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About the Hartland ( Stoke ) AWS site

The Automatic Weather Station (AWS is on a domestic property in Stoke, a hamlet to the west of the village of Hartland (opens in new window) , in the parish of Hartland, Devon .

It is 90m amsl (metres above mean sea level), and 1.30 km West to the sea.

Recommendations on siting and instruments from the World Meteorological Organisation (WMO) (here quoting UK specific details where appropriate) are quite stringent - such as anemometers being on 10 metre masts in open country with nothing but level ground for 100 metres around, and rain gauges having a rim 1 foot above a level grass surface with the grass kept to a consistent height and no object within twice its height above the rim of the gauge.

Many of the WMO recommendations are hard to meet, particularly for domestic sites. Compromise is inevitable as one positions equipment to minimize the effects of the immediate environment on the readings obtained.

Some location factors affecting the Wind Speed readings measured:

Wind measurement is perhaps the most affected by locale, with not only trees and buildings reducing exposure, but also topography and terrain affecting direction and gustiness locally.

At this site, the anemometer is atop a 7 metre mast to take it above many local obstructions. The diagram on the right shows what rises above the anemometer, by how much, how far away, and in what direction.

Topography

The anemometer,7 m above ground level on a mast, is at 97m amsl;

topography gives approximate ground level horizons of:

Exposure

In the immediate vicinity of the site, exposure (here meaning objects that rise above anemometer height and may influence wind speed measurement) is:

Exposure of anemometer

In other words, no shelter from NNW to SE, some shelter from SE to SSE, little shelter from SSE to WNW , and significant shelter from WNW to NNW.

Location factors affecting Rainfall measurement:

The raingauge is sited as well as local circumstances allow , and nothing rises above its rim for at least 3 metres, and with nothing being within twice its height above the raingauge (WMO recommendation) there is no undue shelter from trees or buildings.

Measurement of sunshine

The AWS is fitted with a Davis Instruments solar radiation sensor. A Solar Location Diagram for the site (will be displayed here sometime in the future) shows that from early March until early October the sensor's "view" of the sun is unobstructed from sunrise until an hour or two before sunset