Atmosphere

Investigation 1 Atmosphere

The atmosphere is a thin layer of gases that surrounds the Earth. Often the word “air” is used to describe this layer of gases- but there is so much more to it than that. Composed of several layers. The Atmosphere

Composition of the Atmosphere Atmospheric Component Percent by Volume (%/vol) Nitrogen (N) 78.08 Oxygen (O₂) 21 Argon (Ar) 0.9 Water Vapor (H₂O) 0.4 Carbon Dioxide (CO₂) 0.036 Methane (CH₄) 0.00017 Nitrous Oxide (NO) 0.00003 Ozone (O₃) 0.000004 Particles (dust, soot, etc) 0.000001

Layers of the Atmosphere Troposphere Stratosphere Mesosphere Thermosphere Exosphere

The Troposphere The lowest layer Earth’s atmosphere. Most of the Earth’s weather occurs in the Troposphere Tropo- means “turning” or “changing”. Depth varies from more than 16 km above the equator to less than 9 km above the North and South Poles. Contains almost all of the mass of the atmosphere. As altitude increases in the troposphere, the temperature decreases. The Troposphere

UV light and other forms of energy from the Sun are absorbed or reflected by water and land The heat is transferred to the air directly above the land or water by conduction and radiation The Troposphere

Extends from the top of the troposphere to about 50 km above Earth’s surface. Strato- means “layer” or “spreading out”. Lower stratosphere is cold, about -60°C. The upper stratosphere is warmer than the lower stratosphere. Upper Stratosphere contains ozone (O₃)in the stratosphere absorbs energy from the sun, converting it into heat, and warming the air. Most Clouds are located in the Stratosphere The Stratosphere

The Mesosphere Located above the stratosphere Cooler than the stratosphere Meso- mean s “middle”. Begins 50 km above Earth’s surface and ends at 80 km. The outer mesosphere temperatures approach - 90°C. Most meteoroids burn up in the mesosphere, producing meteor trails. The Mesosphere

The Thermosphere The outermost layer of the atmosphere Extends from 80 km above Earth’s surface outward into space. The air 80 km above Earth’s surface is only about 0.001% as dense as the air at sea level. The thermosphere has no definite outer limit. Atmosphere does not end suddenly at the outer edge of the thermosphere. Gas atoms and molecules there are so far apart that the air blends gradually into outer space. The Thermosphere

The Thermosphere Thermo- means “heat”. Even though the air in the thermosphere is thin, it is very hot, up to 1,800°C. Energy from the sun strikes the thermosphere first. Nitrogen and oxygen molecules convert energy from the sun into heat. The Thermosphere

The Exosphere The outer layer of the thermosphere. Exo- means “outer”. The exosphere extends from 550 km outward for thousand of kilometers. Satellites orbit in the exosphere making it possible for you to make a long distance phone call or watch television. The Exosphere

All areas of the Earth do not receive the same amount of light Earth is tilted 23.5° on its axis The angle the light hits the equator is more direct than the areas away from the equator North and South Pole receive the least amount of direct light Sun and the Earth

Differences in the amount of tdirect light cause differences in the amount of heat More direct light results in more hear that is received Less direct results in less heat received Direct light decreases from the Equator to the Poles Since the Atmosphere is heated by conduction and radiation from the water and land on Earth, the air in the atmosphere above the equator is warmer than the air over the north and south poles Earth’s Tilt

Earth’s Tilt

Earth’s Tilt

Describes how the volume changes with changes in temperature when the pressure of a gas is constant. When the temperature of a gas is increased at constant pressure, it’s volume increases. When the temperature of a gas is decreased at constant pressure, its volume decreases. Charles Law

Volume and density of air changes with changes in temperature. As the temperature of air increases, its volume increases and its density decreases. As the temperature of decreases, its volume decreases and its density increases Air Heated and Cooled

Changes in Temp Affect Density As air is heated its density decreases because its mass remains constant but its volume increases As air is cooled, its density increases because its mass remains constant but its volume decreases Changes in Temp Affect Density

Changes in Density Cause Air Movement Air is fluid. Fluids that are dense sink below those that are less dense (oil and water) The decreases in density as air is heated causes it to rise above cooler, more dense air The increase in density as air is cooled causes it to sink below warmer, less dense air Changes in Density Cause Air Movement

Temperature Differences Affect The Earth’s Atmosphere The warmer air in the atmosphere rises and cooler air in the atmosphere sinks. This causes convection currents in the atmosphere. Temperature Differences Affect The Earth’s Atmosphere

Investigation 2 Atmosphere

Properties of Air Since air has mass, it also has other properties, density and pressure. The amount of mass in a given volume of air is its density. Density=Mass ÷Volume (D = M /V) If there are more molecules in a given volume of air, the density is greater. If there are fewer molecules, the density decreases. Properties of Air

Pressure Measured by meteorologists in units of millibars (mb). The greater the millibars, the higher the pressure Example: 1000 mb is a higher pressure than 500 mb. Pressure is the sum force pushing on an area or surface of the Earth. P = ∑ F / A ∑ F= sum of forces A = area Pressure

Pressure A denser substance has more mass per unit volume than a less dense one. So denser air exerts more pressure than less dense air. Air pressure is the result of the weight of a column of air pushing down on an area.

Types of Air Pressure High Pressure Low Pressure The area has a pressure that is higher than any place next to it When air from the upper atmosphere sinks it leaves an “empty” spot When the sinking air reaches lower levels it pushes some air out of the way- it rises and fills the “empty” spot Clear, Sunny, Calm Weather The area has a pressure that is lower than any place next to it When air close to the Earth’s surface rises it leaves an “empty” spot When the rising air reaches higher levels it pushes some air out of the way- it sinks and fills the “empty’ spot Cloudy, Stormy Weather Types of Air Pressure

Changes in Air Pressure

Areas that have the same pressure are connected by a line called an isobar Air Pressure Map

Changes in Air Pressure- Low Pressure As air rises or is moved upward from the Earth the pressure on the surface of the earth decreases The force of air moving in an upward direction is greater than the force exerted in a downward direction Resulting in the area directly beneath the rising air is lower in pressure- Low Pressure System Changes in Air Pressure- Low Pressure

Changes in Air Pressure- High Pressure System Air that sinks or moves downward from the upper levels of the atmosphere causes the pressure beneath the sinking air to increase The area directly below the sinking air has a pressure that is higher than the areas that surround it- High Pressure System Changes in Air Pressure- High Pressure System

Measuring Air Pressure Falling air pressure is usually indicates that a storm is approaching. Rising air pressure usually means that the weather is clearing. A barometer is an instrument that is used to measure changes in air pressure. There are two kinds of barometers: mercury barometers and aneroid barometers. Measuring Air Pressure

A mercury barometer consists of a glass tube open at the bottom end and partially filled with mercury. The space in the tube above the mercury is almost a vacuum—it contains no air. The open end of the tube rests in a dish of mercury. Mercury Barometers

Mercury Barometers The air pressure pushing down on the surface of the mercury in the dish is equal to the weight of the column of mercury in the tube. When the air pressure increases, it presses down more on the surface of mercury. Greater air pressure forces the column of mercury higher. When the air pressure decreases the column of mercury will fall

Aneroid Barometers The word aneroid means “without liquid”. An aneroid barometer has an airtight metal chamber. The metal chamber is sensitive to changes in air pressure When air pressure increases, the thin walls of the chamber are pushed in. When the pressure drops, the walls bulge out. The changes in the walls of the metal chamber cause the needle of the barometer to move Aneroid Barometers

Aneroid Barometers Aneroid barometers are smaller than mercury thermometers. They don’t contain a liquid. Therefore, they are portable and often more practical for uses such as airplane instrument panels.

Pressure Gradient Force-Wind Wind is the horizontal movement of air between areas of different pressure. The pressure gradient force is a force that is directed from areas of high pressure to lower pressure. The pressure gradient force causes the initial movement of air. PGF = area of higher pressure (mb) – area of lower pressure (mb) distance between areas of pressure (km) Pressure Gradient Force-Wind

Air Movement Causing High and Low Pressure Air that moves from the upper levels of the atmosphere downwards towards Earth create an area of high pressure beneath the falling air. Air that rises or moves upwards from the Earth or from lower levels of the atmosphere create an area of low pressure beneath the rising air. Cold air sinking would increase the pressure in an area while warm air rising would decrease the pressure in an area. Air Movement Causing High and Low Pressure

Differences in Air Pressure Cause Wind When there are pressure differences in the atmosphere air move from areas of high pressure to areas of low pressure. This movement of air creates wind Differences in Air Pressure Cause Wind

Measuring the Differences in Pressure Changes in pressure are measured with a barometer. One type is the mercury barometer. As the pressure of an area increases in the increased downward force of air pushes the mercury in a barometer up into the barometer. As the pressure of the area decreases, the level of mercury in a barometer falls because the downward force of air on the liquid barometer has decreased Measuring the Differences in Pressure

Investigation 3 Atmosphere

Some places on Earth the atmosphere is calm and there are few strong winds. These places develop over areas of the Earth that are flat so that the air remains relatively stationary and takes on the temperature and humidity characteristics of the surface below. The bodies of air that develop over these areas are called air masses. Air Masses

Types of Air Masses Continental Artic Continental Polar Maritime Polar Scientists classify air masses according to two characteristics: temperature and humidity. Whether an air mass is warm or cold depends on the temperature of the region over which the air mass forms. Continental Artic Continental Polar Maritime Polar Maritime Tropical Continental Tropical

Types of Air Masses Type Where it Forms Temperature Abbreviation Used Continental Artic Over the land that is north of the artic circle Very Cold cA Continental Polar Over the Northern plain of Canada Cold cP Maritime Polar Over the Northern Atlantic and Pacific Oceans mP Maritime Tropical Over the Southern Atlantic Ocean and Gulf of Mexico Warm mT Continental Tropical Over the land of the U.S Southwest desert and northern Mexico cT

Air Masses Air Masses do not remain stationary Winds high in the atmosphere such as the jet stream and other with and high and low pressure centers move air masses As air masses move over other areas they take on the temperature and humidity of the surface beneath The more water an air mass contains, the more moist or humid it is The less water an air contains the more dry it is Air masses then to collide in the middle latitudes (30-60 degrees) When Air Masses collide they form a Front

Something happens when two air masses with different temperatures and densities collide. The area where the air masses meet and do not mix becomes a front. When air masses meet at a front, the collision often causes storms and changeable weather. There are four types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts. Fronts

Cold Fronts When a rapidly moving cold air mass runs into a slowly moving warm air mass, the denser cold air slides under the lighter warm air. The warm air is pushed upward. The front that forms is called a cold front. Cold fronts move quickly, so they can cause abrupt weather changes, including violent thunderstorms. After a cold front passes through an area, cool, dry air moves in, often bringing clear skies and cooler temperatures.

Cold Front

Warm Fronts Clouds, storms, and rain also accompany warm fronts. At a warm front, a moving air mass collides with a slowly moving cold air mass. Because cold air is more dense than warm air, the warm air moves over the cold air. Because warm fronts move more slowly than cold fronts, the weather may be rainy or foggy for several days After a warm front passes through an area, the weather is likely to be warm and humid. In winter, warm fronts bring snow. Warm Fronts

Warm Front

Stationary Fronts Occluded Front Sometimes cold and warm masses meet, but neither one has enough force to move the other. Where the warm and cool air meet, water vapor in the warm air condenses into rain, snow, fog, or clouds. a warm air mass is caught between two cooler air masses The denser cool air masses move underneath the less dense warm air mass and push it upward As the warm air cools and its water vapor condenses, the weather may turn cloudy and rainy or snowy. Fronts

Fronts

Water in the Air Different Air Masses can contain different amounts of water vapor If the rate of evaporation is greater than the rate of condensation, more water will exist as water vapor If the rate of condensation is greater than the rate of evaporation, more water will exist in the liquid form When water vapor condenses it can form Clouds and different forms of precipitation Rain Hail Snow Sleet

Precipitation Forming Along Fronts Three factors are necessary for precipitation to occur include differences in density between the warm and cold air masses, an upper atmosphere that has temperatures lower than the air in the rising warm air mass and a significant amount of water vapor in the rising warm air mass Precipitation Forming Along Fronts

Precipitation Along Fronts Density differences The temperature of the atmosphere decreases with the height of the atmosphere. When cold fronts form, air from the cold and warm air masses move as a result of their densities. The more dense cold air pushes under the less dense warm air ahead of it. The air in the warm air mass rises As the warm air rises, it encounters cooler temperatures and the rate of evaporation decreases. As the rate of evaporation becomes slower than the rate of condensation any water vapor in the warm air condenses and forms clouds and precipitation Precipitation Along Fronts

Precipitation Along Fronts Temperature changes When warm fronts form, air from the cold and warm air masses moves as a result of their densities. The less dense warm air behind the cold air masses rises and slide over and above the cold air mass As the warm air rises it encounters cooler temperatures and the rate of evaporation decreases. As a the rate of evaporation becomes slower than the rate of condensation, any water vapor in the warmer air can condense and form clouds and precipitation Precipitation Along Fronts

Precipitation Along Fronts Amount of Water Vapor The more water vapor the rising warm air mass contains, the more likely it is that there will be a greater amount of precipitation than occurs with both a warm and cold front Precipitation Along Fronts

Moisture of an Air Mass Affect Precipitation Along Fronts If fronts are formed between air masses that contain more moisture then more precipitation may occur. Warm air mass over land creates a warm DRY air mass- desert Warm air mass over water creates a MOIST air mass The rising of the warm DRY air mass into the upper levels of the atmosphere produced LESS precipitation A front formed by a cold DRY air mass and a warm MOIST air mass will likely produce MORE precipitation than a front formed between a cold DRY air mass and a warm DRY air mass The meeting of a cold MOIST air mass and a warm MOIST air mass would likely produced MORE precipitation than that produced by the meeting of a cold MOIST and a warm DRY air mass Moisture of an Air Mass Affect Precipitation Along Fronts

Changes Occur with the Passing of a Cold Front In both cold and warm fronts, rising of the warmer air mass is accompanied by a decrease in the atmospheric pressure In cold front, there is a decrease in pressure as the front forms because the cool air mass slides under the warmer air mass and pushes it upward The rising warm air results in a decrease in atmospheric pressure This decrease is followed by an increase in pressure once the front has passed because of the cooler sinking air that moved in behind the warmer rising air Changes Occur with the Passing of a Cold Front

Changes Occur with the Passing of a Warm Front In a warm front, there is a decline in the atmospheric pressure as the front moves into an area because a warm air mass moves in behind a cooler air mass As the Warm air mass slides over the cooler air mass there is a decrease in pressure The pressure continues to drop as the front passes because of the warmer, rising air that moved in behind the cooler air mass Changes Occur with the Passing of a Warm Front