Chapter 7 Flashcards
Circulation size is directly related to…
Lifetime
Microscale Circulation
- lasts a few minutes
- Diameter 1 n.m. or less
e. g. Dust devils, Tornado’s, Thermals
Mesoscale Circulations
- lasts 1 hr - 1 day
- Diameter “a few - several hundred kilometers”(slides)
- t-storms, down bursts, squall lines, land/sea breeze
Macroscale Circulations
- lasts weeks - months - up to 1 year
- diameter 1,000 n.m. +
- jet streams, general circulation, monsoon circulation
Global winds are?
Earths largest scale circulations
Global winds are affected by?
- Equator/pole temp gradients
- Earths rotation
- Location of continents
- Seasonal changes
General Circulation
- Ideal model of global winds
- Macroscale ~ 10,000 n.m.
- 1 full year to cycle
- can be divided according to factors affecting movement
- breaks down into cells
Circulation cells
- 2 groups - 1 per hemisphere
- Temps at poles and equator create pressure gradients
- high pressure at poles
- low pressure at equator
- sets up thermal circulation
North and South poles have high or low pressure? Why?
High - It’s cold and condenses the air
Equator has high or low pressure? Why?
Low - It’s hot and expands the air
Atmospheric circulations are mainly caused by?
Unequal heating of air
Warm equatorial air…
Rises and expands
When Equatorial air reaches the tropopause, what happens?
The air spreads out and moves towards the colder, polar regions
Hadley Cell
- Strongest of the 3 cells
- air rises at equator, diverges at tropopause, deflected right (NH) -becoming upper-level westerly
- ~ 30° N Latitude air sinks and diverges at surface. Creating a semi-permanent high pressure system
- Called “Northeast Trade winds”
What are the northeast trade winds?
- Part of hadley Cell
- ~ 30° north latitude
What are the three cell types
- Hadley Cell
- Ferrel Cell
- Polar Cell
What Cell type is largest?
Hadley Cell
What Cell type is Smallest?
Polar Cell
What is the mid sized Cell type?
Ferral Cell
Ferrel Cell
- sinking air at 30° north lat to 60° north lat
- Product of interactions between Hadley and Polar Cells
- Complicated by Polar air moving South and Tropic air moving North
- winds are prevailing westerlies
Ferrel - Hadley intersection
- Subsiding air at ~ 30° north
- Causes subtropic deserts (limited precipitation)
Polar Cell
- Rising air at ~ 60° north
- Coriolis force causes sharp deflection to the right
- sinking air at poles cause polar fronts
- surface winds are northeasterly
- winds aloft are southwesterly
Coriolis Effect/Force
- North Hemisphere - Surface winds deflect right
- South Hemisphere - Surface winds deflect left
Jetstreams are…
- Immediately under tropopause
- In between cells? (check this)
Are jetstreams straight or do they wiggle?
Wiggle
Name the two types of jetstream
Polar jet
Subtropical jet
Do jetstreams radiate their wind speed?
Yes
Intertropical convergence zone (ITCZ)
- Tropical areas
- lots of evaporation causing air saturation
- persistent band of organized convection
- lots of t-storms
Monsoon
- Seasonal reversal of wind circulation
- causes change in precipitation patterns
El Nino
La Nina
- Oscillation of sea surface temps in the tropical central and eastern pacific ocean
- El Nino is warm cycle
- La Nina is cold cycle
- 3 month average of at least +/- .5 degree C
Effects of El Nino
- Winter SW U.S. wetter
- NE U.S. dryer
- Less Atlantic Hurricanes from strong upper wesrteries
- More Pacific Hurricanes from warmer seas
A wet U.S. winter in the SW could be caused from?
El Nino
Madden-Julian Oscillation
- Circles the earth every 30 - 60 days
- Starts in Indian ocean & moves east in the tropics
- 2 phases - enhanced rainfall and suppressed rainfall
- enhances or weakens smaller patterns
What is SST
Sea Surface Temperature
