Atmospheric Measurements at Capel Dewi field station
Prof. Geraint Vaughan
Where is it?
Aerial view of site
Field of antennae
BungalowLidarcontainer
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 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.
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 overStrong 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 measurementsSignal 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
ReceiverFrom atmosphere
Water vapour measurements by Raman scattering
Aberystwyth Dec 9 2001
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)
SAOZ spectrometer
Stratospheric Nitrogen dioxide column measurements from Aberystwyth, 1990-2005
0
2
4
6
8
10
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Aberystwyth pmAberystwyth amCamborne pmCamborne amAberdeen pmAberdeen amLerwick pmLerwick am
Year
NO
2 ver
tical
col
umn,
1015
cm
-2
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