The Campbell–Stokes recorder (sometimes called a Stokes sphere) is a type of

sunshine recorder A sunshine recorder is a device that records the amount of sunlight, sunshine at a given location or region at any time. The results provide information about the weather and climate as well as the temperature of a geographical area. This informa ...

. It was invented by

John Francis Campbell John Francis Campbell (Scottish Gaelic: Iain Frangan Caimbeul; Islay, 29 December 1821 – Cannes, 17 February 1885), also known as Young John of Islay (Scottish Gaelic: Iain Òg Ìle) was a Scottish author and scholar who specialised i ...

in 1853 and modified in 1879 by Sir

George Gabriel Stokes Sir George Gabriel Stokes, 1st Baronet, (; 13 August 1819 – 1 February 1903) was an Irish migration to Great Britain, Irish English physicist and mathematician. Born in County Sligo, Ireland, Stokes spent all of his career at the University ...

. The original design by Campbell consisted of a glass

sphere A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

set into a wooden bowl with the sun burning a trace on the bowl. Stokes's refinement was to make the housing out of metal and to have a card holder set behind the sphere. The unit is designed to record the hours of bright sunshine which will burn a hole through the card. This basic unit is still in use today with very little change. It is widely used outside the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

(the Marvin sunshine recorder is generally the instrument used by the U.S. National Weather Service).

Technology

The crystal ball is typically 10 cm (4 inches) in diameter, and is designed to focus the rays from the sun onto a card mounted at the back and is set on a stand. The card is held in place by grooves of which there are three overlapping sets, to allow for the altitude of the sun during different seasons of the year. The recording of each day goes onto one card. In the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

the winter cards are used from 15 October to 29 February, the

equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...

cards from 1 March to 11 April and 3 September to 14 October. The summer cards are therefore used from 12 April to 2 September. Each card is marked as to the hour, with local noon being in the centre, and is read in tenths. In the

, the unit is set in a stand facing south to enable the maximum amount of sun to be recorded. It is important to place the unit in an area where the sun will not be blocked by buildings, trees or flagpoles. A modification to the standard unit for

polar region The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the polar circles. These high l ...

s is the addition of a second, north facing, sphere and card, to record the sunlight during the summer when it remains in the sky for 24 hours.

Advantages

The major advantage of this type of recorder is its simplicity and ease of use. There are no moving parts and it thus requires very little maintenance. The unit can be used anywhere in the world with little or no modification to the design. Electrically operated

pyranometer A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m2) from the hemisphere above within a wavelength range 0.3 μm to 3 μm. The name pyran ...

s can do the same work, but the Campbell–Stokes recorder uses solar power.

Disadvantages

When the sun is low in the sky it may not have enough strength to properly burn the card and thus can only measure the amount of bright sunshine as opposed to visible sunshine. This often occurs at dawn and dusk. Rain may cause the card to be torn when removing it and thus making it difficult to read. In areas of high

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

and during periods of

freezing rain Freezing rain is rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow or ice pellets, freezing rain is made entirely of liquid droplets. The raind ...

the sphere may be difficult to clean and may not be removed before the sun is shining again. It is also susceptible to external, non-weather factors such as dust, dirt or dried bird droppings accumulating on the glass sphere which requires frequent inspection and cleaning. The single biggest problem is in the reading of the cards. On days when the sun is alternately covered and exposed by clouds, the amount of burn on the card may be the same for 30 seconds as for 5 minutes. Thus, the reading of the card may differ from one observer to another. Comparisons with automatic instruments at German stations revealed that during summer the differences of the two measurement systems can reach up to 4 h per day. The mean difference was −0.23 h, i.e. the measurements of the Campbell–Stokes recorder are larger than the automatic.Hannak, L., Friedrich, K., Imbery, F., and Kaspar, F.: Comparison of manual and automatic daily sunshine duration measurements at German climate reference stations, Adv. Sci. Res., 16, 175–183, https://doi.org/10.5194/asr-16-175-2019, 2019. Instruments cost $US500–2,000.

References

External links

*
Campbell's manuscript notes
(requires QuickTime) – Alistair Fraser, Penn State University
AMS Glossary of Meteorology: Campbell–Stokes Recorder
– American Meteorological Society
Los Angeles Pierce College Weather Station
– provides examples of exposed record cards and photos of the recorder unit
Photograph of an 1876 version of the Campbell recorder
– National Maritime Museum, UK

– Environment Canada
Blake-Larsen Sun Recorder Web Site
– Blake Larsen Sun Recorder {{DEFAULTSORT:Campbell-Stokes recorder Sunshine recorders

Technology

Advantages

Disadvantages

References

Further reading

External links