| 10 Aug 2026
Measurement Report: Aircraft observations of secondary ice production in convective clouds over the Tibetan Plateau
Abstract. Secondary ice production (SIP) substantially enhances ice concentrations in clouds, thereby modulating precipitation and climate, yet underlying SIP mechanisms over the Tibetan Plateau (TP) remain poorly understood. This study investigated the observational evidence and environmental dependence of SIP in convective clouds over the TP based on aircraft observations. The SIP ratio (measured ice to estimated INP concentrations) was introduced to quantify ice enhancement. Flight observations on 6 July 2014 revealed ice concentrations reached 205.4 L−1 in convective clouds, with the SIP ratio peaking at 1000 near −5 ℃. The SIP effective temperature window extended to −16 ℃, substantially broader than the classical Hallett–Mossop (HM) range. Between −3 ℃ and −8 ℃, the HM process played the dominant role, accompanied by ice-ice collisional breakup (BR) and freezing droplet shattering (DS). Between −8 ℃ and −16 ℃, SIP persisted despite reduced HM efficiency, sustained by DS and BR, plus possible upward transport of supercooled large droplets and columnar crystals from warmer levels. SIP-active legs exhibited bimodal ice particle spectra with peaks below 100 μm and between 200 and 300 μm. The size of supercooled droplets dictated SIP initiation, with thresholds of approximately 24 μm above −8 ℃ and 200 μm below −8 ℃. Seven flights further indicate that temperature determined SIP occurrence and dominant mechanism, and hydrometeor concentration exhibited a pronounced positive correlation with the SIP ratio. These findings provide new insights into SIP processes in high‑altitude convective clouds and important implications for improving cloud microphysical parameterizations in weather and climate models.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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