Lecture 2 (9/16)METR 1111

Meteorological

Instruments

Thermometers

• Thermometers measure temperature.

• Some types of thermometers:

- liquid-in glass

- bimetallic

- infrared

- thermoelectric

Liquid in Glass Thermometer

• Most common for everyday use (medicine, cooking, etc.)

• Liquid is either mercury or alcohol

• Difficult to automate – led to development of other thermometers

Bimetallic Thermometer

• Uses a coil of two different metals attached to one another

• Different metals expand at different rates

• Used in:– round outdoor thermometers – thermostats

• Also difficult to automate

Infrared Thermometer

• Measures the infrared radiation emitted by an object (night-vision uses it)

• Used to take an instant (not delayed) temp reading of the air.

• Easily automated – but other aspects such as ground color can

affect temp readings

Thermoelectric Thermometer

• Most common thermometer for automated stations

• Advantages: Rugged, reliable, wide temperature range, inexpensive, and fast response

• Works by passing a known voltage through a wire who’s resistance varies as a function of temperature.

Anemometer

• Used to measure wind speed

• Most common type = cup anemometer

• When the wind is gusty, it overestimates the avg. wind speed because of momentum

• Must be placed far away from obstacles to be accurate (Distance = 10x the height of tallest object)

Wind Vane

• Measures wind direction

• Points parallel with the wind

• Has a “fatter” tail than head so it won’t point 180º in the wrong direction.

• Easily automated with a rotating sensor inside the joint with the pole.

Barometer

• Measures atmospheric pressure• Works like a weight scale for the air above it• Aneroid barometer uses gears attached to a sealed

air container that expands or contracts with decreasing or increasing pressure, respectively.

• Mercury barometer has a bowl with liquid in it and a tube sealed at the top and open at the bottom immersed in the liquid. When pressure rises, the mercury in the tube rises.

Aneroid Barometer

Rain Gauge

• Several kinds but tipping bucket rain gauge is the most useful since it can be automated.

• How it works:

- Rain falls into one of two buckets

- When it’s fills up with .01” of rain,

gravity causes it to tip

- Other bucket fills and tips

- Number of tips counted electronically

Other instruments

• Many other instruments are used such as a hygrometer which measures humidity.

• There are other instruments to collect data that we will discuss later (radar, satellites, and rawindondes)

• In METR 3613 “Meteorological Instruments” you will learn MUCH more about this subject.

Networks

• Networks are used to collect mass quantities of weather data. (most are stationary)

• ASOS Network (Automated Surface Observation System) – nationwide network for measuring weather conditions every hr.

• Oklahoma Mesonet – unique to Oklahoma, dense network of weather stations in entire state, measuring conditions every 15 min.

View of a Typical Mesonet Station

For next time:

• Read Ch 3 in Weather Book (pg 31-45) – “Why the Wind Blows”

• Do homework 2 and be prepared for the quiz in class next week.

• Class website:– weather.ou.edu/~metr1111