Die Bedeutung von Eisnukleationspartikeln und -moden für die Entstehung der Eisphase und Niederschlag: Modellsimulationen basierend auf Labormesssungen.
Zusammenfassung der Projektergebnisse
In this project we investigated how important the types of ice nucleating particles and the active freezing modes are for atmospheric ice formation and precipitation. In laboratory measurements we used two methods, both utilizing freely levitated single supercooled water droplets: an acoustic levitator (M-AL) and the Mainz vertical wind tunnel (M-WT). We conducted immersion freezing experiments with both techniques; this allowed us to compare the ice nucleating effects by the same particle types with two methods. In the contact mode we used the Mainz vertical wind tunnel only. We developed an improved method to simulate conditions in the tunnel as in the real atmosphere: with freely floated droplets and particles carried along with the air stream and colliding with the droplets. For cloud modeling, we used the 3D convection-resolving model COSMO-SPECS and extended it by our improved spectral-bin microphysics from INUIT-1. Homogeneous freezing as well as the heterogeneous freezing modes immersion, contact, and deposition are included. The descriptions of the heterogeneous freezing modes are specified for different particles types. Results from the cloud modeling indicate that the different freezing processes do hardly compete with and affect each other because they are mainly active at different altitudes or they are dependent on the presence either of supercooled drops or dry particles. In a deep convective cloud, homogeneous freezing is dominant. However, precipitation is modified by additional heterogeneous freezing as so-called small trigger effects. That means small freezing events trigger cloud microphysical responses such as the formation of large drops which leads to changes in precipitation. Not only immersion freezing, but also contact and deposition freezing are important and should not be neglected. During high dust events in the atmosphere, mineral particles such as feldspar are present in large amounts; however, small amounts of mineral ice nucleating particles may favor the initiation of precipitation. Primary biological particles such as bacteria, fungi spores, cellulose, and pollen show high freezing efficiencies but are present in atmospheric clouds in small amounts only. The model simulations did not show small trigger effects of biological particles in comparison to mineral dust particles, thus, the role of biological particles in atmospheric clouds remains still unclear. In the experimental part of our project, we determined the ice nucleation active site (INAS) densities – which is an important parameter in cloud modeling studies – for a variety of ice nucleating particles, as, e.g., mineral and desert dust, and bacteria, employing both M-AL and M-WT for the studies. We participated in two instrument inter-comparison campaigns: one was aiming the experimental characterization of cellulose, which is an important INP of biological origin. The other campaign (FIN02) utilized different aerosol types in order to reveal any deviations among the results of different types of measuring instruments used for ice nucleation characterization studies world-wide. Our facilities proved their applicability in laboratory based ice nucleation studies in both measurement campaigns. Since M-WT is one of the outmost facilities for studying cloud microphysical processes under closely simulated atmospheric conditions, such inter-comparison to other instrumentations is of crucial importance. We could show in designated M-WT experiments that contact freezing is a more efficient freezing process than immersion freezing. Nevertheless, as indicated also by our modeling studies, the latter one plays a more important role in atmospheric clouds because of the sparse presence of dry aerosol particles. A very exciting and interesting result emerged from a synergetic study carried out using both singledroplet levitation based facilities accommodated in our laboratory. By comparing the INAS densities of immersion freezing for different particle types determined by M-AL and M-WT an important characteristic feature of M-AL was discovered. Namely, due to the high cooling rate occurring in M-AL a material dependent temperature shift to low subzero temperatures was observed. With the help of the freezing rate determined in M-WT, the temperature shift in M-AL was successfully understood and described, and so, in the end, the INAS density results from M-WT and M-AL became consistent. This discovery can further help to understand any differences arising among experimental devices using diverse cooling rates. Our activities in the framework of Research Unit INUIT attracted attention even in the public media. A report has been published in the regional broadcast SWR Radio, as well as on their internet site: https://www.swr.de/blog/diedurchblicker/2016/12/13/wolkenforschung-im-windkanal/.
Projektbezogene Publikationen (Auswahl)
- A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of seventeen ice nucleation measurement techniques. Atmos. Chem. Phys., 15, 2489-2518, 2015
Hiranuma, N., S. Augustin-Bauditz, H. Bingemer, C. Budke, J. Curtius, A. Danielczok, K. Diehl, K. Dreischmeier, M. Ebert, F. Frank, N. Hoffmann, K. Kandler, A. Kiselev, T. Koop, T. Leisner, O. Möhler, B. Nillius, A. Peckhaus, D. Rose, S. Weinbruch, H. Wex, Y. Boose, P. J. DeMott, J. D. Hader, T. C. J. Hill, Z. A. Kanji, G. Kulkarni, E. J. T. Levin, C. S. McCluskey, M. Murakami, B. J. Murray, D. Niedermeier, M. D. Petters, D. O'Sullivan, A. Saito, G. P. Schill, T. Tajiri, M. A. Tolbert, A. Welti, T. F. Whale, T. P. Wright, and K. Yamashita
(Siehe online unter https://doi.org/10.5194/acp-15-2489-2015) - Intercomparing different devices for the investigation of ice nucleating particles using Snomax as test substance. Atmos. Chem. Phys., 15, 1463-1485, 2015
Wex, H., S. Augustin-Bauditz, Y. Boose, C. Budke, J. Curtius, K. Diehl, A. Dreyer, F. Frank, S. Hartmann, E. Jantsch, Z.A. Kanji, A. Kiselev, T. Koop, O. Möhler, D. Niedermeier, B. Nilius, M. Rösch, D. Rose, C. Schmidt, I. Steinke, and F. Stratmann
(Siehe online unter https://doi.org/10.5194/acp-15-1463-2015) - New particle-dependent parameterizations of heterogeneous freezing processes: sensitivity studies of convective clouds with an air parcel model. Atmos. Chem. Phys., 15, 12741-12763, 2015
Diehl, K., and S.K. Mitra
(Siehe online unter https://doi.org/10.5194/acp-15-12741-2015) - A comprehensive characterization of ice nucleation by three different types of cellulose particles immersed in water. Lessons learned and future research directions. Atmos. Chem. Phys. Discuss., 1–82, 2018
Hiranuma, N., K. Adachi, D. Bell, F. Belosi, H. Beydoun, B. Bhaduri, B., A. Mayer, O. Eppers, M. Szakáll, et al.
(Siehe online unter https://doi.org/10.5194/acp-2018-933) - Model simulations with COSMO-SPECS: Impact of heterogeneous freezing modes and ice nucleating particle types on ice formation and precipitation in a deep convective cloud. Atmos. Chem. Phys., 18, 1-21, 2018
Diehl, K., and V. Grützun
(Siehe online unter https://doi.org/10.5194/acp-18-3619-2018) - The Fifth International Workshop on Ice Nucleation phase 2 (FIN-02). Laboratory intercomparison of ice nucleation measurements. Atmos. Meas. Tech., 11, 6231–6257, 2018
DeMott, P. J., O. Möhler, D. J. Cziczo, N. Hiranuma, M. D. Petters, S. S. Petters, O. Eppers, M. Szakáll, et al.
(Siehe online unter https://doi.org/10.5194/amt-11-6231-2018)
