Chapter 17 Notes: The Atmosphere

What is the Atmosphere? The atmosphere can be defined as the portion of planet earth that contains gas. Weather can be defined as the current state of the atmosphere at any given time or place. Climate can be defined as the average weather conditions of a given area.

What is the Composition of the Earth's Atmosphere? About 99% of air is Nitrogen and Oxygen. About 0.93% of air is Argon. About 0.039% of air is Carbon Dioxide. Water vapor is also an important component of the atmosphere. One form of oxygen in the atmosphere is ozone. Ozone protects living organisms from harmful ultraviolet radiation from the sun.

Composition of the Atmosphere

Ozone

How does air pressure and temperature change with altitude? As altitude (height above sea level) increases, air pressure decreases. Air pressure is the pressure created by the weight of air above it. Increasing air pressure increases kinetic energy. Increasing kinetic energy increases temperatures. As a general rule, the higher the altitude, the lower the air pressure will become, the lower the air pressure, the colder the temperature.

Air Pressure

How does air pressure and temperature change with altitude? However, not all of the earth's layers of the atmosphere get colder with height. The earth's atmosphere can be divided into four layers based on changing temperatures. The first layer which starts at the earth's surface and goes up to about the height of miles, is called the troposphere. The troposphere gets colder with height.

Troposphere

How does air pressure and temperature change with altitude? Then there is an area of change between layers called the tropopause. The next layer is called the stratosphere. The stratosphere remains a constant temperature until about 15 miles above sea level, where it reaches the ozone layer. Once the stratosphere reaches the ozone layer it heats up until it reaches the next layer, which is the mesosphere.

Troposphere and Stratosphere

How does air pressure and temperature change with altitude? The mesosphere begins about 30 miles high. The mesosphere gets colder with height. The last and final layer is the thermosphere which begins about miles high. Includes the ionosphere and exosphere. Only a small percentage of the atmosphere's mass is in the thermosphere. Increased solar radiation causes the temperature in the thermosphere to increase.

Mesosphere and Thermosphere

Layers of the Atmosphere

Aurora Borealis is Produced in the Thermosphere

What causes the seasons of the earth? The earth rotates on its axis every day. The earth revolves around the sun every year. The earth's axis is not perpendicular to the orbit or the path that it takes around the sun. The earth has a tilted axis. The earth is tilted 23.5 degrees from a line that is perpendicular to the earth's orbit around the sun.

Earth's Tilted Axis

What causes the earth's seasons? It is this 23.5 degree tilted axis that causes the earth to experience seasonal changes in the weather across the earth. In places like the equator, the sun's full force is experienced nearly year round. In places like the north and south pole, daylight and darkness can last for months at a time. Places in between have four distinct seasons.

Earth's Tilted Axis and the Seasons

When are the solstices and equinoxes? In the Northern Hemisphere, the summer solstice or longest day of the year is on June 21 or 22. In the Northern Hemisphere, the winter solstice or shortest day of the year is on December 21 or 22. September 22 or 23 is the autumnal equinox. March 21 or 22 is the spring equinox.

The Seasons

Heat in the Atmosphere The definition of heat is the thermal energy that is transferred from one object to another. The definition of temperature is a measure of the average kinetic energy of the atoms or molecules of an object or substance. Heat always flows from areas of high temperatures to areas of low temperatures.

Energy Transfer as Heat There are three different ways that thermal energy or heat can be transferred. Conduction – the transfer of heat through matter by molecular activity. The energy of molecules is transferred by collisions from one molecule to another. The transfer of heat through metal objects is a good example of conduction.

Conduction

Energy Transfer as Heat Convection – The transfer of heat by mass movement or circulation within a substance. Convection usually occurs in fluids, like the oceans and air, where the atoms and molecules are free to move around. The earth's mantle is also believed to move by convection currents.

Convection

Energy Transfer as Heat Radiation – The transfer of energy (heat) through space by electromagnetic waves. Unlike conduction or convection, radiation does not need a substance to travel through. Radiation can travel through a vacuum or empty space without a medium or any substance containing matter. The Sun’s warmth reaches Earth by radiation.

Radiation

What happens to Solar Radiation that comes into the Atmosphere? Some solar radiation gets absorbed by atmospheric gases and the earth's surface. Some solar radiation is transmitted through transparent objects like water and air. When solar radiation is transmitted through objects, sometimes it is scattered. Some solar radiation is reflected off of clouds and the surface of the earth.

Earth's Radiation Budget

What are some factors that affect temperatures on the earth? Factors that affect the temperature of the Earth include latitude, proximity to land and water, altitude, cloud cover, and wind and ocean currents. Water moderates temperature changes. If a geographic location lies close to a large body of water, the region will experience cooler summers and warmer winters compared to regions located farther away from a large body of water.

Factors influencing Temperatures When cloud cover is high, the sun's solar radiation is reflected back into space, causing cooler daytime temperatures. At night, the cloud cover reflects the radiation of the earth under the clouds back to the Earth. This keeps the nighttime temperatures a little warmer.

What are Isotherms? Isotherms are lines drawn on a map connecting areas of equal temperatures. They are similar to contour lines, but instead of connecting lines of equal elevation they are connecting areas of equal temperatures. They are useful for determining weather patterns and factors affecting temperature.

Isotherms