The Role of Secondary Ice Processes in Midlatitude Continental Clouds

• Published in: Journal of geophysical research. Atmospheres 2018-11, Vol.123 (22), p.12,762-12,777
• Main Authors: Zipori, Assaf, Reicher, Naama, Erel, Yigal, Rosenfeld, Daniel, Sandler, Amir, Knopf, Daniel A., Rudich, Yinon
• Format: Article
• Language: English
• Subjects: aerosols mineralogy; Chemical composition; Climate; Climate system; Cloud droplet size; Cloud formation; Clouds; clouds glaciation; Droplets; Earth; ENVIRONMENTAL SCIENCES; Feldspars; Freezing; Geophysics; Glaciation; Glaciology; Hydrologic cycle; Hydrological cycle; Hydrology; Ice formation; Ice nucleation; Laboratories; Mathematical models; Nucleation; Organic chemistry; Parameterization; Predictions; Radiation; Radiation budget; Rain; rain chemical composition; Rain water; Satellites; secondary ice process; Submerging
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2018JD029146

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. Key Points Ice nucleation efficiency of natural ice nucleation particles is controlled by K‐feldspar Secondary ice processes have a large influence on the ice content in midlatitude orographic‐triggered convective clouds The effect of secondary ice processes on Earth's radiative budget is possibly greater than previously assumed