The Atmosphere and Weather
The Atmosphere and Weather
The Atmosphere and
The Air Around You
What is weather?
The condition of Earth’s atmosphere at a particular time
What is the atmosphere?
The envelope or blanket of gases that surround the
Made of nitrogen, oxygen, carbon dioxide, water vapor
and more making the conditions on Earth suitable for
Air has mass, density, and
Density- amount of mass in a
given volume of air (density=
Pressure- the force pushing
on an area or surface
Air pressure is the result of
the weight of a column of air
pushing down on an area.
Air pressure is measured by
Altitude affects air pressurethe higher you go, less air
Altitude affects density- the
higher you go, less oxygen
Layers of the Atmosphere
Troposphere, stratosphere, Mesosphere,
Troposphere- first layer, lowest, where we live. Weather
occurs here. Contains almost all the mass of the
Stratosphere- second layer, where the ozone layer is.
Temperature warms up as it reaches the top.
Mesosphere- drop in temperature (meso-middle)
protects Earth’s surface from being hit by meteoroids.
Thermosphere- outermost layer of Earth’s atmosphere.
Extends to space. Extremely high temperature though
feels very cold.
Ionosphere and exosphere are part of the
Ionosphere causes aurora borealis, exosphere extends
Energy in the Earth’s
Energy comes from the sun as electromagnetic waves.
Most of the energy from the sun travels to the Earth in the
form of visible light and infrared radiation. A small amount
arrives as ultraviolet light.
Visible light: all the colors of the rainbow
Infrared radiation: wavelengths are longer than red light, is
not visible and felt as heat.
Ultraviolet radiation- invisible energy shorter than violet light.
What is Infrared Radiation?
The light we see with our eyes is really a very small portion of what is called the
"Electromagnetic Spectrum." The Electromagnetic Spectrum includes all types of
radiation - from the X-rays used at hospitals, to radio waves used for communication,
and even the microwaves you cook food with.
Radiation in the Electromagnetic Spectrum is often categorized by wavelength. Short
wavelength radiation is of the highest energy and can be very dangerous - Gamma, Xrays and ultraviolet are examples of short wavelength radiation. Longer wavelength
radiation is of lower energy and is usually less harmful - examples include radio,
microwaves and infrared. A rainbow shows the optical (visible) part of the
Electromagnetic Spectrum and infrared (if you could see it) would be located just beyond
the red side of the rainbow.
Although infrared radiation is not visible, humans can sense it - as heat. Put your hand
next to a hot oven if you want to experience infrared radiation "first-hand!
Some sunlight is absorbed or reflected by the
atmosphere before it can reach the surface. The rest
passes through to the surface.
Some light is scattered (reflected light). Gases scatter
short wavelengths of visible light (blue and violet) more
than long wavelengths (red and orange) making the
sky look blue.
When the Earth’s surface is
heated, it radiates most of
the energy back into the
atmosphere as infrared
radiation. It is absorbed by
water vapor, carbon dioxide,
methane, and other gases.
Greenhouse effect- process
by which gases hold heat in
Wind: a horizontal movement of air from an area of
high pressure to an area of low pressure. Winds are
caused by differences in air pressure.
Convection currents move areas of warm air to cool air.
Global winds: blow steadily from specific directions
over long distances.
The Coriolis Effect: Earth’s
rotation causes winds to curve.
Ex: Global winds in the N.
Hemisphere turn to the right.
Global Wind Belts
Major global wind belts are the trade winds, the polar
easterlies, and the prevailing westerlies.
Trade Winds- when cold air sinks, it produces high
pressure. Due to the Coriolis effect, winds blow toward
the equator and turn west away from it. Located in the
N.H. between 30° N latitude and equator and in S.H.
30° S latitude and the equator.
Prevailing Westerlies- Located between 30° and 60° N
and S latitudes and blow towards the poles and east
due to the Coriolis effect. Play an important role in
weather in the US.
Polar Easterlies- cold air near poles sinks and flows
back towards the lower latitudes. Coriolis effect sends
winds west and meets the Prevailing Westerlies at 60°
N and S latitudes. This mixes warm and cold air and
creates a major effect on weather in the US.
Jet stream- bands of high speed winds. Blow from west
to east at 200-400 km per hr. Wander north and south
in a wavy pattern which brings change in temperature
Humidity and Cloud
Humidity: the amount of
water vapor in the air.
The amount of water vapor
the air can hold depends on
the temperature. Warmer air
holds more water.
Clouds form when water
vapor in the air condenses to
form liquid water or ice
The temperature where condensation starts is called
dew point. (temp above freezing=water droplets; temp
Particles in the air (dust, smoke) allows for
condensation to occur for cloud formation. (on the
ground=dew or frost)
Types of Clouds
3 main types based on shape,
then classified by altitude.
Cirrus Cloudswispy/feathery, form at high
Cirrocumulus- rows of cotton
balls or scales of a fish-a
storm is coming
Cumulus Clouds- fluffy round
piles of cotton- indicate fair
clouds with flat tops- T-storms
Stratus clouds- form in
layers, cover all or most of the
sky in a dull gray color,
stratus clouds produce drizzle,
rain, or snow
Altostratus- based on how
high in the sky they are.
Middle level clouds are higher
than regular stratus and
cumulus clouds but lower than
cirrus and other high clouds.
Fog- clouds that form at or
near the ground.
Types of Precipitation
Depending on the size of water vapor, will depend on if a
cloud will produce precipitation.
Rain-drops of water, smaller drops called mist.
Sleet-when rain falls through a layer of air that is freezing,
frozen particles fall as ice.
Freezing rain-rain that freezes on a cold surface
Hail-round pellets of ice produced by t-storms of rain
freezing being updrafted and forming new ice around it like
layers of an onion. Can be the size of golf balls.
Air Masses and Fronts
Air mass-a huge body of air with similar temperature,
humidity, and air pressure at any given height.
4 major types in N. America: maritime tropical,
continental tropical, maritime polar, and continental
maritime (oceans) tropical (warm)- brings warm humid
air, t-storms in summer or snow in winter (Cali or S.E.
Maritime (oceans) Polar (cold)- cool humid air (cold
N.Pacific and N. Atlantic oceans)
Continental(land) Tropical (warm)- hot dry air (SW and
Continental (land) Polar(cold)-masses that move from
the Artic circle -clear cold, dry air in winter, storms in
summer when clashes with maritime tropical.
In the continental US, air masses are commonly moved
by the prevailing westerlies and jet streams.
Front- boundary where air masses meet. Storms and
changeable weather develop along fronts.
A t-storm is a small storm with heavy precipitation,
thunder and lightening.
T-storms form in large cumulonimbus clouds called
Form on hot humid afternoons when warm air is forced
along a cold front. Air rises rapidly and cools rapidly.
Lightning-sudden spark of an electrical discharge of
positive and negative electrical charges in clouds.
Tornado- rapidly whirling, funnel-shaped cloud that
reaches down from a storm cloud to the Earth’s
Brief but wind speeds can reach 500 km per hr.
Develop in thick cumulonimbus clouds that bring tstorms, typically in the spring and summer.
Tornado alley- middle of the US in the Great Plains due
to cold dry air from north clashing with warm moist air
from the south.
Hurricanes-tropical cyclones w/winds of 119 km per hr or
higher and about 600 km across.
Begins over warm ocean waters as low-pressure area or a
Draws energy from warm humid air above ocean surface.
Bands of high winds and heavy rains
Winds spiral inward towards area of low pressure inside
Storm surges create a dome of water that is pushed in from
the ocean and floods costal areas.