# Definition and measurement of wind

> How wind is defined, measured, and reported in aviation. Learn about compass rose, METAR/TAF true vs magnetic wind, and anemometers.

- **Subject:** 050 — Meteorology
- **Section:** 050-02 — Wind
- **Topic code:** 050-02-01
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/meteorology/wind/definition-and-measurement-of-wind/

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## Definition
Wind is always defined by the direction **from which it comes** (origin).

![Compass rose](https://upload.wikimedia.org/wikipedia/commons/1/17/Compass-rose-32-pt.svg)

*   **NE**: Wind from 045°.
*   **SE**: Wind from 135°.
*   **SW**: Wind from 225°.
*   **NW**: Wind from 315°.

## Measurement
Surface wind is measured by anemometers (speed) and wind vanes (direction) located at a standard height of **10 meters** above the ground.

![Anemometer](https://upload.wikimedia.org/wikipedia/commons/1/1b/Anemometer.jpg)
*Anemometer used for measuring wind speed.*

### Averaging Periods and Reference
How wind is reported depends on the type of report:

1.  **METAR / SPECI (Aerodrome Meteorological Reports)**:
    *   Average: **10 minutes**.
    *   Direction: **True** degrees.
    *   Gusts (G): Reported if the maximum speed exceeds the average by at least **10 knots**.
    *   *Note: VOLMET reports transmit METAR/TAF, so they use true degrees.*

2.  **Local Reports / ATS / Tower (ATIS, Takeoff/Landing Clearances)**:
    *   Average: **2 minutes**.
    *   Direction: **Magnetic** degrees.
    *   This is crucial to match the aircraft compass reference and runway orientation (which is magnetic).

## Effect of Friction
Friction with the Earth's surface reduces wind speed compared to winds aloft (geostrophic/gradient).
*   Over **water**: Speed reduces to approx. **70%**.
*   Over **land**: Speed reduces to approx. **50%**.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.