Air pressure and circulation are driven by global patterns of heating and cooling. Warm air rises at the equator and sinks at 30-60° latitude, driving circulation in three main cells. Additional regional patterns arise from pressure gradients, the Coriolis effect, and surface friction. These global and regional wind systems interact with air mass origins to redistribute heat worldwide. Seasonal shifts in insolation cause pressure belts to migrate, altering prevailing winds and weather. Local winds further modify conditions through convection, mountain valleys, and coastal interactions.

1. Air Pressure & AirAir Pressure & Air
circulationcirculation
The answer is blowin’ in the windThe answer is blowin’ in the wind

2. Layers of the atmosphere:Layers of the atmosphere:
temperature shiftstemperature shifts

3. Pressure/ measurementPressure/ measurement
 Sea level average= 15 lbs per sq inch orSea level average= 15 lbs per sq inch or
 1013mb1013mb
 101,320 pascals101,320 pascals
 Barometer- mercury or aneroidBarometer- mercury or aneroid
 Wind direction – wind vanesWind direction – wind vanes
 Directional arrows/ speedDirectional arrows/ speed

4. Birth of the windsBirth of the winds
 Weather systems travel with windWeather systems travel with wind
movements:movements:
 A. Surface level air movements:A. Surface level air movements:
 1. Pressure gradients1. Pressure gradients
 2. coriolis force2. coriolis force
 3. Friction3. Friction
 Isobars – curved lines outlining pressureIsobars – curved lines outlining pressure
regionsregions
 B. Upper level winds - geostrophic ( noB. Upper level winds - geostrophic ( no

5. Pressure gradientsPressure gradients
HIGH
low

6. corioliscoriolis

7. Friction: only with surfaceFriction: only with surface
windswinds
 Friction bends the surface winds from aFriction bends the surface winds from a
straight path, and a diagonal path isstraight path, and a diagonal path is
formedformed
High
low

8. Cyclones are patterns of windCyclones are patterns of wind
flowflow
 Cyclonic circulation Pattern: upward andCyclonic circulation Pattern: upward and
inward in the Northern Hemisphere (LOW)inward in the Northern Hemisphere (LOW)
 Anticyclonic: Downward and outward inAnticyclonic: Downward and outward in
the Northern Hemisphere (HIGH)the Northern Hemisphere (HIGH)
 Reversed in the Southern HemisphereReversed in the Southern Hemisphere

9. Circulation patterns/ pressureCirculation patterns/ pressure
systems: Northern Hemispheresystems: Northern Hemisphere

10. Isobar mapIsobar map

11. Global scale winds:Global scale winds:
World wind & pressure beltsWorld wind & pressure belts
 World wind & pressure belts:World wind & pressure belts:
 zones –zones –
 natural: Equatorial low, (ITCZ)natural: Equatorial low, (ITCZ)
subtropical highs, subpolar lowssubtropical highs, subpolar lows
( outbreak) & Polar Highs( outbreak) & Polar Highs
 Induced zones – products of the naturalInduced zones – products of the natural
beltsbelts

12. GLOBAL WINDSGLOBAL WINDS

13. Global prevailing windsGlobal prevailing winds

14. 3 cell circulation pattern:3 cell circulation pattern:
equatorial, polar & Ferrell cellsequatorial, polar & Ferrell cells

15. Global flows - continuedGlobal flows - continued
 Hadley ( Equatorial) cells & world wind beltsHadley ( Equatorial) cells & world wind belts
(polar & mid latitude)(polar & mid latitude)
 Modifiers:Modifiers: Surface winds – convective: valley,Surface winds – convective: valley,
Mountain,Mountain,
 Upper level wind systems – Rossby waves, &Upper level wind systems – Rossby waves, &
 jet streams (polar ( ~250 mph) westerlyjet streams (polar ( ~250 mph) westerly
 ----subtropical jet ( westerly winds)----subtropical jet ( westerly winds)
 Tropical easterly jet ( summer in N.Tropical easterly jet ( summer in N.
Hemisphere)Hemisphere)

16. Rossby WavesRossby Waves

17. Polar Jet StreamPolar Jet Stream

18. Air masses – enabling redistributionAir masses – enabling redistribution
of energyof energy
 Classified by latitude / surface conditionsClassified by latitude / surface conditions
of originof origin
 Arctic/Antarctic ,cA(AArctic/Antarctic ,cA(A
 Polar mP,cPPolar mP,cP
 Tropical cT, mTTropical cT, mT
 Equatorial) mEEquatorial) mE

19. Global air masses, source regionsGlobal air masses, source regions

20. North American Source regionsNorth American Source regions

21. Wind / pressure systemsWind / pressure systems
 Global pressure belts – High & lowGlobal pressure belts – High & low
pressure air masses give rise to windpressure air masses give rise to wind
systems: global circulation.systems: global circulation.
 Regional pressure belts give rise toRegional pressure belts give rise to
regional wind systems: (Mistral, Bora,regional wind systems: (Mistral, Bora,
chinook), Santa Anachinook), Santa Ana

22. Monsoons & monsoonal typeMonsoons & monsoonal type
windswinds
 Monsoons - SEASONAL CHANGES IN PRESSURE &Monsoons - SEASONAL CHANGES IN PRESSURE &
WINDSWINDS
 California coastal pressure changes,California coastal pressure changes,
 El Nino- not a wind system per se, just generates them.El Nino- not a wind system per se, just generates them.
 Monsoonal winds ( seasonal, shifting),Monsoonal winds ( seasonal, shifting),
 SEASONAL CHANGES BY LATITUDE: winter – highSEASONAL CHANGES BY LATITUDE: winter – high
pressure in high latitude lands, creates cool dry northerlypressure in high latitude lands, creates cool dry northerly
windswinds
 summer – STH over the oceans, low latitudes- bringssummer – STH over the oceans, low latitudes- brings
rains to the east coasts of continents, dry air to the westrains to the east coasts of continents, dry air to the west
coast of continents.coast of continents.

23. Today’s weatherToday’s weather

24. Monsoon windsMonsoon winds

25. Local windsLocal winds
 Convectional flows ( on-shore, off-shore)Convectional flows ( on-shore, off-shore)
 Mountain/valley breezes ( also known as)Mountain/valley breezes ( also known as)
 drainage winds : Mountain, valleydrainage winds : Mountain, valley
 ( Katabiatic-( Katabiatic-
 ---Chinook (Foehn - Switzerland),---Chinook (Foehn - Switzerland),
(Mistral France),( Bora – Adriatic (Croatia)(Mistral France),( Bora – Adriatic (Croatia)
 Santa Ana ( Western U.S.)Santa Ana ( Western U.S.)

26. On shore & off Shore BreezesOn shore & off Shore Breezes

27. Indications of wind directionIndications of wind direction

28. Seasonal shift of pressure/windSeasonal shift of pressure/wind
patternspatterns
 ASIA Pacific N.Amer. Atl. EurASIA Pacific N.Amer. Atl. Eur
 Winter: Icel.LWinter: Icel.L
 Siberian H Aleutian L HawiianHSiberian H Aleutian L HawiianH
 Summer:Summer:
 Asiatic L Hawaiian H Azores HAsiatic L Hawaiian H Azores H

29. January: Northern HemisphereJanuary: Northern Hemisphere
pressure systems Enc.pressure systems Enc.
BritannicaBritannica

30. July, northern hemishpereJuly, northern hemishpere

31. Southern hemisphereSouthern hemisphere
 Variations are less extreme because ofVariations are less extreme because of
the dominance of water in the hemispherethe dominance of water in the hemisphere

32. RECAP: Additional wind flows-RECAP: Additional wind flows-
override prevailing winds for a timeoverride prevailing winds for a time
 Surface winds – convective: valley,Surface winds – convective: valley,
Mountain, Upper level – Rossby waves,Mountain, Upper level – Rossby waves,
 jet streams (polar ( -250 mph) westerlyjet streams (polar ( -250 mph) westerly
 ----subtropical jet ( westerly winds)----subtropical jet ( westerly winds)
 Tropical easterly jet ( summer in N.Tropical easterly jet ( summer in N.
Hemisphere)Hemisphere)
 GIVE VARIETY TO LOCAL WEATHERGIVE VARIETY TO LOCAL WEATHER
PATTERNSPATTERNS