Download What is temperature and how is it measured?

Elements of
Weather
What is weather?
• Weather is defined as the
condition of the Earth’s
atmosphere at a certain
time and place.
What is temperature and how is it measured?
• Temperature refers to how hot or cold
something is.
• In the case of weather, temperature refers
to the temperature of the air in the Earth’s
Troposphere.
• Temperature is measured with a
thermometer.
What is humidity and how is it measured?
• The amount of water vapor in the air is
called humidity.
• The humidity level in the air depends on
the temperature of the air.
• Warm air is less dense.
– Has more room to hold water vapor.
• Cold air is more dense
– Has less space to hold water vapor
Relative Humidity
• The Relative Humidity is the amount of
water vapor in a given volume of air
compared to the maximum amount of water
vapor that could be present in the air at that
temperature.
amount of water
vapor present
RH = Absolute Humidity
maximum amount of
water vapor that can be
present at that
temperature
Saturation Value
Measuring Relative Humidity
Sling Psychrometer
Psychrometric Chart
• An instrument used to
• A Psychometric Chart is
measure relative humidity,
used along with a Sling
consisting of a wet-bulb
Psychrometer to
thermometer, and a drydetermine relative
bulb thermometer.
humidity.
Sling Psychrometer
Determining Relative Humidity
If the dry-bulb thermometer reads 24°C and the
wet-bulb thermometer reads 20°C, what’s the
relative humidity?
Called the “Depression”
24°C
20°C
Saturated Air
• When the relative humidity of the air is 100%,
the air is described as saturated.
• Saturated air “is holding” the “maximum amount
of moisture it can hold” at a given temperature.
• Air can become saturated when evaporation
adds water vapor to the air.
• Air can also become saturated when it cools to
its dew point. (rising air masses forming clouds)
• Dew Point: The temperature at which
condensation begins.
What is precipitation and how is it measured?
• Precipitation is any form of water that falls
to the Earth’s surface from clouds.
• Rain is the most common type of
precipitation. The amount of rainfall is
measured by a rain gauge.
What is precipitation and how is it measured?
Types of Precipitation
• Rain: Water droplets in clouds get so big
they fall to Earth.
• Sleet: Small ice pellets fall as sleet when
rain falls through cold air on the way down.
• Hail: Hailstones are layered lumps of ice
that fall from cumulonimbus clouds.
• Snow: Snow is made of hexagonal shaped
ice crystals that fall from clouds. They fall
as single crystals or crystals can join
forming snow flakes.
What is air pressure and how is it measured?
• Air pressure is the force of air molecules pushing
on an area.
»Air pressure is measured by an
instrument called a barometer.
• High pressure weather systems are associated
with fair weather since cool, dense air is sinking.
• Low pressure weather systems are associated
with poor weather since warm, less dense air is
rising.
What is air pressure and how is it measured?
FALLING
31.0 to 30.5
30.5 to 30.2
30.2 to 29.8
29.8 to 29.5
29.5 to 29.0
Dark
Yellow
Light
Yellow
White
Light
Gray
Dark
Gray
Fair and warmer
followed by winds.
Storms brewing in direction
of wind.
Unsettled, cloudy, warmer.
Increasing wind, warmer,
stormy.
High winds, squalls, warm.
RISING
29.0 to 29.5
29.5 to 29.8
29.8 to 30.2
30.2 to 30.5
30.5 to 31.0
Dark
Gray
Light
Gray
White
Light
Yellow
Dark
Yellow
High winds, clearing, cooler.
Fail, cool, windy.
Fair, diminishing winds.
Generally fair, cool.
Clear and sunny with light
winds.
What is wind and how is it measured?
• Unequal heating of the Earth’s surface causes
pressure differences from place to place.
• Wind is air that moves horizontally, or parallel to
the ground, from an area of high pressure to an
area of low pressure.
• Wind speed is measured by an instrument called
an anemometer.
• Wind direction is measured by an instrument
called a wind vane.
What is visibility and how is it measured?
• Visibility is a measure of the transparency
of the atmosphere.
• Visibility is the way we describe how far
we can see.
• Poor visibility can be the result of air
pollution or fog.
Ways to Collect Weather Data
• Technological instruments provide measurements
from both stationary and moving locations.
»Ground Stations
»Anchored Weather Buoys
»Ships
»Airplanes
»Satellites