Transcript Moisture, clouds, and precipitation

Moisture, clouds, and
precipitation
BELL RINGER:
1.What are the physical properties of a fluid?
2.Do you think air is fluid? Why or why not?
3.How could you possibly demonstrate that air is fluid?
HOMEWORK:
Mind Map on Cloud formation DUE 12/5-6
Children’s Book
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Weather
S Driven by the power of the SUN, weather is a series of
CYCLES.
S Water evaporates, rises, cools, and falls as rain, only to
evaporate once again.
S The sun rises and sets every day, with the air warming and
cooling in response, and the cycle endlessly repeating.
Weather Continued
S Weather, in all its cycles and clashes, arises from a simple
fact: the sun heats some parts of the Earth more than
others.
S Earth is a globe with a 23.5 degree tilt, therefore the sun’s
rays heat the Earth unevenly.
S Energy moves from HIGH concentrations to LOW
concentrations.
S The sun heats the equator and it begins to flow out towards
the poles seeking to equalize the difference in
TEMPERATURE. This is what fuels weather!
Water in the atmosphere
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When it comes to understanding
atmospheric processes, water
vapor is the most important gas
in the atmosphere.
Water and its Changes
S A change in state requires an energy transfer, usually in the
form of heat.
S Solid to Liquid
S Melting is and example.
S Latent heat is the energy absorbed or released during a change in
state, but does not produce a temperature change. Ice = 0 degrees
and Ice water = 0 degrees and (hidden heat-important in weather).
Water and its Changes
S Liquid to Gas
S Evaporation is the process of changing a liquid to a gas.
S Condensation is the process where a gas, like water vapor,
changes to a liquid, like water.
S Solid to Gas
S Sublimation is the conversion of a solid directly to a gas
without passing through the liquid state.
S Deposition is the conversion of a vapor directly to a solid.
Frost is an example of deposition.
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Humidity
S Humidity is a general term for the amount of water vapor in air.
S Meteorologist use RELATIVE HUMIDITY and DEW
POINT to measure the amount of water vapor in the air.
S Saturated
S Air is saturated when it contains the maximum quantity of
water vapor that it can hold at any given temperature and
pressure.
S When saturated, warm air contains more water vapor than
cold saturated air.
Relative Humidity
S Relative humidity is a ratio of the airs actual water-
vapor content compared with the amount of water
vapor air can hold at that temperature and pressure.
S 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.
Dew Point
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Dew point is the temperature to
which a parcel of air would need
to be cooled to reach saturation.
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Dew forms at night because
temperatures near the ground cool
below the dew point causing
condensation.
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A high dew point (above 65) makes
it feel sticky. High dew point
indicates high humidity and a low
dew point indicates low humidity.
Measuring Humidity
S A hygrometer is an instrument to measure relative
humidity.
S A psychrometer is a hygrometer with dry- and wet-bulb
thermometers. Evaporation of water from the wet bulb
makes air temperature appear lower than the dry bulb’s
measurement. The two temperatures are compared to
determine the relative humidity. Remember the drier the
air, the faster the evaporation so the cooler the temperature
of the wet bulb.
Cloud Formation
S Condensation may form dew, fog, or clouds.
S Air compression and expansion
S When air is compressed, the motion of the gas molecules
increase and the air temperature rises. The opposite is true
when it expands.
Adiabatic Temperature Changes
S Temperature changes that occur even though heat energy
isn’t added or subtracted is adiabatic temperature changes.
S When air is allowed to expand, it cools, and when it is
compressed, it warms.
S Expansion and Cooling
S Dry adiabatic rate is the rate of cooling or heating that applies
only to unsaturated air.
S Wet adiabatic rate is the rate of adiabatic temperature change
in saturated air.
Adiabatic Temperature Changes
S Ascending air encounters lower pressure, rises, expands and
cools.
S Descending air encounters higher pressure, compresses, and
heats
S This rate in unsaturated air is the dry adiabatic rate.
Adiabatic Temperature Changes
S When a parcel of air rises high enough it will reach its dew
point. This is when condensation occurs.
S The latent heat is released. This works against the cooling
process and causes a slower rate of cooling called the wet
adiabatic rate.
S Dry adiabatic rate is from the surface to the condensation
level. The wet adiabatic rate begins at the condensation
level.
Cloud Formation
S Clouds form when air is cooled to its dew point or the
temperature, if the air is cooled, it reaches saturation.
S Air can reach saturation in a number of ways. The most
common way is through lifting.
S As a bubble or parcel of air rises it moves into an area of
lower pressure. As this occurs the parcel expands.
S This requires energy, or work, which takes heat away from
the parcel. So as air rises it cools. This is called an adiabatic
process.
Cloud Formation
S Since cold air can hold less water vapor than warm air,
some of the vapor will condense onto tiny clay and salt
particles called condensation nuclei.
S The reverse is also true. As a parcel of air sinks it encounters
increasing pressure so it is squeezed inward. This adds heat
to the parcel so it warms as it sinks.
S Warm air can hold more water vapor than cold air, so
clouds tend to evaporate as air sinks.
Lifting of Air
S Four mechanisms that can cause air to rise are
orographic lifting, frontal wedging, convergence, and
localized convective lifting.
S Orographic Lifting
S Orographic lifting occurs when mountains act as barriers to
the flow of air, forcing the air to ascend.
S The air cools adiabatically; clouds and precipitation may
result.
S Frontal Wedging
S A front is the boundary between two adjoining air masses
having contrasting characteristics.
S Convergence
S Convergence is when air flows together and rises.
S Localized Convective Lifting
S Localized convective lifting occurs where unequal surface
heating causes pockets of air to rise because of their buoyancy.
Stability
S Stable air tends to remain in its original position, while
unstable air tends to rise.
S Stability Measurements
S Air stability is determined by measuring the temperature of the
atmosphere at various heights.
S The rate of change of air temperature with height is called the
environmental lapse rate.
S The density difference in air causes stable air to stay in its
same position and unstable air tends to rise.
S The rate at which the air cools with increasing elevation is
called the environmental lapse rate.
S Air is stable when the temperature decreases gradually with
increasing altitude.
S The most stable air conditions occur when the air
temperature increases with height-a temperature inversion
Temperature Inversion
S This frequently occurs on clear nights as the result of radiation
cooling.
S It is created when the ground and the air immediately above the
ground cool more rapidly than air higher above the ground.
S There is very little vertical air movement.
S Air is unstable when the air close to the surface of Earth is a lot
warmer than the air above the surface. The air turns over with the
warm air below rises and is displaced by the colder air from above.
Condensation
S Condensation of air occurs when it is saturated. This
occurs when air is cooled to its dew point or when water
vapor is added to the air.
S There generally needs to be a surface for water to condense
upon. These are called condensation nuclei.
S These are important because without them the relative
humidity would need to be above 100% for clouds to form.
Cloud Types
S Clouds are classified on the basis of their form and
height. Here are some of the forms…
S Cirrus (cirrus = curl of hair) are clouds that are high,
white, and thin.
S Cumulus (cumulus = a pile) are clouds that consist of
rounded individual cloud masses.
S Stratus (stratus = a layer) are clouds best described as
sheets or layers that cover much or all of the sky.
Cloud Types-height
S High Clouds
S Cirrus clouds are high, white, and thin.
S Cirrostratus clouds are flat layers of clouds.
S Cirrocumulus clouds consist of fluffy masses.
S Middle Clouds
S Altocumulus clouds are composed of rounded masses that
differ from cirrocumulus clouds in that altocumulus clouds
are larger and denser.
S Altostratus clouds create a uniform white to gray sheet
covering the sky with the sun or moon visible as a bright
spot.
Cloud Types
S Low Clouds
S Stratus clouds are best described as sheets or layers that
cover much or all of the sky.
S Stratocumulus clouds have a scalloped bottom that appears
as long parallel rolls or broken rounded patches.
S Nimbostratus clouds are the main precipitation makers.
Fog
S There is physically no difference between a fog and cloud.
S Fog is defined as a cloud with its base at or very near the
ground.
S Fog Caused by Cooling
S As the air cools, it becomes denser and drains into low areas
such as river valleys, where thick fog accumulations may occur.
S Fog Caused by Evaporation
S When cool air moves over warm water, enough moisture may
evaporate from the water surface to produce saturation.
Precipitation Formation
S In order for precipitation to form cloud droplets must grow
in volume by one million times.
S First there must be a source of moisture. The primary
moisture sources in the U.S. are the Atlantic and Pacific
Oceans as well as the Gulf of Mexico. Winds around high
and low pressure systems (a subject of another lesson)
transport this moisture inland.
S Once the moisture is in place, clouds still need to form. The most
effective way to do this is by lifting the air. This can be accomplished
by forcing the air up and over mountains or, more commonly, by
forcing air to rise near fronts and low pressure areas.
S Cloud droplets and/or ice crystals are too small and too light to fall to
the ground as precipitation. So there must be a process(es) for the
cloud water, or ice, to grow large enough to fall as precipitation. One
process is called the collision and coalescence or warm rain process.
In this process, collisions occur between cloud droplets of varying
size, with their different fall speeds, sticking together or coalescing,
forming larger drops.
S Finally the drops become too large to be suspended in the
air and they fall to the ground as rain. The other process is
the ice crystal process. This occurs in colder clouds when
both ice crystals and water droplets are present. In this
situation it is "easier" for water vapor to deposit directly
onto the ice crystals so the ice crystals grow at the expense
of the water droplets. The crystals eventually become heavy
enough to fall. If it is cold near the surface it may snow,
otherwise the snowflakes may melt to rain.
S The Bergeron process is a theory that relates the formation
of precipitation to super cooled clouds, freezing nuclei, and
the different saturation levels of ice and liquid water.
Forms of Precipitation
S Rain and Snow
S Sleet is the fall of clear-to-translucent ice.
S Hail is produced in cumulonimbus clouds.
S Hailstones begin as small ice pellets that grow by collecting
super cooled water droplets as they fall through a cloud.
Cloud in a Bottle
S Take your bottle and rinse it and remove the label.
S Cover the bottom with warm water.
S Put the pressure cap on and start to pump it. Observe and
record what happens to the temperature.
S I will light a match and put it in your bottle. Pump until the
bottle has a lot of pressure. Release the valve. Observe.
S Explain what happened.
Air as a Fluid
S Fold the file folder in half. I will give you a candle.
S Put a little baking soda in the bottom of the beaker.
S Pour about a ¼ c vinegar into the beaker.
S When the fizzing stops, hold the cardboard funnel so that
one end is near the flame of the candle and the other end
slightly higher.
S Pour the gas in the beaker down the funnel. What happens?