Transcript weather - Net Start Class

When people say that it is going to rain, or that it is cold
outside, what is the “it” that they are talking about?
The “it” refers to the atmosphere – the blanket of air that
surrounds the Earth.
The atmosphere is mainly made up of nitrogen (78%) and
oxygen (21%) gas.
It is an important renewable resource.
The atmosphere is also called the source of weather.
In fact, the weather really is what is happening in the
atmosphere at a given time in a particular place.
The mixed gases in the atmosphere, known as
air, are usually invisible to us.
However, air is a form of matter which means it
has mass and takes up space.
Because we are surrounded by invisible air, we are
not always aware of it.
If you put air into a balloon and squeeze it, you sill
see that air takes up space inside the balloon.
When air moves around us, we can feel it as wind.
Most of the time, we are not aware of the air, but air is always
pushing down on us. We live at the bottom of an ocean of air. The
weight of air high in the atmosphere compresses, or squeezes
together, air closer to the Earth’s surface, causing a higher air
pressure.
The weight of the air causes air pressure – the force applied by
the weight of the air pushing down.
Air pressure is not always the same. It changes based on the
amount of moisture in the air, how cold or warm the air is, and
other factors.
When air pressure changes, the weather usually changes as
well. So, studying air pressure helps meteorologists predict
weather.
Meteorologists use an instrument called a barometer to
measure air pressure.
Barometers generally fall into two main groups:
Some barometers use mercury, a silver
liquid. A long glass tube sits in mercury open
to the air. Air pressure is often measured in
inches of mercury.
A second type of barometer is round in
shape. It uses a metal spring, like the spring
of a spring scale. Air pressure squeezes the
spring. A needle points to the amount of air
pressure.
Air pressure can sometimes be called barometric pressure.
Air pressure can be measured in millibars, kg per cm², or
pounds per square inch.
A barometer is a very effective tool to help
predict what type of weather is ahead.
When there is an increase in air pressure, which causes the
barometer to rise, we can expect mild weather –clear skies, sun,
little wind, and dry weather ahead.
H-High pressure
When there is a decrease in air pressure, which causes the
barometer to fall, the opposite is probably ahead-clouds, less
sun, more wind, and possibly precipitation of some kind.
L-Low pressure
http://demonstrations.wolfram.com/AneroidBarometer/
http://studyjams.scholastic.com/studyjams/jams/science/weather-andclimate/air-pressure-and-wind.htm
Different amounts of pressure in air masses (huge bodies of
air) are what cause wind.
Some air masses have high pressure and others have low
pressure.
Differences in air pressure are caused by the uneven heating of
Earth and the atmosphere.
As air gains heat energy, its particles move faster and spread
out. This makes an air mass that has low pressure.
If an air mass cools, its particles slow down and get closer
together, making an air mass that has high pressure.
The pressure differences between different air masses makes
wind blow from areas of high pressure to areas of lower pressure.
The greater the difference in pressure, the faster the wind
blows.
Wind is important because it moves
weather from place to place.
Meteorologists measure wind speed with an
anemometer.
The simplest anemometer consists of 4 cups,
each mounted on one end of four arms.
The flow of the air turns the cups.
Measuring the cups’ motion over a period of
time can tell the average wind speed in km per
hour.
When is wind helpful to us?
When is wind harmful to us?
http://studyjams.scholastic.com/studyjams/jams/s
cience/weather-and-climate/weatherinstruments.htm
A weather vane or wind sock measures the
direction of the wind.
Knowing the direction of the wind is an
important part of predicting the weather because
wind brings us our weather.
A wind vane spins and points in the direction
from which the wind is coming. (So, if the arrow is
pointing to the east, it means the wind is coming
from the east.
To use a wind vane, you must know where
north, south, east and west are.
http://studyjams.scholastic.com/studyjams/jams/s
cience/weather-and-climate/weatherinstruments.htm
A border that forms when 2 air masses meet (they don’t mix).
http://studyjams.scholastic.com/studyjams/jams/science/weather-and-climate/air-masses-and-fronts.htm
Warm Front: A warm front indicates a warmer air mass is moving in the
direction toward which the semicircles are pointing. The warm front is
drawn at the leading edge of the warm air mass..
•When a warm air mass
catches up to a cold air mass.
•The warm air slides up over
the cold air.
•Clouds form and
precipitation may fall.
•The sky clears, then the
temperature becomes warmer.
Cold Front: A cold front indicates a colder air mass is moving in
the direction toward which the triangles are pointing. The cold
front is drawn at the leading edge of the cold air mass.
http://www.classzone.com/books/earth_science/terc/content/visualizations/
es2002/es2002page01.cfm?chapter_no=visualization
•When a cold air mass catches up to a
warm air mass.
•When the warm air is pushed up, it
forms clouds.
•Rain or thunderstorms may occur.
•After the rain, the temperature is
cooler.
 To describe the weather, meteorologists use
special instruments to measure conditions.
Temperature is the key to all air movement.
Meteorologists use a thermometer to measure
the amount of heat (thermal) energy in matter, or
how hot or cold something is.
They measure temperatures in either in degrees
Celsius (°C) or Fahrenheit (°F).
• Most thermometers are closed glass tubes
containing liquids such as alcohol or mercury.
•When air around the tube heats the liquid, the liquid
expands and moves up the tube.
Meteorologists use a rain gauge to measure the amount of
rain that has fallen in inches or centimeters.
The rain gauge measures the height of the column
of water it captures.
The amount of rainfall is important because it affects
how much water is available to farmers and others.
A map is a diagram representing a place. It shows
where things are located.
A map’s key explains the symbols used on a map.
A direction indicator or compass shows directions
(N, S, E, W).
A weather map is a special kind of map. It shows weather
patterns.
The location of clouds, precipitation, wind speed and direction,
temperatures and air pressure can all be shown on a weather map.
Weather maps can be used to predict future weather.
Weather data can also be recorded in a table or a
graph. Below is a bar graph showing the average monthly
rain fall in Houston, Texas.
Cold Front
Barometer
measures this
Thunderstorm
Rain
Partly Cloudy
Warm Front
Sunny
Cloudy
Snow
The atmosphere is the blanket of air that surrounds the Earth.
The atmosphere is mainly made up of nitrogen and oxygen gas.
The atmosphere is the main source of weather.
When the air moves around us, we feel this as wind.
We measure the weight of the air around us as air pressure. A
barometer is used to measure air pressure.
To describe the weather, scientists use special
instruments to measure conditions:
Temperature- Measures how hot or cold the air is in
Celsius (°C) or Fahrenheit (°F).
Precipitation- Measured with a rain gauge. The amount of
rain that has fallen in inches or centimeters.
Wind- Wind speed with an anemometer.
Wind direction is measured with a weather vane.
Air Pressure- Measured with a barometer
Weather maps- Specialized map that shows weather
patterns. It indicates the conditions present in the
atmosphere.
A key on map is used to explain what each map
symbol represents.
Symbols on a map are used to record information
about the weather.
A weather map often shows:
Temperature
Wind Direction
Air Pressure
Wind Speed
Precipitation
Cloud Conditions