Atmospheric Pressure Ch. 5

1.The atmosphere has weight (14.7 lb/sq in.) 2.We don’t notice b/c we have air and water inside us (blood, tissue, and cells) exerting outward pressure 3.Variations in pres. w/in Earth-Atmos system causes atmospheric circulation = weather and climate The Basics…

Measuring Pressure 1.Mercury Barometer Hear in inches…but really measure in millibars sea lvl = millibars 2.Temp differences influence patterns of high and low pressure

Variations in Atmos Pressure 1.Vertical Height, pressure 2.Horizontal Thermal (temp) – during the day air… heats expands decreases in density rises. Less air at surface = L pressure Dynamic (mvmt of Earth) equator, air rises, moves to poles. B/c of rotation air is pulled eastward

Basic Pressure Systems 1.Low (cyclone) L Converging air circulation Air ascending, lowering the pressure on the surface L 2.High (anticyclone) H Descending air circulation Air blows down and away, increasing H the surface pressure

Wind Essentials The horizontal motion of air across the Earth’s surface Produced by differences in air pressure from one place to another Two principle properties: direction and speed

Driving Forces of Wind Gravity Pressure Gradient Force Coriolis Force Friction Force

Gravity Gravity compresses the atmosphere Causes the atmosphere to be more dense at lower altitudes. Gravity creates atmospheric pressure

Pressure Gradient Force Drives air from areas of higher pressure to lower pressure. Without this force, there would be no wind. Pressure differences are portrayed on maps by isobars.

Coriolis Force Anything that flies or flows across the Earth’s surface is deflected from a straight path by the Coriolis Force. The deflection is caused by the Earth’s rotation. This deflection occurs regardless of the direction in which something is moving.

Coriolis Force

Friction Force Drags on the wind as it moves across the surfaces. The effect of this force decreases with height above the surface. Without friction, winds would move at very high rates of speed.

LOCAL AND GLOBAL WINDS Small Group Work 1.Land Breeze – Sea Breeze 2.Mountain Breeze – Valley Breeze 3.Drainage Winds 4.Chinook-type Winds 5.Monsoons

Global Wind Pressures

Review – Air Pressure: Differences in air pressure are created by the unequal heating of Earth’s surface – Warm, less dense air rises → L – Cool, denser air sinks → H This circular patterns is know as the convection current

Review – Wind: Differences in air pressure create moving air = wind Winds usually travel from areas of H to L Two types of wind: local and global – Local (influenced by geography): Land Breeze – Sea Breeze Mountain Breeze – Valley Breeze Drainage Winds Chinook-type Winds Monsoons

Global Wind Pattern Aka “general circulation” of upper atmospher Move across the Earth in specific directions Polar Easterlies: From degrees latitude. Prevailing Westerlies: From degrees latitude (aka Westerlies). Tropical Easterlies: From 0-30 degrees latitude (aka Trade Winds).

Theoretical Model

Seasonal Variations January = Air over land cools more quickly, therefore there is H pressure over landmasses over Asia = Siberian High over North America = Canadian high over the North Atlantic = Icelandic Low over the North Pacific = Aleutian Low – Air moves towards to Lows, resulting in unstable weather (winter storms) July = lengthy heating of the oceans reverses pressure systems Pacific = Pacific High Atlantic Ocean = Bermuda High (N. Am), Azores High (Euro)

GLOBAL WIND PATTERNS FINDING NEMO TURTLES You Tube Clips