Dr David Hooper


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Capel Dewi Atmospheric Observatory

The National Centre for Atmospheric Science (NCAS) Capel Dewi Atmospheric Observatory (CDAO) is located at 52.424500°N, -4.0054665°E. This is a rural valley location, which is approximately 6 km to the east of the coastal town of Aberystwyth in west Wales, UK. Refer to the Location section below for more details.

Prior to April 2020, the CDAO was known as the Natural Environment Research Council (NERC) Mesosphere-Stratosphere-Troposphere (MST) Radar Facility.

NCAS operates a number of meteorological instruments at the site in support of its long term measurement programme. Most of the datasets span between 10 and 20 years. They are all openly-accessible through the Centre for Environmental Data Analysis (CEDA). NCAS also provides access to output from the Weather Research and Forecasting (WRF) mesoscale model for this location.

AMOF can support projects at the CDAO in a number of ways:

  • through dedicated operation of the MST Radar
  • by hosting guest instruments
  • through provision of radiosonde launch/tracking facilities.

An application for facility support must be submitted in such cases.

Observatory operational status: instrument by instrument break down of instrument performance.

COVID-19 Restrictions: No one may visit the CDAO without first obtaining permission from the observatory manager. Only exceptional cases will be considered, but even these may be affected by regional or national restrictions. Note that restrictions within Wales might be different to those in other parts of the UK.

All instruments are operated on a quasi-continuous basis. There are occasional breaks in coverage as a result of maintenance work or problems with equipment.

Follow the links to find out more about the CDAO instruments that measure the following parameters:

A Noctilucent Cloud (NLC) Camera is operated at the Chilbolton Atmospheric Observatory in support of the M-mode observations made by the MST Radar.

Here is a list of the instruments:

The following principles apply to the data (including photographs taken by automatic cameras) and plots for instruments operated by the Capel Dewi Atmospheric Observatory.

This section covers the following topics:

Licensing and acknowledgements
  • Data files/plots are openly-accessible under the(UK) Open Government Licence. They may be used for any purpose as long as an appropriate acknowledgement is given.
  • Where data/plots are used in any type of publication:
    • The National Centre for Atmospheric Science must be acknowledged as the provider
    • For academic publications, the citation details given in the relevant Centre for Environmental Data Analysis (CEDA) catalogue page for the dataset must be used. Links to the catalogue pages are given within the Data section of the AMOF page for each instrument.


Access to data files/plots
  • Data files/plots are made available through the Centre for Environmental Data Analysis (CEDA).
  • Data are typically made available in netCDF files following the Climate and Forecast (CF) metadata convention. Files from longest running datasets are available in the NASA Ames format.
  • Each file/plot typically covers a day, i.e. the period between 00:00:00 and 23:59:59 in coordinated universal time (UTC). The file naming convention is described in the next section.
  • Data plots are publicly visible, but you will need to have a CEDA account in order to access the data files.
  • You can apply for a CEDA account by following the Register/Login for access link at the top of any of the CEDA catalogue pages.
  • Web links for downloading data files/plots are given within the Data section of the AMOF page for each instrument.
  • Data files/plots can also be accessed via CEDA’s FTP serverand through the JASMIN computer system. The location of the files within the CDEA archive is also given within the Data section of the AMOF page for each instrument.


Availability of data files/plots
  • Data plots will typically become available before 8 am UK time on the morning following data collection.
  • Data plots will occasionally be updated, e.g. to take advantage of improved processing/quality-control. If you are using a plot in a publication, always make sure that you have access to the latest version.
  • Data files are only released to the CEDA archive after the Instrument Scientist has examined the corresponding plots as a final quality control check. The files will usually become available later in the morning following data collection. However, there will be longer delays over weekends and when the Instrument Scientist is unavailable.
  • Any files that contain suspicious-looking data will be withheld from the
    archive. Contact the instrument scientist if you require access to them.
  • Occasionally data files/plots will be missing for reasons that have nothing to do with data quality, e.g. because of delayed file transfers or computer problems. Please bring these gaps to the attention of the instrument scientist.


CEDA file naming convention and archive structure
  • File names follow the CEDA file naming convention, i.e. instrument_location_YYYYMMDD[_extra].ext, where
    • instrument is the name of the instrument
    • location is the name of the instrument’s location, i.e. either capel-dewi for instruments located at the CDAO or frongoch for the Campbell Scientific surface wind sensors.
    • YYYY is a 4 digit representation of the year
    • MM is a 2 digit representation of the month (where 01 represents January and 12 represents December)
    • DD is a 2 digit representation of the day (i.e. 01 to 31)
    • extra is an optional field that gives additional file details
    • ext is the file name extension, i.e. nc for netCDF files, na for NASA Ames format files, jpg for photographs, tar for “tar” files, and png for data plots.
  • Data files and plots in the CEDA archive are typically available in subdirectories by year and then month in YYYY/MM format.


Map showing the location of NCAS's Atmospheric Observatories in southern Britain
Follow this link to see a larger version of the above image in a new tab.

The Capel Dewi Atmospheric Observatory (CDAO) is located at

  • Latitude: 52.424500°N
  • Longitude: -4.0054665°E
  • Altitude: 45 m above mean sea level (amsl)
  • British National Grid Reference: SN6379882627

This is within a rural valley, which is approximately 6 km to the east of the coastal town of Aberystwyth in west Wales, UK. Refer to the Climatology section below for details of how the valley affects the winds measured by the Vaisala WXT510/520 wind sensors. Winds are also measured by the Campbell Scientific surface wind sensors at a hill-top location 3 km to the west of the site. These are more representative of the larger scale flow.

The land to the west of the CDAO is characterised by small hills. The land to the east is dominated by the Cambrian Mountains. These rise to a high point of 752 m amsl at Pumlumon Fawr (known as Plynlimon in English), which is approximately 16 km to the ENE. The terrain map below covers the same area as the Ordnance Survey Landranger 135 map. It is based on the the Ordnance Survey OS Terrain 50 dataset, which is openly-accessible under a (UK) Open Government Licence.

Map of terrain in the vicinity of the CDAO
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The annual rainfall is typically between 900 and 1100 mm.

Temperatures are relatively mild owing to the site’s proximity to the west coast of Wales. Nevertheless, they can drop to between -5°C and -10°C, notably during an exceptionally cold period in late November/early December 2010.

The wind roses below show the distributions of surface wind (from) direction for measurements made at Frongoch and at the CDAO site, which are 3 km apart. They are based on 1 minute interval data for the period 2007/12/22 – 2014/11/21. The Frongoch measurements are made from a 10 m tower at a hill-top location (140 m amsl) – see Location section above. Consequently they can be considered to be representative of the broader scale flow. However, the CDAO site is located within a valley, which rises up from an altitude of 50 m to 140 m on either side, is approximately 1 km wide, and is aligned in an ENE-WSW direction. This constrains the wind to the up-valley and down-valley directions. It can also give rise to turbulent events, characterised by unusually fast and rapidly-varying winds, when the direction of the broader scale flow is perpendicular to the alignment of the valley.

Distribution of wind directions for the Capel Dewi and Frongoch sites
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Mountain wave activity is a common occurrence at this location. This gives rise to vertical wind velocities of the order of +/-1 m/s, which can be observed by the MST Radar. It can also give rise to lenticular cloud formations, which are sometimes apparent in the images taken by the sky-camera – see example video 1 and example video 2.

  • Hard-standing areas for instruments
  • Access to electricity supply
  • Access to internet connection
  • Workshop area
  • Sheltered space for inflating radiosonde balloons
  • Radiosonde antenna

example of how to link to a single page for data click here