Transcript Radar & lidar observations from Chilbolton

The Chilbolton Observatory:
Contribution to Key Science Issues
Robin Hogan and Anthony Illingworth
(Thanks to staff at RAL-STFC and the Met Office)
www.met.reading.ac.uk/radar
Overview
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Science challenges addressed by Chilbolton
2.
Radar and other observing equipment at Chilbolton
3.
Evaluation of clouds and precipitation in models
4.
Met Office Upper Air Network – and equipment at Chilbolton
5.
Radar expertise and experience at Chilbolton
6.
Publications and citations
7.
New directions for radar meteorology
1. Key science challenges
• Cloud representation in climate and NWP models
– One of the largest uncertainties in climate prediction via radiative effect
– A key component of the hydrological cycle; models make rain via clouds.
– We need new microphysical parameterizations based on high resolution
observations involving radar, lidar and aircraft
– Evaluation of clouds in NWP models (e.g. cloud fraction & water content)
essential to test parameterizations in all conditions over many years
• Forecasting hazardous weather in high resolution NWP
– 1.5-km resolution modelling now operational (soon <500 m)
– Large errors remain in intensity, scale, organisation and timing of rain due
to, for example, uncertain microphysics and sub-grid mixing
– Only high resolution radar can provide the necessary detailed
observations required of storms through their lifecycle
• Data assimilation and operational radar products
– Doppler, polarization and refractivity nearly operational
– Research radars needed to develop new retrieval algorithms and data
assimilation methodologies
2. Radars at Chilbolton
All developed in-house (except the insect radar)
1. CAMRa: 3 GHz Doppler and polarization radar
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25 m dish: largest steerable meteorological radar in the world
0.25 beam: high resolution storm structure (250m@60km)
Provides accurate rain rate, hail intensity, ice water content
hydrometeor type, Doppler velocity, turbulent dissipation rate
Frequently used in conjunction with FAAM along southwest
azimuth for cloud microphysics studies
Sensitivity of around –25 dBZ at 10 km: can detect clouds
2. Copernicus: 35 GHz vertically pointing cloud radar
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Continuous operation: with lidar provides long-term
evaluation of cloud fraction & water content in forecast
models by mapping retrievals to model grid
Also Doppler velocity and turbulent dissipation rate
3. Galileo: 94 GHz vertically pointing cloud radar
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Operated on demand: with Copernicus gives ice particle size
and profiles of liquid water content
4. Rothamsted insect radar
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Sited at Chilbolton
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Mounted on the 25 m dish
5. Acrobat: 1.2 GHz clear-air radar (currently unavailable)
Other equipment at Chilbolton
Instrument
– all continuous except for RAMAN lidar
Key Products
Additional information
Lidars
[6] *Vaisala 905-nm
ceilometer
Identification of liquid clouds, aerosols, boundary-layer depth.
Long-term deployment by .ESA
[7] *355-nm Raman lidar
Humidity profiles, and cloud and aerosol extinction.
Designed, built and maintained by facility engineers. Available
[8] *HALO 1.5-mm Doppler
lidar
Boundary layer vertical wind, skewness and dissipation rate; ice
particle type.
Long term deployment by U of Reading.
New technology, installed September 2006.
[9] *355-nm polarization
lidar
Liquid/ice discrimination, cloud and aerosol optical depth, particle
shape . With cloud radars: ice water content and ice particle size.
Long term deployment by U of Reading.
New technology, installed July 2007.
[10] Microwave profiling
radiometer
Water vapour profiles, integrated water vapour and total liquid
water.
Radiometrics: 21 channels between 22 to 30 GHz
HATPRO radiometers.
[11] Broadband
radiometers
Net, and down-welling, solar and infrared radiation.
[13] *Sonic anemometer &
CO2/ H2O probe
Surface fluxes of sensible heat, latent heat, momentum and CO2.
Installed summer 2007 – purchased on NERC grant by U of
Reading.
[14] Lightning sensor
Lightning location.
Long-term deployment by U of Munich.
Part of LINET.
[15] Precipitation sensors
Rain rate from drop-counting and tipping-bucket rain gauges; rain
drop size distributions from distrometer; precipitation (incl. drizzle)
shapes, sizes and fall velocities from a particle sensor.
Commercial units + a number designed, built and maintained
by facility engineers.
[16] Meteorological sensors
Pressure, temperature, dew point, and wind speed/direction. A
cloud camera records sky images every 5 mins.
Commercial units.
[17] GPS receiver
Integrated water vapour path.
Long-term deployment by U of Bath
on demand.
Other equipment
and two
FGAM 1.2-km Tethered Balloon: Permission to operate from Chilbolton (test flights carried out in Summer 2007).
Radiosondes: Permission to launch sondes from Chilbolton, or launch extra sondes from Larkhill 25 km away.
500-m test range: Ideal for terrestrial measurements such as scintillometry
Radar with 1 x 900 m
Velocity (m s-1)
Chilbolton: 0.25 x 300 m
Reflectivity factor (dBZ)
Why do we need high resolution?
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Only high resolution radar can provide the 3D observations needed at the model
resolution
With a 0.25 beam we can track turbulent structures at 250-m scale to infer
updrafts at 2-km scale and quantify turbulence, both key uncertainties in models
US has invested in new 0.45 radar “OU-PRIME”
Next step: What about mounting an X-band (3 cm) radar on the 25-m dish to
provide a 0.08 beam: 80 m resolution at 60 km! Would also be very sensitive to
clouds
New US investment in “high resolution” radar
BAMS – July 2011
3. 3D storm structure in models and reality
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“Dynamical and Microphysical Evolution of Convective Storms” (DYMECS)
– Gathering statistics on hundreds of storms and tracking their evolution with radar
– Will statistically evaluate the evolution of storm size, rain rate, ice water content,
turbulence intensity and updraft strength
– Strong Met Office involvement: will test new configurations and higher resolutions
Radar observations
Forecast plan-view of rainfall
National radar network rainfall
16.00 on 26
August 2011
Rain rate (mm h-1)
Met Office 1.5 km model
Forecast
3D storm
structure
3D structure
observed by
Chilbolton
Radar Zdr
Aircraft
LWC
Microphysics:
combining radar
and aircraft
• Chilbolton provides
excellent contextual
information for
microphysics studies
Hallett-Mossop with FAAM, e.g. Clare’98,
CWVC & Appraise
columns
• For example, this
study demonstrated
that radar Zdr (particle
asphericity) can map
out location of ice
columns produced by
Hallett-Mossop process
Evaluation of clouds in models
Up to a factor of 2 error in ECMWF mean cloud fraction
• Chilbolton has pioneered long-term evaluation of NWP models
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Continuous cloud radar, lidar & microwave radiometer since 2006
Evaluation of cloud fraction, ice & liquid water content in 7 models
Lots of attention: BAMS article has 80 citations in 4 years
Chilbolton being used to evaluate climate models in next IPCC
Same technique now used at US ARM and many European sites
• Next step: cloud radar at 140 or 220 GHz?
– Sizing of small ice particles and much more accurate liquid water
4. Met Office Upper-Air Network
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7 radar windprofilers
– 2 VHF / 5 UHF
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6 radiosonde stations (only 2
manned), 2 launches/day
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+4 defence Range Stations
(launches on demand)
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120 Ceilometers
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AMDAR - from 6 airlines
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One more profiler from FGAM at
Cardington (from time to time,
formal agreement)
Cardington
© Crown copyright (Met Office)
Met Office compound at Chilbolton 2010
Wind profiler
Experimental Microwave
cloud radar
Radiometer
Ceilometer
© Crown copyright (Met Office)
5. Radar expertise and experience at Chilbolton
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Unrivalled experience in building state-of-the-art research radars
Modern RF test equipment at Chilbolton, 42 items - total value > £1M:
Performance Spectrum Analyser with wideband digitizer
Dual-channel pulsed power meter
Wideband power sensor
Vector signal generator
Vector signal generator
Data acquisition / switch unit
Spectrum analyser
Spectrum analyser
Universal frequency counter
GPS time and frequency reference receiver
Vector signal analyser
Vector signal analysis software
10 dB stepped attenuators
1 dB stepped attenuators
Synthesized microwave signal generator
Arbitrary waveform generator
Vector network analyser
3.5 mm calibration kit
3.5 mm verification kit
2.4 mm adaptor kit
Noise-gain analyser
Noise figure analyser
Low-ENR noise source
Noise source
CW Power meter
Spectrum analyser
Pulse power meter
Synthesized signal generator
Microwave frequency counter
Digitizing oscilloscope
40 GHz synthesized signal generator
50 GHz synthesized signal generator
200 MHz analogue oscilloscope
100 MHz digital oscilloscope
Digital phosphor storage oscilloscope
Wideband arbitrary waveform generator
GPS master-clock
Microwave coaxial test cables
Inter-series coaxial adaptors
RF accessories (loads, directional couplers, hybrids)
Attenuators, phase-shifters, standard-gain horns
Specialised millimetre-wave components, 35 and 94 GHz
6. Publications and citations
• Citations
– 129 papers published in 10 years
– Papers using 25-m dish steady
– Papers using other instruments
increasing
– 2307 citations of
Chilbolton ISI papers
1996-2011
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Year of citation
2011
2010
2009
2008
2007
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1996
Number of citations
300
1997
• Peer-reviewed papers
7. New directions for radar meteorology
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NWP models now 1.5 km resolution, <500 m in 5-10 years
– Potential to revolutionise the forecasting hazardous weather
– Does the model represent the weather correctly on these scales?
• X-band (on 25m dish) 80mx80mx80m resolution to 60 km range
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Rainfall rate, hydrometeor type, raindrop spectra, snow/graupel
Horizontal wind, wind shear and turbulence
Inferred vertical wind (convective structures) and mass fluxes
Cloud structure, ice and liquid water content (no wet radome problems)
• Vertically pointing cloud radar at 140 and 220 GHz (2.1 & 1.4 mm)
– New technology, more sensitive (Rayleigh scattering varies as 1/4)
– Extend existing dual-wavelength techniques at 35 & 94 GHz
– At higher frequencies Mie scattering occurs for smaller particles so can
get ice particle size and water content more accurately
– Much more attenuation by liquid water: retrieve better liquid water
content from differential attenuation