Preprints
https://doi.org/10.5194/egusphere-2023-874
https://doi.org/10.5194/egusphere-2023-874
22 Nov 2023
 | 22 Nov 2023

Simulating the seeder-feeder impacts on cloud ice and precipitation over the Alps

Zane Dedekind, Ulrike Proske, Sylvaine Ferrachat, Ulrike Lohmann, and David Neubauer

Abstract. The ice phase impacts many cloud properties as well as cloud lifetime. Ice particles that sediment into a lower cloud from an upper cloud (external seeder-feeder process) or into the mixed-phase region of a deep cloud from cirrus levels (internal seeder-feeder process) can influence the ice phase of the lower cloud, amplify cloud glaciation and enhance surface precipitation. Recently, numerical weather prediction modeling studies have aimed at representing the ice crystal number concentration in mixed-phase clouds more accurately by including secondary ice formation processes. The increase in the ice crystal number concentration can impact the number of ice particles that sediment into the lower cloud and alter its composition and precipitation formation. In the Swiss Alps, the orography permits the formation of orographic clouds, making it ideal for studying the occurrence of multi-layered clouds and the seeder-feeder process. We present results from a case study on May 18, 2016, showing the occurrence frequency of multi-layered clouds and the seeder-feeder process. About half of all observed clouds were categorized as multi-layered, and the external seeder-feeder process occurred in 10 % of these clouds. In between cloud layers, ≈ 60 % of the ice particle mass was lost due to sublimation or melting. The external seeder-feeder process was found to be more important than the internal seeder-feeder process with regard to the impact on precipitation. In the case where the external seeder-feeder process was inhibited, the average surface precipitation and riming rate over the domain were both reduced by 8.5 % and 3.9 %, respectively. When ice-graupel collisions were allowed, further large reductions were seen in the liquid water fraction and riming rate. Inhibiting the internal seeder-feeder process enhanced the liquid water fraction by 6 % compared to a reduction of 5.8 % in the cloud condensate and, therefore, pointing towards the deamplification in cloud glaciation and a reduction in surface precipitation. Adding to the observational evidence of frequent seeder-feeder situations at least over Switzerland Proske et al. (2021), our study highlights the extensive influence of sedimenting ice particles on the properties of feeder clouds as well as on precipitation formation.

Zane Dedekind, Ulrike Proske, Sylvaine Ferrachat, Ulrike Lohmann, and David Neubauer

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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-874', Anonymous Referee #1, 18 Dec 2023
  • RC2: 'Comment on egusphere-2023-874', Anonymous Referee #2, 29 Dec 2023
Zane Dedekind, Ulrike Proske, Sylvaine Ferrachat, Ulrike Lohmann, and David Neubauer
Zane Dedekind, Ulrike Proske, Sylvaine Ferrachat, Ulrike Lohmann, and David Neubauer

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Short summary
Ice particles precipitating into lower clouds from an upper cloud, the seeder-feeder process, can enhance precipitation. A numerical modeling study conducted in the Swiss Alps found that 48 % of observed clouds were overlapping, in which the seeder-feeder process occurred 10 % of these clouds. Inhibiting the seeder-feeder process reduced the surface precipitation and ice particle growth rates, which were further reduced when additional ice multiplication processes were included in the model.