Transcript What is a cloud?

Weather Essentials Concept Map
Sun
Moisture
Temperature
Density / pressure
Highs, lows, and fronts
Sun
Sun
Wind/air motion
(horizontal & vertical)
Other
influences
Climate
Jet streams,
horizontal Pressure
Gradient Force (PGF)
Clouds
Daily weather
Sun
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What is a cloud?
Clouds
Precipitation occurs when cloud droplets grow
large and heavy enough to overcome the rising
air creating the cloud
Clouds are part of the global water transport cycle
Clouds form when: 1) there is enough water vapor
(water in gas form) to change to liquid droplets or
ice; 2) the air is cooled enough from vertical lifting;
and 3) there are particles (sand, dust, salt) onto
which water vapor can condense.
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How is the atmosphere heated? (Solar Radiation/Differential Heating of Water and Land)
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Why does air rise or sink?
Why are the poles cold and the equator hot?
Density differences create areas of high and low pressure. Winds blow
from high to low pressure and create air mass characteristics and
boundaries (fronts).
Uneven heating of Earth’s surface creates air temperature differences, which
result in air density differences. Air that is less dense than the surrounding air
will rise. Air that is more dense that the surrounding air will sink.
Over a year, the tropical latitudes (0–30º) receive the most sun’s energy, the midlatitudes (30–60º) receive less energy, and the polar latitudes (60–90º) even less
energy. The end result is that the poles are colder than the equator.
Uneven heating causes weather processes like high/low pressure,
winds, temperature differences, water transport (water cycle), and
unstable/stable air conditions (density differences).
Although the sun’s energy is constant, Earth’s surface is heated unevenly
because of its tilt.
Solar energy is the driving force that causes weather.
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Where does water come from and how does it travel?
Clouds and Winds in Connection to the Global Water Cycle
Some of the water in clouds falls
as precipitation (rain and snow,
etc.) over oceans and land.
If land
Clouds are also transported by the wind.
The moist air (water vapor in the air)
condenses to form clouds.
If oceans
Winds transport moist air
to other regions.
Precipitation reaching land may
evaporate again, soak into the soil
as groundwater, or run off into
rivers and eventually back to the
ocean.
Plants may take up some of the
groundwater and release water
vapor through
evapotranspiration. Glaciers may
grow or shrink based on the
accumulation or sublimation
occurring at their surfaces.
Sun evaporates water from oceans,
land, and plants, creating water vapor in
the atmosphere.
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What is wind? (High and low pressure systems)
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Does the Coriolis Force affect how water flushes down the toilet?
Mention fronts in the context of high/low pressure systems
The polar-front jet stream influences U.S. weather, especially in
winter by steering weather systems across the country.
Near the Earth’s surface,
the PGF, Coriolis Force
(which results from
Earth’s rotation), and
surface roughness
(which creates friction)
cause winds in the
northern hemisphere to
circulate counterclockwise, inward and
upward for low pressure
areas; and clockwise,
outward, and downward
for high pressure areas.
Locations poleward of these jet streams tend to
be cooler than locations equatorward of them.
Jet streams are narrow bands of strong winds (fastest moving air aloft). Jet streams occur 6 to
9 miles (9 to 14 kilometers) above sea level. The U.S. is influenced by 2 major jet streams: the
southern subtropical jet and the northern polar jet.
Winds above the Earth’s surface (e.g., jet stream) are generally faster than winds near the
Earth’s surface because the PGF increases with altitude (is stronger). Earth’s rotation causes
these winds to blow from west to east. (The Coriolis Force balances the PGF.)
Wind at surface
Upper air wind
Winds are the result of trying to equalize pressure and density differences
caused by unequal heating. A pressure gradient between high and low pressure
centers causes winds to blow from high to low pressure due to the horizontal
pressure gradient force (PGF).
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What is wind? (High and low pressure systems)
Because the Coriolis effect is weak near
the equator, hurricanes develop slightly
poleward of the equator so that air
rotation can be achieved
For people in the Northern Hemisphere,
winds appears to be deflected to the right of
the wind direction.
In the Southern Hemisphere, winds appear
to be deflected to the left of the wind
direction.
The veering of the air is called the Coriolis Effect.
At the Earth’s surface, air moving over
relatively long distances appears to veer (be
deflected) from its intended path.
Earth rotates from west to east. Because the
atmosphere is not generally solid like the Earth, air
movement is influenced by Earth’s rotation.
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What’s the weather going to be like? (Understanding pressure, temperature and wind)
Low pressure areas tend to have stormy weather and stronger
winds (rising air and clouds). The lowest pressure areas on Earth
are the centers of hurricanes and tornadoes.
At Earth’s surface, air moving towards
(converging) a low pressure system must rise,
leading to cooling and cloud development.
High pressure areas tend to have fair weather and
light winds (descending air and clear skies).
At Earth’s surface, air moving outward (diverging)
from a high pressure system sinks, leading to
warming and cloud dissipation.
The boundaries between air masses are called fronts. Cold fronts
occur where warm air is being replaced by cold air. Warm fronts occur
where cold air is being replaced by warm air. Warm and cold fronts
are commonly linked by warm pressure systems.
Air masses are blobs of air identified by their pressure, temperature, and moisture
characteristics, and they represent the conditions from where they originated (e.g.
cold and dry from Canada in the winter, warm and moist air from southeast U.S.)
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Factors influencing climate
What is the temperature profile (daily maximum and minimum)?
How does the temperature profile vary daily and
seasonally? How do these profiles compare?
What is the typical wind direction and speed in
summer and winter?
Do oceans influence the temperature and winds
at the location?
What do the daily and seasonal precipitation profiles
look like – monsoonal, consistent, or very little
precipitation?
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