No evidence for a productive Hallett-Mossop process so far

Abstract

<p>Mixed-phase clouds are essential elements in Earth’s weather and climate system. Atmospheric observation of mixed-phase clouds occasionally demonstrated a strong discrepancy between the observed ice particle and ice nucleating particle number concentration of one to four orders of magnitude at modest supercooling [1-3, 5, 7]. Different secondary ice production (SIP) mechanisms have been hypothesized which can increase the total ice particle number concentration by multiplication of primary ice particles and hence might explain the observed discrepancy [2, 4, 6].</p> <p>In this study we focus on SIP as a result of droplet-ice collisions, commonly known as Hallett-Mossop [9] or rime-splintering process. Our main objectives are (i) to quantify secondary ice particles and (ii) to learn more about the underlying physics. Therefore, we develop a new experimental set-up (Ice Droplets splintEring on FreezIng eXperiment, IDEFIX) in which quasi-monodisperse supercooled droplets collide with a fixed ice particle. IDEFIX is designed to simulate atmospheric relevant conditions such as temperature, humidity, impact velocities and collision rates. The riming process is observed with high-speed video microscopy and an infrared measuring system. Further, the produced secondary ice particles are counted via impaction on a supercooled sugar solution. Preliminary results from a first measurement campaign suggest that we observed single SIP events but did not found evidence for a productive Hallett-Mossop process so far.  We plan to continue with rime-splintering experiment in order to gain better statistics and to expand the parameter space (e.g., droplet size distribution).</p> <p>[1] Crosier, J., et al. 2011, DOI: 10.5194/acp-11-257-2011.</p> <p>[2] Field, P.R., et al. 2016, DOI: 10.1175/amsmonographs-d-16-0014.1.</p> <p>[3] Hogan, R.J., et al. 2002, DOI: 10.1256/003590002321042054.</p> <p>[4] Korolev, A. and T. Leisner 2020, DOI: 10.5194/acp-20-11767-2020.</p> <p>[5] Mossop, S.C. 1985, DOI: 10.1175/1520-0477(1985)066<0264:toacoi>2.0.co;2.</p> <p>[6] Sotiropoulou, G., et al. 2020, DOI: 10.5194/acp-20-1301-2020.</p> <p>[7] Taylor, J.W., et al. 2016, DOI: 10.5194/acp-16-799-2016.</p>