MANU_WIND MEASUREMENT ,Different Ways of Measure of Wind .pptx

In this document, We discuss about different methods of wind measurement

1. Wind Measurement ATS409:Instrumentations in Atmospheric Studies Submitted by: Manu Jangid 2023MSATS012 Submitted to: Dr. Chinmay Mallik Assistant Professor CIA - II PRESENTATION Department of Atmospheric Science School of Earth Sciences Central University of Rajasthan

2. CONTENTS

3. Introduction and Learning Objectives Wind is the motion of air relative to Earth. Wind is a vector quantity with direction and speed, so multiple measurements are required to determine the components of the vector in two or three dimensions Like all measurements, an observation of the wind should include appropriate “provenance” SOURCE-Meted The map shows several local wind systems from around the world The normal unit of wind speed is the knot (nautical mile per hour = 0.51 m/s = 1.15 mph). Wind direction is measured relative to true north (not magnetic north) and is reported from where the wind is blowing. An easterly wind blows from the east or 90 degrees, a southerly from the south or 180 degrees and a westerly from the west or 270 degrees.

4. Winds Fundamentals Temperature, pressure, and wind are causally linked, so measurements of all three are often needed to study the wind fields and especially dynamic changes in those fields. For example, the map shows the relationship between wind and pressure at a global scale SOURCE-Meted

5. Wind passage (L (m)) : The distance that wind (air mass) covers over a given period of time (t). Instantaneous wind speed (Vi (m/s)) : Wind speeds change very quickly Average wind speed (Vm (m/s)) : The average wind speed is the average of the instantaneous wind speed over a ten-minute period Starting threshold speed (V0 (m/s)) : The lowest wind speed at which a rotating anemometer mounted in its normal position starts to turn continuously. Units Speed conversion table Wind-direction scale In synoptic reports, the average wind speed measured over a period of 10 minutes is reported every 0.5 m/s or in knots (kt) and , the average wind direction in degrees to the nearest 10 degrees using a code number from 01 to 36.

6. Wind Estimation Beaufort Scale

7. Categories of Wind Sensors S.N. Category Example(s) Common Uses 1 Mechanical sensors cup or propeller anemometer; wind vane measurements at weather stations (official and home) 2 In situ electronic sensors hot-wire anemometer fast response measurements; turbulence characterization 3 Drifting-position sensors radiosonde, driftsonde, pibal atmospheric soundings 4 Sensors based on impact pressure pitot tube measuring airspeed of moving vehicles including aircraft 5 Sensors that use measurements of a time shift ultrasonic anemometer modern official weather stations; research that investigates turbulence or fluxes 6 Sensors that use measurements of a Doppler shift Doppler radar and lidar; wind profiler remote measurement of wind at a range of positions from the sensor The instruments used to measure wind are known as Anemometers.

8. The Cup Anemometer SOURCE-Meted The cup anemometer provides the wind speed and the vane provides the wind direction The current accepted standard cup anemometer has three cups. The cup anemometer is similar to a first-order system that has an exponential response to changes in wind speed, while the wind vane resembles a second-order system with a dynamic response toward an equilibrium position with damping. The important characteristics of cup anemometers Linear calibration: Cup anemometers are calibrated under steady conditions in a wind tunnel Typical calibrations are linear; v = aω + b where v=wind speed , ω=angular rotation rate, a&b= calibration coefficients There is also a “starting threshold” for v (typically <0.3 m/s) below which the cups do not rotate. Typical values are a=0.4 m and b=0.2 m/s The NCAR Earth Observing Laboratory wind tunnel, specifically designed for testing meteorological instrumentation.

9. 2. Response time: Although the cup anemometer responds exponentially to a change in the wind, the time constant varies with the magnitude of the wind 3. Overspeeding: The cup anemometer responds faster to increases in wind speed than to decreases, which results in a bias error in the average wind called “overspeeding. The green line (v) is the assumed wind speed and the blue line (M) is the modeled measurement, responding faster to an increase in v than to a decrease. SOURCE-Meted

10. The Wind Vane: Wind vanes typically provide uncertainty of <3°, and like cup anemometers are characterized by a distance constant called the delay distance (typically about 1 m; Finkelstein, 1981) that specifies the air motion required to give 50% response to a wind direction change of 10°.

11. Advantages and Limitations The biggest disadvantage of mechanical anemometers is that the bearings have to be replaced on a routine basis. In addition, whether cup or propeller, they have a minimum starting threshold and both exhibit some non-linearity, albeit not much. Response time is longer/slower than other anemometers, including hot-wire and sonic anemometers. SOURCE-Meted Exploded view of cup anemometer with 3D -printed parts

12. REFERENCES https://www.meted.ucar.edu/index.php https://www.metoffice.gov.uk/weather/guides/observations/how-we-measure-wind https://www.jma.go.jp/jma/jma-eng/jma center/ric/Our%20activities/International/CP4-Wind.pdf