Stevenson screen

Short description: Enclosure for meteorological devices

Exterior of a Stevenson screen

A Stevenson screen or instrument shelter is a shelter or an enclosure used to protect meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them.[1] It forms part of a standard weather station and holds instruments that may include thermometers (ordinary, maximum/minimum), a hygrometer, a psychrometer, a dewcell, a barometer, and a thermograph.

Stevenson screens may also be known as a cotton region shelter, an instrument shelter, a thermometer shelter, a thermoscreen, or a thermometer screen. Its purpose is to provide a standardised environment in which to measure temperature, humidity, dewpoint, and atmospheric pressure. It is white in color to reflect direct solar radiation.

## Contents

* 1 History
* 2 Composition
* 3 Size
* 4 Siting
* 5 Future
* 6 References
* 7 External links

## History

American variant (Cotton Region shelter)

It was designed by Thomas Stevenson (1818–1887), a Scottish civil engineer who designed many lighthouses, and was the father of author Robert Louis Stevenson. The development of his small thermometer screen with double-louvered walls on all sides and no floor was reported in 1864.[2] After comparisons with other screens in the United Kingdom , Stevenson's original design was modified.[3]

The modifications by Edward Mawley of the Royal Meteorological Society in 1884 included a double roof, a floor with slanted boards, and a modification of the double louvers.[4] This design was adopted by the British Meteorological Office and eventually other national services, such as Canada . The national services developed their own variations, such as the single-louvered Cotton Region design in the United States .[5]

## Composition

The traditional Stevenson screen is a box shape, constructed of wood, in a double-louvered design.[6] However, it is possible to construct a screen using other materials and shapes, such as a pyramid. The World Meteorological Organization (WMO) agreed standard for the height of the thermometers is between 1.25 and 2 m (4 ft 1 in and 6 ft 7 in) above the ground.

## Size

Interior of a Stevenson screen

The interior size of the screen will depend on the number of instruments that are to be used. A single screen may measure 76.5 by 61 by 59.3 cm (30.1 by 24.0 by 23.3 in) and a double screen 76.5 by 105 by 59.3 cm (30.1 by 41.3 by 23.3 in). The unit is either supported by four metal or wooden legs or a wooden post.

The top of the screen was originally composed of two asbestos boards with an air space between them. These asbestos boards have generally been replaced by a laminate for health and safety reasons. The whole screen is painted with several coats of white to reflect sunlight radiation, and usually requires repainting every two years.

## Siting

The siting of the screen is very important to avoid data degradation by the effects of ground cover, buildings and trees: WMO 2010 recommendations, if incomplete, are a sound basis.[7] In addition, Environment Canada, for example, recommends that the screen be placed at least twice the distance of the height of the object, e.g., 20 m (66 ft) from any tree that is 10 m (33 ft) high.

In the northern hemisphere, the door of the screen should always face north so as to prevent direct sunlight on the thermometers. In polar regions with twenty-four-hour sunlight, the observer must take care to shield the thermometers from the sun and at the same time avoiding a rise in temperature being caused by the observer's body heat.

A special type of Stevenson screen with an eye bolt on the roof is used on a ship. The unit is hung from above and remains vertical despite the movement of the vessel.

## Future

In some areas the use of single-unit automatic weather stations is supplanting the Stevenson screen and other standalone meteorological equipment.[citation needed]

## References

1. ↑ "Stevenson Screen". Environment Canada. http://www.on.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/screen_e.html.
2. ↑ Thomas C.E. Stevenson (June 1864). "New Description of Box for Holding Thermometers". Journal of Scottish Meteorological Society 1: 122. https://hdl.handle.net/2027/nyp.33433110019654?urlappend=;seq=138.
3. ↑ Middleton, W.E. Knowles (1966). A History of the Thermometer and Its Uses in Meteorology. Baltimore: Johns Hopkins Press. ISBN 9780801871535. https://books.google.com/books?id=PApRAAAAMAAJ.
4. ↑ Edward Mawley (January 1884). "Report on Temperatures in Two Different Patterns of Stevenson Screens". Quarterly Journal of the Royal Meteorological Society X (49): 1–7. doi:10.1002/qj.4970104902. Bibcode: 1884QJRMS..10....1M. http://babel.hathitrust.org/cgi/pt?id=chi.73388124;view=1up;seq=275.
5. ↑ Sparks, W.R. (1972). "The Effect of Thermometer Screen Design on the Observed Temperature". Wmo-315 (Geneva: World Meteorological Society). https://library.wmo.int/doc_num.php?explnum_id=8131.
6. ↑ "High May Temperatures in London". Symons's Meteorological Magazine XLVIII (569): 88–90. June 1913. https://books.google.com/books?id=qxc7AQAAMAAJ&pg=PA89. (See p. 89.)
7. ↑ "Commission for Instruments and Methods of Observation". 2–8 September 2010. https://library.wmo.int/doc_num.php?explnum_id=4939.

## External links

* Article - Temperature measurement and the Stevenson screen
* Example of a non-traditional home built Stevenson screen

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Earth-based meteorological equipment and instrumentation

* Anemometer
* Atmometer
* Barograph
* Barometer
* Ceiling balloon
* Ceiling projector
* Ceilometer
* Dark adaptor goggles
* Dewcell
* Disdrometer
* Dropsonde
* Field mill
* Heat flux sensor
* Hygrometer
* Ice accretion indicator
* Lidar
* Lightning detector
* Nephelometer
* Nephoscope
* Pan evaporation
* Pyranometer
* Pyrheliometer
* Radiosonde
* Rain gauge
* Snow gauge
* Snowboard
* Snow pillow
* SODAR
* Solarimeter
* Sounding rocket
* Stevenson screen
* Sunshine recorder
* Tethersonde
* Thermo-hygrograph
* Thermometer
* Tide gauge
* Transmissometer
* Weather balloon
* Weather buoy
* Weather radar
* Weather vane
* Whole sky camera
* Wind profiler
* Windsock

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