Earth Science Chapter 12

Describe how relative humidity can be changed by the removal of water vapor and a change in temperature.

A decrease in temperature results in an increase in relative humidity.

Describe the Collision-coalescence process.

A theory of raindrop formation in warm clouds (above 0 degrees Celsius) in which large cloud droplets (giants) collide and join together with smaller droplets to form raindrops. Opposite electrical charges may bind the cloud droplets together.

Describe the Bergeon process.

A theory that relates the formation of precipitation to super-cooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water.

Explain the first of the three types of fog formed by cooling.

Advection fog - occurs when warm, moist air moves over a cool surface

Cumulonimbus clouds

Although cumulus clouds are often connected with fair weather, they may grow dramatically under the proper circumstances. Once upward movement is triggered, acceleration is powerful, and clouds with great vertical extent form. The end result is often a towering cloud, called a cumulonimbus, that produces rain showers or a thunderstorm.

Adiabatic temperature change

As the compressed gas in an aerosol spray can is released, it quickly expands and cools. This drop in temperature occurs even though heat is neither added nor subtracted. Such variations are known as adiabatic temperature changes and result when air is compressed or allowed to expand. In summary, when air is allowed to expand, it cools, and when it is compressed, it warms. The process that is responsible for most cloud formation.

What is the first of the three basic cloud forms.

Cirrus - high, white, and thin; can occur as patches, veil-like sheets, or wispy fibers that have a feathery appearance

Explain 3 of the 4 common methods that cause air to rise.

Convergence - a pileup of horizontal airflow results in upward movement. When air flow in from more that one direction, it converges and rises This can also occur when an obstacle slows or restricts horizontal airflow When air moves from the ocean to the land, the air speed is reduced and air "piles up" on the land

Deposition

Conversion of a gas directly into a solid without passing through the liquid state Example: "frost" that accumulates in the freezer

Sublimation

Conversion of a solid directly into a gas without passing through the liquid state Example: the shrinking of ice cubes left in the freezer for long periods of time

What is the second of the three basic cloud forms.

Cumulus - globular individual cloud masses; normally have a flat base and the appearance of rising domes or towers

Calorie

Defined as the amount of heat required to raise the temperature of 1 gram of water by 1° C When 10 calories of heat are added to 1 gram of water, the molecules move faster and a 10° C temperature rise occurs

Conditional instability

Develops when moist air has an environmental lapse rate between the dry & wet adiabatic rates. Very common type of atmospheric instability. The atmosphere is stable for an unsaturated parcel of air but unstable for a saturated parcel of air Conditional instability depends upon whether the rising air is saturated The air must be forced aloft (front, orographic lifting) before it becomes unstable and continues to rise on its own.

Explain the third method of the three methods meteorologist used to express the water vapor content in the atmosphere.

Dew-Point Temperature-the temperature to which a parcel or air which a parcel of air would need to be cooled to reach saturation.

Explain the latent heat of fusion.

Freezing, the reverse process, releases these 80 calories per gram to the environment as latent heat of fusion.

Explain the second of the two types of evaporation fogs.

Frontal (or precipitation) fog - when frontal wedging occurs, if precipitation develops and the cold air below is near the dew point, enough rain will evaporate to produce fog

Explain 2 of the 4 common methods that cause air to rise.

Frontal wedging - warmer, less dense air is forced over cooler, denser air. When air masses collide, a front is generated. In this case, the warmer, less dense air will rise over the cooler, more dense air. This process and the development of middle-latitude cyclones will be evaluated in depth in chapter 14.

What is the first of the three basic cloud heights.

High clouds - have bases above 20,000 feet

Wet adiabatic rate

If the air parcel rises enough, it will eventually cool to its dew point temperature. It is at this point that condensation begins. If the air parcel continues to rise, the condensation of water vapor will release latent heat The parcel will be warmer than the surrounding air. As the parcel continues to cool as it rises, it will cool at a lower rate. The rate of cooling will be 5° to 9° per 1,000 meters. This is termed the wet adiabatic rate. The variation in cooling of the wet adiabatic rate is due to the original quantity of moisture in the parcel of air.

Stable air

If the parcel of air is cooler than the surrounding air, it will be more dense than the surrounding air and begin to sink.

Unstable air

If the parcel of air is warmer than the surrounding air, it will be less dense than the surrounding air and begin to rise.

Discuss how the stability of air is determined.

It is determined by measuring the temperature of the atmosphere at various heights. This measure is called the environmental lapse rate.

Explain 4 of the 4 common methods that cause air to rise.

Localized convective lifting - unequal surface heating causes localized pockets of air to rise due to buoyancy. These rising pocket of air are termed thermals. These are not major rain producers but can add to the buoyancy initiated by other mechanisms

What is the third of the three basic cloud heights.

Low clouds - form below 6,500 feet

Explain the latent heat of melting.

Melting 1 gram of ice requires 80 calories, an amount referred to as latent heat of melting.

What is the second of the three basic cloud heights.

Middle clouds - occupy heights from 6,500 to 20,000 feet

Explain the first method of the three methods meteorologist used to express the water vapor content in the atmosphere.

Mixing Ratio-the mass of water vapor in a unit of air compared of the remaining mass of dry air. mixing ratio = mass of water vapor (grams) OVER mass of dry air (kilograms) Because the mixing ratio is expressed in units of mass (usually in grams per kilogram), it is not affected by changes in pressure or temperature.

Explain 1 of the 4 common methods that cause air to rise.

Orographic lifting - air is forced to rise over a mountainous region As air rises over the mountain, adiabatic cooling generates clouds and moisture. Once the air reaches the leeward side of the mountain, much of the moisture has been lost If the air descends down the slope of the mountain, it warms adiabatically, making condensation & precipitation unlikely.

Explain the second of the three types of fog formed by cooling.

Radiation fog - form on cool, clear nights when the Earth's surface cools rapidly by radiation; the thin layer of air in contact with the ground is cooled to the dew point

Explain the second method of the three methods meteorologist used to express the water vapor content in the atmosphere.

Relative Humidity-a ratio of the air's actual water-vapor content compared with the amount of water vapor required for saturation at that temperature (and pressure). Thus, relative humidity indicates how near the air is to saturation rather than the actual quantity of water vapor in the air.

Hygrometer/psychrometer

Relative humidity is commonly determined using a hygrometer One type (psychrometer) compares temperatures of a wet-bulb & dry-bulb thermometer

Hygroscopic nuclei

Some particles (ocean salts) are good condensation nuclei because they can absorb water. These are termed hygroscopic nuclei.

Explain the first of the two types of evaporation fogs.

Steam fog - occurs when cool air moves over warm water so that enough moisture can evaporate to produce saturation; as the rising vapor instantly encounters cold air, it immediately recondenses and rises with the air that is being warmed from below

What is the third of the three basic cloud forms.

Stratus - sheets or layers that cover much or all of the sky; typically have no distinct individual cloud units

Explain the latent heat of vaporization.

The energy absorbed by water molecules during evaporation is used to give them the motion needed to escape the surface of the liquid and become a gas. This energy is referred to as the latent heat of vaporization.

Explain how snow amount are measured.

The general ratio is 10 parts snow equals 1 part water This ratio varies considerable based on the physical properties of snow (wet snow vs. fluffy snow)

Explain how rain amounts are measured.

The standard measuring instrument is a rain gauge (see illustration right) Uses a funnel to collect and conduct rain. Cylindrical measuring tube measures rainfall in centimeters or inches

Dew point

The temperature to which a parcel of air would need to be cooled to reach saturation

Explain the latent heat of condensation.

This reverse process, condensation, occurs when water vapor changes to the liquid state. During condensation, water-vapor molecules release energy (latent heat of condensation) in an amount equivalent to what was absorbed during evaporation.

Latent heat

Under certain situations, heat can be added or removed from water without an accompanying rise or fall in temperature. It plays a crucial role in atmospheric processes.

Explain the third of the three types of fog formed by cooling.

Upslope fog - occurs when relatively humid air moves up a sloping terrain; as the air moves upslope, it expands and cools adiabatically (if it cools below the dew point, fog develops)

What is solid (ice)?

Water molecules are held together by molecular attractions, forming a tight, orderly arrangement of the molecules. Water molecules in ice are not free to move about but vibrate about fixed sites. When the rate of molecular movement increases, the bonds between some water molecules are broken, resulting in melting

Liquid (water)

Water molecules are still tightly packed but are moving fast enough to slide past one another As the rate of molecular movement increases, the remaining molecular attractions are broken allowing the molecules to escape from the surface becoming water vapor

Gas (water vapor)

Water molecules are widely spaced and exhibit energetic, random motion Water vapor is distinguished from liquid water in that it is compressible When water changes states of matter, the only change that occurs is the distances and interactions among the water molecules

Describe the water molecule and the characteristics of water in each of the three states of matter.

Water vapor is an odorless, colorless gas that can change states of matter at Earth's temperatures and pressures Water is the only substance that exists as a solid, liquid, & gas in the atmosphere. It is composed of 2 hydrogen atoms bonded to an oxygen atom. In each state of matter, the molecules are in constant motion. The higher the temperature, the faster the motion. The difference between the states of matter of the water molecule is in the arrangement of the water molecules.

Condensation nuclei

When condensation occurs in the atmosphere, tiny bits of particulate matter (condensation nuclei) serve as surfaces for water vapor condensation

Describe how relative humidity can be changed by the addition of water vapor and a change in temperature.

When water vapor is added to a parcel of air, its relative humidity increases until saturation occurs (100 percent relative humidity.) Excess water vapor (over 100 percent) condenses to form liquid water.

Dry adiabatic rate

Within this scenario, as altitude increases, atmospheric pressure decreases. Therefore, as this parcel moves upward, it passes through regions of successively lower pressure This results in the expansion of the parcel of air. As the parcel expands, it cools adiabatically. Unsaturated air cools at the constant rate of 10° C for every 1,000 meters it rises. Descending air warms as it encounters increasing pressure at a rate of 10° C for every 1,000 meters it sinks.

Clouds

are defined as visible aggregates of minute droplets of water or tiny ice crystals. Clouds can consist of water droplets, ice crystals, or both!

What is rime?

deposit of ice crystals formed by the freezing of supercooled fog or cloud droplets on objects whose surface temperature is below freezing

Absolute instability

develops when the environmental lapse rate is greater than the dry adiabatic rate. Typically only found near the Earth's surface On hot, sunny days, the air above some surfaces is heated more. These pockets of air rise rapidly, generating small, fluffy white clouds.

Absolute stability

develops when the environmental lapse rate is less that the wet adiabatic rate. The most stable atmospheric conditions develop when temperatures increase with increasing altitude.

What is rain?

drops of water that fall from a cloud which has a diameter of at least 0.5 millimeters. Raindrops rarely exceed 5 millimeters in diameter

What is drizzle?

fine uniform drops of water having a diameter of less than 0.5 millimeters

Fog

is defined as a cloud with its base at or very near the ground. There is no physical difference between fog and clouds. The distinction between the two is how they form and where they form. Most fogs result from radiation cooling or the movement of air over a cold surface. Clouds result as air rises and cools adiabatically.

convective lifting

occurs when a mass of air is warmer and therefore less dense than the surrounding air

What is hail?

precipitation in the form of hard, rounded, pellets or irregular lumps of ice

What is snow?

precipitation in the form of ice crystals (snowflakes) or, more often, aggregates of crystals

What is glaze?

raindrops that fall and, upon impact, freeze resulting in a thick coating of ice on all solid objects.

What is sleet?

refers to the fall of small particles of ice that are clear to translucent

humidity

the amount of water vapor in the air

vapor pressure

the part of the total atmospheric pressure that can be attributed to the water-vapor content