Transcript Clouds - Mount Mansfield Union High School

Clouds
Predicting the Weather
• Meteorologists are
primarily concerned
with viewing the
weather at a common
point in time.
• This map shows the
positions of high and
low pressure systems
as well as locations of
weather fronts.
When viewed from space, much can be learned looking at clouds
What are clouds?
Clouds are water-
Either small liquid water drops or tiny
pieces of ice that are suspended above
Earth’s surface.
Changing Forms of Water
Water exists in 3 states:
•Liquid
•Solid
•Gas
Water changes from one
phase to another when
heat energy is
absorbed or released
The Water Cycle
condensation
precipitation
transpiration
Run off
condensation
evaporation
infiltration
accumulation
How do Clouds Form?
o Clouds form when air is cooled to
its dewpoint or the temperature, if
the air is cooled, it reaches
saturation.
o The most common way is through
lifting.
o As a bubble or parcel of air rises, it
moves into an area of lower pressure
(pressure decreases with height).
o As this occurs the parcel expands.
This requires energy, or work, which
takes heat away from the parcel.
o So as air rises it cools.
o This is called an adiabatic process.
Humidity
•……is water vapor in the atmosphere
•Controlled by rates of condensation and evaporation
•Evaporation is determined by the temperature of the air
•The higher the temp, the higher the rate of evaporation
•Condensation is determined by vapor pressure
•The vapor pressure is high, the condensation rate is too
• When rate of evaporation and rate = rate of condensation,
air is said to be saturated.
•The temp at which the condensation rate= evaporation rate is
called the dew point.
Absolute vs. Relative
Absolute humidity
•The measure of the actual amount of water vapor in
the air
= mass of water vapor (grams)
volume of air (cubic meters
Relative humidity
•The ratio of actual water vapor content of the air to
the amount of water vapor needed to reach saturation.
•how close the air is to reaching its dew point
•Ex. 25°c air is saturated when it contains 20g of water vapor
per 1 kg of air
•If air that is 25°c contains 5 g of water vapor, the relative
humidity is 25%
How are Clouds Formed?
•Clouds form when the moist air rises.
•As air rises it expands and gets colder
•colder air cannot hold as much water
as warmer air.
•Temperature and air pressure continue
to drop, so tiny water droplets group
together into clumps called cloud
droplets.
•These droplets becomes a visible
cloud. If the cloud keeps going up, the
cloud droplets will clump together and
form water droplets.
•These water droplets are too heavy to
float in the air and they fall from the sky
as either rain or snow.
Cloud Formation Cont.
Cloud Condensation nuclei•suspended particles that provide
the necessary surfaces for cloudforming condensation.
•Ash
•Dust
•salt
•Small– less that 0.001 mm in
diameter
•Water molecules become
attached to the particles and
water droplets form
Cloud Classification
• Clouds are classified based on characteristics, such as,
altitude, appearance, or origin
– high clouds - have bases above 18,000 feet (6000 m)
– middle clouds - have bases between 6,500 and 18,000 ft
– Low clouds - have bases below 6,500 feet
–multi-level cloudsvertically thick
spanning multiple
layers
–fog - cloud in contact
with the ground
–orographic clouds clouds that form via
interaction between
wind and mountains
•Cirrus• “curly”
•Stratus•“sheetlike” or “layered”
•Cumulus•“piled” or “heaped”
•Alto•“high”
•Nimbus•“rain”
High Clouds
• Cirrus- high altitude wispy clouds
•Cirrocumulous- high clouds that have a
distinct patchy and/or wavelike appearance
•Cirrostratus- are high clouds that usually
blanket the sky in ill-defined sheets
•often looks like haze
Cirrus Clouds are often composed of ice crystals are slow to
evaporate and change very slowly with time
Middle Elevation Clouds
Altocumulus- Altocumulus is a white or grey cloud consisting of
scattered tufts
•This cloud is indicative of changeable weather but without
imminent rain.
Altostratus- form a bluish or grayish veil that totally or
partially covers the sky producing overcast conditions.
•The sun can barely be seen through altostratus and its edges
are not distinct
http://www.mountain-images.co.uk/mountain-pictures_full/085-lochlinnhe-sunset.jpg
•This cloud is indicative of imminent rain
Cumulous
•Small clouds that look like lumps of cotton.
•Can be found at various heights
Low Elevation Clouds
Stratus- the lowest cloud and forms as a featureless
grey layer.
•Precipitation from this cloud occurs as weak drizzle
rain or snow
Stratocumulus- occurs in patches or layers,
composed of rounded masses or rolls.
• often gives a sheet of almost total cloud cover.
Rain Clouds
Nimbostratus- Nimbostratus is an overall sheet of
grey cloud producing continuous rain or snow.
•Base tends to be at 2,000 to 8,000 ft (600 to
2500m). The sun cannot be seen through it
Cumulonimbus
• Heaped rain clouds of great vertical
extent.
• Bases tends to be below 6,500 ft (2,000 m)
and can extend up to 6 miles (10 km) into
the atmosphere.
• Most common inland in the afternoon in
spring and summer.
• This cloud is associated with heavy
showers hail and thunder
http://www.centennialofflight.gov/2003FF/clues/clipart/cumulonimbus.jpg
Cap Clouds
A smooth cap-shaped
cloud on top of a mountain
Formed when humid air
(maybe moistened by the
mountain terrain) is forced
to flow over the mountain,
condensing into a cloud
Lenticular Clouds
• Lenticularis clouds are lens-shaped clouds, with a
smooth layered appearance
• They are stationary lens-shaped clouds that form at
high altitudes
They sometimes get confused as flying saucers or UFOs!
Mammatus
Rare, pouch-like cloud structures
caused by sinking air.
•Only occur where cumulonimbus are present; however, they can drift
up to 25 miles away from a thunderstorm.
•Moist and unstable middle to
upper atmosphere over a very
dry, lower layer of the
atmosphere.
•Uplift shapes the mammatus
into the pouch-like shape.
Fog
• Fog is a cloud in contact with the earth's surface.
• It occurs b/c of evaporation from the surface of
the Earth.
– air cools to a point at which water vapor in it
condenses into tiny water droplets
– The temperature at which water vapor will begin
condensing is called the "dewpoint."
Types of Fog
Radiation fog– results from the nightly cooling of the earth.
•The layer of air in contact with the earth becomes chilled
below its dew point
•Water vapor condenses into droplets
•Usually forms on calm, clear nights and is thickest in valleys.
Advective Fog
•Forms when warm air moves across a cold
surface.
•Common along coasts– where warm moist
air from above the water moves over a
cooler land surface
Upslope Fog
•Formed by the lifting and adiabatic
cooling of air as it rises along land slopes
Steam Fog
•Forms over inland rivers and lakes
•A shallow layer of fog formed when cool
air moves over a warm body of water
Contrails
•a.k.a condensation trail
• They are cirrus-like trail of condensed water vapor
•They are produced at high altitudes where cold
temperatures freeze water droplets before they can
evaporate.
•Exhaust fumes from a jet engine inject
water vapor into the atmosphere
•To remain in tact for a long period of
time, the air must have a high relative
humidity with relatively light winds.