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Grading Your Weather Station

Altitude

Before you can complete your station details, you must find out the altitude, in metres, of your weather station. If you are in Britain, the best way to do this is to use an Ordnance Survey map. You can do this online by visiting their Get-a-Map website and finding your location.

  • If you have not registered or do not wish to register with the OS, you can still use this facility - just close the opening dialogue box down by clicking the X in its top right corner.
  • Enter your post code into the Locate search box at the top left and click the button
  • Switch to 'Leisure' view to bring up the actual OS map

Determining Your Station's Grade

Temperature, rainfall, wind speed and many other weather parameters are highly dependent on the precise location of a weather station, the equipment being used, and times of observations. To enable readers of the bulletin to judge the quality of the data relating to specific stations, we operate a station exposure grading system.

The exposure code consists of 7 characters, representing factors affecting:

  • Temperature
  • Rainfall
  • Sunshine
  • Hour of terminal observations
  • Exposure
  • Urban influence
  • Network of station types to which your station will belong

The characters are then written as a 'word' with no spaces in the form 'TRSHEUN'. Examples might include 'CB-A37-' or 'AA-A35R'.

To work out your TRSHEUN code follow the guidance below. Scrolling down and assessing your site exposure first would help, as this will affect other grades.

T MEASUREMENTS OF AIR TEMPERATURE
A Standard instruments in Stevenson Screen or approved AWS radiation screen, calibration within last 5 years, site exposure minimum = 3
B Standard instruments in Stevenson Screen or approved AWS radiation screen, calibration within last 5 years, site exposure = 2 or 3
C Non-standard instruments and/or no or non-standard radiation screen and/or sheltered site, site exposure 2 or less
U Instruments unknown or not stated
- No air temperature measurements made at this site
Standard instruments in this context means – Calibrated mercury-in-glass thermometers or electronic sensors exposed in a standard pattern of Stevenson Screen, or a model of AWS screen which has been trialled alongside a Stevenson screen and been shown to provide similar or better performance than the Stevenson screen.
R MEASUREMENTS OF RAINFALL
A Standard 'five inch' manually-read raingauge, at standard height above ground (30 cm), site exposure minimum = 3
B Standard 'five inch' manually-read raingauge or calibrated 0.1 mm or 0.2 mm capacity tipping-bucket
raingauge, the rim mounted at standard height above ground (30 cm), exposure = 2 or 3
C Non-standard raingauge and/or tipping-bucket raingauge with capacity > 0.2 mm, and/or raingauge rim
mounted higher than 30 cm above ground (30 cm), and/or sheltered site, exposure 2 or less
U Instruments unknown or not stated
- No rainfall measurements made at this site
Standard instruments in this context means – Standard-pattern (Snowdon or Met Office Mk II pattern) 'five-inch' copper raingauge, with deep funnel, the rim of the gauge level and mounted at 30 cm above ground level, meeting the minimum 'twice the height' exposure requirement.
S MEASUREMENTS OF SUNSHINE
A Standard sunshine recorder, nil or very slight exposure obstruction (average obstruction 5% or less across
the year, maximum 10% at any time of year)
B Standard sunshine recorder, partially obstructed exposure (average obstruction 10% or less across the year,
maximum 20% at any time of year)
C Non-standard sunshine recorder or sunshine estimated from pyranometer/solarimeter record and/or very
obstructed exposure
U Instruments unknown or not stated
- No sunshine measurements made at this site
Standard instruments in this context means – Campbell-Stokes sunshine recorder or electronic sunshine recorder (R&D Electronics model, or the Met Office standard Kipp& Zonen CSD sensor). The instrument should be mounted in a location where it has the best possible view of the sky at all
seasons.
H TERMINAL HOURS
A Morning terminal hours. Air temperature and rainfall terminal hour is between 0600 and 0900 GMT, daily temperature and rainfall values relate to standard 24 hour period morning to morning
B Midnight terminal hours. Air temperature and rainfall terminal hour is 0000 GMT daily. (This is the default on most AWS.)
C Other terminal hours. Air temperature and rainfall terminal hour is other than A or B above, or extremes do not relate to 24 hour periods
U Terminal hours unknown or not stated
E EXPOSURE
5 Very open exposure; no obstructions within 10 x the height, or more, of temperature or rainfall instruments
4 Open exposure; most obstructions/heated buildings 5 x the height or from temperature or rainfall instruments, none within 2 x the height
3 Standard exposure; no significant obstructions or heated buildings within 2 x the height of temperature or rainfall instruments
2 Restricted exposure; most obstructions/heated buildings 2 x the height, or more, from temperature or rainfall instruments, none within 1 x the height
1 Sheltered exposure; significant obstructions or heated buildings within 1 x the height of temperature or rainfall instruments
0 Very sheltered exposure; site obstructions or sensor exposure severely limit exposure to sunshine, wind, rainfall
R Rooftop site. Rooftop sites for temperature and rainfall sensors should be avoided where possible.
U Exposure unstated or unknown
  • Exposure ratings relate to the site of the temperature and rainfall instruments only, which should normally be at ground level. Sensors for sunshine, wind speed etc are best exposed as freely as possible and rooftop or mast mountings are often preferable.
  • Exposure guidelines are based on a multiple of the height (h) of the obstruction above the sensor height; the standard is a minimum distance of twice the height (2h). Thus for a raingauge at 30 cm above ground, a building 5 m high should be at least 9.4 m distant (5 m less 0.3 m, x 2), and a 10 m building should be at least 17 m from a thermometer screen (10 m less 1.5 m, x2)
  • If the temperature and rainfall sensors are not on the same site, use code for the most limited sensor exposure.
U OKE'S URBAN CLIMATE ZONE INDEX
1 Intensely developed urban zone with detached close-set high-rise buildings with cladding, e.g. downtown towers
2 Intensely developed high density urban with 2 – 5 storey, attached or very close-set buildings often of brick or stone, e.g. old city core
3 Highly developed, medium density urban with row or detached but close-set houses, stores & apartments e.g. urban housing
4 Highly developed, low density urban with large low buildings & paved parking, e.g. shopping mall, warehouses
5 Medium development, low density suburban with 1 or 2 storey houses, e.g. suburban housing
6 Mixed use with large buildings in open landscape, e.g. institutions such as hospital, university, airport
7 Semi-rural development with scattered houses in natural or agricultural area, e.g. farms, estates
U Urban Climate Zone unstated or unknown
These are taken from Oke, T.R., 2007: "Siting and exposure of meteorological instruments at urban sites".
N NETWORK
S Synoptic site. Contributes one or more daily observations in real-time to the WMO synoptic network
C Climatological site. Contributes daily climatological data to the national climatological network (Met Office/Met Eireann), normally monthly
R Rainfall site. Contributes daily rainfall data to the national raingauge network (Met Office/Environment Agency/Met Eireann), normally monthly
- Station data not provided to other national networks apart from COL

 

Make a note of your Altitude and TRSHEUN code then return to the Membership Application Page.

 

 

Stratocoumulus clouds over Lindisfarne Harbour Stratocumulus clouds over Lindisfarne Harbour