1. Lecture 2 (9/16) METR 1111 Meteorological Instruments

2. Thermometers Thermometers measure temperature. Some types of thermometers: - liquid-in glass - bimetallic - infrared - thermoelectric

3. 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

4. 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

5. 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

6. 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.

7. 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)

8. 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.

9. 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

10. 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

11. 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.

12. 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.

13. View of a Typical Mesonet Station

14. 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