Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments
Author:
Clauss T.,Kiselev A.,Hartmann S.,Augustin S.,Pfeifer S.,Niedermeier D.,Wex H.,Stratmann F.
Abstract
Abstract. We report on the development and test results of the new optical particle counter TOPS-Ice (Thermostabilized Optical Particle Spectrometer for the detection of Ice particles). The instrument uses measurements of the depolarized component of light scattered by single particles into the near-forward direction (42.5° ± 12.7°) to distinguish between spherical and non-spherical particles. This approach allows the differentiation between liquid water droplets (spherical) and ice particles (non-spherical) having similar volume equivalent sizes and therefore can be used to determine the fraction of frozen droplets in a typical immersion freezing experiment. We show that the numerical simulation of the light scattering on non-spherical particles (ellipsoids in random orientation) with account for the actual scattering geometry used in the instrument supports the validity of the approach, even though the cross polarized component of the light scattered by spherical droplets is not vanishing in this scattering angle. For the separation of the ice particle mode from the liquid droplet mode, we use the width of the pulse detected in the depolarization channel instead of the pulse height. Exploiting the intrinsic relationship between pulse height and pulse width for Gaussian pulses allows us to calculate the fraction of frozen droplets even if the liquid droplet mode dominates the particle ensemble. We present test results obtained with TOPS-Ice in the immersion freezing experiments at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator) and demonstrate the excellent agreement with the data obtained in the same experiment with a different optical instrument. Finally, the advantages of using the cross-polarized light measurements for the differentiation of liquid and frozen droplets in the realistic immersion freezing experiments are discussed.
Publisher
Copernicus GmbH
Reference35 articles.
1. Ansmann, A., Tesche, M., Althausen, D., Muller, D., Seifert, P., Freudenthaler, V., Heese, B., Wiegner, M., Pisani, G., Knippertz, P., and Dubovik, O.: Influence of Saharan dust on cloud glaciation in southern Morocco during the Saharan Mineral Dust Experiment, J. Geophys. Res.-Atmos., 113, D04210, https://doi.org/10.1111/j.1600-0889.2008.00384.x, 2008. 2. Bailey, M. and Hallett, J.: A comprehensive habit diagram for atmospheric ice crystals: Confirmation from the laboratory, AIRS II, and other field studies, J. Atmos. Sci., 66, 2888–2899, 2009. 3. Baran, A. J., Yang, P., and Havemann, S.: Calculation of the single-scattering properties of randomly oriented hexagonal ice columns: a comparison of the T-matrix and the finite-difference time-domain methods, Appl. Opt., 40, 4376–4386, 2001. 4. Bohren, C. F. and Huffmann, D. R.: Absorption and Scattering of Light by Small Particles, Wiley, 1983. 5. Bundke, U., Nillius, B., Jaenicke, R., Wetter, T., Klein, H., and Bingemer, H.: The fast Ice Nucleus chamber FINCH, Atmos. Res., 90, 180–186, Sp. Iss. SI, 2008.
Cited by
2 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|