Abstract
Abstract. We provide the first dedicated laboratory study of collisions of supercooled water drops with ice particles as a secondary ice production mechanism. We experimentally investigated collisions of supercooled water drops (∼ 5 mm in diameter) with ice particles of a similar size (∼ 6 mm in diameter) placed on a glass slide at temperatures >-12 ∘C. Our results showed that secondary drops were generated during both the spreading and retraction phase of the supercooled water drop impact. The secondary drops generated during the spreading phase were emitted too fast to quantify. However, quantification of the secondary drops generated during the retraction phase with diameters >0.1 mm showed that 5–10 secondary drops formed per collision, with approximately 30 % of the secondary drops freezing over a temperature range between −4 and −12 ∘C. Our results suggest that this secondary ice production mechanism may be significant for ice formation in atmospheric clouds containing large supercooled drops and ice particles.
Highlights
Most surface rainfall events that occur across the globe are associated with the ice phase within clouds in Earth’s atmosphere (Field and Heymsfield, 2015), as are severe weather events such as freezing rain, hail and thunderstorms (Changnon, 2003; Púcik et al, 2019; Elsom, 2001)
This subset of aerosol particles, called ice-nucleating particles (INPs), are relatively rare, and while number concentrations of INPs vary in time and space, they typically fall between 1 × 10−5 to 1 L−1 at ∼ −10 ◦C (Kanji et al, 2017)
We present a secondary ice production (SIP) mechanism involving the formation of secondary drops from the collision of a supercooled water drop with a larger ice particle
Summary
Most surface rainfall events that occur across the globe are associated with the ice phase within clouds in Earth’s atmosphere (Field and Heymsfield, 2015), as are severe weather events such as freezing rain, hail and thunderstorms (Changnon, 2003; Púcik et al, 2019; Elsom, 2001). Where subzero temperatures are warmer than the homogeneous freezing point of −35 ◦C, supercooled water drops can heterogeneously freeze via a subset of aerosol particles present in the atmosphere. This subset of aerosol particles, called ice-nucleating particles (INPs), are relatively rare, and while number concentrations of INPs vary in time and space, they typically fall between 1 × 10−5 to 1 L−1 at ∼ −10 ◦C (Kanji et al, 2017). Our understanding of ice formation from SIP mechanisms is incomplete (e.g. see reviews by Field et al, 2017; Korolev and Leisner, 2020), resulting in poor representation of SIP mechanisms in numerical weather prediction (NWP) models
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