Numerical Simulation of Hygroscopic Seeding in a Convective Cloud

Shalva Tzivion Department of Geophysics and Planetary Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel

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Tamir Reisin Department of Geophysics and Planetary Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel

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Zev Levin Department of Geophysics and Planetary Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Israel

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Abstract

An axisymmetrical nonhydrostatic convective cloud mode with detailed treatment of warm cloud microphysics is presented. Ale microphysical processes considered aere nucleation on cloud condensation nuclei, condensation/evaporation, collisional coalescene/breakup (Low and List kernel), and sedimentation. An accurate multi-moment treatment is implemented in the calculations of the microphysical processes. The results indicate that the collisional breakup process is very important in warm clouds and inhibits the growth of drops to large sizes where spontaneous breakup is significant. This diminishes the importance of the Langmuir chain-reaction mechanism for rain formation. The effect of salt seeding are examined for three different cases: one maritime case and two continental cloud cases. No significant effect followed the injection of up to half a ton of salt particles for the maritime cue, while the effect was very significant for the continental clouds. The sensitivity to various seeding parameters was also investigated, including size of seeding particles, quantity of seeding material, timing and duration of seeding and location of seeding The size of the seeded particles and the timing of seeding were found to be crucial parameters. Premature seeding could have a negative effect. Up to 71% increase in total rainfall was obtained under optimal seeding conditions.

Abstract

An axisymmetrical nonhydrostatic convective cloud mode with detailed treatment of warm cloud microphysics is presented. Ale microphysical processes considered aere nucleation on cloud condensation nuclei, condensation/evaporation, collisional coalescene/breakup (Low and List kernel), and sedimentation. An accurate multi-moment treatment is implemented in the calculations of the microphysical processes. The results indicate that the collisional breakup process is very important in warm clouds and inhibits the growth of drops to large sizes where spontaneous breakup is significant. This diminishes the importance of the Langmuir chain-reaction mechanism for rain formation. The effect of salt seeding are examined for three different cases: one maritime case and two continental cloud cases. No significant effect followed the injection of up to half a ton of salt particles for the maritime cue, while the effect was very significant for the continental clouds. The sensitivity to various seeding parameters was also investigated, including size of seeding particles, quantity of seeding material, timing and duration of seeding and location of seeding The size of the seeded particles and the timing of seeding were found to be crucial parameters. Premature seeding could have a negative effect. Up to 71% increase in total rainfall was obtained under optimal seeding conditions.

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