Download Weather Part One PPT

State Objectives 4.c, 4.e, 4.h.
Discussion
What are some ways in
which weather affects your
everyday life?
What is Weather?
 Atmosphere layer of gases surrounding Earth.
 Weather is the conditions of the atmosphere.
 Temperature
 Air Pressure
 Humidity
 Wind
 Clouds
 Precipitation
 Main cause for changes in weather is energy
from the sun.
Weather Tools:
 Hygrometer - an instrument for measuring the water
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vapor content of the atmosphere (air)
Barometer - an instrument that measures atmospheric
pressure (air pressure)
Anemometer - also called a wind gauge an instrument for
recording the speed and how often the direction of winds
changes
Psychrometer - an instrument for determining
atmospheric humidity by the reading of two
thermometers, the bulb of one being kept moist and
ventilated and the other remaining dry
Rain Gauge - an instrument for measuring rainfall.
Temperature
 Indicates the amount of heat (kinetic energy) in
the atmosphere.
 Represents the speed of the molecules.
 The higher the temperature, the faster the air
molecules are moving.
 Warmer air rises and cooler air sinks which
causes convection currents.
 Measured with a thermometer.
 Standard unit is Fahrenheit (°F)
 SI Unit is Celsius (°C)
Convection in the Atmosphere
Convection Currents:
 Convection Currents are formed by the upward movement
of warm air and the downward
movement of cool air.
 Convection Currents move heat
throughout the troposphere
Heat Transfer:
 Conduction – the direct transfer of heat from one
substance to another substance that it is touching
 Example – a pot on the eye of a stove
 Convection – transfer of heat by the movement of a fluid
 Example – rising of warm air versus the sinking of cool air
 Radiation – direct transfer of
energy by electromagnetic
waves
 Example – Microwave oven
Air Pressure/Barometric Pressure
 Air has weight because it has mass.
 Air pressure is a measure of the force of
air being exerted on a given area of Earth’s
surface.
 As temperature increases pressure decreases.
Cool air is more dense, which causes it to
sink (high pressure).
 As altitude increases air pressure decreases.

Weather and Air Pressure
 Changes in pressure indicated a change in
weather is approaching.
 Low pressure systems are associated with
clouds & precipitation.
 High pressure systems are associated with
clear skies.
 Steady pressure indicates current
conditions will continue.
 Measured with a barometer
in inches of mercury or in millibars.
Cyclone:
 A cyclone is a swirling center of LOW air
pressure.
 Cyclones play a large part in the weather of
the United States. As air rises in a cyclone, the air cools,
forming clouds and precipitation.
 Cyclones and decreasing air pressure are associated with
clouds, wind, and precipitation.
Anticyclones:
 Anticyclones are HIGH pressure centers of dry air
 Opposite of a cyclone (LOW pressure)
 Because air moves out from the center of
the anticyclone, cool air moves downward
from higher in the troposphere.
 As the cool air falls, it warms up,
so its relative humidity drops. The
descending air in an anticyclone
generally causes dry, clear weather.
Humidity
 Amount of water vapor in the air.
 Relative humidity is a percentage of the amount
of water vapor in the air compared to the
maximum amount of water vapor it can
hold at that temperature.
 The warmer the temperature the more
water vapor it can hold.
 Saturated means the air is holding
100% of the water vapor it can hold
at that temperature.
 Measured with a hygrometer or a
psychrometer.
Relative Humidity Chart
Dew point
 Dew is the water vapor that has condensed
on a surface into a liquid.
 Depends on two factors:
 Amount of water vapor in the air
 Temperature near the surface
 Dew point is the temperature at which water
vapor condenses into a liquid.
Wind
 Caused by differences in air pressure
 Air moves from areas of high pressure to areas
of low pressure
 Wind Speed
 Measure of how fast the air is
moving.
 Measured with an anemometer.
 Wind Direction
 Direction from which the wind is coming, NOT
the direction it is blowing
 Ex. North winds blow from N to S
 Measured with a wind vane.
Global Wind Patterns
 Blow steadily across Earth in paths that are
thousands of kilometers long
 Steer weather in certain directions (usually
west to east in the U.S.)
 Caused by thermal energy from the sun
 The sun does not heat the surface evenly
causing uneven heating of the atmosphere.
Global Winds
Types of Global Winds
 Surface winds at low altitudes:
 Trade winds: blow from east to west near
the equator.
 Westerlies: blow from west to east in the
mid-latitudes.
 Coriolis Effect: Earth’s rotation causes
winds to curve to the right in the Northern
Hemisphere and to the left in the Southern
Hemisphere.
Types of Global Winds
 Jet streams at high altitudes are bands of
strong winds (up to 350 km/h) near the top of
the troposphere at the northern and southern
boundaries of the prevailing westerlies.
 Race from west to east
 Two types: polar & subtropical
Clouds
 Clouds form when air rises, cools, and
condenses. They are classified
according to their height and shape.
Types of Clouds
 1. cumulus- a low, puffy cloud that forms
on sunny days when heat from the surface
causes warm air to rise.
 2. stratus- a low, gray, sheet-like cloud that
forms when warm, moist air moves over
cooler ground. They are seen most often
during the winter and may bring steady
rain.
Cumulus and Stratus
Types of Clouds
 3. cumulonimbus (thunderheads) -
vertical clouds that may be over four
miles tall. They form where cold air
forces warm air to rise quickly.
 4. cirrus- high, featherlike clouds.
They are the highest clouds in the sky.
They do not produce precipitation.
Cumulonimbus and Cirrus
Altocumulus and Altostratus Clouds
 Part of a cloud’s name may be based on its height. The
names of clouds that form between 2 and 6 kilometers
about the Earth’s surface have the prefix alto-, which
means high.
 The two main types of these clouds are altocumulus and
altostratus.
 These are “middle-level” clouds that are higher than
regular cumulus and stratus clouds, but lower than cirrus
and other “high” clouds.
Precipitation
Precipitation – occurs when drops of water
or crystals of ice become too large to be
suspended in a cloud and fall in the form of
rain, freezing rain, sleet, snow, or hail.
The Water Cycle
Earth’s surface is about 70%
water and it exists in all three
states (solid, liquid, gas).
The water cycle is the constant
movement of water on Earth.
The Sun provides the energy for
the water cycle.
Parts of the Water Cycle
 1. Evaporation occurs when water
changes from a liquid into a gas after
gaining heat energy from the Sun.
 2. Transpiration is the evaporation of
water from the leaves of plants.
Parts of the Water Cycle
 3. Condensation occurs when water
vapor changes into liquid water to
form clouds or fog.
 4. Precipitation occurs when water
droplets fall to Earth.
What is an Air Mass?
 An air mass is a large body of air that
develops over a particular region.
 It has characteristics of the area over
which it develops.
 Cold, dry air masses come from Canada
and warm, dry air masses develop over
Mexico.
Air Masses
Air Mass Locations
Weather Maps
Satellite map: allow
meteorologists to monitor
weather on the global scale
Radar Map: uses
electromagnetic waves to
monitor velocity and altitude.
Types of Maps
Weather Map Symbols
Weather Map Symbols
HIGH
PRESSURE
SYMBOL
LOW
PRESSURE
SYSTEM