Observation of secondary ice production in clouds at low temperatures

Abstract

Abstract. Ice particles play an important role in precipitation formation and radiation balance. Therefore, an accurate description of ice initiation in the atmosphere is of great importance for weather prediction models and climate simulations. Despite the abundance of ice crystals in the atmosphere, the mechanisms for their formation remain not well understood. There are two major sets of mechanisms of ice initiation in the atmosphere: primary nucleation and secondary ice production. Secondary ice production occurs in the presence of preexisting ice, which results in an enhancement of the concentration of ice particles. Until recently, secondary ice production was mainly attributed to the rime-splintering mechanism, known as the Hallett–Mossop process, which is active in a relatively narrow temperature range from −3 to −8 ∘C. The existence of the Hallett–Mossop process was well supported by in situ observations. The present study provides an explicit in situ observation of secondary ice production at temperatures as low as −27 ∘C, which is well outside the range of the Hallett–Mossop process. This observation expands our knowledge of the temperature range of initiation of secondary ice in clouds. The obtained results are intended to stimulate laboratory and theoretical studies to develop physically based parameterizations for weather prediction and climate models.

Secondary ice growth mechanism for ice nuclei in the atmosphere

“…The Hamaker constant A123 and its contributions from the zeroth Matsubara term A123;0 for various threelayer configurations with partially melted ice (1) with different amount of water (Φ) interacting with vapor (3). We consider two cases with the intermediate media (2) being either ice (i) or water (w). a ( µ m) Φ = 0.1 (d2 ∼ 1.09 µ m) Φ = 0.9 (d2 ∼ 1.…”

“…The condensation on such nucleus promotes the growth of ice crystals. The exact mechanisms for deposition are not fully understood yet [1,2], despite several proposed theories, e.g., Wegener-Bergeron-Findeisen [3,4] process. This process, due to the thermodynamic instability of waterice mixtures, turns liquid clouds into ice clouds.…”

“…Observations of much higher concentrations of ice particles than expected were offered with various potential explanations by Lloyd et al [11]: (i) presence of more efficient ice nucleating particles, (ii) recycling of ice within the downwelling mantle of the convective cloud, and finally (iii) through a secondary ice production process. Different secondary ice production mechanisms have been discussed in the past [2], including (1) fragmentation in connection with droplet freezing, (2) the Hallett-Mossop process (rime-splintering mechanism), (3) fragmentation via ice-ice collision, (4) thermal shock induced ice particle fragmentation, (5) fragmentation of sublimating ice, and (6) the activation of ice-nucleating particles in transient supersaturation around freezing drops. We will here propose one additional, previously missing, secondary ice production process.…”

van der Waals induced ice growth on partially melted ice nuclei in mist and fog

“…16 Observations of much higher concentrations of ice than expected were offered with various potential explanations by Lloyd et al : 16 (i) the presence of more efficient ice nucleating particles, (ii) recycling of ice within the downwelling mantle of the convective cloud, and finally (iii) through a secondary ice production process. Different ice production mechanisms have been discussed in the past, 8 including (1) fragmentation in connection with droplet freezing, (2) the Hallett–Mossop process (rime-splintering mechanism), (3) fragmentation via ice–ice collision, (4) thermal shock induced ice particle fragmentation, (5) fragmentation of sublimating ice, and (6) the activation of ice-nucleating particles in transient supersaturation around freezing drops.…”

“…6 However, while the importance of ice formation is profound, the exact mechanisms for all systems are not fully understood yet. 7,8 Still, many theories useful for specific systems exist, including the atmospheric thermodynamic Wegener-Bergeron-Findeisen 9,10 process. This process, due to the thermodynamic instability of water-ice mixtures, turns liquid clouds into ice clouds.…”