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In-situ and remote sensing of cloud microphysics for the development of NWP assimilation schemes

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.

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In-situ and remote sensing of cloud microphysics for the development of NWP assimilation schemes

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  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.

  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 Campaign • Future Developments

  3. 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

  4. Scattering Forward Model Ch 16 TBs Observed Modelled • The forward models appear to be sufficiently mature • Although not perfect they are unlikely to be the most significant contribution to assimilation errors Doherty et. al. 2005

  5. Poor Microphysics Representation in Model Ch 20 TBs Observed Modelled • Model does not include sufficient scattering in convective areas • Poor representation of microphysics Doherty et. al. 2005

  6. Parameterisations of Microphysics RTM Model Variables: Ptle density, size distribution, shape, phase etc. On scale of radiometer footprint NWP Model Variables: IWC, T, p, q etc. On GCM grid 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. Parameterisation

  7. 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

  8. Field research tools • FAAM BAe146-301 Atmospheric Research Aircraft • Chilbolton Radar Observatory • Satellite Microwave Instrumentation • AMSU • AMSR • SSMI/S

  9. 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

  10. FAAM Instrumentation - Radiation • MARSS microwave radiometer 89, 157 & 183 GHz • Deimos microwave radiometer 23.8 & 50.1 GHz • ARIES infrared interferometer • SWS short wave spectrometer • Broadband radiometers

  11. Met Office Microwave Radiometers

  12. 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)

  13. 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.

  14. Aircraft Only Aircraft provides microwave brightness temperatures Aircraft provides in-situ microphysics

  15. Aircraft and Satellite Satellite provides microwave brightness temperatures Aircraft provides in-situ microphysics

  16. Aircraft and Radar Aircraft provides microwave brightness temperatures Aircraft provides validation of radar retrievals of microphysics Radar provides real time, large volume microphysics

  17. 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

  18. Example Sortie B085 – Frontal precipitation over S. England, 10th February 2005

  19. 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

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