Our atmosphere is perilously thin. Yet it provides important solar protection as well as oxygen.

Components of Earth’s Atmosphere 78% Nitrogen 21% Oxygen ~1% Trace gases CO 2 H 2 O Argon Methane Trace gases are critical because they regulate temperatures on Earth.

Other Components: Aerosols Tiny, microscopic particles of solids that stay suspended in the air Fine dust, volcanic ash, sea salt, pollen, etc.

Important because: –Act as condensation nuclei for raindrops to form. –Can absorb or reflect solar radiation.

Other Components: Ozone 0 3 molecules –Absorb ultraviolet (UV) rays Critical in stratosphere Pollutant in troposphere

Layers of Earth’s Atmosphere Earth’s atmosphere is divided into layers, each with different characteristics: Troposphere Stratosphere Mesosphere Thermosphere Ionosphere Exosphere

Closest to Earth Thinnest/densest layer Convection Where weather occurs —water vapor and clouds Temperature decreases with altitude —6°C per kilometer Troposphere

Above troposphere to 50 km above surface Ozone layer —Absorbs harmful UV radiation Temperature increases because of ozone absorption of UV radiation. Stratosphere:

Other layers: Mesosphere Thermosphere Ionosphere Aurora Borealis Exosphere The average temperature of Earth’s atmosphere varies in a zig-zag pattern with altitude.

Solar radiation- electromagnetic energy emitted by the Sun. Visible, short-wavelength radiation Terrestrial radiation is reemitted solar radiation from Earth’s surface. Infrared, longer-wavelength radiation

Radiation-Conduction- Convection The Sun sends ultraviolet and visible light to Earth by radiation. Infrared (heat) is produced at the surface and warms Earth’s atmosphere by conduction. Convection works in the atmosphere.

Solar Energy Solar intensity is highest where the Sun’s rays strike Earth’s surface straight on. Flashlight beam at 90° angle to the surface Equatorial regions Solar intensity is weaker where the Sun’s rays strike Earth’s surface at an angle. Flashlight beam at an angle Higher latitudes

The Sun’s rays don’t strike all places on the Earth with the same intensity.

Solar Energy Variation in solar intensity with latitude helps to explain the different climates.

Seasons When the Sun’s rays are closest to perpendicular at any spot on the Earth, that region’s season is summer. Six months later, as the rays fall upon the same region more obliquely, the season is winter. In between are the seasons fall and spring.

Air Pressure Atmospheric pressure = force the atmosphere exerts on an area of surface. Force = weight of air molecules above that surface.

Air Pressure At any level in the atmosphere, force = total weight of air above that level. At higher elevations, fewer air molecules above— atmospheric pressure is less.

Air Characteristics Warm air: Expanded-lower density and lower pressure Rises due to density differences Cool air: Contracts-higher density and higher pressure Sinks due to density differences This process is called convection and drives the weather

What is the wind? Wind is air that flows horizontally from higher pressure to lower pressure.

What causes the wind? Pressure differences (gradient) - caused by uneven heating of the Earth’s surface. The greater the pressure gradient, the stronger the wind.

Water has a high specific heat. It takes a long time to warm up but a long time to cool down again. This contributes to the pressure differences.

Coriolis Effect Earth’s rotation greatly affects the path of moving air. Moving bodies (such as air) deflect to the right in the Northern Hemisphere, to the left in the Southern Hemisphere. Deflection of wind varies according to speed and latitude. —Faster wind, greater deflection —Deflection greatest at poles, decreases to zero at equator

Global Wind Circulation Patterns The atmosphere is divided into circulation cells. This results from: unequal heating of Earth’s surface and Earth’s rotation.

Latitudes have different characteristics due to circulation cells. Equator- low pressure, clouds form, rainy climate. Low winds (doldrums) Rainforests 30° N and S- high pressure, dry air (horse latitudes) Deserts 60° N and S- low pressure, cool, dry air meets warm, moist air— (Polar Front)

Wind Patterns Equator to 30°N and S Trade winds- strong winds that blow westward (0°–) 30° to 60 ° N and S Westerlies –winds blow eastward 60°– 90° N and S Polar easterlies-winds blow westward

There are 5 major gyres in the ocean. Each gyre is powered by both the trade winds and the westerlies.