Atmospheric Motion

Nonrotating Earth Equator – Warming and rising of air – Rising air cools as it ascends – Surface winds blow towards equator to replace ascending air Poles – Cool, dry air descends

Global Wind Bands Hadley cells – Subtropical cells – Air rises at the equator due to solar heating, and falls due to cooling at ~30º

Global Wind Bands Ferrel cells – Temperate cells – Occurs between 30º and 50-60º latitude – Some air descending at 30º turns poleward

Global Wind Bands Polar cells – Centered over each pole – At 50-60º, the air is warm and wet enough to ascend, but too dense to mix with Ferrel cell

Wind Patterns Between Cells: – Vertical air movement – Weak surface winds Within Cells: – Horizontal air movement – Strong surface winds

Wind Patterns Between Cells: Hadley cells – Doldrums Near the equator Decrease in pressure gradient Variable breezes – Intertropical Convergence Zone (ITCZ)

Wind Patterns Between Cells: Hadley and Ferrel cells – Horse latitudes 30º latitude Subtropical high pressure Sinking air; dry – Many deserts are found at this latitude

Wind Patterns Within Cells: – Hadley cell Trade Winds – Easterlies Centered at 15º – Ferrel cell Westerlies Centered at 45º – Polar cell Easterlies 60-90º

Radiation and Latitude More heat gained at equator More heat lost at higher latitudes

Atmospheric Pressure

High vs. Low Pressure High Pressure Cell Anticyclonic rotation (clockwise) in N hemisphere Downward vertical motion Air is compressed and warmed Dry weather

High vs. Low Pressure Low Pressure Cell Cyclonic rotation (counter clockwise in N hemisphere) Upward vertical motion Air expands and cools as it rises Wet weather

Fig. 8.16

Wind Band Modification Seasonal Changes

Wind Band Modification Seasonal Changes

Wind Band Modification Seasonal Changes

Wind Band Modification Seasonal Changes

Monsoons - Summer Land heats more rapidly than ocean Air above land expands and rises creating low pressure Cool air flows from ocean Cool air is heated, expands, rises and condenses

Monsoons - Winter Land cools more rapidly than ocean Air contracts and sinks creating high pressure Dry surface winds move seaward

Onshore & Offshore Breezes (small, daily mini-monsoons) Onshore Breeze

Onshore & Offshore Breezes (small, daily mini-monsoons) Offshore Breeze

Topographic Effect Windward = wet Leeward = dry

Rain shadow

Jet Streams High speed winds in the upper troposphere Polar Subtropical Weather of temperate zone

Hurricanes Easterly wave > 26.5  C (80  F) Typhoon or cyclone

Hurricanes

El Niño – Southern Oscillation

El Niño Sea surface topography and temperature Normal El Niño End of El Niño

La Niña Colder phases

Storm Surge Low atmospheric pressure Strong onshore winds