2 Atmospheric Circulation Patterns and Global Climate

gases in the atmosphere move around in response to two primary driving forces

2.1 Convection

(a) Warm air is less dense and rises -- causes low pressure

(b) Cool air is more dense and sinks -- causes high pressure

(c) On large scale, this causes circulation from the equator to the poles

-- on a small scale, winds blow from highs to lows

2.2. Coriolis Effect

(a) Spinning Earth causes lateral deflection of air currents and makes large convection cells unstable

- right deflection in north, left deflection in south

(b) Causes generation of several smaller convection cells called Hadley Cells, each about 30° wide

2.3 Hadley Circulation Cells and Deserts

- amount of moisture air can hold is directly proportional to atmospheric pressure

- amount of moisture air can hold is directly proportional to atmospheric temperature

- remember warm air rises and cold air sinks

(a) Air gets heated and rises at equator

- rising hot air carries a lot of water

(b) As air cools and flows laterally to north and south, it can hold less water

- condensation and rainfall adjacent to equator - rain forests

(c) Continues to cool and flow laterally until about (+ or - ) 30° latitude where Coriolis effects and increased density make it sink

- descending, warming air pulls moisture into it making deserts
- deserts associated with aridity, not temperature

2.4 El Niņo

a regional climate pattern that results from a change in oceanic circulation patterns off the coast of Peru

(a) Atmospheric and Oceanic Components of El Nino

(1) distribution, movement and temperature of surface waters (< 200 m)

(2) distribution, movement and temperature of deeper waters (> 700 m)

(3) strength of westward-moving tradewinds

- affects the movement of surface water and upwelling

(b) The Process

(1) "Normal" Conditions

- warmer surface water is pushed westward by tradewinds and replaced by upwelling, cold, deep nutrient-rich water

- anchovies and other fish thrive in this nutrient-rich water

- storms over western Pacific

(2) El Niņo Conditions

- weakening of westward tradewinds allows eastward flow of warmer surface waters, shutting down upwelling of deep, cold water

- warming waters pump heat and moisture into eastern Pacific atmosphere causing low pressure systems and associated storms that repeatedly pound western South America

(3) La Niņa Conditions

- very strong tradewinds push warmer surface waters far into the western Pacific, cooling the eastern Pacific and causing intense storms in the western Pacific

the 1997 El Niņo event

 

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