CR Earth Science Unit 5/6
You might have heard the phrase "inches of mercury," which is used by the media to describe atmospheric pressure. This expression dates from
1643, when Torricelli, a student of the famous Italian scientist Galileo, invented the mercury barometer.
The process of changing a liquid to a gas is called evaporation. It takes approximately
2,500 joules of energy to convert 1 gram of liquid water to water vapor. The energy absorbed by the water molecules during evaporation gives them the motion needed to escape the surface of the liquid and become a gas. This energy is referred to as latent heat of vaporization.
What are adiabatic temperature changes?
Adiabatic temperature changes are changes in temperature that take place due to pressure changes in the absence of addition or removal of heat. These changes happen when air is compressed or allowed to expand.
You can calculate that the air pressure exerted on the top of a 50-centimeter-by-100-centimeter school desk exceeds 5,000 kilograms, which is about the mass of a 50-passenger school bus. Why doesn't the desk collapse under the weight of the air above it?
Air pressure is exerted in all directions—down, up, and sideways. The air pressure pushing down on an object balances the air pressure pushing up on the object.
How is the stability of air determined?
Air stability is measured by measuring the temperature of the atmosphere at different heights. The temperature of stable air increases gradually as altitude increases.
In meteorology, the term rain means drops of water that fall from a cloud and have a diameter of at least 0.5 mm. Smaller drops are called drizzle. When the surface temperature is above 4°C, snowflakes usually melt and continue their descent as rain before they reach the ground.
At very low temperatures (when the moisture content of air is small) light, fluffy snow made up of individual six-sided ice crystals forms. At temperatures warmer than -5°C, ice crystals join into larger clumps.
When the surface temperature is above 4°C, snowflakes usually melt before they reach the ground. Even on a hot summer day, a heavy downpour may have started as a snowstorm high in the clouds. Why do cloud droplets fall so slowly?
Cloud droplets fall slowly because they are very tiny and many of them evaporate before falling.
Relative humidity can be changed in two ways:
First, it can be changed by adding or removing water vapor. In nature, moisture is added to air mainly by evaporation from the oceans and smaller bodies of water. Second, because the amount of moisture needed for saturation depends on temperature, relative humidity varies with temperature. Notice in the figure that when the flask is cooled from 20°C to 10°C, the relative humidity increases from 50 to 100 percent. However, once the air is saturated, further cooling does not change the relative humidity. Further cooling causes condensation, which keeps the air at its saturation level for that temperature.
If adding heat does not raise the temperature, then where does this energy go?
In this case, the added heat breaks apart the crystal structure of the ice cubes. The bonds between water molecules in the ice crystals are broken, forming the noncrystalline substance liquid water. You know this process as melting.
In a mercury barometer, a glass tube filled with mercury is held upright in a dish of mercury. What happens to the barometer when air pressure increases?
Mercury is pushed into the tube, causing the level of mercury to rise.
At 9:00 a.m., the air is saturated with water. What happens to the relative humidity as the day continues and the temperature increases? (Assume that the water vapor content of the air remains constant.)
Relative humidity decreases.
A sling psychrometer would not be all that useful in a weather balloon used to monitor conditions in the upper atmosphere. A different type of hygrometer is used in instrument packages that transmit data back to a station on the ground:
The electric hygrometer contains an electrical conductor coated with a chemical that absorbs moisture. The passage of current varies with the amount of moisture absorbed.
What would happen to falling snowflakes if the temperature close to the surface was more than 4°C?
The falling snowflakes will melt and turn into rain.
How does temperature affect the formation of dew, fog, and clouds?
When air is cooled to its dew point, it gets saturated. This results in condensation in the form of dew, fog, and clouds.
A barometer is
a device used for measuring air pressure (bar = pressure, metron = measuring instrument).
Relative humidity is
a ratio of the air's actual water vapor content compared with the amount of water vapor needed for saturation at that temperature and pressure.
Stratus clouds are
a uniform, fog-like layer of clouds that frequently covers much of the sky. Occasionally, these clouds may produce light precipitation. When stratus clouds develop a scalloped bottom that appears as long parallel rolls or broken rounded patches, they are called stratocumulus clouds.
Temperature changes that happen even though heat isn't added or subtracted are called
adiabatic temperature changes. They result when air is compressed or allowed to expand. When air is allowed to expand, it cools, and when it is compressed, it warms.
A radiosonde is
an instrument designed to collect weather data high in the atmosphere. Radiosondes are often carried into the air by balloons.
Stratus (stratum = a layer) clouds
are best described as sheets or layers that cover much or all of the sky. While there may be minor breaks, there are no distinct individual cloud units.
Cirrus (cirrus = a curl of hair) clouds
are high, white, and thin. They can occur as patches or as delicate veil-like sheets or extended wispy fibers that often have a feathery appearance.
When cirrus clouds are followed by
cirrocumulus or cirrostratus clouds and increased sky coverage, they may be a sign of approaching stormy weather.
Three cloud types make up the family of high clouds:
cirrus, cirrostratus, and cirrocumulus. Cirrocumulus clouds consist of fluffy masses, while cirrostratus clouds are flat layers
Clouds are classified on the basis of their form and height. The three basic forms are:
cirrus, cumulus, and stratus. All other clouds reflect one of these three basic forms or are combinations or modifications of them.
When air far above Earth's surface is cooled below its saturation level, some of the water vapor condenses to form
clouds. Because clouds are made of liquid droplets, this moisture is no longer part of the water vapor content of the air. To summarize, when the water vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity.
Water vapor is the source of all
condensation and precipitation, which is any form of water that falls from a cloud.
Generally, there must be a surface for water vapor to condense on. When dew forms, objects at or near the ground, such as grass and car windows, serve this purpose. But when condensation occurs in the air above the ground, tiny bits of particulate matter, called
condensation nuclei, serve as surfaces for water-vapor condensation. These nuclei are important because if they are absent, a relative humidity much above 100 percent is needed to produce clouds.
The opposite process where water vapor changes to the liquid state is called
condensation. In the atmosphere, condensation generates clouds and fog. For condensation to occur, water molecules must release their stored heat energy, called latent heat of condensation, equal to what was absorbed during evaporation. This released energy plays an important role in producing violent weather and can transfer great quantities of heat from tropical oceans toward the poles.
Cumulus (cumulus = a pile) clouds
consist of rounded individual cloud masses. Normally, they have a flat base and the appearance of rising domes or towers. These clouds are frequently described as having a cauliflower structure.
The collision of contrasting air masses forces air to rise. In a more general sense, whenever air in the lower atmosphere flows together, lifting results. This is called
convergence. When air flows in from more than one direction, it must go somewhere. Because it cannot go down, it goes up, as shown in the figure. This leads to adiabatic cooling and possibly cloud formation.
A blanket of fog is produced in some West Coast locations when warm, moist air from the Pacific Ocean moves over the cold California Current and then is carried onshore by prevailing winds. Fogs also can form on
cool, clear, calm nights when Earth's surface cools rapidly by radiation. As the night progresses, a thin layer of air in contact with the ground is cooled below its dew point. As the air cools, it becomes denser and drains into low areas such as river valleys, where thick fog accumulations may occur.
Warm air can hold more water vapor than cold air, so
cooling increases the relative humidity. Water vapor begins to condense when relative humidity reaches 100 percent.
Hail is produced in
cumulonimbus clouds. Hailstones begin as small ice pellets that grow by collecting supercooled water droplets as they fall through a cloud. If the ice pellets encounter a strong updraft, they may be carried upward and begin the downward journey once more. Each trip through the supercooled portion of the cloud may be represented by another layer of ice.
As you travel from Earth's surface upward through the atmosphere, the atmospheric pressure
decreases. This happens because there are fewer and fewer gas molecules. Any time a volume of air moves upward, it passes through regions of successively lower pressure. As a result, the ascending air expands and cools. Unsaturated air cools at the constant rate of 10°C for every 1,000 meters of ascent.
The covalent bonds within a water molecule and the adherence among water molecules require large amount of heat to overcome. This makes water an
excellent insulator—especially for our bodies.
If a volume of air was forced to rise, its temperature would drop because of
expansion. If this volume of air was cooler than the surrounding environment, it would be denser, and if allowed to do so, it would sink to its original position. Air of this type, called stable air, resists vertical movement.
Torricelli correctly described the atmosphere as a vast ocean of air that exerts pressure on us and all objects around us. To measure this force, he
filled a glass tube, closed at one end, with mercury. He then put the tube upside down into a dish of mercury, as shown in the figure. The mercury flowed out of the tube until the weight of the column was balanced by the pressure that the atmosphere exerted on the surface of the mercury in the dish. In other words, the weight of mercury in the column (tube) equaled the weight of the same size column of air that extended from the ground to the top of the atmosphere. When air pressure increases, the mercury in the tube rises. When air pressure decreases, so does the height of the mercury column. With some improvements, the mercury barometer is still the standard instrument used today for measuring air pressure.
In central North America, masses of warm air and cold air collide, producing a
front. Here the cooler, denser air acts as a barrier over which the warmer, less dense air rises. This process is called frontal wedging. Weather-producing fronts are associated with specific storm systems called middle-latitude cyclones.
Variations in air pressure from place to place can
generate winds. The winds, in turn, bring change in temperature and humidity. Air pressure is one of the basic weather elements and is an important factor in weather forecasting. Air pressure is closely tied to the other elements of weather in a cause-and-effect relationship.
The heat used to melt ice does not produce a temperature change, so it is referred to as
heat. Latent means "hidden," like the latent fingerprints hidden at a crime scene. This energy, measured in joules or calories, becomes stored in the liquid water and is not released as heat until the liquid returns to the solid state. Latent heat plays a crucial role in many atmospheric processes. For example, the release of latent heat aids in forming the towering clouds often seen on warm summer days. It is the major source of energy for thunderstorms, tornadoes, and hurricanes.
The process of changing state requires that energy is transferred in the form of
heat. When heat is transferred to a glass of ice water, the temperature of the ice water remains a constant 0°C until all the ice has melted.
There are three levels of cloud heights:
high, middle, and low. High clouds normally have bases above 6,000 meters. Middle clouds generally occupy heights from 2,000 to 6,000 meters. Low clouds form below 2,000 meters. The altitudes listed for each height category are not hard and fast. There is some seasonal and latitudinal variation. For example, at high latitudes or during cold winter months in the mid-latitudes, high clouds often are found at lower altitudes.
The Florida peninsula provides an example of
how convergence can cause cloud development and precipitation. On warm days, the airflow is from the ocean to the land along both coasts of Florida. This leads to a pileup of air along the coasts and general convergence over the peninsula. This pattern of air movement and the uplift that results is helped along by intense solar heating of the land. The result is that the peninsula of Florida experiences the greatest number of mid-afternoon thunderstorms in the United States.
The general term for the amount of water vapor in air is
humidity. Meteorologists use several methods to express the water vapor content of the air. These include relative humidity and dew point temperature.
Relative humidity is commonly measured by using a
hygrometer. There are various types of hygrometers. Some are digital, like the one in the figure.
When the water vapor content of air remains constant, lowering air temperature causes an
increase in relative humidity, and raising air temperature causes a decrease in relative humidity.
Physically, there is no difference between a fog and a cloud. Their appearance and structure are the same. The difference is
is the method and place of formation. Clouds result when air rises and cools adiabatically. Most fogs are the result of radiation cooling or the movement of air over a cold surface. Fogs also can form when enough water vapor is added to the air to bring about saturation. Fog is defined as a cloud with its base at or very near the ground. When fog is dense, visibility may be only a few dozen meters or less, making travel not only difficult but often dangerous.
You might have experienced a cooling effect when stepping dripping wet from a swimming pool or bathtub. This cooling results because
it takes considerable energy to evaporate water. In this situation, the energy comes from your skin—hence the expression that "evaporation is a cooling process."
Cloud droplets are very tiny, averaging
less than 20 micrometers in diameter. Because of their small size, the rate at which cloud droplets fall is incredibly slow. Most cloud droplets would evaporate before falling a few meters into unsaturated air below. For precipitation to form, cloud droplets must grow in volume by roughly one million times.
The process that produces rising thermals is known as
localized convective lifting. Birds such as hawks and eagles use these thermals to carry them to great heights where they can gaze down on unsuspecting prey. People have learned to use these warm parcels effectively for hang gliding. When warm parcels of air rise above the condensation level, clouds form. These clouds may produce mid-afternoon rain showers.
Which property is the difference between fogs and clouds?
location
Air stability is determined by
measuring the temperature of the atmosphere at various heights. The rate of a change of air temperature with height is called the environmental lapse rate. This rate is determined from observations made by aircraft and by radiosondes.
In contrast, clouds associated with the lifting of unstable air are towering and often generate thunderstorms and occasionally even a tornado. So you can conclude that, on a dreary, overcast day with light drizzle, stable air has been forced above Earth's surface. However
on a day when cauliflower-shaped clouds appear to be growing as if bubbles of hot air are surging upward, it is easy to tell that the air moving up is unstable.
Nimbostratus clouds derive their name from the Latin word nimbus, which means "rainy cloud," and stratus, which means "to cover with a layer." As the name suggests, nimbostratus clouds are
one of the main precipitation makers. Nimbostratus clouds form during stable conditions. You might not expect clouds to develop in stable air. But cloud growth of this type is common when air is forced upward, as occurs along a mountain range, a front, or where converging winds cause air to rise. Such a forced upward movement of stable air can result in a cloud layer that is largely horizontal compared to its depth.
When elevated terrains, such as mountains, act as barriers to air flow-
orographic lifting of air occurs. As air goes up a mountain slope, adiabatic cooling often generates clouds and precipitation. Many of the rainiest places on Earth are located on these windward mountain slopes. By the time air reaches the leeward side of a mountain, much of its moisture has been lost. If the air descends, it warms adiabatically. This makes condensation and precipitation even less likely. A rain shadow desert can occur on the leeward side of the mountain. For example, the Great Basin Desert of the western United States lies only a few hundred kilometers from the Pacific Ocean, cut off from the ocean's moisture by the Sierra Nevada Mountains.
Four mechanisms that can cause air to rise are:
orographic lifting, frontal wedging, convergence, and localized convective lifting.
On warm summer days, unequal heating of Earth's surface may cause
pockets of air to be warmed more than the surrounding air. For example, air above a paved parking lot will be warmed more than the air above an adjacent wooded park. Consequently, the parcel of air above the parking lot, which is warmer and less dense than the surrounding air, will move upward, as shown in the figure. These rising parcels of warmer air are called thermals.
When cool air moves over warm water, enough moisture may evaporate from the water surface to
produce saturation. As the rising water vapor meets the cold air, it immediately condenses and rises with the air that is being warmed from below. This type of fog over water has a steaming appearance. It is fairly common over lakes and rivers in the fall and early winter, when the water may still be relatively warm and the air is rather crisp.
When condensation takes place, the initial growth rate of cloud droplets is
rapid. It diminishes quickly because the excess water vapor is quickly absorbed by the numerous competing particles. This results in the formation of a cloud consisting of millions upon millions of tiny water droplets. These droplets are all so fine that they remain suspended in air.
Water in the liquid state below 0°C is said to be supercooled. Supercooled water will
readily freeze if it touches a solid object. Freezing nuclei are materials that have a crystal form that closely matches that of ice. Freezing nuclei can cause supercooled water to freeze.
The most familiar and most misunderstood term used to describe the moisture content of air is
relative humidity. Relative humidity is a ratio of the air's actual water vapor content compared with the amount of water vapor air can hold at that temperature and pressure. Relative humidity indicates how near the air is to saturation, rather than the actual quantity of water vapor in the air.
For every 10°C increase in temperature, the amount of water vapor needed for saturation doubles. Therefore
relatively cold saturated air at 0°C contains about half the water vapor of saturated air at a temperature of 10°C, and roughly one-fourth that of hot saturated air with a temperature of 20°C, as shown in the table. Because the dew point is the temperature at which saturation occurs, high dew point temperatures indicate moist air, and low dew point temperatures indicate dry air.
Condensation happens when water vapor in the air changes to a liquid. This may be in the form of dew, fog, or clouds. For any of these forms of condensation to occur, the air must be
saturated. Saturation occurs most commonly when air is cooled to its dew point, or less often when water vapor is added to the air.
As more and more molecules escape from the water surface, the pressure in the air above increases steadily. This forces more and more water molecules to return to the liquid. Eventually, the number of vapor molecules returning to the surface will balance the number leaving. At that point, the air is said to be
saturated. The amount of water vapor required for saturation depends on temperature. When saturated, warm air contains more water vapor than saturated cold air.
Air pressure is
simply the pressure exerted by the weight of air above. Average air pressure at sea level is about 1 kilogram per square centimeter. This pressure is roughly the same pressure that is produced by a column of water 10 meters in height.
There are three members in the family of low clouds:
stratus, stratocumulus, and nimbostratus.
The Bergeron process relies on two physical processes:
supercooling and supersaturation. Cloud droplets do not freeze at 0°C as expected. In fact, pure water suspended in air does not freeze until it reaches a temperature of nearly -40°C.
When air is saturated (100% relative humidity) with respect to water, it is
supersaturated with respect to ice (greater than 100% humidity). Ice crystals cannot coexist with water droplets in the air because the air "appears" supersaturated to the ice crystals.
Air is stable when the temperature decreases gradually with increasing altitude. The most stable conditions happen when air temperature actually increases with height, called a
temperature inversion. Temperature inversions frequently happen on clear nights as a result of radiation cooling off Earth's surface. The inversion is created because the ground and the air immediately above the ground will cool more rapidly than air higher above the ground. Under these conditions, there is very little vertical air movement.
The three states of matter are solid, liquid, and gas. Water can change from one state of matter to another—at
temperatures and pressures experienced on Earth. This unique property allows water to freely leave the oceans as a gas and return again as a liquid, producing the water cycle. All water in the cycle must pass through the atmosphere as water vapor, even though the atmosphere only holds enough to make a global layer about 2 millimeters deep.
In contrast, air is considered unstable when
the air close to the surface of Earth is significantly warmer than the air higher above the surface, indicating a large environmental lapse rate. Under these conditions, the air actually turns over, as the warm air below rises and is displaced by the colder air higher above the ground.
The need for a smaller and more portable instrument for measuring air pressure led to the development of
the aneroid barometer. The aneroid barometer uses a metal chamber with some air removed. This partially emptied chamber is extremely sensitive to variations in air pressure. It changes shape and compresses as the air pressure increases, and it expands as the pressure decreases. One advantage of the aneroid barometer is that it can be easily connected to a recording device, shown in the figure. The device provides a continuous record of pressure changes with the passage of time.
Much rainfall can be associated with clouds located well below the freezing level, especially in the tropics. In warm clouds, the mechanism that forms raindrops is
the collision-coalescence process. Some water-absorbing particles, such as salt, can remove water vapor from the air at relative humidities less than 100 percent, forming drops that are quite large. As these large droplets move through the cloud, they collide and coalesce (join together) with smaller, slower droplets.
Water also can be transformed from a solid to a vapor state. Sublimation is
the conversion of a solid directly to a gas, without passing through the liquid state.You may have observed this change in watching the sublimation of dry ice, or frozen carbon dioxide. Dry ice sometimes is used to generate "smoke" in theatrical productions.
In contrast, descending air encounters higher pressures, compresses, and is heated 10°C for every 1,000 meters it moves downward. This rate of cooling or heating applies only to unsaturated air and is called
the dry adiabatic rate.
Sleet is
the fall of small particles of clear-to-translucent ice. For sleet to form, a layer of air with temperatures above freezing must overlie a subfreezing layer near the ground. Glaze, also known as freezing rain, results when raindrops become supercooled (below 0°C) as they fall through subfreezing air near the ground and turn to ice when they impact objects.
Near Earth's surface, heat is quickly exchanged between the ground and the air above. During evening hours, the surface radiates heat away, causing the surface and adjacent air to cool rapidly. This radiational cooling causes
the formation of dew and some types of fog. In contrast, clouds, like those shown in the figure, often form during the warmest part of the day. Clearly, some other process must cool air enough to generate clouds.
Condensation nuclei such as microscopic dust, smoke, and salt particles from the ocean are abundant in
the lower atmosphere. Because of these plentiful particles, relative humidity rarely exceeds 100 percent. Some particles, such as ocean salt, are especially good nuclei because they absorb water.
When meteorologists measure atmospheric pressure, they use a unit called
the millibar. Standard sea-level pressure is 1,013.2 millibars.
When it comes to understanding atmospheric processes, water vapor is
the most important gas in the atmosphere. Water vapor makes up only a small fraction of the gases in the atmosphere, varying from nearly 0 to about 4 percent by volume. But the importance of water in the air greatly exceeds what these small percentages would indicate.
When air is compressed-
the motion of gas molecules increases and the air temperature rises. The opposite happens when air is allowed to escape from a bicycle tire. The air expands and cools. The expanding air pushes on the surrounding air and cools by an amount equal to the energy used up.
Clouds that appear in the middle range, from about 2,000 to 6,000 meters, have
the prefix alto- as part of their name. Altocumulus clouds are composed of rounded masses that differ from cirrocumulus clouds in that altocumulus clouds are larger and denser. Altostratus clouds create a uniform white to grayish sheet covering the sky with the sun or moon visible as a bright spot. Infrequent light snow or drizzle may accompany these clouds.
If orographic lifting was the only mechanism that lifted air then-
the relatively flat central portion of North America would be an expansive desert instead of the nation's breadbasket. Fortunately, this is not the case.
Deposition is
the reverse process, the conversion of a vapor directly to a solid. This change happens when water vapor is deposited as frost on cold objects such as grass or windows.
Which factor most affects the type of precipitation that falls on Earth's surface?
the temperature profile in the few kilometers above the surface
The type of precipitation that reaches Earth's surface depends on
the temperature profile in the lowest few kilometers of the atmosphere. Temperature profile is the way the air temperature changes with altitude. Even on a hot summer day, a heavy downpour may have begun as a snowstorm high in the clouds overhead.
Another important measure of humidity is the dew point temperature. The dew point temperature or simply the dew point is
the temperature to which a parcel of air would need to be cooled to reach saturation. If the same air was cooled further, the air's excess water vapor would condense, typically as dew, fog, or clouds. During evening hours, objects near the ground often cool below the dew point temperature and become coated with water. This is known as dew
If a parcel of air rises high enough, it will eventually cool to its dew point. Here, the process of condensation begins. From this point on as the air rises, latent heat of condensation stored in the water vapor will be released. Although the air will continue to cool after condensation begins, the released latent heat works against the adiabatic cooling process. This slower rate of cooling caused by the addition of latent heat is called
the wet adiabatic rate. Because the amount of latent heat released depends on the quantity of moisture present in the air, the wet adiabatic rate varies from 5-9°C per 1,000 meters.
Some clouds do not fit into any one of the three height categories mentioned. Such clouds have
their bases in the low height range but often extend upward into the middle or high altitudes. They all are related to one another and are associated with unstable air. Although cumulus clouds are often connected with fair weather, they may grow dramatically under the proper circumstances. After upward movement is triggered, acceleration is powerful, and clouds with great vertical range form. The end result often is a cumulonimbus cloud that may produce rain showers or a thunderstorm.
All high clouds are
thin and white and are often made up of ice crystals. This is because of the low temperatures and small quantities of water vapor present at high altitudes. These clouds are not considered precipitation makers.
Depending on atmospheric conditions, dew can form overnight on plants in a process called
transpiration
Another type of hygrometer, called a psychrometer, consists of
two identical thermometers mounted side by side. One thermometer, the dry-bulb thermometer, gives the present air temperature. The other, called the wet-bulb thermometer, has a thin cloth wick tied around the end. To use the psychrometer, the cloth wick is saturated with water, and air is continuously passed over the wick. This is done either by swinging the instrument freely in the air or by fanning air past it. Water evaporates from the wick, and the heat absorbed by the evaporating water makes the temperature of the wet bulb drop. The loss of heat that was required to evaporate water from the wet bulb lowers the thermometer reading. This temperature is referred to as the wet-bulb temperature. The amount of cooling that takes place is directly proportional to the dryness of the air. The drier the air, the more moisture evaporates, and the lower is the temperature of the wet bulb. The larger the difference is between temperatures observed on the thermometers, the lower the relative humidity is. If the air is saturated, no evaporation will occur, and the two thermometers will have identical readings. To determine the precise relative humidity and to calculate the dew point, standard tables are used.
If this imaginary volume of rising air was warmer and therefore less dense than the surrounding air, it would continue to rise until it reached an altitude where its temperature equaled that of its surroundings. This is exactly how a hot-air balloon works. The balloon rises as long as it is warmer and less dense than the surrounding air, as shown in the figure. This type of air is classified as
unstable air. Stable air tends to remain in its original position, while unstable air tends to rise.
In general, air resists
vertical movement. Air located near the surface tends to stay near the surface. Air far above the surface tends to remain far above the surface. Some exceptions to this happen when conditions in the atmosphere make air buoyant enough to rise without the aid of outside forces. In other situations, clouds form because there is some mechanical process that forces air to rise.
During a temperature inversion on a clear night, the air near the ground is _____.
very stable
Which example of warm air will become cooler in an adiabatic process?
warm air rising from the surface into the upper troposphere
Condensation occurs when
water vapor changes to a liquid. Condensation may form dew, fog, or clouds. Although these three forms are different, all require saturated air to develop. Saturation occurs either when enough water vapor is added to air or, more commonly, when air is cooled to its dew point.
Clouds are among the most striking and noticeable effects of the atmosphere and its weather. Clouds are a result of condensation best described as visible mixtures of tiny droplets of water or tiny crystals of ice. Clouds are of interest to meteorologists because clouds show
what is going on in the atmosphere.
When stable air is forced above Earth's surface, the clouds that form are
widespread and have little vertical thickness when compared with their horizontal dimension. Precipitation, if any, is light to moderate.