Transcript Weather Measurements at Capel Dewi field station

Atmospheric Measurements at
Capel Dewi field station
Prof. Geraint Vaughan
Where is it?
Aerial view of site
Lidar
container
Bungalow
Field of antennae
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 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 infrared 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
Transmitter
Nd-YAG laser
(SPECTRON)
355 nm
To atmosphere
X10 Beam expander
(refracting telescope)
From
atmosphere
Receiver
Nitrogen filter (387 nm)
PMT
Spatial filter
Water vapour filter (407 nm)
Beamsplitter
Aerosol filter (355 nm)
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
8
NO2 vertical column, 10
15
cm
-2
10
Aberystwyth pm
Aberystwyth am
Camborne pm
Camborne am
Aberdeen pm
Aberdeen am
Lerwick pm
Lerwick am
6
4
2
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Year
Stratospheric Nitrogen dioxide column
measurements from Aberystwyth, 1990-2005
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