Weather Instruments
Anemometers, Barometers, Sling Psychrometers, Thermometers, and Weather Charts.
Air Temp and Thermometer
• “Thermo” = Heat– Measures the amount of heat
energy in the atmosphere.– Heat comes from solar radiation
that was absorbed by the OZONE layer in the Stratosphere and goes into the air.
– Measured by THERMOMETER
Can you read this
thermometer?
Humidity and Sling Psychrometer
• “Psychro” = Cold – Measures the amount of water vapor in the air.– Relative humidity is the current amount of water
vapor in the air compared to the total amount of water vapor the air can hold.• When the air is nearly completely filled with vapor, it
feels “muggy” if the air is hot. What word would you use to describe humidity?
– Measured by PSYCHROMETER
Comparing Humidity Levels
How humid is it?
• If the relative humidity of the air is 88%... How would it feel outside?
Wind Speed and Anemometer
• “Anemo” = Wind– Measures the wind speed in the air.– Changes in the heating of Earths surface (uneven),
air temp, and air pressure cause air to move– Horizontal (side to side) movement of air: WIND– Vertical (up and down) movement of air: AIR
CURRENT– Measured by ANEMOMETER
Anemometer… Close Up!
Convection Currents or Cells
• Wind is caused by…– Warm air rises because it is less dense, cooler
sinks because it is more dense.– This pattern
is called a convection cell
Air Pressure and Barometer• “Baro” = Weight– A barometer works by measuring the amount of
force exerted by the air’s molecules hitting a surface area.
– Measured in millibars (mb)– When air heats up, the molecules spread apart
and become less dense and the air pressure goes down (becomes low pressure).
– Measured by BAROMETER
Reading a Barometer• Can you read
this Barometer?
• Standard air pressure is 1013.25 mb. Does this barometer read at standard air pressure?
1018 mb
Air Pressure and ISOBARS• Isobar = (baros, meaning 'weight') is a line of
equal or constant pressure on a graph, plot, or map.
ISOBARS – lines of pressureThe rules for drawing isobars are…1. Isobar lines may never cross or touch. 2. Isobar lines may only pass through pressures
of 1000 + or - 4. In other words, allowable lines are 992, 996, 1000, 1004, 1008, & so on.
3. The atmospheric pressure is given in millibars (mb).
4. Low Pressure – increase with distance.5. High Pressure – decreases with distance.
Weather Charts
• Weather Charts have lots of symbols and information.
Fronts and Symbols
• Warm air mass behind a cold air mass– warm front
• Cold air mass behind a warm air mass– cold front
• Occluded fronts can signal weakening of storm
• Stationary fronts prolong bad weather
Pressure Systems
• High pressure: typically fair weather • Low pressure: typically cloudy, unstable
conditions… Bad weather • General movement: west to east in the US
Can you read this map?
Map Questions…
• What is located where the rain is happening - High or Low pressure?
• What do you notice the weather conditions are like near the H’s?
• What type of front is located in the central United States?
• What can you predict about future weather conditions in Arkansas based on this map?