Transcript Weather PPT (Aug 8th and 29th)

Weather:
Temperature,
winds, air masses, moisture, air
pressure, and weather maps
Weather is....
•The current state of the
atmosphere...what is
happening right now
Main points to remember as we learn
about weather:
• The sun warms the earth’s surface and therefore all
the air above the surface
• The earth is warmed most at the equator and least
at the poles.
• **The air above land is warmed more quickly than
air above water.
• **Warm air expands and rises, creating an area of
low pressure; cold air is dense and sinks, creating an
area of high pressure
Temperature
TEMPERATURE: the average motion of
molecules
↑ TEMP= ↑movement of molecules= feels hot
↓ TEMP= ↓movement of molecules= feels cold
Air Pressure
•Warm air= expanding or rising air=
leaves behind Low pressure
•Cold Air=sinking air= leaves an area of
High pressure
Wind Movement
What causes winds?
•A wind is a
horizontal
movement of air
from a area of high
pressure to an area
of low pressure
•It is this difference in
pressure that makes
the air move=wind
• Winds are measured by
direction and speed
• The anemometer is the
tool we use to measure
this
•Wind chill=↑ cooling
the wind causes
Local Winds:
Sea Breezes
• The land cools and heats faster
than the ocean. Water holds
heat longer than land, and takes
longer to heat or cool.
During the day, the land
gets hotter faster than the
water. The heated air
rises, leaving behind an
area of low pressure.
Wind from the cooler sea
blows in to take the place
of that warmer air. These
happen during the day!
Land Breezes
At night the lands cools off faster than the
sea. Cool air sinks creating an area of high
pressure. Wind blows from the land to the
sea.
Global Circulation and Wind Systems
• Solar energy is at its greatest around the equator.
Global Winds
Wind belts:
Horse Latitudes= 30°N and S of
equator =calm winds= worlds
desert areas
Jet Streams: 10km above the
surface and blow from the west
to the east (California to North Carolina)
Intense heat = Powerful
CONVECTION
• Warm, moist air rises and leaves behind an area of low
pressure. This is why most rain forests are found along
equatorial regions.
• That air rises until it reaches the top of the troposphere,
where it can’t rise any further.
• It spreads out towards the polar regions HOT follows COLD
wanting to share its warmth.
• As it spreads it begins to cool and sink-usually 30°N and S
of the equator- sinking air produces an area of H pressure
with dry conditions= desert regions on earth
Tradewinds move back towards the
equator as they sink...
Water in the
Atmosphere
Humidity
• Humidity: measure of the amount of water vapor stuck
between molecules in the air. The air’s ability to hold water
depends on the air temperature
•The hotter the air, the more water the air
can hold
• Cold air: molecules move slower so droplets of water can
start to stick together=condensation
• Relative humidity: the amount of water vapor(%)
compared to the amount the air can hold- tool used is a
psychrometer.
• 100%=air is saturated
Cloud Formation
•Clouds form when water vapor
condenses on dust, salt particles in
the air
•The temperature in which
condensation begins is called the
dew point
Air Masses
•Air masses are masses of air that
have the same characteristics of the
surface over which it develops
•Pressure Systems
High Pressure: descending (going
down
Low Pressure: ascending (going
up
Fronts: the boundary between 2
air masses
WARM FRONT ->
•Warm Front: warm air slides over departing
cold air- large bands of precipitation form
Cold Fronts

cold front
•Cold air pushes under a warm air mass.
Warm air rises quickly=narrow bands of
violent storms form
occluded
Occluded Front
front
•2 air masses merge and force warm air
between them to rise quickly. Strong winds
and heavy precipitation will occur
stationary
Stationary Front
front
•Warm or cold front stops moving.
Light wind and precipitation may
occur across the front boundary
Reading a weather map
• ISOBAR= connects areas of equal pressure.
• BAR comes from BARometric pressure
Reading a weather map...
• Isotherm: Connects areas of equal temperature;
therm means temperature