The Atmosphere and Climate

The atmosphere and climate

u  Weather - A description of physical conditions of the atmosphere

u  Climate - A description of the long-term weather pattern in a particular area

–  Weather and climate are primary determinants of biomes and ecosystem distribution

Distribution of biomes

u  Temperature and precipitation are controlled by:

–  Solar heat

–  Global atmospheric circulation

–  Prevailing winds

–  Topography

–  Latitude

–  Elevation

–  Ocean currents

Solar radiation

Seasonality in solar radiation

Global circulation

Global atmospheric circulation

u  Creates areas low rainfall about 20° to 40° north and south of the equator

Prevailing winds

u  Areas far from oceans - in a windward direction are usually relatively dry

Regional climates

u  Mediterranean climates caused by prevailing westerlies that blow during summer from a cool ocean to warm land

–  Hot, rainless summers

u  Monsoon areas in southern Asia and India caused by winds blowing off the cool land to the warm sea in summer and reversing direction in winter, causing rain

Topography

u  Mountains act as cloud formers and rain catchers

Rain shadows

u  Air sweeps up the windward side of a mountain, pressure decreases, and the air cools

u  Eventually saturation point is reached, and moisture in the air condenses

u  Rain falls on the mountaintop

u  Cool, dry air descends and warms, absorbing moisture from other sources

–  Rain shadow

u  Mt Waialeale windward side receives 12 m/year, while the leeward side receives 46 cm

Latitude

Elevation

Ocean currents

u  Warm and cold ocean currents strongly influence climate conditions on land

–  As surface water moves, deep water wells up to replace it

Upwelling

u  Upward movement of water along a coast; replaces surface waters that move away from shore

El Niño (ENSO)

u  El Niño Southern Oscillation

u  Climactic event that involves changes in sea surface temperature and air circulation patterns in the equatorial Pacific Ocean

El Niño southern oscillation (ENSO)

u  Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America

–  Most years, the pool is held in western Pacific by steady equatorial trade winds

u Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east

ENSO

–  During an El Niño year, the northern jet stream pulls moist air from the Pacific over the U.S.

u Intense storms and heavy rains

–  El Niño from 1991-1995 caused floods of the century in Mississippi Valley

u During intervening La Niña years, hot, dry weather is often present

Between ENSOs

u  Warm water and heavy rainfall move west across the Pacific

u  Warm moist air rises in the western Pacific causing storms

u  Upwelling of cool water along western coasts

During an ENSO

u  Trade winds weaken and warm water flows east across the Pacific

u  Sea surface temperatures rise

u  Upwelling along western coasts ceases

u  Heavy rainfall occurs along coasts, droughts elsewhere

Sea temperature

Cholera Connection

u  Cholera outbreaks are correlated with rises in sea temperature

u  Dormant stage of causative organism lives in copepods

u  Copepod population increases when phytoplankton increase in warming seas