Reichert, A.

Rettinger, M.

Sussmann, R.

KITopen

www.imk-ifu.kit.edu KIT – The Research University in the Helmholtz Association 3000 4000 5000 6000 7000012345total H2O line parms Solar FTIR calibration H2O profile shapeAOD further species Solar FTIR noise H2O column T profileradiance relative uncertainty [%]wavenumber [cm-1]Principle of radiative closure                   radiance [W/(m² sr cm-1)] wavenumber [cm-1] Modeled spectral radiance Radiometric calibration method Goal • Missing quantitative knowledge of water vapor continuum absorption is a key problem that limits accuracy of atmospheric radiative transfer calculations, e.g. in climate models • Lack of atmospheric measurements of continuum absorption in the near infrared (NIR), no consensus among recent laboratory studies, laboratory results are not easily transferable to atmospheric conditions    ⇒ Derive more accurate NIR water vapor continuum constraints from atmospheric closure experiment Instrumental setup           References: Bicknell, W. E., et al.: Search for Low-Absorption Regions in the 1.6- and 2.1-μm Atmospheric Windows, J. Directed Energy, 2, 151–161, 2006. Mlawer, E. J. et al.: Development and recent evaluation of the MT_CKD model of continuum absorption, Phil. Trans. R. Soc. A, 370, 2520–2556, doi:10.1098/rsta.2011.0295, 2012. Mondelain, D. et al.: Temperature dependence of the water vapor self-continuum by cavity ring-down spectroscopy in the 1.6 µm transparency window, J. Geophys. Res. Atmos., 119, 9, 2169-8996, doi:10.1002/2013JD021319, 2014. Ptashnik, I. V. et al.: Water vapour foreign-continuum absorption in near-infrared windows from laboratory measurements, Phil. Trans. R. Soc. A, 370, 2557-2577, doi:10.1098/rsta.2011.0218, 2012. Ptashnik, I. V. et al.: Near-infrared water vapour self-continuum at close to room temperature, J. Quant. Spectrosc. Radiat. Transf, 120, 23-35, doi:10.1016/j.jqsrt.2013.02.016, 2013.  Acknowledgment: This research project is funded by the Bavarian State Ministry of the Environment and Consumer Protection (via contracts TLK01U-49581 and VAO-II TP I/01) as well as by the Deutsche Bundesstiftung Umwelt (DBU) via a dissertation fellowship. The Zugspitze radiative closure experiment: Quantification of the near-infrared water vapor continuum from atmospheric measurements A. Reichert, R. Sussmann, and M. Rettinger Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany  minimization of spectral residuals via adjustment of absorption parameters Spectral radiance measurements NIR spectral radiance measurements:  Solar FTIR 2500-7800 cm-1, radiometric calibration by means of a high-temperature (1970 K) blackbody source in combination with spectrally resolved Langley method   Atmospheric state H2O column CO2, CH4 and N2O column H2O profile, pT profile NCEP data  AOD SSARA-Z sun photometer  Solar FTIR  Solar FTIR (NIR) O3 column Dobson/ Brewer Measured spectral radiance Radiative transfer model (LBLRTM) Difference spectrum (“residuals”) ←  Contributions to residual uncertainty budget and overall uncertainty (2 σ) of the NIR closure experiment ← High-temperature (1970 K) calibration blackbody source in the Zugspitze FTIR dome wavenumber [cm-1] radiance [arbitrary units] ↓ Solar FTIR radiometric calibration: measurement (blue), calibration coefficients (bottom) derived from Langley fit (red circles) in combination with blackbody measurements (black line) and comparison of result (grey) with LBLRTM calculation (red) wavenumber [cm-1] calibration coefficient ↑ Mean NIR water vapor continuum absorption coefficients derived from Zugspitze measurements (black), MT_CKD 2.5.2 model (Mlawer et al., 2012) (blue), CRDS measurements of Mondelain et al. 2015 (orange),  calorimetric-interferometric measurements of Bicknell et al. (2006) (green) and FTIR measurements of Ptashnik et al. (2012; 2013) (red) Res lt                

The Zugspitze radiative closure experiment: Quantification of the near-infrared water vapor continuum from atmospheric measurements

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The Zugspitze radiative closure experiment: Quantification of the near-infrared water vapor continuum from atmospheric measurements

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