Dr. rer. nat. Benjamin Kühnreich

Certified LabVIEW Associate Developer (CLAD)

ISOCLOUD – isotopic fractionation in clouds

In-situ observations from aircraft instruments that reach the coldest near-tropospheric regions and carry in-situ water vapor instruments show persistent, repeatable supersaturations in the presence of ice particles at these low temperatures. This supersaturation in the presence of ice particles is surprising and suggests that some unknown factors inhibits condensation of water vapor and growth of ice crystals at temperatures below 200 K. This has led to hypotheses for the surface interaction between the ice nucleus surface and the surrounding water vapor ranging from meta-stable forms of ice [1] to growth inhibition by glassification of water vapor [2]. Understanding and resolving the processes in the boundary layer of the ice surface is important for basic science and more widely for understanding climate [3]. To investigate potential inhibitors of ice growth we measure the evolving isotopic composition of water as cirrus forms. Water isotopic composition is a potentially useful tracer because the different vapor pressures of isotopically substituted and unsubstituted water mean that processes involving condensation or evaporation produce changes in isotopic ratios.

With the method of TDLAS (tunable diode laser absorption spectroscopy) at 2.7 µm we measure water vapor an its isotopic composition (the ratio of HDO or H218O to H216O) to diagnose factors affecting ice nucleation and growth at cold temperatures characteristic of the tropical tropopause. The research based on our expertise in detecting atmospheric water in low concentrations [4,5] includes both adaptation and development of instrumentation specific to measurements at the AIDA experimental chamber in Karlsruhe. With-Cell with an absorption Path of 300 m will be developed for in situ measurements at AIDA where a series of experimental campaigns will take place.

[1] B.J. Murray, D. a Knopf, A.K. Bertram, The formation of cubic ice under conditions relevant to Earth’s atmosphere., Nature. 434 (2005) 202-5.

[2] B.J. Murray, T.W. Wilson, V. Ebert, S. Dobbie, Z. Cui, S.M.R.K. Al-Jumur, et al., Heterogeneous nucleation of ice particles on glassy aerosols under cirrus conditions, Nature Geoscience. 3 (2010) 233-237.

[3] K.-N. Liou, Influence of Cirrus Clouds on Weather and Climate Processes: A Global Perspective, Monthly Weather Review. 114 (1986) 1167-1200.

[4] S. Hunsmann, K. Wunderle, S. Wagner, U. Rascher, U. Schurr, V. Ebert, Absolute, high resolution water transpiration rate measurements on single plant leaves via tunable diode laser absorption spectroscopy (TDLAS) at 1.37 ?m, Applied Physics B. 92 (2008) 393-401.

[5] V. Ebert, H. Teichert, C. Giesemann, H. Saathoff, U. Schurath, Fibre-Coupled In-situ Laser Absorption Spectrometer for the Selective Detection of Water Vapour Traces down to the ppb-Level, Tm – Technisches Messen. 72 (2005) 23-30.