11.1
 About 99% of the atmosphere is composed of nitrogen and oxygen (78% nitrogen, 21% oxygen)
– The remaining 1% consists of small amounts of argon, hydrogen, carbon dioxide, water vapor, & other gases.

 The levels of CO2 and water vapor vary constantly.
– The level of these gases are critical because they play an important role in regulating the amount of energy the atmosphere absorbs.

 Ozone (O3) is important because it absorbs
UV radiation from the Sun thus warming the layer.

 The atmosphere is divided into five layers:
– Troposphere
 The lowest layer is where most of the weather occurs.
– Stratosphere
 Contains Ozone layer
– Mesosphere
 Meteors burn up, coldest layer
– Thermosphere
 The aurora caused by
- Exosphere
Outermost layer particles from the Sun i nteracting with Earth’s atm.
– Ionosphere
 Charged particles reflect radio signals

 Radiation is the transfer of energy through space by visible light, UV radiation, and other forms of electromagnetic waves
– ~30% of incoming solar radiation is reflected into space by Earth’s surface
– ~20% is absorbed by the atmosphere itself
 Only 50% of incoming solar radiation is absorbed by
Earth’s surface

 The rate of absorption for any area varies depending on the physical characteristics of the area and the amount of solar radiation it receives.
– *Land heats and cools faster than water
– Darker objects absorb energy faster than lighter ones

 Energy is transferred throughout the atmosphere by the process of conduction, convection & radiation.
 Conduction is the transfer of energy that occurs when molecules collide.
– Energy is transferred from the particles of air near Earth’s surface to the particles of air in the lowest layer of the atmosphere.

 Convection is the transfer of energy by the flow of a heated substance.
– Pockets of air near Earth’s surface are heated, become less dense than the surrounding air & rise.
– As the warm air rises, it expands and starts to cool.
– When it cools below the temperature of the surrounding air, it increases density and sinks.
 Convection Currents

 1. Name the 5 layers of the atmosphere in order from farthest to closest to Earth’s surface.
 2. What is significant about the ionosphere?
 3. What are the 2 main gases in our atmosphere and what is the percent they make up of the atmosphere?
 4. ____________ is the transfer of energy that occurs when molecules collide.
 5. The level of __________ & __________ are critical because they play an important role in regulating the amount of energy the atmosphere absorbs.

11.2
 Temperature is a measurement of how rapidly or slowly molecules move around.
– fast moving molecules = higher temp.
– Slow moving molecules = lower temp.
 Heat is the transfer of energy that occurs because of a difference in temperature between substances.
– Heat flows from area of high temp. to area of low temp.

 The dew point is the temperature to which air must be cooled at constant pressure to reach saturation.
– Saturation is the point at which the air holds as much water vapor as it possibly can.
 Condensation occurs when matter changes state from a gas to a liquid.

 When the air is holding as much moisture as it can, the air is saturated .
– The air’s ability to hold water vapor depends upon the temperature.
– The warmer the air, the more moisture the air can hold.
 The dew point is the temperature to which the air must be cooled to become saturated.
– If the temperature falls below the dew point, condensation occurs as water vapor changes to liquid water.

 Dry Adiabatic Lapse Rate: the rate at which unsaturated air (which no heat is added or removed) will cool.
– 10°C for every 1,000m increase in altitude.
 Moist Adiabatic Lapse Rate : the rate at which saturated air cools.
– ~4°C/1,000m in very warm air to ~9°C/1,000m in very cold air.

 Lifted Condensation Level (LCL): the height at which condensation occurs.
– LCL often corresponds to the base of clouds
– Air above the LCL is saturated and cools slower than air below the LCL.

 Air has mass and exerts pressure on our bodies.
– Atmospheric pressure increases as you near the bottom of the atm because of the greater mass of atm above you.
– Atmospheric pressure decreases with height because there are fewer gas particles exerting pressure.

 The density of air is proportional to the number of particles of air occupying a particular space.
– The density of air increases as you get closer to the bottom of the atmosphere.
– The density of air decreases as you increase elevation.

 Temperature is directly proportional to pressure.
– As temp increases/decreases, pressure does too
– As pressure increases/decreases, temperature does too

 The relationship between temperature and density is inversely proportional.
– As temperature increases, density decreases
– As temperature decreases, density increases
 **Temperature is proportional to the ratio of pressure to density, which decreases with increasing altitude.

 A temperature inversion is an increase in temperature with height in an atmospheric layer.
– temp-altitude relationship is inverted

 Cool air = more dense, sinks
 Warm air = less dense, rises
– **Air flows from areas of high pressure to areas of low pressure
 Wind changes with height in the atm
– Near the surface, wind is disrupted by the friction that results from contact with trees, buildings, etc.
– Farther up from Earth’s surface, air encounters less friction & wind speeds increase

 The amount of water vapor in air is referred to as humidity .
 The ratio of water vapor in a volume of air relative to how much water vapor that volume of air is capable of holding is called relative humidity .
– RH is expressed as a percentage %

 Compares how much moisture the air is actually holding with how much moisture it could hold if the air were saturated.
– It is expressed as a percent of saturation.
 Air is saturated if it is holding all the moisture it can hold at its present temperature.
 Determined with a psychrometer and a relative humidity table.

 Warm air is capable of holding more moisture than cool air.
– If the temp. of a room increased, the air in the room would be capable of holding more moisture.
 If no additional water vapor was added to the air, its relative humidity would decrease.
 If more water vapor was added to the air, its relative humidity would increase.

11.3

 Clouds form when rising air is cooled below its dew point.
 Tiny particles called condensation nuclei (small
 particles in the air) allow a cloud to form.

 Clouds can also form when wind encounters a mountain and the air has nowhere to go but up.
– As the air rises it cools and condenses.
– This is method of cloud formation is called orographic lifting .

 Another method of cloud formation involves the collision of air masses of different temps.
– Cold, more dense air mass will collect near the surface.
– As warm air moves into the area, some of it will warm up the cold air but the bulk will rise over the cold air.
 As the warm air cools, the water vapor in it condenses and forms a cloud.

 stability = tendency of air to remain in in its original position (resist rising).
– The rate at which an air mass cools depends on the temperature of the surface beneath the air.
 If the air = cooler; it is going to want to sink  stable
 If the air = warmer; it is going to want to rise  unstable

 As water vapor in the air condenses, heat is released.
 It takes energy to change liquid water into gaseous state
– That energy is stored in the water vapor and will not be released into the air until condensation occurs.
 The stored energy is called latent heat .
– When condensation occurs, latent heat is released and warms the air.

 Clouds are classified by the altitude at which they form and by their shape.

 Typically form below 2,000m
– Stratocumulus : gray/whitish patch/sheet that is flattened out and spread horizontally
– Cumulus : detached, generally dense clouds with sharp outlines that develop vertically in the form of rising mounds.
– Stratus : layered gray cloud that covers much or all of the sky in a given area
– Cumulonimbus : thunderstorm cloud, dark at the bottom that produces rain and/or hail.

Cumulus
Stratus
Cumulonimbus
Stratocumulus

 Form at heights between 2,000 and 6,000m
– Altocumulus : white/gray patch or sheet layered clouds (resemble fish scales)
– Altostratus : dark but thin veils of clouds that sometimes produce mild precipitation and cover totally or partially the sky. Thin enough to see the sun.
– Nimbostratus : the continuous rain cloud resulting from thickening altostratus. Completely block out the Sun. Dark gray in color; associated with precipitation.

Altostratus
Altocumulus
Nimbostratus

 Form at heights of 6,000m
– Temps are below freezing, thus made up of ice crystals.
– Cirrus : wispy, indistinct (detached) appearance
– Cirrostratus : transparent, whitish veil clouds with a smooth appearance. continuous layer that covers the sky
– Cirrocumulus : thin, white patch sheet or layered clouds

Cirrus
Cirrostratus
Cirrocumulus

 When cloud droplets collide, they join together to form a larger droplet in a process called coalescence .
 As the process continues the droplet becomes too heavy to be held aloft and falls to earth as precipitation .
– Rain, snow, sleet, and hail

 Rain and snow are the most common forms of precipitation.
 Drizzle is small raindrops that fall slowly
 Sleet is a partially frozen mixture of rain and snow that occurs when the temperature is just above freezing.
 Hail is in the form of ice balls, which usually occurs in violent thunderstorms.
– Hailstones begin as snowflakes that start to melt and gather more moisture as they fall.

 Water moves between Earth’s surface and its atmosphere  water cycle
1. Radiation from the Sun causes liquid water to change into a gas  evaporation
2. As water vapor rises, it cools and changes back into a liquid  condensation
3. Water droplets combine to form larger drops that fall to Earth  precipitation

 The short-term (a few hours or days) condition of the atmosphere at a given location.
– Temperature, sky conditions, precipitation, atmospheric pressure, humidity, wind speed, and wind direction.
 Meteorologists are scientists who study and predict the weather.

 In the daily cycle, temperature is usually lowest in the early morning and warmest at mid-afternoon.
 In the season cycle, winters are generally cold, while summers tend to be hot.
 Short term factors such as cloud cover and regional weather systems affect temperatures.
– Clouds reduce daytime temperature by reflecting sunlight back into space.
– At night, clouds help hold heat energy to Earth.

 Measured with a thermometer .
– A bulb that contains liquid that expands into a narrow, calibrated neck when it is heated and moves down the neck when the temperature decreases.
 When meteorologists record official air temperature, the thermometer is kept in a special weather shelter to protect the instruments from direct sunlight.

 A temperature of zero on the Fahrenheit scale is the temperature of a mixture of equal parts ice, water, and salt.
 The freezing point of water is what sets the zero point on the
Celsius (centigrade) scale.
 The point at which all particle motion stops is defined as zero on the Kelvin scale.

 Is caused by the weight of the atmosphere.
 Above each square inch of Earth’s surface is a column of air the weighs 14.7 pounds.

 A barometer is an instrument used to measure air pressure using the dense liquid metal mercury.
 Meteorologists measure air pressure in millibars .
 Standard sea level pressure is 1013.2 millibars.
 On a weather map, isobars connect places that have the same air pressure.

 If air is cooled, it contracts and becomes denser.
– This causes pressure to rise.
 If air is heated, it expands and becomes less dense.
– This causes pressure to fall.
 Humid air is lighter than dry air.
– This is because water molecules are lighter than the gasses they displace in the air.

 Meteorologists use a sling psychrometer and a dew-point temperature table to determine the dew point.
– The psychrometer consists of two thermometers mounted side by side which can be swung through the air.
– One thermometer measures the air temperature.
– The bulb of the other thermometer is covered by a wet cloth.
– As the thermometers are swung through the air, evaporated cooling causes the wet-bulb thermometer to register a lower temperature.
– When you subtract the wet-bulb temperature from the drybulb temperature, you can use the dew-point table to determine the dew point.



– This uneven heating causes differences in air pressure to develop.

 Winds always blow from areas of high pressure to areas of low pressure.
– Winds blow fastest where the gradient in air pressure is greatest, where the isobars are close together.

 To measure the wind, you need to determine both the wind speed and the wind direction.
 Wind speed is measured with an anemometer .
– The cups catch the wind, causing it to spin.
 Wind direction is indicated by a wind vane, which points into the wind.

 The Earth’s rotation causes winds to curve.
– to the right in the Northern
Hemisphere .
– to the left in the Southern
Hemisphere.

 Winds move in a clockwise outward spiral around high-pressure systems.
 Winds move in a counterclockwise inward spiral around low-pressure systems.

 Rising warm, moist air at the center of the low causes winds and air masses to blow into the low-pressure system.
 The rising air cools, which causes cloud formation and precipitation.
 The descending air turns a high-pressure system into a single mass of cool, dry air that spreads across the surface of Earth.