Surface temperature measurements
Temperatures over three different surfaces – grass, bare soil and concrete – are measured within the observatory:
Grass temperatures are measured just above the tips of short-mown grass.
Soil temperatures are measured within a bare soil plot approximately 1 m².
Concrete surface temperatures are measured on the surface of a concrete slab, approximately 60 x 90 cm and 3 cm thick.
The 'bare soil' patch, containing the bare soil minimum thermometer (upper) and the soil thermometers at (left to right) 5 cm, 10 cm and 20 cm respectively.
The grass minimum thermometer.
The concrete minimum thermometers.
All photographs taken March 2016: Photographs Copyright © Stephen Burt.
Climatological measurements of surface temperature are made using standard, calibrated sheathed minimum thermometers (note that only the minimum temperature is observed, as these thermometers are exposed to sunshine during daylight). The thermometers are read once daily at the 0900 UTC observation, when the thermometers are reset. If the thermometers are covered by snowfall, the readings will be unreliable - the record may be flagged accordingly on the archive.
Automatic observations of grass, bare soil and concrete surface temperatures are made using four-wire 100 Ω Class B platinum resistance thermometers (PRTs), manufactured by Farnell. These are exposed just above the relevant surfaces as for the liquid in glass thermometers: the relevant PRT and minimum thermometer are closely co-located towards the centre of the observatory plot. All surface PRTs are polled once per second using the Campbell Scientific CR9000X logger: standard ‘meteorological’ output consists of 1 minute averages of the polled PRT values in compliance with World Meteorological Organization specifications. Normally only the minimum temperature for any specified period (usually daily, either 0000-0000 UTC or the ‘climatological day’ 0900-0900 UTC) is quoted. Note that these ‘open’ sensors are exposed to solar radiation during daylight, and the indicated values may not be representative of the true surface temperature during daylight hours, particularly in bright sunshine.
Period of record available
Daily grass minimum temperatures for the university are available from January 1920, soil minimum from January 1961 and concrete minimum from January 1971
Sensor manufacturer link:
Farnell 100 Ω platinum resistance thermometers (PRTs)