Global Circulation Patterns

Three Cell Model

Horse Latitudes

The Horse Latitudes are 25‐30 N-S

Trade winds weaken in this region, & would stall early Spanish ships sailing to NewWorld

When particular areas were too calm, they were forced to toss over their frightened horses into the sea, or eat them

The legend is the horses would swim after them for miles before they drowned, & the superstitious sailors would hear the horse screams in their haunted dreams for the rest of the voyage

Westerlies

Occur between 30‐60 N (S) Latitude

Blowing from the high P area in horse latitudes towards the poles

Steer extratropical cyclones

Can redirect Tropical Storms

The Westerlies are:
1. strongest in winter hemisphere & times, when the P is lower over the poles
2. weakest in the summer hemisphere, when P are higher over the poles

The strongest westerly winds in the middle latitudes can come in the Roaring Forties, between 40° & 50° latitude S

Roaring Forties (& Furious Fifties)

The strong west‐to‐east air currents are caused by the combination of air being displaced from the Equator to S Pole & the Earth’s rotation, & there are few landmasses toserve as windbreaks

Jet Streams

Region of the upper atmosphere where a narrow band of airmoving REALLY fast

Location of jet stream influences local weather

LARGE T contrasts

Polar Jet Stream (Mid‐Latitude)

Where the Polar Frontis located: Where the cold polar easterlies interact with the warm westerlies

It’s Geostrophic Wind if it’s high up in atm

Meanders west to east

Can exceed 500 km/hour
In winter it travels at 75 km/h
In summer 65 km/h

Subtropical Jet Stream

Semi‐permanent jet that exists over the subtropics

Is mainly a wintertime phenomenon

Due to the weak summertime T gradient, the subtropical jet is relatively weak during the summer

Slower than the polar jet

Still travels west to east

Usually at about 25 N

Usually at an altitude of about 13 km

Global Winds & Ocean Currents

Winds are the driving force for ocean currents

A relationship exists between ocean & atmosphere circulation

Ocean currents move more slowly than prevailing winds

Pacific Trash Vortex

Trash gets “Stuck” in the N Pacific Gyre

Floating mass of trash

Mostly Plastic that is non‐biodegradable

Rubber duckies got free & went all over the world following ocean currents

El Niño & La Niña

El Niño Southern Oscillation

Ocean phenomenon that occurs in the Equatorial Pacific

As the southeast trade winds decrease in strength (weaken) the warm water can make it farther across the Pacific to wards S American

Named because it starts during Christmas

Usually happens every 3‐7 years

P changes & reversals in the Pacific trigger the change in winds

The End