: 90°

EQUATORIAL LOW

Major Pressure Belt

0° (EQUATOR)

LOW PRESSURE, WARM AIR RISES

EQUATORIAL LOW FUNCTIONS

Major Pressure Belt

ENCOURAGES: CLOUD FORMATION & HEAVY RAINFALL

DRIVES: HADLEY CIRCULATION

SUBTROPICAL HIGH

Major Pressure Belt

30° (N&S)

HIGH PRESSURE, AIR SINKS

SUBTROPICAL HIGH FUNCTIONS

Major Pressure Belt

ENCOURAGES: DRY & CLEAR WEATHER

DRIVES: SURFACE WINDS TOWARD EQUATOR & 60° LATITUDE

CREATES: MAJOR DESERTS

SUBPOLAR LOW

Major Pressure Belt

60° (N&S)

LOW PRESSURE, AIR RISES

SUBPOLAR LOW FUNCTIONS

Major Pressure Belt

ENCOURAGES: CHANGEABLE WEATHER & STORMS

MARKS: BOUNDARY BETWEEN FERREL & POLAR CELL

POLAR HIGH

Major Pressure Belt

90° (N&S)

HIGH PRESSURE, COLD DENSE AIR SINKS

POLAR HIGH FUNCTIONS

Major Pressure Belt

ENCOURAGES: COLD & DRY CONDITIONS

DRIVES: SURFACE AIR AWAY FROM POLES TOWARD 60°

HELPS: PRODUCE POLAR EASTERLIES

POLAR JETSTREAM

50°- 60° LATITUDE

• Guides MIDLATITUDE CYCLONES (West to East)

• Shifts SOUTHWARD (Winter), Shifts NORTHWARD (Summer)

SUBTROPICAL JETSTREAM

25°- 30° LATITUDE (UPPER part of HADLEY CIRCULATION)

• Moves air RAPIDLY EASTWARD

RIDGE

NORTHWARD BULDGE in Jetstream (Northern Hemisphere)

RIDGE FUNCTION

Allows WARMER AIR to extend FURTHER NORTH

TROUGH

SOUTHWARD DIP in Jetstream (Northern Hemisphere)

TROUGH FUNCTION

Allows COLDER AIR to move FURTHER SOUTH