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?