Initiation of secondary ice production in clouds

Abstract

Abstract. Disparities between the measured concentrations of ice-nucleating particles (INPs) and in-cloud ice crystal number concentrations (ICNCs) have led to the hypothesis that mechanisms other than primary nucleation form ice in the atmosphere. Here, we model three of these secondary production mechanisms -rime splintering, frozen droplet shattering, and ice-ice collisional breakup -with a sixhydrometeor-class parcel model. We perform three sets of simulations to understand temporal evolution of ice hydrometeor number (N ice ), thermodynamic limitations, and the impact of parametric uncertainty when secondary production is active. Output is assessed in terms of the number of primarily nucleated ice crystals that must exist before secondary production initiates (N (lim) INP ) as well as the ICNC enhancement from secondary production and the timing of a 100-fold enhancement. N ice evolution can be understood in terms of collision-based nonlinearity and the "phasedness" of the process, i.e., whether it involves ice hydrometeors, liquid ones, or both. Ice-ice collisional breakup is the only process for which a meaningful N INP here suggest that, under appropriate thermodynamic conditions for secondary ice production, perturbations in cloud concentration nuclei concentrations are more influential in mixed-phase partitioning than those in INP concentrations.

The effect of secondary ice production parameterization on the simulation of a cold frontal rainband

“…These lower magnitudes reflect to some extent the "selflimiting nature" of ice-ice collisional breakup as well because ice hydrometeors must be consumed to generate them in this process. The absence of a defined rainband structure in Figure S3 corroborates the idea of Sullivan et al (2018) that secondary ice production processes involving the liquid phase rely more heavily on dynamical "sweet spots" than those involving just the 30 ice phase. Higher enhancement and dynamical dependence of the processes involving the liquid phase should be even more true for simulations at higher spatial resolutions: convection would be better resolved and higher liquid water contents would be generated.…”

“…In mixed-phase parcel model simulations, we have also calculated slower but longer-lasting secondary ice production rates than in these mesoscale simulations (Sullivan et al, , 2018. In simulations that include rime splintering and ice-ice collisional breakup, the model generates about 0.001 L…”

“…Future studies should add dependency on droplet size and perhaps temperature to this parameter. Shattering probability is given by a normal 10 distribution in temperature, centered at a temperature T µ of 258 K, with a default standard deviation σ of 3 K and default maximum probability p max is 20% similar to Sullivan et al (2018). Examples of this distribution are shown in Figure 2b and d. Then ∂N f reez /∂t is the number of frozen raindrops for a given time step, predicted by the Bigg (1953) heterogeneous freezing parameterization (see Appendix A for details).…”

A representation of the collisional ice break-up process in the two-moment microphysics LIMA v1.0 scheme of Meso-NH

“…According to a concluding remark by Vardiman (1978), this secondary production of ice could lead to concentrations as high as 1000 times the natural concentrations of ice crystals in clouds that would be expected from heterogeneous nucleation on ice freezing nuclei. Another laboratory study by Takahashi et al (1995) also revealed a huge production of ice splinters after collisions between rimed and deposition-grown graupel. However, because as many as 400 fragments could be obtained, their experimental set-up was more appropriate to very large, artificially grown crystals and to large impact velocities.…”

Characterization of Ice‐Nucleating Particles Over Northern India

“…Journal of Geophysical Research: Atmospheres secondary ice production (DeMott et al, , 2018Field et al, 2016;Hallett & Mossop, 1974;Mossop, 1963;Petters & Wright, 2015;Sullivan et al, 2018). However, if secondary ice processes (Field et al, 2016;Hallett & Mossop, 1974) start to dominate ice production after some unspecified initial number of primary freeze events, a temperature shift of −10°C in INP spectra toward warmer temperature would imply that the ice microphysical processes associated with precipitation formation and latent heating would occur lower in the atmosphere.…”