The meteorological station at our Wallingford site has been measuring local weather conditions, including daily rainfall, sunshine and temperature parameters, since 1962. Observations are also made of cloud cover, present weather and visibility.
Such long-term observations are important parameters for climatological analyses. They help develop an understanding of hydrometeorological systems and may also show trends over time that could be linked to environmental change.
Data are submitted regularly to the Met Office as part of the UK Climatological Observation Network (station 5558). Records from the site are used to support instrumentation calibration and other scientific projects.
Meteorological observations are made manually on a daily basis and recorded automatically every 15 minutes by an Automatic Weather Station. These data are available free of charge: please contact Stephen Turner or CEH Enquiries for retrievals requests.
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Daily readings are taken at 09:00 GMT, 365 days of the year by CEH staff. Instruments on the site are used to record data for rainfall, temperature, sunshine and wind speed and wind direction (each instrument is detailed below). Observations are also made of visibility, present weather conditions, ground state and cloud cover. Measurements of snow depth are also taken when necessary.
Air temperatures: Measured with thermometers housed in a Stevenson screen (a white louvered rectangular cabinet angled so that the opening door points north). The cabinet is designed to shield the thermometers inside against precipitation and solar radiation. Thermometers measuring dry bulb, wet bulb, maximum and minimum temperature are housed inside:
- Dry bulb temperature: Vaisala Digital thermometer measuring the current air temperature.
- Wet bulb temperature: Alcohol-in-glass thermometer measuring the reduction in temperature caused by evaporation. The difference between dry and wet bulb is used to calculate relative humidity.
- Maximum temperature: Vaisala Digital thermometer measuring the maximum air temperature recorded in the previous 24 hours.
- Minimum temperature: Alcohol-in-glass thermometer measuring the minimum air temperature recorded in the previous 24 hours. The thermometer has to be reset after reading to record the minimum temperature over the next 24 hours.
Soil temperatures: Alcohol-in-glass thermometers placed at 10cm, 30cm and 100cm depth in the soil. At 10cm depth, a right angled thermometer is placed into the ground which does not need to be removed for readings. The 30cm and 100cm thermometers are hung by a chain inside a metal-lined tube which is bored into the ground. These two thermometers are removed and replaced for each observation.
Surface temperatures: Alcohol-in-glass thermometers to measure the minimum temperature at ground level across grass and concrete surfaces in the previous 24 hours. Each thermometer has to be reset after reading to record the minimum temperature over the next 24 hours.
Rainfall: Measured using two different rain gauges to allow the assessment of undercatch by gauges mounted above the ground surface.
- Standard rainfall gauge: Met Office standard raingauge, 5” in diameter and 1’ above the ground surface. Acts as a storage raingauge, so any precipitation collected is emptied daily for measurement at the 09:00 observation and the recorded amount is assigned to the previous day.
- Ground level rainfall gauge: Measured using a raingauge developed by the Institute of Hydrology. The 5” diameter raingauge sits in a pit, with its rim at ground level. Acts as a storage raingauge, so any precipitation collected is emptied daily for measurement at the 09:00 observation and the recorded amount is assigned to the previous day.
Sunshine hours: Measured using a Campbell-Stokes sunshine recorder, a glass sphere mounted on an adjustable stand which holds shaped cards. The sun’s rays are focused on the glass ball which burns a trace of sunshine through the card. The duration of sunshine hours is then calculated from each daily card.
Wind direction: Measured from a wind vane on a 3m high steel pole. The wind direction is read to the nearest 10 degrees.
Wind speed: Measured using a cup anemometer on a 2m high steel pole which measures in 1/100th mile. Two readings are taken 10 minutes apart to calculate wind speed, which is expressed in knots.