© Crown copyright Met Office CAVIAR ARIES water vapour continuum results Stuart Newman Reading, 6 December 2010

© Crown copyright Met Office 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

© Crown copyright Met Office ARIES instrument line shape Retrieved 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

© Crown copyright Met Office 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 H 2 O monomer lines but not too sensitive to H 2 O continuum (assumes spectroscopy errors are minor for monomer lines)

© Crown copyright Met Office Channel selection Dry case, IWV = 0.5 kgm -2

© Crown copyright Met Office Channel selection Moist case, IWV = 3.6 kgm -2

© Crown copyright Met Office Channel selection Go ahead and use these 109 channels in retrieval

© Crown copyright Met Office 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

© Crown copyright Met Office ARIES retrievals - results

© Crown copyright Met Office ARIES retrievals - results

© Crown copyright Met Office CAVIAR cases Continuum 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

© Crown copyright Met Office Continuum coefficients

© Crown copyright Met Office Continuum coefficients including ARIES Jungfraujoch results

© Crown copyright Met Office Need to consider self continuum?

© Crown copyright Met Office Self/foreign contribution Dry case, IWV = 0.5 kgm -2

© Crown copyright Met Office Self/foreign contribution Moist case, IWV = 3.6 kgm -2

© Crown copyright Met Office Summary and things to do ARIES instrument line shape has been revised for convolving simulated radiances to compare with measured radiances Using H 2 O 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

© Crown copyright Met Office Questions and answers

© Crown copyright Met Office Field campaign summary: UK (Camborne), Switzerland (Jungfraujoch) FlightDateWeather conditionsNotes B Persistent boundary layer cloudPartial NPL data B Persistent boundary layer cloudPartial NPL data B Good clear sky conditionsSonde chase, good flight B Cloud at times over JungfraujochPartial NPL data B Initially thin cirrus which clearedGood NPL data B Good clear sky conditionsFLASH sonde + MetOp overpass B Cloud at times over JungfraujochPartial NPL data B Some thin cirrus encroachingGood NPL data B Excellent clear sky conditionsMetOp overpass B Excellent clear sky conditionsARIES failure B Excellent clear sky conditionsNo TAFTS B Partial cloud over JungfraujochCancelled am flight, pm only