Barometric pressure measurements

A manual reading of a Kew-pattern mercury barometer is made by the observer at or close to 0900 UTC. This instrument is located immediately outside the Sutcliffe Lecture Theatre on the ground floor of the Meteorology building (see photograph). It was originally located within the David Grimes Synoptic Laboratory, and moved around 2010. The readings are reduced to mean sea level after corrections for specific gravity (latitude dependent), instrument calibration error, instrument temperature and outside air temperature using a standard correction table for the altitude of the barometer (taken as 66.0 m above mean sea level).

The Kew-pattern mercury barometer outside the Sutcliffe Lecture Theatre in the Meteorology building, read every day at or close to 0900 UTC. Photograph March 2016: Copyright © Stephen Burt.

Automatic observations of barometric pressure at station level are made using a Druck DPI140 precision digital barometric pressure sensor, housed adjacent to the Campbell Scientific CR9000X logger within one of the teaching huts in the observatory enclosure (a second Druck unit is housed in the Instrumentation laboratory for student classes). This unit utilises a Druck resonant pressure transducer providing pressure readings between 800 and 1150 hPa absolute, to an accuracy of ±0.15mbar. This is the Department’s pressure standard against which other barometers are compared and therefore no height correction is applied to this. The pressure reading is displayed as an LED display on the front of the instrument. An analogue DC voltage output is utilised to log the pressure reading, polled once per second using the . Standard ‘meteorological’ output consists of (i) 1 minute averages of the polled values in compliance with World Meteorological Organization specifications, and (ii) correcting the observed average station-level pressure to mean sea level (MSL) once per minute using a standard correction formula for observed external air temperature (see ‘derived parameters’ for details derivation method).

Druck DPI140 precision digital barometric pressure sensor

CALIBRATION
The barometer is regularly checked (2-3 times per year) against the ‘synoptic field’. In this method, our PMSL values are compared against six-hourly observations from four nearby Met Office synoptic stations – currently Odiham 03761 to the south, Lyneham 03740 to the west, Benson 03658 to the north and Heathrow 03772 to the east: observations are weighted for distance to obtain a point value very close to the Observatory’s location. The results are averaged over the 24 hours and typically over a 7-10 day period to minimise minor timing, wind direction and synoptic situation differences; the results of the latest check are given in the ‘Operational notes’ below.

PRIOD OF RECORD AVAILABLE
Daily 0900 UTC readings of mean sea level barometric pressure are available from January 1908 to date. Automatic (logged sub-daily) barometric pressure observations are available from January 2009 to date.

How to request climatological data from the Observatory

Sensor manufacturer link:

Druck DPI140 precision digital barometeric pressure sensor manual (PDF)

Operational notes or changes:

This page updated January 2018