Atmospheric Measurements at Capel Dewi field station Prof. Geraint Vaughan

Where is it?

Aerial view of site Field of antennae Bungalow Lidar container

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

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

Example day: 15 June 2005

Wind measurements Plot shows 24 hours wind measurements on 15 June 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.

Echo power measurements Same day, 15 June 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

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.

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

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

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

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

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

Ceilometer data for 2/4/07

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

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

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

Water vapour measurements by Raman scattering Aberystwyth Dec

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

SAOZ spectrometer Stratospheric Nitrogen dioxide column measurements from Aberystwyth,

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