Fraser Noble Sunshine Data

The Fraser Noble sunshine recorder is part of the national network of solar radiation stations that reports hourly sunshine data to the Met Office and thence to an archive kept by the WMO (World Meteorological Organisation). We are one of the longest standing stations on the network, having been in operation since 1967. The data from the whole network is available under the usual arrangements from the Met Office.

The recording head is a thermopile, housed under a double quartz dome. It has to be kept clean on a regular basis of bird crap and muck from the nearby chimney and other places. The data is recorded in an automatic data logger, programmed to integrate over hourly intervals in local solar time. It is then downloaded daily by landline upon commands sent from near Bracknell in the South of England. The signal is accurately converted into the international standard units of kJ hr-1 m-2. THE DATA SHOWN IN THE GRAPHS ARE THEREFORE PLOTS OF TOTAL ENERGY RECEIVED PER HOUR IN KILO JOULES PER SQUARE METRE.

Accuracy of calibration is essential when collecting data for comparison with other stations in the country or, indeed, around the world. Every 2 years, the signal is calibrated. Long-term stability is ensured by using a sensor of proven design from an agreed supplier. Our head is a type CM11 supplied through the Met Office by Kipp & Zonen, whose detector is especially designed to record uniformly whatever the altitude or azimuth of the sun. Its spectral range is from 305 nm to 2800 nm (the 50% sensitivity points). The device therefore reads the incident solar energy flux and does not record the longwave radiant energy flux that reaches the Earth's surface from the atmosphere and clouds.

Making the monthly data available here is a new departure for us. Choose your month:

July 2000	August 2000	September 2000	October 2000	November 2000	December 2000
January 2001	February 2001			May 2001

Some further technical information

For those who would like to know a little more about our detector, it is of the Moll-Gorczynski type. At its heart is a blackened set of manganin-constantan thermocouples connected in series. The junctions at the edge of the surface are in good thermal contact with the base plate. The junctions near the centre warm up in response to the incident solar radiation. The excess temperature they reach, and hence the voltage produced, depends on the loss of excess heat by conduction to the base, by convection through the air and by radiation. This combined heat loss can't be accurately predicted from first principles so the device has to be calibrated. However, once calibrated, the simplicity of design and the structural stability of the materials give the solarimeter an intrinsic long-term performance stability. The double quartz dome isolates the crucial thermopile from the influence of the wind on the heat loss process. Devices like ours that measure radiation from all around are called pyranometers. Devices that measure direct solar radiation only are called pyrheliometers.

Schematic diagram of solarimeter detecting element

The response time of the device to changes produced by passing clouds is about 30 seconds. Electrically, the thermopile produces a voltage of about 5 microvolts for each W m^-2 of incident energy. This signal is amplified and converted to a digital reading.

At night, the solarimeter reading is zero, corresponding to no radiation received in the sensitive wavelength range. A negative thermocouple voltage means that the thermopile is a bit cooler than its surroundings, which can happen when it is looking at a cloudless night sky. Exactly the same process is sufficient in winter to turn condensation into frost.

JSR