Chapter 17

As a psychrometer, which is used to measure relative humidity, consist of a wet bulb and a dry bulb thermometer. Circle the correct answers in the following statement: as water molecules evaporate from a wet bulb they (a)___________ heat, causing the wet bulb to become (b)___________ than the dry bulb period

(a) release (b) colder

From the altitude where condensation begins until the air reaches the top of the mountain, the rising air will continue to expand and recall at a rate of about ________. What term is applied to this rate of cooling?

- 5 degrees Celsius per 1000 meters - Wet Adiabatic Rate

What are all of the phase changes that would release heat into the air?

- Vapor changes to liquid - Liquid water changes to ice - Vapor changes to frost

Which of the following molecules have the highest, lowest, and medium kinetic energy? -Water vapor molecules -Frozen water molecules -Liquid water molecules

-(Highest) Water vapor molecules -(Medium) Frozen water molecules -(Lowest) Liquid water molecules

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: At what elevation will clouds begin to form (with relative humidity=100%)?

1 km

At what rate will the temperature of the rising air change?

10 degrees Celsius/1000 meters

The cumulonimbus cloud pictured on figure 17.28 is roughly 12 kilometers tall, 8 kilometers wide, and eight kilometers long period assume that the droplets in each cubic meter of the cloud total .5 cubic centimeters. How much liquid does the cloud contain? How many gallons is this? (Note: 3785 cm3 = 1 gallon.)

101,453,104.36 gallons

Weather radar provides information on the intensity of precipitation in addition to the total amount of precipitation that falls over a given time period. Table C shows the relationship between radar reflectivity values and rainfall rates. If radar measured a reflectivity value of 47 dBZ for 2 1/2 hours over a location, how much rain will have fallen there?

3.25 inches of rain will have fallen.

Refer to table 17.1 to answer this question. How much more water is contained in saturated air at a tropical location with a temperature of 40 degrees Celsius compared to a polar location with a temperature of -10 degrees Celsius?

45 grams

The accompanying graph shows how air temperature and relative humidity change on a typical summer day in the Midwest. Assuming that the dew point temperatures remain constant, what would be the best time of day to water a lawn to minimize evaporation of the water spread on the grass?

5 AM

Compare absolute instability and conditional instability.

Absolute instability is when air low in the atmosphere is warmer than air aloft, making the ascending air warmer than its environment and having a tendency to continue rising. Conditional instability is when the atmosphere is stable if the air parcel is unsaturated but unstable if the parcel is saturated.

As rain falls through very dry air, much or all of the rain may evaporate. As this falling rain evaporates, the water molecules ___________.

Absorb heat from their surroundings as liquid changes to vapor.

When air temperature remains constant will adding water increase or decrease relative humidity?

Adding water vapor will increase relative humidity.

What are the advantages and disadvantages of using rain gauges compared to weather radar in measuring rainfall?

Advantages: larger area coverage than rain gauge (rain gauge is single point location); continual data collection transmitted real time Disadvantage: radar estimates precipitation via mathematical algorithms which may under- or overestimate actual totals.

A fog formed when warm, moist air is blown over a cool surface

Advection Fog

During hot summer weather, many people put koozies around their beverages to keep the drinks cold period in addition to preventing a warm hand heating the container through conduction, what other mechanisms slow the process of warming beverages?

Air

Briefly describe the two ways relative humidity can change in nature

Air temperature and rain

Describe absolute stability in your own words.

Air tends to return to the surface rather than continuing to rise. This is true even if the parcel of air were forced above the condensation level.

White to gray clouds often composed of separate globules; "sheep back" clouds.

Altocumulus

Stratified veil of clouds that are generally thin and may produce very light precipitation. When thin, the Sun or Moon may be visible as a bright spot, but no halos are produced.

Altostratus

Why does air cool when it rises through the atmosphere?

As air rises, it enters a region of fewer air molecules. The air expands and as it does so it cools.

Cloud droplets form and grow as water vapor condenses onto hydroscopic condensation nuclei. Research has shown that the maximum radius for cloud droplets is about 0.05 millimeters. However, typical raindrops have volumes thousands of times greater. Explain how cloud droplets become raindrops.

As cloud droplets fall, they fall into many other droplets which causes them to combine into a bigger drop.

The contents of an aerosol spray can are under very high pressure. Explain why the spray feels cold when it is allowed to escape the container.

As the contents are released, they expand; therefore the contents cool with expansion

Describe how the amount of water vapor needed for saturation relates to temperature.

As the temperature gets higher, the amount of water vapor needed gets higher.

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: Determine the air temperature and dew point temperature for the air parcel at each location (B-G) shown on the diagram.

B: Air Temperature- 17° Celsius Dew-Point Temperature- 17° Celsius C: Air Temperature- 12° Celsius Dew-Point Temperature- 12° Celsius D; Air Temperature- 7° Celsius Dew-Point Temperature- 7° Celsius E: Air Temperature- 17° Celsius Dew-Point Temperature- 7° Celsius F: Air Temperature- 27° Celsius Dew-Point Temperature- 7° Celsius G: Air Temperature- 37° Celsius Dew-Point Temperature- 7° Celsius

Explain why the air in a cool basement is relatively humid or damp in the summer.

Basements take hold so the relative humidity goes up.

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: Compare the air temperatures at point A and G. Why are they different?

Because it is completely dry where G is located, and A has clouds and precipitation moving above it.

Explain how the absorption of latent heat accounts for the temperature changes that occurred before the ice melted as compared to after the ice melted.

Before the ice melted, there was heat being released. After the ice melted, there was heat being absorbed.

Refer to the data for Phoenix, Arizona, and Bismarck, North Dakota, in table B, to complete the following: In which city is the air closest to its saturation point with respect to water vapor?

Bismarck, ND

Refer to the data for Phoenix, Arizona, and Bismarck, North Dakota, in table B, to complete the following: Which city has a higher relative humidity?

Bismarck, ND

Thin, white, ice-crystal clouds in the form of ripples, waves, or globular masses, all in a row. May produce a "mackerel sky." Least common of the high clouds.

Cirrocumulus

Thin sheet of white, ice crystal clouds that may give the sky a milky look. Sometimes produce halos around the sun or moon

Cirrostratus

Thin, delicate, fibrous, ice-crystal clouds. Sometimes appear as hooked filaments called "mares' tails"

Cirrus

What is the basis for the classification of clouds?

Clouds are classified by their form and their height in the atmosphere.

What types of clouds and precipitation, if any, form when stable air is forced aloft?

Clouds tend to be thin layers with minimal to no precipitation.

Which phase change is the reason a meteorologist might comment that a particular storm "has lots of energy?"

Condensation

What is the difference between precipitation and condensation?

Condensation is when water vapor forms liquid cloud droplets. Precipitation is when these cloud droplets fall to the ground.

List four mechanisms that cause air to rise.

Convective lifting, orographic lifting, frontal wedging, and convergence.

If the amount of water vapor in the air remains constant, will cooling the air raise or lower the relative humidity?

Cooling will raise the relative humidity.

Towering cloud sometimes spreading out on top to form an "anvil head." Associated with heavy rainfall, thunder, lighting, hail, and tornadoes.

Cumulonimbus

Dense, billowy clouds, often characterized by flat based. May occur as isolated clouds or closely packed.

Cumulus

How does frost form?

Deposition of water vapor to a solid that is at or below freezing.

How is the formation of dew different from cloud formation?

Dew forms on the surface when Earth experiences radiation cooling. Clouds form as air rises and cools adiabatically at warmer times of day.

Small uniform drops that fall from stratus clouds, generally for several hours.

Drizzle

Which change is responsible for releasing the heat that makes the Chinook winds warm?

Evaporation

Define fog.

Fog is a cloud with its base at or near the ground.

Which phase change is the reason for the temperature increase at the end of the experiement?

Freezing

Fog formed when rain evaporates as it falls through a layer of cool air.

Frontal Fog

Produced when supercooled raindrops freeze on contact with solid objects. Glaze can form a thick coating of ice having sufficient weight to seriously damage trees and powerlines.

Glaze

Sometimes called soft hail, ________ forms when rime collects on snow crystals to produce irregular masses of "soft" ice. Because these particles are softer than hailstones, they normally flatten out upon impact.

Graupel

Precipitation in the form of hard, rounded pellets or irregular lumps of ice. Produce in large cumulonimbus clouds, where frozen ice particles and supercooled water coexist.

Hail

Most of the water in the clouds over Alabama come from the Gulf of Mexico. What do water molecules absorb as they evaporate from the ocean?

Heat

When water evaporates, is heat absorbed or released?

Heat is absorbed.

Write a general statement describing the relationship between temperature and relative humidity throughout the time period shown in the figure.

High air temperature equals low relative humidity.

Describe how water vapor content of air saturation is related to air temperature.

Higher temperatures require more water vapor to reach saturation.

If the amount of water vapor in the air remains unchanged, how does a decrease in temperature affect relative humidity?

It causes an increase in relative humidity

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: How did the water vapor content of the air change as the parcel of air transverse the mountain? (Hint: compare dew point temperatures.)

It decreased because it reached dew points

What do meteorologists mean when they use the word parcel?

It is a volume of air that acts independently of the air around it.

What is latent heat?

It is energy that is stored in water and not released to its surroundings.

The accompanying photo shows a cup of hot coffee. What state of matter is the "steam" rising from the liquid? Explain your answer.

It is in the state of evaporation because water particles are rising from the liquid.

Why does the adiabatic rate of cooling change when condensation begins? Why is the wet adiabatic rate not a constant number?

Latent heat of condensation stored in the water molecule is released. The wet adiabatic rate is not constant because the amount of latent heat released depends on how much moisture is present in the air.

On a warm summer day when the relative humidity is high, it may seem even warmer than the thermometer indicates. Why do we feel so uncomfortable on these muggy days?

Less water vapor is able to evaporate from our skin

What is supercooled water?

Liquid water at temperatures below freezing is referred to as super cold.

Droplets large enough to be felt on the face when air is moving 1 meter/second. Associated with stratus clouds.

Mist

List three measures that are used to express humidity.

Mixing ratio, relative humidity, and dew point temperature.

Amorphous layer of dark gray clouds. Some of the chief precipitation-producing clouds

Nimbostratus

What causes the Florida peninsula to experience the greatest frequency of mid-afternoon thunderstorms in the United States?

On warm days, there is a convergence of air from two large water bodies and one landmass. Speed of the air moving off the water is reduced over land, causing air to pile up, generate uplift, and create thunderstorm clouds.

How do orographic lifting and frontal wedging force air to rise?

Orographic lifting occurs when a laterally-moving mass of air encounters elevated terrain; it is forced up the mountainside. Frontal wedging occurs when warm and cold air collide, generating a front and forcing the warmer, less dense air to rise.

In which city would it be easier to stay cool by perspiring? Explain your choice.

Phoenix

Refer to the data for Phoenix, Arizona, and Bismarck, North Dakota, in table B, to complete the following: In which city does the air require the most water vapor in order to reach saturation?

Phoenix, AZ

Refer to the data for Phoenix, Arizona, and Bismarck, North Dakota, in table B, to complete the following: Which city has the greatest quantity of water vapor in the air?

Phoenix, AZ

Fog resulting from radiation heat lost from earth.

Radiation Fog

Why does radiation fog form mainly on clear nights rather than on cloudy nights?

Radiation fog forms when earth's surface cools rapidly. Earth's surface cools easier at night when there are no clouds because clouds act as a blanket.

Generally produced by nimbostratus or cumulonimbus clouds. When heavy, it can show high variability from one place to another.

Rain

How does relative humidity change when water vapor content is reduced?

Reducing water vapor will decrease relative humidity.

In the winter, air in homes is heated. What effect does heating have on the relative humidity inside the home? What can be done to lessen this effect?

Relative humidity decreases. You can get a humidifier.

Describe the relationship between the difference in the dry bulb and wet bulb temperatures compared to the relative humidity of the air.

Relative humidity is higher when the difference is lower.

What happens to relative humidity when the air temperature is increased?

Relative humidity lowers when temperature increases.

As the air descends in warms on the Leeward side of the mountain, will its relative humidity increase or decrease?

Relative humidity will decrease.

As winds forced very humid air up the western slopes of mountains in some regions of the western US, the air is cooled by expansion, causing clouds to form. As vapor changes to solid cloud crystals, the water molecules ___________.

Release heat, making the surrounding air warmer

Deposits usually consisting of ice feathers that point into the wind. These delicate, frostlike accumulations form as supercooled cloud or fog droplets encounter objects and freeze on contact.

Rime

At what height will the rising air reach its dew point temperature and water vapor begin to condense?

Rising air will reach dew point at 1000 meters.

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: Where in the United states might you find a situation like what is pictured here?

Sierra, Nevada

Small, spherical to lumpy ice particles that form when raindrops freeze while falling through a layer of subfreezing air. Because the ice particles are small, damage, if any, is generally minor. Can make travel dangerous.

Sleet

How is sleet different from glaze? Which is usually more hazardous?

Sleet is frozen rain that freezes before hitting the ground as ice pellets. Glaze does not freeze until it hits a surface that is below freezing. Glaze is more hazardous.

The crystalline nature of snow allows it to assume many shapes, including six-sided crystals, plates, and needles. Produced in supercooled clouds, where water vapor is deposited as ice crystals that remain frozen during their descent.

Snow

Explain why snow can sometimes reach the ground as rain, but the reverse does not occur.

Snow is an aggregation of ice crystal formed in clouds; it cannot form from falling droplets of rain. Snow can, however, melt into liquid raindrops.

Fog having the appearance of steam, produced by evaporation from a warm water surface into the cool air above.

Steam Fog

Soft gray clouds in globular patches or roll.s Rolls may join together to make a continuous cloud.

Stratocumulus

Low uniform layer resembling fog but not resting on the ground. May produce drizzle.

Stratus

Describe the Bergeron process in your own words.

Supercooled water exists below freezing in cloud tops with few condensation nuclei. As ice crystals form in this environment, they create a condensation nuclei, allowing the supercooled water to help the ice crystals grow in size. These ice crystals begin their descent as snowflakes but generally warm enough to melt into raindrops before hitting the ground.

Assume that the relative humidity of the air is below 100% during its descent to the valley. At what rate will the temperature change?

Temperature will change at 10 degrees Celsius/1000 meters.

As the air descends the Leeward side of the mountain, will it expand or be compressed?

The air will expand.

As the air moves up the windward side of the mountain, will it get cooler or warmer?

The air will get cooler.

Is the amount of latent heat associated with the process of deposition (the same as or less than) the total energy required to condense water vapor and then freeze the water?

The amount of latent heat is less than the total energy required.

Explain the difference between the environmental lapse rate and adiabatic cooling.

The environmental lapse rate is a measure of the actual temperatures of the air as you move upwards or downwards in the troposphere. Adiabatic cooling is a change in temperature caused by expansion or compression as a parcel of air rises or descends.

When sweat (mostly liquid water) evaporates from your skin, why does this help to cool your body?

The evaporation absorbs the heat.

As you drink an ice-cold beverage on a warm, humid day the outside of the glass or bottle becomes wet. Explain.

The glass is cooler than the surrounding air and provides a surface on which the water vapor in the air can condense into a liquid.

How do relative humidity and mixing ratio differ?

The mixing ratio is a ratio of the mass of water vapor to the mass of dry air while relative humidity is the ratio of water vapor content in the air to water vapor content potential of the air.

Which winter storm is likely to produce deeper snowfall: a low pressure system that passes through the Midwestern states of Nebraska, Iowa and Illinois (26 degrees Fahrenheit average temperature at the time of the storm) or exactly the same system passing through North Dakota, Minnesota, and Wisconsin (16 degrees Fahrenheit average temperature at the time of the storm).

The storm passing through North Dakota, Minnesota, Wisconsin.

Will the temperature of the descending air increase or decrease?

The temperature will increase.

TV weather broadcasters occasionally say that a storm has "lots of energy," indicating that it has greater potential for precipitation and wind. Why is it that storms with "lots of moisture" would also have "lots of energy?"

The water molecules in the air absorb heat in order to evaporate from the ocean.

Explain why the Great Basin areas of the western United States are dry. What term is applied to this situation?

These areas are called rain shadow deserts. They are dry because they are on the leeward side of a mountain, where much of the moisture has been lost from the air as it moves over the mountain range, largely due to cooling and condensation due to orographic lifting on the other side of the mountain.

Why are high clouds always thin?

They are made of ice crystals and there are small quantities of water vapor at those heights.

What is function of condensation nuclei in cloud formation?

They give the water vapor something to condense onto.

Explain why mountains might cause dry conditions on their Leeward sides.

They have high temperatures and low relative humidity.

Is the air at sea level saturated or unsaturated?

Unsaturated

Describe the weather associated with unstable air.

Unstable air tends to generate thunderstorms, towering clouds, and possibly tornadoes.

Fog created when air moves up a slope and cools adiabatically.

Upslope Fog

What are clouds made of?

Visible aggregates of minute droplets of water or tiny crystals of ice.

Summarize the processes by which water changes from one state of matter to another. Indicate whether energy is absorbed or released.

Water can change from a solid to a liquid via melting, from a liquid to a gas via evaporation, or from a solid to a gas via sublimation. These processes all absorb energy. Water can change from a gas to a liquid via condensation, from a gas to a solid via deposition, or from a liquid to a solid via freezing. These processes all release energy.

In which state of matter is water compressible?

Water is compressible when it is in a liquid state.

a. In which state of matter is water densest?

Water is densest when it is frozen.

In which state of matter are the water molecules most energetic?

Water molecules are most energetic when they are vapor.

When a hard frost is expected, orange growers may spray their trees with water to help keep the oranges from freezing. As the water on the oranges freeze, the ice provides insulation for the fruit within. Also, as the water freezes, this helps prevent the fruit from freezing because ___________.

Water molecules release heat as they change from liquid to ice.

During condensation, do water molecules absorb or release heat?

Water molecules release heat.

Explain why relative humidity does not give an accurate indication of the actual amount of water vapor in the air.

Water vapor content depends on the temperature as well.

What is a common example of sublimation?

When dry ice (solid) turns directly to vapor.

The primary mechanism by which the human body cools itself is perspiration. Explain how perspiring cools the skin.

When people sweat, evaporation is occurring. When evaporation occurs, heat leaves with it because it is being absorbed by the water molecules.

What conditions favor the collision-coalescence process?

When the clouds are warm.

The accompanying diagram shows air flow from the ocean over a coastal mountain range. Assume that the dew point temperature remains constant in dry air (that is, relative humidity less than 100% ). If the air parcel becomes saturated, the dew point temperature will cool at the wet adiabatically rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: On which side of the mountain might you expect lush vegetation, and on which side would you expect desert like conditions?

Windward would have vegetation, Leeward would have desert conditions.

The water molecules absorb heat if they change ___________.

from a phase where they have less kinetic energy to a phase where they have more kinetic energy

List five main types of fog and describe how each types of forms.

• Radiation fog - air near the surface is close to saturation and a small amount of radiative cooling allows vapor in the air to condense. • Upslope fog - humid air moves up a slope, adiabatically cools, and reaches the dew point along the surface. • Evaporation fog - water vapor is added to the air at the surface and it condenses. • Steam fog - cool air moves over warm water, allowing water evaporated from the water surface to cool and condense. • Frontal fog - with frontal wedging, warm air is lifted over cold air that is at or near the dew point, causing enough rain to evaporate and generate fog.

List the forms of precipitation and the circumstances of their formation.

• Rain - forms in nimbostratus clouds or towering cumulonimbus clouds. • Snow - forms when temperatures are below freezing. • Sleet - precipitation starts to fall as a liquid but freezes into ice pellets before hitting the ground. • Glaze - precipitation falls as a liquid but freezes upon contact with the ground or other surface at or below freezing. • Hail - produced in cumulonimbus clouds where ice pellets are repeatedly blown back into cloud tops by updrafts. It is a summer phenomenon. • Rime - ice crystals form when supercooled fog or cloud droplets freeze on a surface that is below freezing.

Which cloud types are associated with the following characteristics: thunder, halos, precipitation, hail, lightning, mares' tails?

• Thunder - cumulonimbus • Halos - cirrostratus • Precipitation - stratus, nimbostratus, cumulonimbus • Hail - cumulonimbus • Lightning - cumulonimbus • Mares' tails - cirrus