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What is Weather?
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
 2) Air Pressure
 3) Humidity (moisture
content)
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4)
5)
6)
7)
Wind
Cloud Cover
Precipitation
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?
Convection, Conduction and Radiation
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/j
w/foucault_pendulum.html
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.
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
 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.
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.
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!!!!
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/cldtyp/home.rxml
 http://www.weatherwizkids.com/weatherclouds.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
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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.
How do we measure precipitation?
 A rain gauge is used to measure
precipitation.
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.
The States of Matter
The Heating/Cooling Curve of
Water

Lab Activity #5: Phase Changes of
Water
 We will now complete lab activity #5: Phase
Changes of Water. You will need to
complete this lab in full.
HW #5, July 19, 2010
 Please complete the following:
 Questions 13-24 on pages 86-87 in your
regent review book.
 Questions 31-45 on p.94 in your regent
review book.
 Study for your quiz