Weather is the state or condition of the variables of
the atmosphere at any given location for a short
period of time.
What is Climate?
 Climate is the average weather conditions of a specific
region over a long time including the range of weather
conditions.
Who Studies Weather?
 Do you know this man?
What does a Meteorologist do?
 A Meteorologist is a person who studies weather (the
troposphere) and how it changes.
What are the Variables of Weather?
 1) Temperature
 4) Wind
 2) Air Pressure
 5) Cloud Cover
 3) Humidity (moisture
 6) Precipitation
content)
 7) Storms
Atmospheric Temperature
(see ref. table p.13)
 Air temperature is usually measured using a liquid
filled glass tube called a thermometer.
What heats our atmosphere?
This big ball of hydrogen fusion. You know it better
as the sun.
What is Hydrogen Fusion?
 Under extreme conditions of heat and pressure within
the sun hydrogen nuclei join to form a helium nucleus.
Let’s see how
 The Water Cycle
Insolation
 Incoming

Solar
 Radiation
Heating of the Atmosphere
How is Heat Transferred From One Area to
Another?
Three Ways Energy Is Transferred
 1) Radiation: The amount of heat received
directly from the sun by earth
 2) Conduction: When molecules come into
contact, energy is passed along from molecule to
molecule.
 3) Convection: A form of heat flow that moves
both matter and energy as density currents under
the influence of gravity.
 4) The Coriolis Effect: Results from the
rotation of Earth and wind. This causes friction
where the atmosphere and Earth’s surface meet.
The Coriolis Effect
 The Coriolis effect results from the rotation of Earth
and wind. This causes friction and this friction
produces heat some of which is absorbed from the
atmosphere.
The Coriolis Effect
How do we know there is a Coriolis Effect?
 The Foucault Pendulum is our proof that the the Earth
rotates. The Coriolis effect is caused by Earth’s
rotation.
 http://www.animations.physics.unsw.edu.au/jw/fouca
ult_pendulum.html
Differences in Density
 Cold air is more dense than warm air.
 Cold Air: More Oxygen and Nitrogen Gas





Oxygen = 16 g (O2)
Nitrogen= 14 g (N2)
(O2) = 32
(N2) = 28
Total: 60 grams
The States of Matter
Differences in Density (Warm Air)
 Energy (in the form of heat) is stored in the
atmosphere as water vapor (H2O(v)).

Hydrogen (H2) = 1 g x 2 = 2g
Oxygen (O) = 16g x 1 = 16g
Total weight = 18g
The Heating/Cooling Curve of Water

Which one Weighs More?
Warm Air or Cold Air?
 The answer is: COLD AIR
 Cold air with a mass of 60g weighs far more than warm
air at 18g. Density is Mass/Volume.
 The ratio of mass to volume for cold air will always be
greater than warm air.
Heating and Cooling of Air by Expansion and
Compression
 When a gas expands, its temperature decreases.
 When a gas compresses, its temperature increases.
The Orographic Effect
(you must know this!!!)
What is Atmospheric Pressure?
P.128 in your regent workbook
 Atmospheric Pressure (air pressure) is the pressure
due to the weight of the overlying atmosphere pushing
down on any given area.
 Atmospheric pressure is measured by using a
barometer. There are two types of barometers: a
mercury barometer and the aneroid barometer.
What does of a barometer look like?
 Mercury Barometer
Aneroid Barometer
Conversions of Barometric Pressure
(see p.13 in ref table)
 Standard air pressure (one atmosphere) at sea level is
15.7 pounds per square inch, 29.92 inches of mercury
or 1013.2 millibars.
Effect of Temperature on Air Pressure
 Changes in the temperature of the air causes changes
in the air pressure.
 As the temperature of air increases (gets hotter), the
air expands and its density and pressure decreases.
 As the temperature of air decreases (gets colder), the
air compresses and its density and pressure increases.
Effect of Water Vapor on Air Pressure
 The greater the amount of water vapor in the air
(absolute humidity or humidity) the lower the air
density and pressure.
 Recall the weight of cold air vs. warm air.
 Cold air with a mass of 60g weighs far more than warm
air at 18g.
Effect of Altitude on Atmospheric Pressure
 As altitude, or elevation (distance from sea level),
increases atmospheric density and pressure decrease.
 As you go up higher in the atmosphere, there is less
gas. Less gas, less weight exerted on Earth.
 See p.14 of your reference table.
 Remember this page? (you better)
What is Wind?
Page 131 in your regent workbook
Wind is horizontal movement of air parallel to Earth’s
surface.
Wind is a type of vector. It is a vector because it
requires two measurements, magnitude (strength) and
direction (where is it coming from) to totally describe
it.
What tool is used to measure wind?
 An instrument called an anemometer is used to
measure wind speed (magnitude). Wind speed is
measured in miles per hour and knots.
Wind Direction
 Air (wind) moves from areas of high pressure to low
pressure.
 High pressure air (air low in water vapor) moves
towards low pressure air (air high in water vapor).
Air Pressure Gradient
 See Regent Handout (Jan. 2010)
 The difference in air pressure for a specific distance is
called the air pressure gradient.
 The closer together the isobars on a weather map, the
greater (the steeper) the pressure gradient.
 The greater the pressure gradient, the faster the
speed.
The Coriolis Effect
 The Coriolis effect results from the rotation of Earth
and wind. This causes friction and this friction
produces heat some of which is absorbed from the
atmosphere.
The Coriolis Effect
How do we know there is a Coriolis Effect?
 The Foucault Pendulum is our proof that the the Earth
rotates. The Coriolis effect is caused by Earth’s
rotation.
 http://www.animations.physics.unsw.edu.au/jw/fouca
ult_pendulum.html
Differences in Density
 Cold air is more dense than warm air.
 Cold Air: More Oxygen and Nitrogen Gas





Oxygen = 16 g (O2)
Nitrogen= 14 g (N2)
(O2) = 32
(N2) = 28
Total: 60 grams
Differences in Density (Warm Air)
 Energy (in the form of heat) is stored in the
atmosphere as water vapor (H2O(v)).

Hydrogen (H2) = 1 g x 2 = 2g
Oxygen (O) = 16g x 1 = 16g
Total weight = 18g
Which one Weighs More?
Warm Air or Cold Air?
 The answer is: COLD AIR
 Cold air with a mass of 60g weighs far more than warm
air at 18g. Density is Mass/Volume.
 The ratio of mass to volume for cold air will always be
greater than warm air.
How do we record wind?
 A wind is named for the direction from which it comes
from.
 For example, a wind blowing from the south toward
the north is a south wind. A wind blowing towards the
south east is a northwest wind (the direction it is
coming from).
Wind Vane
 An instrument called a wind vane is often used to
determine wind direction.
Formation of Waves on Surface Water
 Wind blowing over bodies of water creates friction
where the air and liquid water meet.
 The friction transfers energy from the wind to the
body of water and produces waves.
 These energy waves move out from the area where
they are produced and toward where the energy
results in wave erosion at shorelines.
Review of Wind
 Answer questions 18-24 on pages 132-133 in your
workbook.
Zone of Convergence
 Referred to as a cyclone. Regions of low pressure. Air
converges comes together and rises.
Zones of Divergence
 Referred to as an anticyclone. Regions of high
pressure. Cold dry air sinks below warm moist air.
Difference between a Cyclone and an
Anticyclone
 Cyclone: Low pressure, winds move counter
clockwise (left)
 Anticyclone: High pressure, winds move clockwise
(right)
Let’s see this
Heating and Cooling of Air by Expansion and
Compression
 When a gas expands, its temperature decreases.
 When a gas compresses, its temperature increases.
The Orographic Effect
(you must know this!!!)
Wind Belts
 Planetary Wind Patterns
Wind Pressure Belts
Very Important!!!! (see p.14 of ref. table)
 Wind Pressure Belts are produced in the atmosphere
as a result of convection.
 Low pressure belts are found at the equator and at
the 60 degree North and South Latitudes.
 High pressure belts are found at the 30 degree North
and South Latitudes as well as at both the North and
South Poles.
Location of Earth’s Pressure Belts
The location of Earth’s pressure belts and the affect of
Earth’s rotation determines the general position and
direction of planetary wind circulation.
Factors such as:
 Altitude
 Position relative to mountains
 Position relative to bodies of water
May modify the wind pattern.
Humidity and Dew Point
 Humidity is the term that refers to the amount of
water vapor in the atmosphere.
 The amount (mass) of water vapor in each unit volume
of air is called absolute humidity.
 The absolute humidity (moisture capacity) increases
rapidly with an increase in air temperature (gets
hotter).
Hot air can hold more water vapor than cold
air.
 Relative Humidity
 The ratio of the amount of water vapor in the air to
the maximum amount it can hold (the moisture
capacity).
 Relative humidity is expressed as a percent
therefore representing the amount of moisture the
air is holding.
 For example: at a relative humidity of 100% the air
is holding as much moisture as it can.
Water Vapor is the Most Important
Reservoir of Energy in the Atmosphere
 Water vapor stores solar energy. (see p. 1 of ref. table.)
 For each gram of water to change from a liquid to a gas,
2260 joules (unit for energy) must be absorbed by a
water molecule.
 That’s quite a bit of energy.
Relative Humidity and Temperature
 As temperature increases (gets hotter) the relative
humidity will decrease. This occurs because the
capacity of the atmosphere to hold water increases.
 As temperature decreases (gets colder) the relative
humidity will increase (gets closer to 100%). As
temperature gets colder there is less heat in the
atmosphere and the capacity to hold water decreases.
Dew Point
 Dew Point is the temperature (in degrees Celsius)
at which air is saturated with water vapor.
 The dew point depends on the absolute humidity
and not on the relative humidity.
 As the amount of water vapor in the air increases,
the dew point also rises because the more water
vapor in the air the closer the air is to its saturation
point----the dew point.
Tools used to Measure Dew Point
 Sling Psychrometer:
Parts of a Sling Psychrometer
Wet Bulb and Dry Bulb
 The Wet Bulb has a wick (piece of gauze). This
measure the temperature of evaporation. (This
temperature can either be equal or less than the air
temperature.)
 The Dry Bulb measures the air temperature.
Tools used to Measure Dew Point (part 2)
 Hygrometer
How to Find Dew Point
(Use p. 12 of your reference table)
 To find dew point:
Subtract the wet bulb from the dry
bulb.
Go to p.12 of your reference table and line up the dry
bulb temperature with the difference between the wet
and dry bulbs.
Remember dew point is represented in degrees per
Celsius. Don’t forget your units!!!!
How to Find Relative Humidity
(Use p. 12 of your reference table)
 This is very similar to dew point. The one thing
you need to do is use the right table.
 Use the table at the bottom of p. 12. Pay attention
to the titles.
 To find relative humidity (answer in %):
Subtract the wet bulb from the dry
bulb.
Go to p.12 of your reference table and line up the dry
bulb temperature with the difference between the
wet and dry bulbs.
The final answer is in % not degrees Celsius.
Cloud Cover
 Clouds form by a process called condensation.
 Condensation releases 2260 joules into the
atmosphere as water vapor changes into tiny water
droplets and ice crystals to form clouds.
 *Notice Condensation is the opposite of
Evaporation.
Types
of
Clouds
 Clouds are classified into a system that uses Latin
words to describe the appearance of clouds as seen by
an observer on the ground
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/c
ldtyp/home.rxml
 http://www.weatherwizkids.com/weather-clouds.htm
How Do Clouds Form?
 1) Cooling of Air
 Air must be cooled below dew point.
 What happens when air expands? Expansion of a gas
causes the gas to cool. If air cools below its dew point,
condensation will create a cloud.
How Do Clouds Form?
 2) Condensation Nuclei
 When dew or frost forms this means air is below its
dew point. We see dew and frost because water is
condensing on a surface.
 In the atmosphere those surfaces are provided by
particles of solids suspended in the air. These solids
are called condensdation nuclei.
Examples of Condensation Nuclei
 Dust from dust storms
 Fires
 Exhaust from Cars
 Exhaust from Homes
 Exhaust from Factories
 Exhaust from Power Plants
Have you ever noticed that after
precipitation, there are no clouds in the
sky?
 Precipitation in the form of rain, snow, sleet and/or
hail bring condensation nuclei to ground level.
 Now, lets make a cloud. Beginning of Lab #19.
What is Precipitation?
Refer to p.141 in Regent workbook
Precipitation is the falling of liquid or solid water from
clouds toward the surface of the Earth.
Ice crystals or water droplets formed by condensation
come together to become big enough so that they will
fall under the influence of gravity.
What are the forms of Precipitation?
 Rain: liquid precipitation, droplets are larger than 0.2
mm in diameter; may be melted snow.
Forms of Precipitation (continued)
 Drizzle: Falling liquid droplets from 0.2-0.5 mm in
diameter. Atmospheric temperature is above 32
degrees Fahrenheit.
 Snow: Falling ice crystals formed by combining cloud
ice crystals. Atmospheric temperature is below 32
degrees Fahrenheit.
Forms of Precipitation (continued)
 Sleet: Solid pellets of ice that form by freezing of rain
drops as they fall. Temperature of the atmosphere
where the clouds are is above 32 degrees Fahrenheit
but at the surface of the earth the temperature is below
32 degrees Fahrenheit.
Forms of Precipitation (continued)
 Freezing Rain: Rain or drizzle that freezes on contact
with features of Earth’s surface.
 Hail: Layers of ice, snow and water formed by many
up and down movements in a thunderstorm cloud.