Measuring weather

Newer inventions in thermometers
Thermocouples relate temperature to electricity. They consist of contacting pieces of two different metals. The contacting metals produce an electrical voltage that is dependent on temperature in a known way, so measuring the voltage is equivalent to measuring the temperature. Thermocouples are cheap to make, and since they are made of metals that are good thermal conductors, they are quick to respond to temperature changes, especially if they are small.

Thermistor and Resistance Thermometer Detectors (RTDs) are electrical resistors whose resistance changes with temperature. The difference is that thermistors use metal oxides and RTDs use pure metals. First deployed in 1985, a platinum resistance thermometer is a common device for temperature measurement found in an ASOS. Thermistors have a fast response time when they are small and can be very accurate, to 0.001 degrees centigrade, especially when sheathed in glass.

Temperature data collected from surface thermometers is checked for quality, used for forecast initializations and daily weather reports, and entered into the historical climate record.

Make your own thermometer!
You can make your own thermometer with the following materials:

• clear plastic bottle
• water
• rubbing alcohol
• clear plastic drinking straw
• modeling clay
• food coloring

Fill the bottle about 1/4 full with equal parts of water and rubbing alcohol. Add a few drops of food coloring. Put the straw in the bottle without letting it touch the bottom. Take the modeling clay and seal the neck of the bottle so that the straw stays in place. The straw must not touch the bottom of the bottle. Hold your warm hands on the bottom of the bottle. The liquid will move up through the straw.

As your warm hands heat the bottom of the jar, the liquid expands as it warms. So it no longer fits in the bottom of the bottle. As the alcohol expands, the colored mixture moves up through the straw. If the bottle gets extremely hot, the mixture will rise up through the top of the straw - but never put a plastic bottle on a hot surface like a stove!

Next page   -> in situ, surface observations, humidity

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