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Dr Chris Walden

chris.walden@ncas.ac.uk

01235 445601

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Calendar 2:
Chilbolton Atmospheric Observatory (CAO)

Chilbolton Atmospheric Observatory (CAO)

Chilbolton Atmospheric Observatory is hosted by the Science and Technology Facilities Council (STFC) in rural Hampshire in the South of England.  Through a combination of long-term observations and tailored operations it provides national capability for the study of clouds, rainfall, boundary-layer processes and aerosols, and is particularly well suited as a site for hosting field campaigns involving visiting instruments.

The observatory operates more than twenty major instruments, many continuously, while others are available on-demand according to user configuration requirements. The portfolio includes a powerful combination of dual-polarisation Doppler radars, lidars, radiometers, and supporting instruments; the continuous round-the-clock operation of lidar and cloud radar instruments at Chilbolton is unique within the UK. These are supplemented by a suite of meteorological instrumentation including rain gauges, and disdrometers.  A multi-wavelength sun photometer provides continuous measurements of aerosol optical depth in clear skies, and contributes to the Aerosol Robotic Network (AERONET).

The Chilbolton Advanced Meteorological Radar (CAMRa) is mounted on a 25-metre, fully steerable antenna, and is able to probe clouds and storms with unparalleled sensitivity and resolution. In addition, zenith-pointing polarimetric, Doppler 35 GHz and 94 GHz cloud radars are routinely operated for detailed microphysical studies of cloud processes and cloud climatology.  A transportable, scanning 35 GHz cloud radar system is also hosted at Chilbolton, further enhancing the available capability.

Chilbolton was one of the pilot cloud profiling sites for the CLOUDNET project, and continues to make observations that feed into the Aerosol Clouds and Trace Gases Research Infrastructure (ACTRIS).   Capability at the site will be enhanced in 2022, with the incorporation of a Raman lidar, with the ambition being for this to form an ACTRIS observational platform for aerosol profiling.

The presence (since January 2016) of a Defra air quality monitoring supersite at the observatory site (providing rural background measurements as part of national and transboundary networks) offers the research community further excellent opportunities for intercomparison campaigns and instrument evaluation.

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

Meteorological measurements

  • temperature and relative humidity
  • air pressure
  • wind speed and direction
  • rainfall accumulation
  • raindrop size distribution

Broadband radiation

  • A shorter wavelength band measuring radiation received from the sun. This encompasses a wavelength range of approximately 0.29 – 2.8 µm. It shows a clear response to the day/night cycle. Clouds and other aerosols reduce the detected radiation.
  • A longer wavelength band (approximately 4.5 – 32 µm) produced by emission from the atmosphere and earth’s surface. It does not respond significantly to the day/night cycle but changes according to the time of year and degree of cloud cover.

As well as measuring the total shorter wavelength radiation from across the sky, the measurement can be split to measure the radiation coming only from the sun (direct solar radiation) and the radiation coming from the remainder of the sky (diffuse solar radiation). The ratio of these measurements gives information on the scattering of solar radiation by clouds, fog and aerosols in the atmosphere. To make these measurements, instruments are mounted on an automated solar tracker which correctly points the direct measurement instrument at the sun and shades the diffuse measurement instrument from the sun.