in-situ and remote sensing of cloud microphysics for the development of nwp assimilation schemes

© Crown copyright 2005

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.


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


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


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


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


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


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


Field research tools

FAAM BAe146-301 Atmospheric Research

AircraftChilbolton Radar ObservatorySatellite Microwave Instrumentation

AMSU

AMSR

SSMI/S


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


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


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


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)


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.


Aircraft Only

Aircraft provides microwave brightness temperatures

Aircraft provides in-situ microphysics


Aircraft and Satellite

Aircraft provides in-situ microphysics

Satellite provides microwave brightness temperatures


Aircraft and Radar

Aircraft provides microwave brightness temperatures

Aircraft provides validation of radar retrievals of microphysics

Radar provides real time, large volume microphysics


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


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


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

in-situ and remote sensing of cloud microphysics for the development of nwp assimilation schemes

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