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 Title: PROGRESS ON THE FT-IR MEASUREMENTS OF WATER CONTINUUM IN THE FAR-INFRARED REGION AT 252 – 296 K Author(s): Sung, Keeyoon Contributor(s): Wishnow, Edward H.; Crawford, Timothy J.; Drouin, Brian Subject(s): Mini-symposium: Far-Infrared Spectroscopy Abstract: \begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.25]{B0157.4b.water-cntm4.eps} \end{wrapfigure} Water is the strongest greenhouse gas in the Earth atmosphere, which plays a critical role in the energy balance of the earth atmosphere. It has long been observed particularly in the far-infrared that there is significant longwave continuum absorption due to water vapor (dimers or multimers), not attributable to the Lorentz line contribution within 25 cm$^{-1}$ from the line center for individual water vapor lines. The MT\_CKD model offers the water vapor continuum predictions, which are to be validated by a laboratory study in the far infrared. In order to directly measure this water vapor continuum absorption, we have obtained a series of spectra of water vapor broadened by Self, N$_2$, and O$_2$ in the 50 – 500 cm$^{-1}$ (200 – 20 $\mu$m) at temperatures between 251 and 296 K. For this, we used a coolable White cell system (whose optics are optimized for the far-infrared spectrometry) with passive temperature control, configured to the Fourier transform spectrometer, Bruker IFS-125HR at the Jet Propulsion Laboratory (JPL). We have been analyzing the spectra to make direct measurement of the far-infrared water continuum in two steps; (1) we obtained their transmission spectra by ratioing the sample spectrum to their corresponding background spectrum, (2) we obtained the continuum part of the transmission by dividing the measured spectrum by a synthetic spectrum of the resonant lines calculated using the HITRAN database. As shown in Figure 1, it has revealed the underlying water-water, water-O$_2$, and water-N$_2$ continua in the temperature range, depending on the spectrum type. The preliminary results from this on-going analysis are presented along with their comparison with the MT\_CKD (ver.3.5) model predictions. Temperature dependence of the water vapor continuum will be discussed as part of future work.\footnote{Government sponsorship acknowledged}. Issue Date: 06/21/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100473 DOI: 10.15278/isms.2018.RI02 Other Identifier(s): RI02 Date Available in IDEALS: 2018-08-172018-12-12
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