Measuring the weather at at Woburn

Air temperature

Recorded over the 24 hour period up to 0900GMT, for the previous day's maximum temperature.

Since 1999, recorded by a thermistor (electronic temperature probe, Campbell Scientific, type 107). Previously recorded with a mercury-in-glass sheathed maximum thermometer housed in a naturally aspirating temperature screen. Missing data was supplied by the Met. Office for 18/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Recorded over the 24 hour period up to 0900GMT, for the current day's minimum temperature.

Since 1999, recorded by a thermistor (electronic temperature probe, Campbell Scientific, type 107). Previously recorded with a spirit-in-glass with indicator bar minimum thermometer, housed in a naturally aspirating temperature screen. Missing data was supplied by the Met. Office for 18-19/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Recorded at 0900GMT.

Since 1999, measured by a thermistor (electronic temperature probe, Campbell Scientific, type 107). Previously measured with a mercury-in-glass sheathed thermometer housed in a naturally aspirating temperature screen, the bulb covered by a cotton wick kept moist from a water reservoir. Until 2009 used with DRYB to calculate relative humidity (RELH), vapour pressure (VAP) and dew point (DEWP). There were problems with WETB drying out and there is no data 16/06/2009-08/10/2009.

Discontinued on 1st December 2009 and replaced by a Relative Humidity Sensor to measure RELH and from which VAP and DEWP are now calculated.

Recorded at 0900GMT.

Since 1999, measured by a thermistor (electronic temperature probe, Campbell Scientific, type 107). Previously measured with a mercury-in-glass sheathed thermometer housed in a naturally aspirating temperature screen. Missing data was supplied by the Met. Office for 18-19/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Used with WETB and then RELH to derive other variables including VAP and DEWP.

Recorded at 0900GMT.

Derived from DRYB and RELH since December 1st 2009, calculated after the method of Lowe (1977). From 10th September 2020 calculated after the method of Buck (1981), within the datalogger. Previously derived from DRYB and WETB, calculated within the datalogger (see derived variables). Before 1999 calculated from hygrometric tables. There were problems with WETB drying out and there is no data 16/06/2009-08/10/2009. Missing data was supplied by the Met. Office for 18-19/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Recorded at 0900GMT

Since 1999 recorded by a thermistor (electronic temperature probe, Campbell Scientific, type 107), approx. 1cm above grass surface, measurement period 1800-0900GMT, measured according to Met Office Procedure. Previously recorded with a glass sheathed spirit-in-glass with indicator bar minimum thermometer, with cotton sleeve and anti-condensation shield on upper part of the instrument, minimum temperature 0900-0900GMT. Missing data was supplied by the Met. Office for 18-19/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Recorded at 0900GMT.

Since 1999, measured by thermistors (electronic temperature probes, Campbell Scientific, type 107), buried in the soil at the appropriate depth. First recorded in 1928 using specially adapted mercury thermometers, set at depths of 1 foot and 4 feet (approximately 30 and 100cm) under grass cover. Other depths added later.

30cm depth recorded as E30T 1928-1970; 1988-current, and as G30T1971-1987. For soil temperature at approximately 1 metre depth, use E100T 1928-1967; 1971-current date, and E122T 1968-1970.

Recorded at 0900GMT.

Since 1999 measured by thermistors (electronic temperature probes, Campbell Scientific, type 107), buried in the soil at the appropriate depth. First recorded in 1968 using specially adapted mercury thermometers, set at depths of 10 and 20cm under bare soil.

Recorded at 0900GMT, for the total rainfall over the previous 24 hours,

Since Sept 10th 2020 recorded with an SBS500 tipping bucket rain gauge, funnel diameter 25.2cm and calibrated to tip at 0.2mm, manufactured by Environmental Measurements Ltd (EML), supplied and calibrated by Campbell Scientific. From 1999 until Sept 2020, rainfall was measured by an electronic tipping bucket rain gauge of 25.4cm (10 inch) diameter, calibrated to tip at 0.2mm, ARG100 (manufactured by EML, supplied and calibrated by Campbell Scientific). It was originally measured manually using a 12.7cm (5 inch) copper cylindrical rain gauge.

EML state that the "ARG100 rain gauge typically captures over 5% more rainfall than most traditionally-shaped cylindrical gauges due to its unique aerodynamic shape and reduced evaporation-loss properties". This has been found to be the case at Rothamsted, were rainfall in the 5" rain gauge continued to be measured on a twice weekly basis. The 5" gauges at Woburn ceased to be used at the time of automation, so it is not possible to make a comparison.

"Missing values" There are some instances before 1968 when no data is shown for RAIN (rather than zero). This is because a 'trace' of rain, snow, mist, dew or fog was manually recorded. A 'trace' is less than 0.05mm. For most purposes a missing value can be assumed to be zero.

Missing data was supplied by the Met. Office for the following dates: 01/07/2009-08/10/2009; 18/07/2013-26/07/2013; 09/10/2013-11/10/2013; 20/06/2015-28/06/2015; 16/06/2016-20/07/2016. © Crown Copyright 2009; 2013; 2015; 2016. Published by the Met. Office.

Sunshine

Hours of bright sunshine in previous 24 hours, 0000GMT to 2400GMT.

Since 1999, recorded automatically, calculated using the Campbell-Stokes equation from solar radiation measurments using a Kipp and Zonen thermopile pyranometer, model CM5, then model CM6B until 2016, currently model CMP6. Previously measured manually with a Campbell-Stokes sunshine recorder, at 2m above the ground. The sun's rays are focused onto a card (treated to prevent it from catching fire) and the brown scorch mark on the card is then measured. The cards are of varying lengths applicable to the time of year (winter, equinox, and summer).

Total (global) solar radiation in previous 24 hours, 0000GMT to 2400GMT.

Since July 1999 solar radiation has been recorded automatically using a Kipp and Zonen thermopile pyranometer, model CM5, then model CM6B until 2016, currently model CMP6. Previously it was recorded manually. No data was recorded 1/12/1998-28/6/1999.

Missing data was supplied by the Met. Office for the following dates: 18/07/2013-26/07/2013; 09/10/2013-11/10/2013; 07/06/2015-20/07/2016; 18/06/2023. © Crown Copyright 2013, 2015, 2016, 2023 Published by the Met. Office.

Recorded at 0900GMT.

Observed cloud cover on a scale of 0 to 9 Oktas. 0 oktas represents the complete absence of cloud. 1 okta represents a cloud amount of 1 eighth or less, but not zero. 7 oktas represents a cloud amount of 7 eighths or more, but not full cloud cover. 8 oktas represents full cloud cover with no breaks. 9 oktas represents sky obscured by fog or other meteorological phenomena.

From 1928-1960s, cloud cover shown in 10th, ie scale of 0-10, with 10 = full cover.

Recorded at 0900GMT.

Wind direction (WDIR) has been recorded since 1928 and was originally estimated by a wind vane with fixed ordinal points. It is shown as an angle (0-360 degrees), going clockwise from North. 360 = North, 90 = East, 180 = South, 270 = West. The reading 0 (or 000) indicates that there is no wind, ie the windspeed is 0 m/s. A WDIR reading of 0 with a windspeed greater than 0 implies that the WDIR is 360 degrees (North).

Since 1999 measured by an electronic wind vane (Vector Instruments, W200P) at 2m height, as an average over 10 minutes from 0850 to 0900GMT.

Recorded at 0900GMT.

Wind speed was first estimated at Woburn using the Beaufort scale, which describes wind speed on a scale of 0 (no wind) to 12 (hurricane) based on observations of the movement of smoke, leaves, branches, etc. It is shown in e-RA as wind force (WFORCE). From 1968 onwards this was replaced by direct measurements of wind speed (WINDSP).

The Beaufort scale can be adjusted to wind speed as follows: V = 0.836 x SQRT (B³) where V is the equivalent wind speed (m/s) at 10 metres above ground level and B is Beaufort scale number (see Conversion factors)

Recorded at 0900GMT.

From July 1st 1999, measured with an automated cup anemometer at 2m height, multiplied by 1.28 to upscale to the standard 10m height (see Conversion factors). This sensor was replaced in July 2008 with a new automated cup anemometer (Vector Instruments, A100LK) also at 2m, adjusted to the standard 10m height. Before July 1999 measured with an electronic sensor Didcot DWR201 cup anemometer.

From 1999 WINDSP, has been calculated as an average over 60 seconds sampled at 0900GMT. Average 24 hour windspeed can be calculated from total daily WINDRUN, correcting for height (see Conversion factors).

Average daily (24 hour) windspeed can be calculated from total daily WINDRUN, correcting for height (see Conversion factors).

Recorded at 0900GMT, for the run of wind in the previous 24 hours.

Since July 1999 measured with an automated cup anemometer at 2m high, replaced in July 2008 with a A100LK automated cup anemometer (Vector Instruments) also at 2m. Before July 1999 measured with a cup anemometer at 2m high, with a calibrated counter.

Recorded at 0900GMT.

Manual observations indicating if hail was present during the day, and if so, what type. Code 0-7. 1 = Ice prisms; 2 = Snow grains; 3 = Snow pellets; 4 = Ice pellets; 5 = Hail (5-9mm diameter); 6 = Hail (10-19mm diameter); 7 = Hail (20mm diameter or more). Null or code 0 = No hail.

Recorded at 0900GMT.

Manual observations recording if snow or sleet was present. Code 1 = sleet; code 5 = snow crystals. Null or code 0 = no snow.

Recorded at 0900GMT.

Manual observations recording if thunder was present. Code 1 = thunder present during the day. Null or code 0 = no thunder during the day.

Recorded at 0900GMT.

Manual observations recording if fog was present at time of observation. Code 1 = fog present. Null or code 0 = no fog.

Recorded at 0900GMT.

Manual observation recording if snow was present on the ground at the time of the observation. Code 1 = more than 50% ground at the station covered with snow; Null or code 0 = no snow lying. This may include snow from a previous day. See FSNOWD for depth of freshly fallen snow for the current day

Recorded at 0900GMT.

Manual reading of total depth of snow at time of observation. This may include snow from a previous day. See FSNOWD for depth of freshly fallen snow for the current day.

Recorded at 0900GMT.

Manual recording of total depth of freshly-fallen snow at time of observation.

Recorded at 0900GMT.

Since July 3rd 2018 measured by a Relative Humidity sensor EE181 (manufactured by E+E Elektronic Corporation, supplied and calibrated by Campbell Scientific). This replaced the MP100A RH Sensor (manufactured by Rotronics, supplied by Campbell Scientific) used from December 2009. Before December 2009 available as a derived variable within e-RA, derived from WETB and DRYB (see derived variables). Missing data was supplied by the Met. Office for 18-19/06/2023. © Crown Copyright 2023. Published by the Met. Office.

Recorded at 0900GMT.

A mercury barometer was used to measure atmospheric pressure. Attached thermometer readings (THERM) are available from the e-RA curators.

Recorded at 0900GMT

From December 2009 onwards calculated within the datalogger from RELH and DRYB after the method of Lowe (1977). From 10th September 2020 calculated after the method of Buck (1981), within the datalogger.

Before December 2009 calculated within the datalogger from WETB and DRYB, (see derived variables). There were problems with WETB drying out and there is no data 16/06/2009-08/10/2009. Before 1999 calculated from hygrometric tables.

Recorded at 0900GMT.

Manual recording of visibility at time of observation. Codes 1962-1999: Code X = Dense fog. Visibility range 0-19m; CODE E = Dense fog. Visibility range 20-39m; CODE 0 = Thick fog. Visibility range 40-99m; CODE 1 = Thick fog. Visibility range 100-199m; CODE 2 = Thick fog. Visibility range 200-399m, CODE 3 = Moderate fog. Visibility range 400-999m; CODE 4 = Very poor visibility, range 1000-1999m; CODE 5 = Poor visibility, range 2000-3999m; CODE 6 = Moderate visibility, range 4-9km; CODE 7 = Good visibility, range 10-19km; CODE 8 = Very good visibility, range 20-39km; CODE 9 = Excellent visibility, range 40km or over.