Earth’s Atmosphere Structure, Components and Temperature

Vocabulary Weather Climate Ozone Troposphere Stratosphere Mesosphere Thermosphere Summer solstice Winter solstice Autumnal equinox Spring equinox

Weather vs. climate Weather is the state of the atmosphere at any given time and place. Weather is constantly changing. Climate is based on observations of weather that have been collected over many years. Climate helps describe a place or region.

Measurable properties of weather and climate Air temperature Humidity Type and amount of precipitation Air pressure Speed and direction of the wind

History of the Atmosphere Most scientists believe that Earth’s early atmosphere was made of gases emitted during volcanic eruptions.

Composition of the Atmosphere Air is a mixture of gases and particles each with its own unique properties.

Nitrogen – 78% Oxygen – 21% Argon – 0.93% Carbon dioxide – 0.01 to 0.1% Water vapor – 0 to 4% Air composition varies from time to time and place to place (water vapor, dust, pollutants)

Variable Components If water vapor, dust, and other variable components were removed from the atmosphere, its makeup would be very uniform up to an altitude of about 80 kilometers or about 40 miles.

Variable components CO 2 (carbon dioxide) – plays an important role in heating the atmosphere as it absorbs heat given off by Earth. Water vapor – Varies from 0 to 4% by volume. It is the source of all clouds and precipitation. It absorbs heat from both the Earth and the Sun.

Variable components Particulates – sea salts from breaking waves, fine soil, smoke and soot from fires, pollen and microorganisms, and ash and dust from volcanic eruptions. Ozone – A type of oxygen made of 3 atoms in each molecule instead of the usual two. Ozone is concentrated in a region from 10 to 50 km above the surface with the maximum concentration at km (stratosphere).

Ozone Formation Diatomic molecules of oxygen gas (O 2 ) disassociate when they absorb UV radiation. Ozone is produced when a single atom of oxygen and another diatomic molecule of oxygen collide in the presence of a third, neutral molecule that acts as a catalyst (allows a reaction to take place without being consumed itself).

Ozone Layer Ozone is critical to life on Earth because it absorbs harmful UV (ultraviolet) radiation from the Sun. It acts as a filter, preventing most UV radiation from reaching Earth’s surface and the living things upon it. Without ozone, our planet would be inhospitable to most living organisms! ‘Thanks, ozone!’ (signed) All life on Earth

Human Influence on the Atmosphere Primary pollutants are emitted directly into the air from identifiable sources. Secondary pollutants form in the air from reactions among primary pollutants and other substances. They are NOT emitted directly into the air. Acid rain (sulfuric acid) forms from the primary pollutant sulfur dioxide.

Some reactions can be triggered by strong sunlight. These are called PHOTOCHEMICAL REACTIONS. These can form secondary products that are reactive, irritating, and toxic – such as smog.

Structure of the Atmosphere There is no sharp boundary between the atmosphere and space – it just thins out as you travel away from Earth’s surface, until there are too few gas molecules to detect.

Structure of the Atmosphere Atmospheric pressure (the weight of the air above) decreases with height. At sea level, the average pressure is slightly more than 1000 millibars, or slightly more than 1 kilogram per square centimeter. One half of the atmosphere lies below an altitude of 5.6 km.

Structure of the Atmosphere The atmosphere is divided into 5 layers based on temperature.

Troposphere The bottom layer, where temperature decreases with an increase in altitude, is the troposphere. It is in this layer that essentially all important weather phenomena occur. The troposphere varies in thickness from season to season and with different latitudes, but its average height is about 12 km. The outer boundary of the troposphere is called the tropopause.

Stratosphere The stratosphere is the next layer, from 12 km to 50 km. In the stratosphere, the temperature remains constant to a height of about 20 km, but then temperatures increase with height. The atmosphere’s ozone layer is concentrated here (20 to 30 km) because there is both absorption of UV radiation (the source of heating) and enough oxygen molecules for the production of ozone.

Mesosphere The mesosphere is the next layer, which extends from 50 to 85 km. In the mesosphere, temperatures again decrease with height until the mesopause, the upper boundary of this layer, which is the coldest part of the atmosphere. It can get down to -90 °C (-130 °F) there! It is not easy to study the mesosphere directly. Weather balloons can't fly high enough and satellites can't orbit low enough, so scientists use sounding rockets (a suborbital rocket that carries scientific instruments).

Mesosphere What happens in the mesosphere? Most meteors burn up there. A type of lightning called sprites sometimes appears in the mesosphere above thunderstorms. Strange, high-altitude clouds called noctilucent clouds sometimes form in this layer above the North and South Poles.

Thermosphere The fourth layer is the thermosphere. It extends from the mesopause at about 90 km to between 500 and 1000 km! Temperatures go up in the lower thermosphere (200 to 300 km) because oxygen and nitrogen absorb high energy, short-wave solar radiation. Above that, temperatures hold steady with height. Temperatures in the upper thermosphere can range from about 500 °C (932 °F) to 2,000 °C (3,632 °F) or higher. The top of the thermosphere is the thermopause.

Thermosphere Although the thermosphere is considered part of Earth's atmosphere, the air density is so low that most people think of it as outer space, especially since the space shuttle orbited and the International Space Station orbits here! The aurora borealis and aurora australis occur in the thermosphere.

Exosphere The exosphere is the fifth and uppermost layer, where the atmosphere thins out and merges with interplanetary space. It is located directly above the thermosphere. The exosphere has no clearly defined upper limit. Here gas molecules can escape to space but the density is so low they do not collide with each other. The exosphere contains only a small fraction of the mass of the atmosphere.

You probably thought it always got colder the higher up you go, but that’s not true for two of the layers of the atmosphere! ‘Hotter’ means the gas molecules have more energy and move faster.

Seasonal changes in the atmosphere The vertical structure of the atmosphere changes with the seasons. The troposphere and stratosphere get warmer in summer, but the mesosphere gets colder!

Earth-Sun Relationships Nearly all the energy that drives Earth’s weather and climate comes from the Sun, but it is only a tiny fraction of the energy given off by the Sun (less than one-two billionth). Solar energy is not distributed equally over the Earth, varying with latitude, time of day, and season of the year. This unequal heating is what causes winds and ocean currents which transport heat from the tropics toward the poles and result in weather.

Earth’s Two Principal Motions Rotational motion about its axis  Once every 24 hours, produces daily cycle of daylight and darkness  Axis is an imaginary line that runs through North and South Poles Revolution about the Sun Orbital motion, one revolution every days. Earth travels at nearly 113,000 km/h!

The earth is tilted at an angle of 23.5 degrees from the vertical and this causes seasonal variations in how much sunlight reaches the surface and at what angle. The angle of the noon sun can vary up to 47 degrees during the year at many locations.

Solstices On June 21 or 22 each year the axis is such that the Northern Hemisphere is “leaning” 23.5 degrees toward the sun. This is known as the summer solstice, or the first “official” day of summer. This is the longest day of the year because the length of daylight on the summer solstice in the Northern Hemisphere is greater than the length of darkness.

Winter Solstice December 21 or 22 is the winter solstice, the first day of winter. In the Northern Hemisphere, the Earth’s axis is tilted 23.5 degrees away from the sun. This is the shortest day of the year.

Equinoxes March 21 or 22 is the date of the spring (or vernal) equinox for the Northern Hemisphere, while September 21 or 22 is the date of the autumnal equinox. All latitudes receive 12 hours of daylight during the vernal and autumnal equinoxes (Latin for equal night) because the Earth’s axial tilt is neither toward nor away from the sun.

In the Northern Hemisphere during summer, Earth is tilted toward the sun and receives sunlight more directly overhead than in winter. At this time we also receive more hours of sunlight than in winter. The opposite is true for the Southern Hemisphere. On the Autumnal Equinox and the Vernal (Spring) Equinox, the amount of sunlight is the same all over the Earth (12 hours) because the axial tilt is neither toward nor away from the Sun.