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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 othermometers
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 = 10 x 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 Aneroid 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.
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/~metr 1111