Transcript Slide 1

Humidity and Condensation
Water is unique because it is the only substance that
commonly exists in all ____________________________ of matter.
Depending upon temperature, water can be a _____________, a
_________________ or a ________________.
Water is in a solid state at temperatures of _______ or below,
appearing as ice, __________________, _____________________
and ice crystals.
Water is in a liquid state between _________ and ________________,
present as _______________ and cloud droplets.
At _________________ or above, water evaporates and enters
the atmosphere as _________________________________, an invisible gas.
The bubbles in boiling water are an example of
water vapor.
___________________ and _____________________ are liquid droplets, not gas.
Although you can't see water vapor, sometimes you can feel it. The
more water vapor the air contains, the more ________________________ the air feels.
Water often changes state in the
atmosphere. Changing from one
state to another requires ________________ to
either be ___________________ or given off.
Condensation occurs when water
vapor becomes a ________________- this
creates ____________, _______________
and clouds.
The opposite of condensation is ____________________________. While
condensation ___________________ heat, evaporation __________________ heat.
So condensation slows down
the rate at which air _______________.
Evaporation, by contrast, is a
_______________ process. After you
get out of a swimming pool
you may feel chilly, because
the water molecules on your
skin are stealing ____________ from
your body as they evaporate.
Frost forms by _____________________ when water
vapor condenses as a solid.
Snow often disappears as much through
________________________ as by evaporation.
Sublimation is when water changes
directly from a ______________ to a ___________,
without becoming a liquid.
The amount of water vapor present in the air varies widely.
The actual amount of water vapor in the air at a given time
and place is called the ________________________________________.
It is expressed as the number of grams of water vapor per
________________________________. On a humid summer day, for example, the
humidity may be about ______________________ per kilogram.
There is a limit to the amount of water vapor that can be present in the air.
Imagine a fish tank with a glass lid.
Some water molecules have enough
energy to escape from the
surface and become ______________________.
Other water vapor molecules lose
energy and return to the liquid
state though _____________________.
When there is so much water vapor in the air that the rate of
condensation _________________ the rate of evaporation, the air is ______________________.
If any more water evaporates into saturated air, an _______________________________ will
__________________. This explains why _________________________ may form on the lid
of the fish tank. These drops confirm that as water continues to _______________________,
an equal amount of water condenses from the ___________________________ air.
The amount of water vapor present in saturated air depends upon
the _____________________________ of the air. The warmer the air, the ___________
water vapor it can contain. The water vapor _____________________ of air roughly
doubles for every rise in air temperature of about ___________
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Relative Humidity
When meteorologists refer to the relative humidity,
they are telling us how near the air is to its ___________________
capacity for holding water.
Relative humidity compares the ___________________ amount of
water vapor that is present in air with the
maximum amount of water vapor that can be present
at a given __________________________________________________.
It is usually stated as a ______________________. Saturated air has a relative humidity
of ______________; air that contains no water vapor has a relative humidity of _____________
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To calculate the relative humidity of a kilogram of air, _________________ its
specific humidity by its maximum capacity.
If the air holds 11 grams per kg of water vapor and it can contain
at most 22 grams per kg, then it holds half of the water vapor it
can contain.
Thus, its relative humidity is _______________.
Measuring humidity
Humidity is typically measured with a
________________________ - an instrument that works on the
principle that evaporation causes _______________.
A psychrometer consists of ________ thermometers.
One is a __________________ thermometer that shows the
air temperature. The other is a ______________________
thermometer that has a water-soaked wick
wrapped around its bulb.
The wet-bulb thermometer usually has a ____________________ temperature
because water evaporating from the wick cools the wet bulb. The
drier the air, the ____________________ the difference in the readings. If both the
wet-bulb and the dry-bulb thermometers read the same, this shows
that ______________________ is evaporating from the wet bulb, and the air must be
____________________________.
Relative humidity can be determined by using a _____________________
along with a __________________ like the one on the next page.
Condensation
At night, the air _____________________________. Its ability to contain water vapor
_________________________. The air becomes ___________________________.
If the air continues to cool past the point of saturation, __________________________ occurs.
The water vapor may condense into
droplets, forming clouds or ____________.
If the water vapor condenses on a
surface, such as grass, it's called ____________.
The temperature at which saturation occurs and condensation begins
is called the ______________________.
Name: _______________________________________________
The dew point is a measure of the amount of _____________________________ in the air.
The more water vapor the air contains, the ________________the air has to cool in order for
condensation to start, so the _______________________the dew point.
Cooling and Condensation
Two conditions are necessary for water vapor to condense.
1 - There must be ______________________ for water vapor
to condense onto and,
2 - Air must cool to or below its ________________________.
When fog or clouds form, the water
vapor is condensing on tiny particles
called ___________________________________.
Condensation nuclei are usually substances
such as _________________, sulfate particles or nitrate particles.
The salts usually come from ___________________
evaporating. The sulfates and
nitrates come from natural sources
and from the burning of _______________________.
These particles are so small
that one puff of smoke
contains _________________________ of
condensation nuclei.
The cooling of the air occurs in the following ways:
- _________________ with a colder surface.
- radiation of heat
- mixing with colder air
- ____________________ as it rises
Dew and frost form when moist air contacts a colder surface.
Fog forms when air cools through contact and mixing.
Even when air is cooled below its dew point, condensation into fog or
clouds may not occur if there are no __________________________________________ available.
Formation of Dew and Frost
When air cools to its dew point through
___________________________________________,
water vapor condenses directly onto that surface.
If the temperature is above ______, dew forms.
If the air temperature is below 0 C, the water
vapor becomes frost through _______________________. This
type of frost is often called a "killing frost"
because it causes liquid in the cells of some
plants to _____________________. As liquid water freezes, it
expands, bursting the cell walls and killing
the plants.
Formation of Fog
Fog forms when a cold surface cools the ________________________________ air above it.
As water vapor condenses in the air, tiny droplets fill the air and
form fog. Each droplet is centered around a condensation nucleus.
The droplets are so tiny that they fall slowly. The slightest air
movement keeps them ________________________________ in the air. At very cold
temperatures, the fog may consist of tiny _______________________________.
________________________________ Fog
- forms when the night sky is _____________________and the ground loses heat
rapidly through _____________________________. As the ground cools, light winds
mix the cooled bottom air with the warmer air just above it.
Eventually, the whole _____________________cools to its dew point.
The radiation fog occurs at ground level and is _____________________ than the air
above it. This arrangement of cold air beneath warm air is called a
__________________________________________________.
Radiation fogs are common in ______________________________ near rivers or lakes.
They are most frequent in the __________________________ and in winter. These fogs
are thickest in the early morning and are “________________________________" by the
later morning sunshine.
_________________________________ Fog
- forms when warm, moist air _______________________________________________.
In the northern US and southern Canada, advection fogs form when
warm, moist ____________________________ winds blow over ______________-covered ground.