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Lecture

EESA09H3 Lecture Notes - Radiosonde, Anemometer, Weather Vane


Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin

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MEASURING WIND
- wind direction wind vane or weather vane
- wind speed anemometer
what type of device is used to measure higher level winds? These winds are measured using radiosonde
(weather balloons) or deduced using pressure distribution
- radiosonde is used to deduce pressure measurements.
- Upper level winds are geostrophic , so the knowledge of pressure gradient enables us to
calculate… WIND SPEED AND DIRECTION
PEOPLE TO REMEMBER
- Leon Batista Deflection anemometer
- James Lind pressure anemometer
- Thomas. R. Robinson four cup anemometer
- John Patterson three cup anemometer
- Dr. Andreas Pflitschsonic anemometer
- FITROY thermometer
- TORICELLIbarometer
DEFLECTION ANEMOMETER
- Was the first anemometer
- The first anemometer (deflection) was invented by ? Leon Batista Alberti in Italy in 1450
- How does a deflection anemometer work? He linked wind speed to the deflection of a
horizontal plate.
- Wind pushed horizontal platethe plate is connected to a springcompression of the spring is
proportional to WIND SPEED
- Leonardo Da Vinci created a similar anemometer a few decades later
- A century later Robert HOOKE of England created a Hooke anemometer
Pressure Anemometers
- James Lind in 1774 developed a tube anemometer
- U tube wind blows into tube and pushes liquid in the tube
- How does a tube anemometer work? Wind blows into the tube, and causes liquid to move up
and down the tube. The anemometer measures the force of the wind, relative to the force the
gravity.
- WHAT DOES THE PRESSURE ANEMOMETER MEASURE?force of wind, relative to force of gravity
- Higher wind speed- greater the amount of displaced liquid
- Dines anemometer
- 1892
Cup anemometer
- The cup anemometer was invented in 1846 by Thomas R. Robinson of England.
- How many cups did the anemometer have? It had four cups that were 90 degrees apart.
- What is the relationship between cup speed and wind speed? The relationship is that, cup speed
is nearly 1/3 of wind speed.
- What is an advantage of the cup anemometer ? An advantage of the cup anemometer is that it
doesn’t need to be reoriented as the wind direction changes. It changes direction on its own

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- Who created the three cup anemometer? The three cup anemometer was created in 1926 by
Canadian John Patterson. It
proved to be more accurate, usually within 3% up to 100 km/h.
Windmill Anemometer
- Similar to a cup anemometer but, it uses a propeller rather than a cup to gauge the wind
- speed.
- What is used to ensure that the anemometer is pointing into the direction of the wind?
Aerovane.
Thermoelectric Anemometerwind cooling effects
- Thermoelectric anemometers involve the use of? A wire
- How is this wire used as a part of the device ? In a thermoelectric anemometer a wire is heated
to above the ambient temperature.
- How does the device work? The rate of cooling of the wire is PROPORTIONAL TO THE WIND
SPEED.
- How can u distinguish the different types of winds ? Higher speed winds cool objects more
quickly.
- What is an advantage of the device? The instrument has the advantage of no moving parts.
Laser Radar Anemometer
- What principle does the Laser Radar Anemometer follow? It follows the Doppler principle , to
measure wind speed.
- What is the Doppler principle? Explains how sound waves from objects moving towards us have
a higher pitch (frequency) , than sound waves moving away from us (lower frequency)
- So , objects close to us have a HIGHER FREQUENCY , and objects away from us have a LOWER
FREQUENCY
- This explains the apparent change in pitch of train whistles and emergency vehicle sirens as the
vehicles travel past.
- How does the anemometer work ? uses a LASER BEAM, A fraction of the laser light reflects off
of nearby air molecules; some of this is returned to the anemometer (backscatter).
- Operates off of backscattered light
- What is backscattered light? The laser light reflects off of NEARBY AIR MOLECULES, and some of
this light returns to the anemometer.
- How is this anemometer used? The frequency of the backscattered light indicates the speed of
the air molecules (and wind)
Sonic Anemometer
- Dr. Andreas Pflitsch
- Measures how sound waves are modified by wind. (CHANGE IN THE SPEED OF SOUND)
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