17 Mar 2022
17 Mar 2022
Status: this preprint is currently under review for the journal AMT.

Contactless optical hygrometry in LACIS-T

Jakub L. Nowak1,, Robert Grosz1,, Wiebke Frey2, Dennis Niedermeier2, Jędrzej Mijas3, Szymon P. Malinowski1, Linda Ort2,a, Silvio Schmalfuß2, Frank Stratmann2, Jens Voigtländer2, and Tadeusz Stacewicz3 Jakub L. Nowak et al.
  • 1Institute of Geophysics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-293 Warsaw, Poland
  • 2Experimental Aerosol and Cloud Microphysics, Leibniz Institute for Tropospheric Research, Permoserstr. 15, 04318 Leipzig, Germany
  • 3Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-293 Warsaw, Poland
  • anow at: Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • These authors contributed equally to this work.

Abstract. The Fast Infrared Hygrometer (FIRH), employing open-path tunable diode laser absorption spectroscopy at the wavelengths near 1364.6896 nm line, was adapted to perform contactless humidity measurements at the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T), a unique turbulent moist-air wind tunnel. The configuration of the setup allows for scanning at various positions without the need for repeated optics adjustments. We identified three factors which significantly influence the measurement – self-broadening of the absorption line, interference in the glass windows and parasitic absorption in the ambient air outside the tunnel – and developed correction methods which satisfactorily account for these effects. The comparison between FIRH and a reference hygrometer (dew-point mirror MBW 973) indicated a good agreement within the expected errors across the wide range of water vapor concentration 1.0 . . . 6.1 cm−3 (equivalent to dew-point temperature of −5.4 . . . + 21 °C at the temperature of 23 °C).

High temporal resolution (∼2 kHz) allowed for studying turbulent fluctuations in the course of intensive mixing of two air streams which had the same mean velocity but differed in temperature and humidity, including also the settings for which the mixture can be supersaturated. The obtained results complement the previous characterizations of turbulent velocity and temperature fields in LACIS-T. The variance of water vapor concentration exhibits a maximum in the center of the mixing zone which coincides with the steepest gradient.

Jakub L. Nowak et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-79', Anonymous Referee #1, 08 Apr 2022
  • RC2: 'Comment on amt-2022-79', Anonymous Referee #2, 19 Apr 2022

Jakub L. Nowak et al.

Jakub L. Nowak et al.


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Short summary
High resolution infrared hygrometer FIRH was adapted to measure humidity and its rapid fluctuations in turbulence inside a moist-air wind tunnel LACIS-T where two air streams of different temperature and humidity are mixed. The measurement was achieved from outside the tunnel through its glass windows and provided an agreement with a reference dew-point hygrometer placed inside. The characterization of humidity complements previous investigations of velocity and temperature fields.