atmospheric measurements at capel dewi field station n.
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Atmospheric Measurements at Capel Dewi field station

Atmospheric Measurements at Capel Dewi field station

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Atmospheric Measurements at Capel Dewi field station

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  1. Atmospheric Measurements at Capel Dewi field station Prof. Geraint Vaughan

  2. Where is it?

  3. Aerial view of site Lidar container Bungalow Field of antennae

  4. Instruments on site • UK Mesosphere-stratosphere-troposphere (MST) radar • Boundary-layer wind profiler • Surface weather station • Five-wavelength mobile ozone-aerosol lidar • Fixed ozone and water vapour lidars • Lidar ceilometer • GPS receiver (total water vapour column) • Spectrometer for stratospheric measurements

  5. The MST radar This is a VHF radar: 47.5 Mhz, or a wavelength of about 6 m. It consists of a field of 400 antennae (the aerial) and transmitter/receiver equipment in the bungalow. It runs continuously, measuring profiles of winds, atmospheric structure and turbulence every 2 minutes, from 2 to ~16-20 km altitude

  6. Example day: 15 June 2005

  7. Wind measurements Plot shows 24 hours wind measurements on 15 June 2005. High winds near 10 km show a jet stream – note that it changes direction over the course of the day. Note strong wind shear above and below the jet.

  8. Echo power measurements Same day, 15 June 2005. Radar measures tropopause height (crosses) where the signal increases with height. Note relation between tropopause and jet stream. Low power at lower levels is due to water vapour, but rain suppresses echoes. Note: Low power 0300 – 0600 as front passes over Strong layering later in the day, indicating descending air and stability to convection

  9. Boundary-layer wind profiler Similar to MST radar but measures at lower heights – 100 m to around 3 km. Radar system working at 1.29 GHz – around 24 cm wavelength Antennae are much smaller and each panel contains an array of 64 of them (8x8) Three panels pointing in different directions measure winds Measurements of winds and echo power every 2 minutes, continuously.

  10. Wind profiler measurements Signal to noise ratio, 15 June 2005 Wind direction, 15 June 2005

  11. Surface Met Data Vector Instruments Anemometer on 10 m tower on top of hill nearby Campbell Scientific Weather station: Temperature, rainfall, RH, sunshine

  12. Surface measurements Note zero rainfall: rain did not reach ground during frontal passage

  13. Lidar: Basic principles • LIDAR – Light Detection and Ranging • Similar principle to RADAR – pulses of light emitted into the atmosphere and scattered back by clouds, aerosols or air molecules. • Time-of-flight gives scattering height z=½ct • Light collected by a telescope • Spectrometers or interference filters isolate wavelength concerned z

  14. Ceilometer LIDAR instrument using infra-red wavelengths to measure cloud height

  15. Ceilometer data for 2/4/07

  16. Mobile aerosol-ozone lidar Lidar using five ultraviolet wavelengths to measure aerosol and ozone profiles

  17. Ozone/aerosol measurements Black line denotes top of boundary layer – below this the air is polluted with lots of aerosol. But ozone is relatively low: note how the ozone increases above the boundary layer on this day

  18. 355 nm Nd-YAG laser (SPECTRON) X10 Beam expander (refracting telescope) Raman lidar Transmitter To atmosphere From atmosphere Receiver

  19. Water vapour measurements by Raman scattering Aberystwyth Dec 9 2001

  20. Ozone measurements June 5 2000 Above: tropospheric measurements from 289/299 nm pair. Below: stratospheric measurements from 299 alone. (We now do DIAL with 299/316 for stratosphere)

  21. SAOZ spectrometer Stratospheric Nitrogen dioxide column measurements from Aberystwyth, 1990-2005

  22. Health and Safety • On entering the site, please report directly to the site bungalow. Vehicle speed should not excede 10 mph. Do not stray from the track. • At the site bunglow, please report directly to the site manager (or other representative of the Facility). • Within the site bungalow, on no account enter the transmitter room, unless given permission to do so by the site manager. • Outside of the site bungalow, please do not touch any equipment. Do not enter the antenna array unless given permission to do so by the site manager. • Do not enter cordoned-off areas