MEA 130 Chapter 10: Wind: Global Systems

What is the general circulation of the atmosphere?

• The average global movement of air, redistributing heat between equator and poles

• Driven by unequal solar heating

• Transports warm air poleward, cold air equatorward

In the single-cell model of the atmosphere, why does low pressure build at the equator and high pressure at the poles?

• Equator: Intense heating → air rises → low pressure

• Poles: Cooling → air sinks → high pressure

Creates one circulation cell per hemisphere

What causes temperature differences to build up at different latitudes?

Unequal solar heating: equator receives more direct sunlight; polar receive less

Why does the coriolis force turn air to the right in the NH and to the left in the SH?

•  Due to earth’s rotation - objects moving across the surface appear deflected

• Rightward in NH, leftward in SH

What is the ITCZ?

• boundary where NE & SE trade winds meet near equator 

• Warm, moist air converges and rises → frequent thunderstorms

How does ITCZ shift?

north in July and south in January following the sun

What are the trade winds and how do they blow?

• Easterly winds blowing from east to west in the tropics (0–30°).

• Converge at the ITCZ 

What are westerlies and how do they blow?

• Mid-latitude winds (30–60°) blowing from west to east

• Caused by air moving poleward from subtropical highs and deflected by coriolis

What/where are the subtropics and what typically forms there?

• Around 30° latitude.

• Region of sinking air and high pressure (subtropical highs)

• Associated with deserts due to dry descending air.

Subtropical highs

Atlantic (Bermuda High) & Pacific High

Subpolar lows

Aleutian Low, Icelandic Low

Rainfall most common

Near ITCZ (rising, humid air) and 40–55° (polar fronts).

Rainfall least common

Near 30° (dry subtropical highs) and poles (cold, dry air).

What are jet streams and their common characteristics (speed, cause, location)?

• Narrow bands of strong upper-level winds near tropopause (10-15 km)

• 100 knots (can exceed 200)

• Found near 200 mb level

• Polar jet (~60°N) and Subtropical jet (~30°N).

• Stronger in winter (larger temp gradients)

What effect do jet streams have on global circulation?

• Transport heat, moisture, and pollutants

• Steer weather systems (cyclones, fronts)

• Bring warm air north or cold air south depending on position

How do the oceans and atmosphere interact?

• Oceans provide moisture via evaporation

• Pressure centers drive surface currents

• Currents affect regional climate (warm or cool nearby land).

Relate semi-permanent surface pressure systems to ocean currents.

• Highs and lows drive clockwise/anticlockwise currents that move warm/cold water

• Ex: Subtropical highs drive warm water poleward along western ocean edges (e.g., Gulf Stream)

What is the gulf stream and its importance?

• Warm ocean current along eastern U.S. coast

• Carries warm tropical water northward → moderates eastern U.S. and European climates. 

Normal ocean-atmospheric circulation

trade winds push warm water west → cold upwelling in east → storms in west Pacific

El Niño

trade winds weaken → warm water shifts east → storms in east Pacific, drought in west

La Niña

stronger trade winds → enhanced upwelling in east → opposite pattern of El Nino (cooler east, stormier west).