The Role of Secondary Ice Processes in Midlatitude Continental Clouds

Abstract

Clouds contribute very large uncertainties to our understanding of Earth's climate system. This is partly attributed to the insufficient predictive abilities of ice formation processes in clouds and the ramifications for the hydrological cycle and climate. To improve predictions of ice particle concentrations in clouds, a better understanding of the relative contributions of ice nucleating particles and secondary ice processes (SIPs) is needed. To address this challenging question, we combine ice nucleation measurements via immersion freezing of particles filtered from rainwater, with satellite‐retrieved cloud top glaciation temperatures (Tg) of the same clouds, while considering the chemical composition of the rainwater, the particles, and the particles' mass loads. In addition, laboratory‐derived ice nucleation parameterization of K‐feldspar was implemented in an ice nucleation model in order to reconstruct Tg considering primary ice nucleation only. We show that the observed Tg does not correlate with the median freezing temperature of the drops from the laboratory measurements froze (T50), and are significantly warmer than the model prediction. This suggests that SIP play a major role in glaciating the investigated clouds system. Furthermore, we show that the difference between Tg and T50 best correlates with the size of the cloud droplets at −5 °C, indicating that SIP is controlled by cloud droplet sizes. Hence, our results suggest that the effect of SIP on Tg, and therefore on Earth's radiation budget, may be significant.

Stochastic nucleation processes and substrate abundance explain time-dependent freezing in supercooled droplets

“…By following the immediate changes in the gray scale level of a freezing droplet, the freezing events are detected automatically for each individual droplet. A temperature calibration was applied by detection of the liquefaction and eutectic temperatures of solutions with different water activity as described by Reicher et al 59 and Zipori et al 16…”

“…10 However, laboratory and field observations are limited, and these secondary processes may only occur at specific temperature and droplet size ranges. [11][12][13][14][15][16] Detailed cloud modeling studies indicate that ice activation should persist over long time to maintain the observed cloud structure and the amount of glaciation. [17][18][19] In other words, continual ice nucleation may explain the observed discrepancy between INP number concentration and the actual ice crystal number concentrations with potential consequences for explaining observed cloud structure and precipitation amount.…”

On-chip density-based sorting of supercooled droplets and frozen droplets in continuous flow

“…This concept is particularly timely given the recent surge in microfluidic platforms being developed for the droplet-based study of ice nucleation, [43][44][45][46][47][48] including for applications such as cryobiology [49][50][51][52][53] and atmospheric science. 34,[54][55][56][57][58][59][60][61][62]…”

Cloud history changes water–ice–surface interactions of oxide mineral aerosols (e.g. Silica)

“…Understanding the role of surface properties and their potential variations 5 under atmospheric conditions remains challenging. For example, the ice nucleation (IN) ability of an ice nucleating particle (INP) may be influenced by the change in surface properties due to aging processes in ice nuclei (Coluzza et al, 2017) or other secondary ice processes (Zipori et al, 2018). Solutes are able to affect freezing (Zobrist et al, 2008) and as recently shown even in minor concentration (Whale et al, 2018).…”