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

1. 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 ChilboltonAll developed in-house (except the insect radar)

1. CAMRa: 3 GHz Doppler and polarization radar– 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 clouds2. Copernicus: 35 GHz vertically pointing cloud radar

– 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 rate3. Galileo: 94 GHz vertically pointing cloud radar

– Operated on demand: with Copernicus gives ice particle size and profiles of liquid water content

4. Rothamsted insect radar– Sited at Chilbolton

5. Acrobat: 1.2 GHz clear-air radar (currently unavailable)– Mounted on the 25 m dish

Instrument 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 on demand.

[8] *HALO 1.5-m 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.

Other equipment

[10] Microwave profiling radiometer

Water vapour profiles, integrated water vapour and total liquid water.

Radiometrics: 21 channels between 22 to 30 GHz and two 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

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

Other equipment at Chilbolton – all continuous except for RAMAN lidar

Why do we need high resolution?

• 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

Chilbolton: 0.25 x 300 m Radar with 1 x 900 m

Ve

loci

ty (

m s

-1)

R

efle

ctiv

ity f

act

or

(dB

Z)

New US investment in “high resolution” radar

BAMS – July 2011

“During the design phase of OU-PRIME,

researchers decided that a high-resolution,

C-band, polarimetric radar system had the

potential to reveal new science and create

opportunities for the university

community… Therefore, one of the major

design decisions was to build a radar with

a 0.45°intrinsic beamwidth”

Forecast 3D storm structure

3D structure observed by Chilbolton

3. 3D storm structure in models and reality• “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

Met Office 1.5 km model

National radar network rainfall

16.00 on 26 August 2011

Ra

in r

ate

(m

m h

-1)

Radar observations

Forecast plan-view of rainfall

Microphysics: combining radar

and aircraft

• Chilbolton provides excellent contextual information for microphysics studies with FAAM, e.g. Clare’98, CWVC & Appraise

• For example, this study demonstrated that radar Zdr (particle asphericity) can map out location of ice columns produced by Hallett-Mossop process

Radar Zdr

Aircraft LWC

Melting layer

Hallett-Mossop columns

Evaluation of clouds in models

• Chilbolton has pioneered long-term evaluation of NWP models– 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

Up to a factor of 2 error in ECMWF mean cloud fraction

© Crown copyright (Met Office)

4. Met Office Upper-Air Network

• 7 radar windprofilers– 2 VHF / 5 UHF

• 6 radiosonde stations (only 2 manned), 2 launches/day

• +4 defence Range Stations (launches on demand)

• 120 Ceilometers

• AMDAR - from 6 airlines

• 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 profilerCeilometer

Microwave Radiometer

Experimentalcloud radar

5. Radar expertise and experience at Chilbolton

• 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

Noise figure analyser

Dual-channel pulsed power meter Low-ENR noise sourceWideband power sensor Noise sourceVector signal generator CW Power meterVector signal generator Spectrum analyserData acquisition / switch unit Pulse power meterSpectrum analyser Synthesized signal generatorSpectrum analyser Microwave frequency counterUniversal frequency counter Digitizing oscilloscopeGPS time and frequency reference receiver 40 GHz synthesized signal generatorVector signal analyser 50 GHz synthesized signal generator Vector signal analysis software 200 MHz analogue oscilloscope10 dB stepped attenuators 100 MHz digital oscilloscope1 dB stepped attenuators Digital phosphor storage oscilloscopeSynthesized microwave signal generator Wideband arbitrary waveform generatorArbitrary waveform generator GPS master-clockVector network analyser Microwave coaxial test cables3.5 mm calibration kit Inter-series coaxial adaptors3.5 mm verification kit RF accessories (loads, directional couplers, hybrids)2.4 mm adaptor kit Attenuators, phase-shifters, standard-gain horns

Noise-gain analyserSpecialised millimetre-wave components, 35 and 94 GHz

6. Publications and citations

• Peer-reviewed papers– 129 papers published in 10

years– Papers using 25-m dish steady– Papers using other instruments

increasing

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• Citations– 2307 citations of

Chilbolton ISI papers 1996-2011

7. New directions for radar meteorology

• 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– 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