Partitioning the primary ice formation modes in large eddy simulations of mixed-phase clouds

Abstract

<p><strong>Abstract.</strong> State of the art aerosol dependent parameterisations describing each heterogeneous ice nucleation mode, as well as homogeneous nucleation, were incorporated into a large eddy simulation model. Several cases representing commonly occurring cloud types were simulated in an effort to understand which ice nucleation modes contribute the most to total concentrations of ice crystals. The cases include a completely idealised warm bubble, semi-idealised deep convection, an orographic cloud, and a stratiform case. Despite clear differences in thermodynamical conditions in each case, the results are remarkably consistent between the different cloud types. In all the investigated cloud types and under normal aerosol conditions, immersion freezing dominates and contact freezing also contributes significantly. At colder temperatures, deposition nucleation plays little role, and homogeneous freezing is important. To some extent, the temporal evolution of the cloud determines the dominant freezing mechanism, and hence the subsequent microphysical processes. Precipitation is not correlated with any one ice nucleation mode, instead occurs simultaneously when several nucleation modes are active. Furthermore, large variations in the aerosol concentration have only a minor influence on the precipitation amount.</p>

Cloud Top Phase Distributions of Simulated Deep Convective Clouds

“…The model resolution used for this case is 300 m, with 1,000×800 horizontal grid cells and 64 vertical levels. Similar simulations with the COSMO model were presented, for example, by Hande and Hoose (), Paukert et al (), and Zeng et al ().…”

“…The second setup is semiidealized, with realistic topography and an initial temperature and humidity profile (CAPE of 774 J/kg) from radiosoundings near Jülich, Germany (Hande & Hoose, ; Hande et al, ). The initial wind profile is taken from Weisman and Klemp (; unidirectional shear of 5 m/s, with a wind direction of 225° ), and the boundary conditions are fixed.…”

Ice-nucleating particles impact the severity of precipitations in West Texas

“…INPs greatly influence cloud properties, especially in MPCs, which are typically observed in the altitude range of 2 km to 9 km above ground level (Hartmann et al, 1992). Out of all heterogeneous ice-nucleation modes, the immersion freezing is the most dominant mode of ice formation in MPCs (Ansmann et al, 2008;De Boer et al, 2010;Hande and Hoose, 2017;Vergara-Temprado et al, 2018). In Hande and Hoose (2017), different cloud types such as orographic, stratiform and deep-convective systems were simulated and analyzed for different freezing modes under various polluted conditions.…”

“…Out of all heterogeneous ice-nucleation modes, the immersion freezing is the most dominant mode of ice formation in MPCs (Ansmann et al, 2008;De Boer et al, 2010;Hande and Hoose, 2017;Vergara-Temprado et al, 2018). In Hande and Hoose (2017), different cloud types such as orographic, stratiform and deep-convective systems were simulated and analyzed for different freezing modes under various polluted conditions. The authors demonstrate that immersion freezing is the predominant IN mode under various simulated circumstances, accounting for 85 to 99%, while other IN paths play a less significant role.…”

The Role of Secondary Ice Processes in Midlatitude Continental Clouds

“…Since most ice nucleation in mixed‐phase clouds occurs after liquid droplets have formed (Ansmann et al, ; de Boer et al, ), immersion freezing is thought to be the dominant mechanism of primary ice nucleation in these clouds (Hande & Hoose, ; Niehaus et al, ). Contact freezing (where freezing occurs following a collision of an INP and a water droplet), may be an important ice nucleating process (Hoose et al, ; Lohmann & Diehl, ; Lohmann & Hoose, ).…”