Download Humidity

WATER IN THE ATMOSPHERE
I.
Humidity
A. Defined as water vapor or
moisture in the air (from
evaporation and condensation).
B. The atmosphere gains
moisture from the evaporation
of water from oceans, lakes,
rivers, soil, plants and animals.
WATER IN THE ATMOSPHERE
II. Relative Humidity
A. Defined as the percentage of moisture
the air hold relative to the maximum it
can hold at a certain temperature.
B. Warm air can hold more moisture than
cold air.
C. The temperature at which water vapor
in the air condenses and turns back into a
liquid is called the dew point temperature.
WATER IN THE ATMOSPHERE
III. Measuring Relative Humidity
A. Meteorologists use a psychrometer
to measure relative humidity.
B. You must find the temperatures
of the wet-bulb and dry-bulb
thermometers.
Relative Humidity – must use a chart like
this to find % of relative humidity!
Clouds
IV. Clouds
A. Form when water vapor in the atmosphere
cools to dew pt. temp and condenses onto a
small particles of dust or other solid particles in
the air.
B. Clouds are classified according to their shape
and size.
a. Cumulus: clouds that look like piles of
cotton balls in the sky with flat bottoms.
1. Form at an altitude of 2.4 to 13.5km.
2. Usually mean fair (good) weather.
3. They may develop into cumulonimbus
clouds, which are larger clouds that produce
thunderstorms (and hail).
Clouds
B. Stratus: Gray, smooth clouds that cover the whole
sky and block out the sun.
1. Form at an altitude of 2.5 kilometer.
2. Light rain and drizzle are associated with
stratus clouds.
3. Nimbostratus clouds bring rain or snow.
4. Stratus clouds that form low to the ground are
called fog.
C. Cirrus: Clouds that form at very high altitudes (wispy
and feathery clouds).
1. Made of ice crystals
2. Often appear when the weather is fair, but
indicate that it will rain or snow within several
hours.
Clouds
Clouds form when the water vapor in the air cools
to the dew point temperature and condenses
back into a liquid. The water or ice must be able
to stick to a piece of dust or dirt in the air too.
Determining cloud height
• Abbreviations
• Ta =
• Td =
surface air temperature (0F)
dew point temperature (0F) - temperature at
which water vapor condenses
Determining Cloud Height
Cloud Height = [(Ta-Td)/4.5] x 1000
EX: If the air temperature is 58oF and the dew point is
50oF, what is the height of the clouds?
• Cloud Height = [(Ta-Td)/4.5] x 1000
• Cloud Height = [(58-50)/4.5) x1000
• Cloud Height = 1778 ft
You must write the formula, substitute in the
numbers and then solve every time with units!
Air Masses and Fronts
I. Air masses
A. Defined as a huge body of air that has
similar temperature, humidity and air
pressure throughout.
B. Will it be HOT or COLD?
1. This depends on the temperature of
the region over which it forms!
Air Masses and Fronts
a. Tropical, or warm, air masses form in the tropics
and have low pressure
b. Polar, or cold, air masses for north of 50o north
latitude or south of 50o south latitude and will have
high pressure
C. Will it be HUMID or DRY?
1. This depends on whether it formed over water or
land.
a. Maritime air masses form over water and are
humid.
b. Continental air masses form over land and are
dry.
Air Masses and Fronts
D. Four types of air masses in the United
States and are moved FROM the west to
the East by the prevailing westerlies and
jet streams.
1. Maritime Tropical (mT) - warm and humid
2. Maritime Polar (mP) – cool and humid
3. Continental Tropical (cT) – warm and dry
4. Continental Polar (cP) – cool and dry
Air Masses and Fronts
II. Fronts
1. The area where air masses meet and do not
mix are called fronts.
2. Types of fronts
a. Cold Front: leading edge
of a cold air mass. They
move quickly, so they cause
abrupt weather changes
eventually bring clear skies
and cooler temperatures.
that
Air Masses and Fronts
b. Warm Front: leading edge of a warm
air mass. Clouds, storms and rain
accompany a warm front. When it
passes, the weather is usually warm
and humid.
Air Masses and Fronts
c. Stationary Front: nonmoving
mass. It may bring days
clouds and precipitation.
d. Occluded Front: Cold air
mass overtaking a warmer
air mass. Warm air cools
and water vapor condenses;
may cause clouds, rain
or snow.
air
of
Air Masses and Fronts
3. Front symbols for weather map: