© Crown copyright Met Office CAVIAR ARIES water vapour continuum results Stuart Newman Reading, 6...

© Crown copyright Met Office

CAVIARARIES water vapour continuum resultsStuart Newman

Reading, 6 December 2010


Contents

This presentation covers the following areas

• New ARIES instrument line shape

• Monomer/continuum channel selection

• ARIES profile (water vapour) retrievals

• Continuum coefficients, compare with Igor’s data


ARIES instrument line shapeRetrieved from high S/N nadir-viewing data

• Important to represent ILS when convolving simulation to compare with measured radiances

• ILS becomes more non-ideal towards higher wavenumbers


Retrieval method as means of reducing profile uncertainties

• Uncertainties of order of 10% in absolute water vapour amounts are a problem when attempting to retrieve continuum strengths from ARIES data

• Bayesian retrieval of water vapour profile from a good first guess and using ARIES spectral information can potentially reduce uncertainties

• Don’t want to use same (continuum) channels in water vapour retrieval as are used to derive continuum strengths

• Therefore define set of channels in ARIES spectrum that are sensitive to H2O monomer lines but not too sensitive to H2O continuum (assumes spectroscopy errors are minor for monomer lines)


Channel selection

Dry case, IWV = 0.5 kgm-2


Channel selection

Moist case, IWV = 3.6 kgm-2


Channel selection

Go ahead and use these 109 channels in retrieval


Uplooking Jacobians

• Decreasing water vapour amount with height means all Jacobians are peaked just above the observation height

• Use Jacobians for water vapour retrieval using monomer lines only


ARIES retrievals - results


CAVIAR casesContinuum coeffs

• Derive continuum strength, compare to MT_CKD model in LBLRTM

• Re-do LBLRTM simulations using ARIES (monomer line) water vapour retrievals

If ARIES measures lower emission than LBLRTM/MT_CKD implies smaller continuum coefficient

If ARIES measures higher emission than LBLRTM/MT_CKD implies larger continuum coefficient


Continuum coefficients


Continuum coefficientsincluding ARIES Jungfraujoch results


Need to consider self continuum?


Self/foreign contribution

Dry case, IWV = 0.5 kgm-2


Self/foreign contribution

Moist case, IWV = 3.6 kgm-2


Summary and things to do

• ARIES instrument line shape has been revised for convolving simulated radiances to compare with measured radiances

• Using H2O monomer lines in ARIES spectrum to constrain/retrieve humidity profile seems to be practical way of dealing with uncertainties in profile measurements

• Foreign-broadened continuum coefficients seem to be biased low compared to Igor’s results with RAL data

• Even towards the edges of 2 band it appears that self continuum can be neglected for “high dry” Jungfraujoch cases, i.e. can fit to foreign-broadening coefficient directly

• Same approach on monomer line retrievals can be extended to other cases (B400 ARIES/IASI nadir spectra)

• Including temperature as well as humidity in ARIES retrievals may change results - priority


Questions and answers


Field campaign summary:UK (Camborne), Switzerland (Jungfraujoch)

Flight Date Weather conditions Notes

B396 19.08.08 Persistent boundary layer cloud Partial NPL data

B397 22.08.08 Persistent boundary layer cloud Partial NPL data

B400 18.09.08 Good clear sky conditions Sonde chase, good flight

B466 16.07.09 Cloud at times over Jungfraujoch Partial NPL data

B467 19.07.09 Initially thin cirrus which cleared Good NPL data

B468 20.7.09 Good clear sky conditions FLASH sonde + MetOp overpass

B469 25.07.09 Cloud at times over Jungfraujoch Partial NPL data

B470 26.07.09 Some thin cirrus encroaching Good NPL data

B471 27.07.09 Excellent clear sky conditions MetOp overpass

B472 29.07.09 Excellent clear sky conditions ARIES failure

B473 01.08.09 Excellent clear sky conditions No TAFTS

B474 04.08.09 Partial cloud over Jungfraujoch Cancelled am flight, pm only

© Crown copyright Met Office CAVIAR ARIES water vapour continuum results Stuart Newman Reading, 6...

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