© Crown copyright Met Office Mid-infrared observations of the water vapour continuum from CAVIAR field campaigns Stuart Newman and co-workers Coseners House, Abingdon, December 2009

© Crown copyright Met Office Acknowledgements Many thanks to colleagues involved in collaboration Imperial CollegeNPL Paul Green, Ralph BeebyTom Gardiner, Marc Coleman University of ReadingFAAM Keith Shine, Igor Ptashnik, Liam Tallis Met Office Jonathan Taylor, Fiona Hilton, Andrew Collard, Steve Wardle, Jean-Claude Thelen, Stephan Havemann (and many others…)

© Crown copyright Met Office Contents This presentation covers the following areas NPL laboratory calibration of ARIES Camborne case study: B400 A preliminary look at Jungfraujoch data Water vapour continuum at 4 m

© Crown copyright Met Office NPL lab calibrations

© Crown copyright Met Office CAVIAR work package 3.2 Low temperature blackbody calibration ARIES calibrated against NPL low temperature blackbody Range of temperatures relevant to atmospheric remote sensing – we achieved a range of -75 to +30 ºC ARIES blackbody target temperatures also varied as a test of target emissivity

© Crown copyright Met Office ARIES target emissivity tests Positive bias with hot target at 81ºC, cold target at 20ºC Negative bias with hot target at 12ºC, cold target at 41ºC (c.f. NPL target with emissivity at -74.8ºC)

© Crown copyright Met Office Finding best fit target emissivities

© Crown copyright Met Office ARIES target emissivity results hot target at 81ºC, cold target at 20ºC hot target at 12ºC, cold target at 41ºC

© Crown copyright Met Office Applying lab calibration to flight data Most impact seen for cold scenes (uplooking data) Aim to recalibrate ARIES flight data once nonlinearity correction to longwave MCT detector has been applied Alan Vance is working on ARIES lineshape

© Crown copyright Met Office Camborne case study: flight B400

© Crown copyright Met Office B400 flight (18 Sep 2008) Very good clear sky conditions Flight included chase of radiosonde for water vapour intercomparison 6 dropsondes released 8 aircraft runs over Camborne at different altitudes Coincides with near-nadir IASI overpass

© Crown copyright Met Office Comparison of humidity data Spiral ascent of FAAM aircraft to track radiosonde balloon Radiosonde (corrected), aircraft hygrometer and dropsondes generally agree well Slightly larger discrepancies are apparent at higher altitudes

© Crown copyright Met Office Comparison with simulations residual differences (obs-calc) / K Down-looking brightness temperatures

© Crown copyright Met Office Residuals due to continuum? Retrieved continuum strength (relative to MT_CKD) compared with results of Rowe and Walden IASI spectrum and selected channels sensitive to the continuum Residuals using different sources of water vapour profiles

© Crown copyright Met Office Sources of uncertainty New water vapour spectroscopy in HITRAN 2008 (Coudert et al.) also has a small impact Uncertainty in water vapour profile is important

© Crown copyright Met Office HTFRTC (PC-based) 1dVar retrievals Minimization of the cost function J(x) = (x-x 0 ) T B -1 (x-x 0 ) + (y-y(x)) T R -1 (y-y(x)) x is the state vector (x 0 is the a priori) T, ln(q) and ln(O 3 ) (43 levels), TSurf, ε (15 PC), y are the observations (100 Principal Components) y(x) is the HT-FRTC forward model B is the background error covariance matrix R is the observations+model error covariance matrix

© Crown copyright Met Office IASI assumed errors This is done by modelling the impact of removing 100% continuum (drastic) Include uncertainty due to continuum in R matrix

© Crown copyright Met Office IASI atmospheric retrieval

© Crown copyright Met Office Flight B400 – ARIES retrieval of upper tropospheric water vapour ARIES retrieval initiated with ECMWF forecast - succession of 467 retrievals show moistening of upper tropopshere and deepening of this moist layer to North

© Crown copyright Met Office Radiosonde profiles show similar structure

© Crown copyright Met Office Spectral retrieval

© Crown copyright Met Office Intercomparison case 4 May 2007 JAIVEx flight over Gulf of Mexico Atmospheric stability: agreement between simulations using profiles from different dropsondes All residuals show slowly varying structure – related to water vapour continuum?

© Crown copyright Met Office A preliminary look at Jungfraujoch data

© Crown copyright Met Office Jungfraujoch Mönch Jungfrau Eiger

© Crown copyright Met Office Summary of flights Weather conditionsComments B466 Cloud at times over JungfraujochPartial NPL data B467 Initially thin cirrus which clearedGood NPL data B468 Good clear sky conditionsFLASH sonde* + MetOp overpass B469 Cloud at times over JungfraujochPartial NPL data B470 Some thin cirrus encroachingGood NPL data B471 Excellent clear sky conditionsMetOp overpass B472 Excellent clear sky conditionsARIES failure B473 Excellent clear sky conditionsNo TAFTS B474 Partial cloud over JungfraujochCancelled am flight, pm only * Institute of Applied Physics in Bern launch radiosondes from Payerne equipped with RS92, Snow White and FLASH-B (Lyman-alpha) hygrometers

© Crown copyright Met Office ARIES data: B471 spiral descent FAAM spiral descent measurements of temperature (Rosemount de-iced probe) and dew point (FWVS) ARIES zenith data during spiral descent over Jungfraujoch

© Crown copyright Met Office Continuum at 4 m

© Crown copyright Met Office Test of dimer model at 4 m? (data courtesy Igor Ptashnik) 4 m = (2500 cm -1 )

© Crown copyright Met Office B400 case study (Camborne) Weak signal?

© Crown copyright Met Office Other cases… Ideally need data at night to avoid solar scattering at 4 m A high water vapour loading is beneficial as the self continuum signal is much stronger FAAM aircraft flew at night during Middle East Validation Experiment (MEVEX) based in Oman in 2009 – potentially a useful case study But need to be careful about effects of desert dust aerosol (large particles may affect IR wavelengths)

© Crown copyright Met Office Aerosol impact? (courtesy Steve Wardle, IR aerosol optical depth inferred from visible nephelometer scattering probe via Mie scattering calculations)

© Crown copyright Met Office ARIES downwelling spectrum Low level run off coast of Oman ARIES data LBLRTM sim

© Crown copyright Met Office Any other data available? US Atmospheric Radiation Measurement (ARM) facilities operate AERI IR interferometers at sites around the globe

© Crown copyright Met Office ARM site: Nauru (tropical Pacific)

© Crown copyright Met Office ARM site: Barrow (Alaska)

© Crown copyright Met Office Trends? Include data from Barrow, Oklahoma and Nauru Fit data to simulations by varying continuum strength in LBLRTM For water vapour self continuum a scaling factor of at least 10 is required

© Crown copyright Met Office Strow, L. L., S. E. Hannon, S. De-Souza Machado, H. E. Motteler, and D. C. Tobin (2006), Validation of the Atmospheric Infrared Sounder radiative transfer algorithm, J. Geophys. Res., 111, D09S06 AIRS data (L. Strow)

© Crown copyright Met Office ARIES downwelling spectrum Low level run off coast of Oman Self x10

© Crown copyright Met Office Summary and future work NPL lab calibrations this year have been used to estimate ARIES target emissivities and are good basis for absolute ARIES calibration for Jungfraujoch campaign Analysis of data from Camborne flight shows evidence (backed up by JAIVEx case and Rowe and Walden paper) that some revisions to continuum in strong water vapour band may be beneficial HITRAN 2008 updates (some strong water vapour transitions increased in strength by 5-10%) are being included in LBLRTM simulations for Jungfraujoch campaign HTFRTC 1dVar code is being used (with ARIES and IASI) to account for uncertainties in water vapour profiles; in turn an improved continuum may improve quality of retrievals of atmospheric water vapour Evidence from ARIES data that self continuum at 4 m is stronger than currently modelled in MT_CKD

© Crown copyright Met Office Questions and answers

© Crown copyright Met Office CAVIAR work package 3.2 Low temperature blackbody calibration ff Following on from first set of calibrations at NPL, tests (Alan Vance) showed that ARIES exhibited weak secondary field of view displaced ~6 degrees from primary FoV

© Crown copyright Met Office Secondary FoV exhibited similar shape (approx. 3 degrees full angle spread) as primary FoV Ratio FoV1:FoV2 approx : 0.027, i.e. approx. 2.7 % radiance contribution – important for uplooking zenith data ARIES was returned to manufacturer to replace wedged input window, removing the secondary FoV problem Radiance map of primary FoVRadiance map of secondary FoV

© Crown copyright Met Office Finding best fit target emissivities

© Crown copyright Met Office CAVIAR flights 9 flights Runs 15,000 to 35,000 feet Spiral descents over Jungfraujoch Dropsondes from high level MetOp underflights FL150 FL350

© Crown copyright Met Office Jungfraujoch

© Crown copyright Met Office Profile comparison #1: B471

© Crown copyright Met Office Profile comparison #2: B473

© Crown copyright Met Office Profile comparison #2: B474