Weather
Weather
• Weather is the condition of Earth’s
atmosphere at a particular time and place.
– Short-term: Hours and days
– Localized: Town, Region or State
•
•
•
•
Rain showers
Snow storm
Tornado
Hurricane
Causes of Weather
1. Uneven distribution of thermal energy, heat, in
Earth’s atmosphere.
– The sun’s energy, by radiation.
2. The Earth’s tilt and revolution
• Described by:
–
–
–
–
–
Density
Air pressure
Temperature
Wind
Water
Density
• Air consists of atoms and molecules that have
mass and occupy space, volume = density.
– Colder air:
• Particle Speed = slower molecule speed
• Volume = lower volume
• Density = increased density
– Cold air sinks!
– Warmer air:
• Particle Speed = faster molecule speed
• Volume = increased volume
• Density = decreased density.
– Hot air rises!
Convection
Air Pressure
• Air pressure – the result of the weight of a
column of air pushing down on an area.
– The closer to Earth’s surface the higher the air
pressure.
• Sea level = greatest air pressure
– The farther away from Earth’s surface, altitude or
elevation, the lower the air pressure.
• On top of a mountain = lowest air pressure.
Factors Affecting Air Pressure
Elevation
High
Low
Air Pressure
Low
Density
High
High
1. Altitude is greatest at
point: A
2. Air pressure is greatest
at point: B
3. Density of the air is
least at point: A
Low
Measuring Air Pressure
1. Mercury Barometer
a. Mercury adjusts to the
amount of pressure pushing
down on it.
•
As air pressure increases,
the mercury in the tube rises/high.
–
•
Sunny and Clear
As air pressure decreases,
the mercury in the tube falls/low.
–
Cloudy and Rainy
Measuring Air Pressure
2. Aneroid Barometer
a. Aneroid = “without liquid”
•
When air pressure increases,
the walls push in, higher
readings
–
•
Fair to Dry conditions
When air pressure decreases,
the walls bulge out, lower
readings
–
Stormy and Rainy
Low
High
Temperature
• Air temperatures vary over time due to the
thermal energy content of the atmosphere.
– About half of the sun’s energy is absorbed and
converted to heat by Earth’s surface.
– The other half is either absorbed by the
atmosphere or reflected back into space.
Factors Affecting Temperature
1. Earth’s rotation
– Earth rotates, spins, once in 24 hours.
•
Half of earth is facing the sun
–
•
Warmer temperatures
Half of earth is facing away from the sun.
–
Cooler temperatures
Night
Day
Factors Affecting Temperature
2. Earth’s tilt and Revolution
– Earth’s axis is tilted at 23.5 off perpendicular.
– Earth orbits once around the sun in 365 days (1
year)
• Causes different amounts of sunlight to be absorbed or
scattered during different seasons.
Factors Affecting Temperature
3. Clouds
– Thicker clouds reflect more solar radiation
4. Surface Color
– Lighter colors reflect more solar radiation
• Snow and sand
– Darker colors absorb more solar radiation
• Forests
5. Surface Texture
– The rougher the surface the more solar radiation gets
trapped and is absorbed.
Solar Radiation Reflection
• Which two surfaces absorb the greatest amount of the
sun’s energy?
Forests and water – reflect the least amount of solar radiation
• Which two factors reflect the most solar radiation?
Thick clouds and snow = 75-90%
• On a winter day, where would you be warmer – a sandy
beach or a grassy field? Grassy field = absorbs more sunlight
Charting Air Pressure & Temp
• Isobars – similar air pressure recordings
connected by a solid line.
Low Pressure:
• Cold
• Wet and Stormy
L
High Pressure:
• Hot
• Warm and Humid
Close Lines:
• Windy
H
Farther Apart Isobars:
• Calm
Air Pressures move from regions of High to regions of Low
Isobars
Low
•
4 millibars.
Each isobar differs from the next isobar by ______
•
The lowest air pressure reading on the map is _____
992 millibars.
•
What weather conditions would they most likely be experiencing?
•
The highest air pressure reading on the map is ______
1016 millibars.
•
What weather conditions would they most likely be experiencing?
•
What pressure range is New York City located in?
1004-1008
Stormy
Change
High
Reading Isotherms
• Isotherms – Similar temperature recordings
connected by a solid line.
1. Pittsburgh, Cincinnati and
Indianapolis are all at this
temperature:
NYC
40
2. Name one city that is currently
at 45. NYC, DC, Richmond
Roanoke
3. The farther South you travel,
the temperature gets:
warmer
South
Where Does Weather Occur?
• Weather takes place in the atmosphere.
– The layer of gases that surround planet Earth.
• Importance of the Atmosphere:
1.
2.
3.
4.
Make conditions on Earth suitable for living things.
Contains oxygen (O)and other gases.
Keeps Earth warm enough for liquid water to exist.
Protects organisms from radiation from the sun and
meteoroids.
Composition of the Atmosphere
• Made up of a mixture
of gases:
– Nitrogen – 78%
Argon & Carbon Dioxide – 1%
Oxygen –
21%
• The most abundant gas
– Oxygen – 21%
– Argon - .93%
– Carbon Dioxide - .036%
Nitrogen – 78%
Layers of the Atmosphere
• The atmosphere is divided
into 4 main layers based
on temperature and air
pressure changes.
1.
2.
3.
4.
Troposphere
Stratosphere
Mesosphere
Thermosphere
The Troposphere
• Closest to Earth’s surface.
– Earth’s weather occurs
here!
• 0-16 km above sea level
• Contains almost all the
mass of the atmosphere
• As altitude increases,
temperature decreases
– 1 km increase = 6.5C
cooling.
• At -60C it levels off.
The Stratosphere
• Extends from 16-50km
above the earth’s surface
• Increases in temperature
as altitude increases due
to the ozone layer.
– Protective layer that
absorbs the sun’s energy
and converts it to heat.
The Mesosphere
• As altitude increases,
temperature decreases.
– The coldest layer at -90C
• 50-80km above the
Earth‘s surface.
• Protective layer where
most meteoroids burn
up.
The Thermosphere
• Extends from 80km to
infinity – has no outer
limit.
– Divided into two different
sections:
1.
Ionosphere
– aurora borealis
2.
Exosphere
– satellites orbit Earth.
• The hottest layer at
1800C
– due to heat coming in.
Aurora Borealis
• A natural light display caused by the collision
of energetic charged particles with atoms in
the high altitude atmosphere