Preprints
https://doi.org/10.5194/acp-2021-513
https://doi.org/10.5194/acp-2021-513

  02 Jul 2021

02 Jul 2021

Review status: a revised version of this preprint was accepted for the journal ACP.

Model emulation to understand the joint effects of ice-nucleating particles and secondary ice production on deep convective anvil cirrus

Rachel E. Hawker1, Annette K. Miltenberger2, Jill S. Johnson1, Jonathan M. Wilkinson3, Adrian A. Hill3, Ben J. Shipway3, Paul R. Field1,3, Benjamin J. Murray1, and Ken S. Carslaw1 Rachel E. Hawker et al.
  • 1Institute for Climate and Atmospheric Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
  • 2Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, 55128, Germany
  • 3Met Office, Exeter, EX1 3PB, United Kingdom

Abstract. Ice crystal formation in the mixed-phase region of deep convective clouds can affect the properties of climatically important convectively generated anvil clouds. Small ice crystals in the mixed-phase cloud region can be formed by heterogeneous ice nucleation by ice-nucleating particles (INP) and secondary ice production (SIP) by, for example, the Hallett-Mossop process. We quantify the effects of INP number concentration, the temperature dependence of the INP number concentration at mixedphase temperatures, and the Hallett-Mossop splinter production efficiency on the anvil of an idealised deep convective cloud using a Latin hypercube sampling method, which allows optimal coverage of a multidimensional parameter space, and statistical emulation, which allows us to identify interdependencies between the three uncertain inputs.

Our results show that anvil ice crystal number concentration (ICNC) is determined predominately by INP number concentration, with the temperature dependence of ice-nucleating aerosol activity having a secondary role. Conversely, ice crystal size is determined predominately by the temperature dependence of ice-nucleating aerosol activity, with INP number concentration having a secondary role. This is because in our simulations ICNC is predominately controlled by the number concentration of cloud droplets reaching the homogeneous freezing level which is in turn determined by INP number concentrations at low temperatures. Ice crystal size however is more strongly affected by the amount of liquid available for riming and the time available for deposition growth which is determined by INP number concentrations at higher temperatures. This work indicates that the amount of ice particle production by the Hallett-Mossop process is determined jointly by the prescribed Hallett-Mossop splinter production efficiency and the temperature dependence of ice-nucleating aerosol activity. In particular, our sampling of the joint parameter space shows that high rates of SIP do not occur unless the INP parameterisation slope (the temperature dependence of the number concentration of particles which nucleate ice) is shallow, regardless of the prescribed Hallett-Mossop splinter production efficiency. The effect of a shallow INP parameterisation slope and consequently high ice particle production by the Hallett-Mossop process in our simulations leads to a sharp transition to a cloud with extensive glaciation at warm temperatures, higher cloud updrafts, enhanced vertical mass flux and condensate divergence at the outflow level, all of which leads to a larger convectively generated anvil comprised of larger ice crystals. This work highlights the importance of quantifying the full spectrum of INP number concentrations across all mixed-phase altitudes, and the ways in which INP and SIP interact to control anvil properties.

Rachel E. Hawker 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 acp-2021-513', Anonymous Referee #1, 09 Aug 2021
  • RC2: 'Comment on acp-2021-513', Xiaohong Liu, 17 Aug 2021
  • AC1: 'Comment on acp-2021-513', Rachel Hawker, 06 Oct 2021

Rachel E. Hawker et al.

Rachel E. Hawker et al.

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Short summary
Convectively generated anvil cirrus can have large effects on the global radiation budget. We find that ice-nucleating particles (INP), aerosols that can initiate the freezing of cloud droplets, can cause substantial changes to the properties of convective anvils. The number and source of INP were important for the anvil properties indicating that we need INP measurements covering a large temperature range, and that climate models should represent the interaction of INP with cloud glaciation.
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