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EARTH SCIENCE LECTURE
CHAPTER 23
23.1 Atmospheric Moisture
▪Water exists in the atmosphere mainly in its gaseous form called ________________.
▸Water in the atmosphere exists in ___________________________________
I. Heat Energy and Water
▸Terms you should know from this section:
–1)
–2)
–
____________________________ forms this way
–3)
II. Humidity
▸The amount of water vapor in the atmosphere is known as _____________________.
–
–
As water molecules evaporate into the air, the ______________________________.
When the air holds all the water vapor it can at a given temperature,
_________________________________________________.
▪The amount of water vapor that a volume of air can hold ________________________
_________________________________________________.
▸
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IIa. Relative Humidity
▸A common way to express the amount of water vapor in the atmosphere is by
relative humidity.
–
▸It compares the mass of water vapor ___________________________ with the
_______________________________________________ at its saturation
point.
▪Example:
▸1 m3 of air at a temperature of 200 C contains 13.9 g of water vapor.
It is known that
at the same temperature, 1m of air can contain 17.1 g of water vapor.
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– (present) 13.9 g/m3
–------------------------–
(saturated) 17.1 g/m
x 100 = 81%
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▪Changes in Relative Humidity:
▸1)
▸2)
▪Measuring Relative Humidity
▸ A _______________________________________ is an instrument used to measure
relative humidity
–
–
Sometime referred to as a “_________________________________________”
It consists of ___________________________________________.
–
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–
▪When the air is _______________, the rate of evaporation in the wick of the wetbulb thermometer _______________________________________.
▪The drier the air is, the more rapidly water evaporates from the bulb of the
wet-bulb thermometer and the more quickly the wet bulb cools.
▪The rate of evaporation will ___________________________________________.
▪Approximate relative humidity can be determined by using a table (Page 481)
▸ Example:
–
–
Dry Bulb Temp = 200 C
Wet Bulb Temp = 140 C
–What is the Relative Humidity??
▪Another instrument used to measure humidity is based on the fact that
__________________ stretches when the moisture in air increases.
▸A piece of human hair will stretch about _____________________ when the relative
humidity increases from __________________________.
–
The ____________________________________ is an instrument that records the
changing length of a bundle of hairs when humidity changes.
–A variation in length causes a pointer to move on a scale or causes a pen to
move on a graph, showing changes in relative humidity.
▪To measure humidity at _____________________, an __________________________
is used.
▸It may be taken up into the atmosphere in an instrument package known as a
______________________________, which is attached to a ____________________.
–
The electric hygrometer is triggered by passing an electrical current through a
moisture-attracting chemical substance.
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–The amount of moisture changes the electrical conductivity of the chemical
substance.
–The change can then be measured and expressed as the relative humidity of
the surrounding air.
Radiosonde
▪IIb. Specific Humidity
▸ Meteorologists use specific humidity to express the actual amount of moisture in air.
–
III. Dew Point
▪
▸ The temperature to which air must be cooled to reach saturation is called
____________________________________________.
At any temperature lower than the dew point,
▪The dew point temperature of air depends upon the amount of water vapor already
present in the air.
▸ When the air is nearly saturated with a relative humidity of nearly 100 percent,
only a small temperature drop is needed for air to reach its dew point.
–Dew is most likely to form on
▪If the dew point falls below the freezing temperature of water, water vapor will change
directly into solid ice crystals, or _____________________________.
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▸ Since frost forms from water vapor without first becoming liquid,
–____________________________, which is relatively uncommon, forms
as clear beads of ice.
23.2 Clouds and Fog
▪
_______________________________ are visible masses of tiny water or ice
particles suspended in the atmosphere.
▪Clouds result from the ________________________________________ throughout a
large volume of air.
▸ For water vapor to condense, a ___________________________________ must be
available on which condensation can take place.
▸ Although the troposphere contains no large solid surfaces, it does contain millions of
_______________________________________________________________.
–These suspended particles, called ____________________________, provide
the necessary surfaces for cloud-forming condensation.
▪Because the condensation nuclei are so small –
less than _______________ in
diameter – they remain suspended in the atmosphere for a long time.
▸Water molecules become attached to the particles, and as the molecules
collect, __________________________________ are formed.
▸In order for clouds to form,
▸When air temperature reaches the dew point, the air is saturated, and water vapor
begins to condense.
▸Because the amount of water vapor that air can hold decreases as temperature goes
down,
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▪Several processes may bring about the cooling necessary for clouds to develop:
▸ 1)
–
The higher layers of air compress the lower layers, the lower layers are more
dense and have a higher pressure.
–When air rises into a region with a lower atmospheric pressure, its
molecules move farther apart.
▸The work of expanding the distance between molecules of air uses potential energy
that is stored in compressed air.
▸ As this energy is used,
–
–
The lowering of the temperature of a mass of air due to its rising and expanding is
called ___________________________________________.
Just as expansion causes air to cool,
▪Changes in temperature that result solely from the expansion or compression of air are
called adiabatic temperature changes, or the _________________________________
▸ The adiabatic temperature changes associated with cloud formation take place at
predictable rates.
–Dry Adiabatic Rate:
–Wet Adiabatic Rate:
–This (WAR) occurs when TD is reached, condensation is occurring and
____________________________________________ is released.
▪Most clouds form by _____________________________________.
▸ On a sunny day, one area of the earth's surface may absorb more solar energy than do
the areas around it.
▸ The air above this area of extra warmth becomes heated through conduction.
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–The warmed air rises by convection and undergoes _____________________
and adiabatic cooling.
--
▪This level at which condensation forms, called the _____________________________,
is marked by the base of the clouds.
▸Further condensation allows clouds to expand above the condensation
level.
▪Often air does not rise spontaneously; rather,
▸The forced upward movement of air commonly results in the cooling of air
and in cloud formation.
▸Air can be forced upward when a moving mass of air meets sloping terrain,
such as a mountain range.
▪The forced rising air expands and cools, and clouds may form.
▸ The large areas of clouds evident during storms are also formed by
_______________________________________.
–These clouds are formed when a mass of warm air is pushed above
a denser mass of cooler air. (Discuss this later)
▪Clouds will also form when one body of moist air mixes with another body of moist air
with a different temperature.
▸ The mixing of the two bodies of air into one
▸ This temperature change may cool the combined air below its dew point.
–The result is
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▪_______________________________________ is cooling produced when wind carries
warm, moist air across a cold ocean or region of land.
▸ The __________________________________________ from the air, and the air
cools.
▸ If the air is cooled below its dew point, condensation and fog or cloud formation takes
place.
–Clouds formed by _____________________________________ are often
very low in the atmosphere.
II. Classification of Clouds
▪
Clouds are classified by two ways:
▸ 1)
▪
and
2)
Results in:
–
–
▪1)
▸
▸
▸
▪2)
▸
▸
▸
▸
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▪3)
▸
▸
▸
▪1)
▸
–A.
–B.
–C.
▪
▸
▸
▪2)
▸
▸
–A.
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–B.
▪3)
▸
–A.
– B.
– C.
▸
▸
▸
▸
▪4)
▸
▸
▸
▸
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▪A.
–
–
▪B.
–
–
–
–
III. Fog
▪Fog, like clouds, is the result of the condensation of water vapor in the air.
The chief difference between the fog and clouds is that fog forms very
____________________________________ of the earth when air close to the
ground is cooled.
▪1)
▸
–It results from the ________________________________________.
–You may be familiar with one type of fog because it results from the nightly
cooling of the earth.
–It is also called _________________________________.
▪Radiation fog usually forms on ______________________________________.
▸It is thickest in valleys and low places because the _____________________
in which it forms sinks to the lower elevations.
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▸Radiation fog is _________________________________________, where
there are more sources of smoke and dust particles to act as condensation
nuclei.
▪2)
▸
–Advection fog is common along __________________________, where
warm, moist air from above the water moves in over a cooler land surface.
–Dense fogs may form over the ocean when warm, moist air is carried over
_________________________________________.
▪3)
▸ This is formed by the _________________________________________________
of air as it rises along _______________________________.
–Upslope fog is really a kind of cloud formation at __________________
▪4)
▸ This usually forms over _______________________________________________.
–Steam fog is a _________________________ of fog formed when
__________________________________________________.
23.3 Precipitation
▪Any moisture that falls from the air to the earth's surface is called
______________________________________.
▪It’s either in __________________________________________________.
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▪The four major types of precipitation are:
▸
▪1)
▸If the raindrops are smaller than _______________________ in diameter, it is
called _______________________________.
–
Drizzle results in ____________________________________________________
▸__________________ are between ___________________________________.
▪Lab Condensation Rates:
▸1 second == 0.01 mm
▸10 minutes == 0.1 mm (cloud droplet)
▸3 hours == 1.0 mm (small raindrop)
▸24 hours == 3.0 mm (medium raindrop)
▪2) The most common form of solid precipitation is ____________________________,
which consists of ice particles.
These particles may fall as __________________________,
___________________________________, or as
____________________________________.
▸Most snow takes the form of _________________________________.
▸Snowflakes may be as small as several millimeters in diameter or as large as several
centimeters.
▸
–
This size difference occurs because ______________________________________.
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▪3)
Extremely cold temperatures near the ground sometimes produce clear ice pellets
called _______________________________, which forms when rain falls
through a layer of freezing air.
▸
–
It forms a thick layer of _____________________________________.
–Conditions that produce glaze ice occur in what is called an
___________________________________________.
▪4) _______________ is solid precipitation in the form of lumps of ice.
▸ These lumps can be nearly _______________________________________.
▸ Hail usually forms in ____________________________________________
–___________________________ within the clouds carry raindrops to high
levels, where they freeze.
–As the frozen raindrops fall, they accumulate additional layers of liquid water
on their surface.
▸Hailstones often consist of alternate _______________________________________.
–
The clear ice
–
The cloudy layer
II. Causes of Precipitation
▪A cloud produces precipitation when its droplets or ice crystals become large enough to
fall as rain or snow.
▸ Most cloud droplets have a diameter of about _____________________________.
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–A micrometer equals
▪One way cloud droplets reach the precipitation stage is in a process called
________________________________________.
▸ Coalescence involves differences in ______________________________________.
–
▪
▸Large droplets drift downward and, in doing so, collide and combine with
smaller droplets.
▸Each large droplet continues to coalesce until it contains at least a million
times as much water as it did originally.
▸
▪Precipitation may also form in clouds that contain water vapor, ice crystals, and
water
droplets that have gone through ____________________________________.
▸Supercooled water droplets have a temperature of ____________________________.
–The temperature of water droplets in these cold clouds may fall as
_______________________.
▪Yet even at this low temperature the water droplets __________________________.
▸
Freezing nuclei are
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–Because only a few ice crystals will form, most of the water in the cloud
remains as supercooled water droplets.
▪Molecules evaporate more rapidly from the supercooled water droplets and condense on
the ice crystals.
▪The ice crystals increase in size until
▪It is believe that almost all
▸
▪Knowing how ice crystals form in clouds, meteorologists are able to take the first steps
toward producing rain when it is needed.
▸The method used in attempting to cause or increase precip. Is called
_____________________________________.
▪In cloud seeding,
▸In one method of cloud seeding, _____________________________,
which resemble _________________________, are used as freezing
nuclei.
▪A _____________________________ is an instrument for measuring the amount of
rainfall.
▪One type of rain gauge consists of a
▸ Rainwater passes through the funnel into the container below.
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▪In many rain gauges the mouth of the funnel is much larger than the container under
it.
▪Another type of rain gauge consists of a
▸Rain caught in the funnel fills one side of the bucket.
▸The bucket then tips, dumping the water and allowing the other half to fill up.
▸Each time one side of the bucket fills with 0.25 mm of rainwater, it tips and sets
off an electrical device that records the amount.
▸The rainwater dumped from the bucket is collected and weighed to check the
accuracy of the record.
▪A third type of gauge catches the water in a large bucket that _____________________
continuously.
▸The weight is recorded directly on a graph as ______________________.
▪Snow is measured by both the depth of accumulation and the water content.
▸ The water content is determined simply by melting the snow and measuring the
amount of water that results.
–The amount of water contained in any given volume of snow
depends on _________________________________.
▪As much as
▪Only
▸
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