Science and Technology and Engineering: Earth Science and Weather (Review)

Layers Above the Surface of Earth
The ozone layer, although contained within the stratosphere, is determined by ozone () concentrations. It absorbs the majority of ultraviolet light from the Sun. The ionosphere is part of both the exosphere and the thermosphere. It is characterized by the fact that it is a plasma, a partially ionized gas in which free electrons and positive ions are attracted to each other, but are too energetic to remain fixed as a molecule. It starts at about 50 km above Earth's surface and goes to 1,000 km. It affects radio wave transmission and auroras.
The ionosphere pushes against the inner edge of the Earth's magnetosphere, which is the highly magnetized, non-spherical region around the Earth. The homosphere encompasses the troposphere, stratosphere, and mesosphere. Gases in the homosphere are considered well mixed. In the heterosphere, the distance that particles can move without colliding is large. As a result, gases are stratified according to their molecular weights. Heavier gases such as oxygen and nitrogen occur near the bottom of the heterosphere, while hydrogen, the lightest element, is found at the top.


Tropospheric Circulation
Most weather takes place in the troposphere. Air circulates in the atmosphere by convection and in various types of 'cells.' Air near the equator is warmed by the Sun and rises. Cool air rushes under it, and the higher, warmer air flows toward Earth's poles. At the poles, it cools and descends to the surface. It is now under the hot air, and flows back to the equator. Air currents coupled with ocean currents move heat around the planet, creating winds, weather, and climate. Winds can change direction with the seasons. For example, in Southeast Asia and India, summer monsoons are caused by air being heated by the Sun. This air rises, draws moisture from the ocean, and causes daily rains. In winter, the air cools, sinks, pushes the moist air away, and creates dry weather.

Common Weather Phenomena and Equipment to Measure Them
Common atmospheric conditions that are frequently measured are temperature, precipitation, wind, and humidity. These weather conditions are often measured at permanently fixed weather stations so weather data can be collected and compared over time and by region.
Measurements may also be taken by ships, buoys, and underwater instruments.
Measurements may also be taken under special circumstances. The measurements taken include temperature, barometric pressure, humidity, wind speed, wind direction, and precipitation. Usually, the following instruments are used: A thermometer is used for measuring temperature; a barometer is used for measuring barometric/air pressure; a hygrometer is used for measuring humidity; an anemometer is used for measuring wind speed; a weather vane is used for measuring wind direction; and a rain gauge is used for measuring precipitation.

Weather, Climate, and Meteorology
Meteorology is the study of the atmosphere, particularly as it pertains to forecasting the weather and understanding its processes. Weather is the condition of the atmosphere at any given moment. Most weather occurs in the troposphere. Weather includes changing events such as clouds, storms, and temperature, as well as more extreme events such as tornadoes, hurricanes, and blizzards. Climate refers to the average weather for a particular area over time, typically at least 30 years. Latitude is an indicator of climate. Changes in climate occur over long time periods.

Winds and Global Wind Belts
Winds are the result of air moving by convection.
Masses of warm air rise, and cold air sweeps into their place. The warm air also moves, cools, and sinks. The term 'prevailing wind' refers to the wind that usually blows in an area in a single direction. Dominant winds are the winds with the highest speeds. Belts or bands that run latitudinally and blow in a specific direction are associated with convection cells. Hadley cells are formed directly north and south of the equator. The Farrell cells occur at about 30° to 60°. The jet stream runs between the Farrell cells and the polar cells. At the higher and lower latitudes, the direction is easterly. At mid latitudes, the direction is westerly. From the North Pole to the south, the surface winds are Polar High Easterlies, Subpolar Low Westerlies, Subtropical High or Horse Latitudes, North-East Trade winds, Equatorial Low or Doldrums, South-East Trades, Subtropical High or Horse Latitudes, Subpolar Low Easterlies, and Polar High.

Relative Humidity, Absolute Humidity, and Dew Point Temperature
Humidity refers to water vapor contained in the air.
The amount of moisture contained in air depends upon its temperature. The higher the air temperature, the more moisture it can hold. These higher levels of moisture are associated with higher humidity. Absolute humidity refers to the total amount of moisture air is capable of holding at a certain temperature. Relative humidity is the ratio of water vapor in the air compared to the amount the air is capable of holding at its current temperature. As temperature decreases, absolute humidity stays the same and relative humidity increases. A hygrometer is a device used to measure humidity.
The dew point is the temperature at which water vapor condenses into water at a particular humidity.

Precipitation
After clouds reach the dew point, precipitation occurs. Precipitation can take the form of a liquid or a solid. It is known by many names, including rain, snow, ice, dew, and frost. Liquid forms of precipitation include rain and drizzle. Rain or drizzle that freezes on contact is known as freezing rain or freezing drizzle. Solid or frozen forms of precipitation include snow, ice needles or diamond dust, sleet or ice pellets, hail, and graupel or snow pellets. Virga is a form of precipitation that evaporates before reaching the ground. It usually looks like sheets or shafts falling from a cloud. The amount of rainfall is measured with a rain gauge.
Intensity can be measured according to how fast precipitation is falling or by how severely it limits visibility. Precipitation plays a major role in the water cycle since it is responsible for depositing much of the Earth's fresh water.

Clouds
Clouds form when air cools and warm air is forced to give up some of its water vapor because it can no longer hold it. This vapor condenses and forms tiny droplets of water or ice crystals called clouds. Particles, or aerosols, are needed for water vapor to form water droplets. These are called condensation nuclei. Clouds are created by surface heating, mountains and terrain, rising air masses, and weather fronts. Clouds precipitate, returning the water they contain to Earth.
Clouds can also create atmospheric optics. They can scatter light, creating colorful phenomena such as rainbows, colorful sunsets, and the green flash phenomenon.

High, Middle, and Low Cloud Types
Most clouds can be classified according to the altitude of their base above Earth's surface. High clouds occur at altitudes between 5,000 and 13,000 meters. Middle clouds occur at altitudes between 2,000 and 7,000 meters. Low clouds occur from the Earth's surface to altitudes of 2,000 meters. Types of high clouds include cirrus (Ci), thin wispy mare's tails that consist of ice; cirrocumulus (Cc), small, pillow-like puffs that often appear in rows; and cirrostratus (Cs), thin, sheet-like clouds that often cover the entire sky. Types of middle clouds include altocumulus (Ac), gray-white clouds that consist of liquid water; and altostratus (As), grayish or blue-gray clouds that span the sky. Types of low clouds include stratus (St), gray and fog-like clouds consisting of water droplets that take up the whole sky; stratocumulus (Sc), low-lying, lumpy gray clouds; and nimbostratus (Ns), dark gray clouds with uneven bases that indicate rain or snow. Two types of clouds, cumulus (Cu) and cumulonimbus (Cb), are capable of great vertical growth. They can start at a wide range of altitudes, from the Earth's surface to altitudes of 13,000 meters.

Air Masses
Air masses are large volumes of air in the troposphere of the Earth. They are categorized by their temperature and by the amount of water vapor they contain. Arctic and Antarctic air masses are cold, polar air masses are cool, and tropical and equatorial air masses are hot. Other types of air masses include maritime and monsoon, both of which are moist and unstable. There are also continental and superior air masses, which are dry. A weather front separates two masses of air of different densities. It is the principal cause of meteorological phenomena.
Air masses are quickly and easily affected by the land they are above. They can have certain characteristics, and then develop new ones when they get blown over a different area.

Weather Fronts and Weather Maps
A weather front is the area between two differing masses of air that affects weather. Frontal movements are influenced by the jet stream and other high winds. Movements are determined by the type of front. Cold fronts move up to twice as fast as warm ones. It is in the turbulent frontal area that commonplace and dramatic weather events take place. This area also creates temperature changes. Weather phenomena include rain, thunderstorms, high winds, tornadoes, cloudiness, clear skies, and hurricanes. Different fronts can be plotted on weather maps using a set of designated symbols.
Surface weather maps can also include symbols representing clouds, rain, temperature, air pressure, and fair weather.