in-situ and remote sensing of cloud microphysics for the development of nwp assimilation schemes
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In-situ and remote sensing of cloud microphysics for the development of NWP assimilation schemes. David Pollard Observations Based Research, Met Office, UK. 2 nd GPM Ground Validation Workshop 27 th – 30 th September 2005. Taipei, Taiwan. Outline. - PowerPoint PPT PresentationTRANSCRIPT
© Crown copyright 2005 Page 1
In-situ and remote sensing of cloud microphysics for the development of NWP assimilation schemes
David Pollard
Observations Based Research, Met Office, UK
2nd GPM Ground Validation Workshop
27th – 30th September 2005. Taipei, Taiwan.
© Crown copyright 2005 Page 2
Outline
Motivation - Problems Specific to Assimilation
of Cloud and Precipitation Affected Radiances
Fast Scattering Models
Representation of microphysics
Facility for Airborne Atmospheric
Measurements (FAAM)MICROMIX Aircraft CampaignFuture Developments
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Motivation
Assimilation at the Met Office
The ability to assimilate cloud and precipitation affected microwave radiances is
likely to significantly improve NWP forecasts.
The process of assimilating these observations into current NWP models is
non-trivial
The assimilation cost function:
Current problems with assimilating cloud and precipitation affected
radiances:
Need a effective, fast scattering radiative transfer model.
Current NWP models do not describe cloud microphysics in sufficient detail for
RTMs.
Problems of spatial and temporal scaling
xHyRxHyxxBxxxJ Tb
Tb 11
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Scattering Forward Model
The forward models appear to be sufficiently matureAlthough not perfect they are unlikely to be the most
significant contribution to assimilation errors
Doherty et. al. 2005
Observed ModelledCh 16 TBs
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Poor Microphysics Representation in Model
Model does not include sufficient scattering in
convective areasPoor representation of microphysics
Doherty et. al. 2005
Observed ModelledCh 20 TBs
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Parameterisations of Microphysics
Require a parameterisation which can translate between prognosed model variables and those required by the RTM as well as its adjoint.
E.g. Field et. al.
NWP Model Variables:
IWC, T, p, q etc.
On GCM grid
RTM Model Variables:
Ptle density, size distribution, shape, phase etc.
On scale of radiometer footprint
Parameterisation
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PSD parameterisation
Use IWC and Temperature to predict concentration and in turn scale particle size distribution
Limitations:
Derived from aircraft measurements of midlatitude stratiform clouds
Ignores particles smaller than 100 μm
Parameterisations of different regimes required.
Field et. al. 2004 QJRMS
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Field research tools
FAAM BAe146-301 Atmospheric Research
AircraftChilbolton Radar ObservatorySatellite Microwave Instrumentation
AMSU
AMSR
SSMI/S
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FAAM BAe146-301
Facility for Airborne Atmospheric Measurements
Jointly operated by Natural Environment Research Council (NERC) and the Met Office
Based at Cranfield, UK, but can be detached ‘nearly’ anywhere in the world
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FAAM Instrumentation - Radiation
MARSS microwave radiometer 89, 157 & 183 GHz
Deimos microwave radiometer 23.8 & 50.1 GHz
ARIES infrared interferometerSWS short wave spectrometerBroadband radiometers
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Met Office Microwave Radiometers
Instrument Deimos MARSS
AMSU Channel 1 3 16 17 18 19 20
Frequency (GHz) 24 50 89 157183±1
183±3
183±7
View angles along track
Up or Down +35˚ to -5˚
Up and Down +40˚ to -40˚
Beamwidth (FWHM) 11˚ 11˚ 12˚ 11˚ 6˚ 6˚ 6˚
Sensitivity NEΔT (K) 0.6 0.6 0.5 0.7 0.6 0.4 0.3
Cal Acc. (K) 3 3 0.9 1.1 1.0 0.9 0.8
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FAAM Instrumentation – Cloud Physics
FFSSP - # concentration, LWC, mean volume radius & size spectrum (1 – 47 μm)
SID 1 – Spherical equivalent size spectrum (1 – 50 μm)2D-C - # concentration, condensed water content, mean
volume radius & size spectrum (25 – 800 μm)2D-P – as above (200 – 6400 μm)Cloudscope – Hydrometeor & Aerosol images (3 – 400 μm)CPI – Images, counts and size spectrum (5 – 2300 μm)
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MICROMIX - MICROwave investigation of MIXed phase clouds
Field campaign to be conducted Nov/Dec 2005 in conjunction with CAESAR (CLOUDSAT GV)
Aims:
Investigate performance of RTMs in the presence of cloud and precipitation.
Investigate model initiation using UM cloud fields.
Validate retrievals of cloud microphysics from radar data.
Aircraft sorties conducted in conjunction with Chilbolton Radar facility and/or satellite overpasses.
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Aircraft Only
Aircraft provides microwave brightness temperatures
Aircraft provides in-situ microphysics
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Aircraft and Satellite
Aircraft provides in-situ microphysics
Satellite provides microwave brightness temperatures
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Aircraft and Radar
Aircraft provides microwave brightness temperatures
Aircraft provides validation of radar retrievals of microphysics
Radar provides real time, large volume microphysics
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Aircraft and Satellite and Radar
Satellite provides microwave brightness temperatures
Aircraft provides validation of radar retrievals of microphysics
Radar provides real time, large volume microphysics
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Example Sortie B085 – Frontal precipitation over S. England, 10th February 2005
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Future Developments
Instrumentation:
LIDAR – DIAL Water Vapour and O3
New Microwave Radiometers
Higher frequency channels
Improve viewing geometry of low frequency channels
Polarisation of most channels
94 GHz Cloud Radar Campaigns:
EU Framework 6 programme RAINCLOUDS
Has not been funded although FAAM participation had been planned
Gap in schedule in early 2007
Room in aircraft programme from 2008 onwards for this type of activity New assimilation techniques