Sensitivity of precipitation formation to secondary ice production in
winter orographic mixed-phase clouds

Dedekind, Zane; Lauber, Annika; Ferrachat, Sylvaine; Lohmann, Ulrike

doi:10.5194/acp-2020-1326

Cited by 3 publications

(10 citation statements)

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“…This result is in line with the modeling study of Dedekind et al (2021), who also highlighted the inefficiency of this mechanism in wintertime alpine clouds.…”

Section: Model Simulationssupporting

confidence: 91%

“…Mesoscale model simulations of winter alpine clouds formed at temperatures lower than -8 o C indicate that DS is not contributing to the modeled ICNCs (Dedekind et al, 2021), while field observations suggest the increasing efficiency of the mechanism at temperatures warmer than -3 o C (Lauber et al, 2021).…”

Section: Introductionmentioning

confidence: 89%

“…However, in-situ observations of MPCs forming over mountain-top research stations or near mountain slopes regularly reveal that there is a mismatch between the scarcity of primary INPs and the measured ice crystal number concentrations (ICNCs)the latter being several orders of magnitude more abundant (Rogers and Vali, 1987;Geerts et al, 2015;Lloyd et al, 2015;Beck et al, 2018;Lowenthal et al, 2019;Mignani et al, 2019). Model simulations of alpine MPCs frequently fail to reproduce the elevated ICNCs dictated by observations (Farrington et al, 2016;Henneberg et al, 2017;Dedekind et al, 2021). The fact that primary ice cannot explain the observed ICNCs in orographic MPCs has often been attributed to the influence of surface processes such as the lofting of snowflakes (i.e., blowing snow; Rogers and Vali, 1987;Geerts et al, 2015), detachment of surface hoar frost (Lloyd et al, 2015), turbulence near the mountain surface or convergence of ice particles due to orographic lifting (Beck et al, 2018) and riming on snow-covered surfaces (Rogers and Vali, 1987).…”

Section: Introductionmentioning

confidence: 99%

“…Parameterizations of this mechanism are implemented in small-scale models (Fridlind et al, 2007;Phillips et al, 2017a, b;Sotiropoulou et al, 2020Sotiropoulou et al, , 2021bSullivan et al, 2018a;Yano and Phillips, 2011;Yano et al, 2016), mesoscale models (Hoarau et al, 2018;Sullivan et al, 2018b;Qu et al, 2020;Sotiropoulou et al, 2021a;Dedekind et al, 2021) and global climate models (Zhao and Liu, 2021). These modeling studies followed several approaches to implement the effect of BR.…”

Section: Introductionmentioning

confidence: 99%

“…For instance, Hoarau et al (2018) assumed a constant number of fragments generated per collision in the Meso-NH model, while Sullivan et al (2018b) implemented a temperature-dependent relationship in the COSMO-ART mesoscale model based on the results of Takahashi et al (1995). This simplified formulation was further modified to account for the hydrometeor size scaling, which improved the representation of ICNCs in alpine clouds (Dedekind et al, 2021). Sotiropoulou et al (2020) and(2021a) reproduced the observed ICNCs in polar clouds, by applying the physically-based parameterization developed by Phillips et al (2017a, b).…”

Section: Introductionmentioning

confidence: 99%

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Secondary ice production processes in wintertime alpine mixed-phase clouds

Georgakaki¹,

Sotiropoulou

Vignon

et al. 2021

Preprint

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Abstract. Observations of orographic mixed-phase clouds (MPCs) have long shown that measured ice crystal number concentrations (ICNCs) can exceed the concentration of ice nucleating particles by orders of magnitude. Additionally, model simulations of alpine clouds are frequently found to underestimate the amount of ice compared with observations. Surface-based blowing snow, hoar frost and secondary ice production processes have been suggested as potential causes, but their relative importance and persistence remains highly uncertain. Here we study ice production mechanisms in wintertime orographic MPCs observed during the Cloud and Aerosol Characterization Experiment (CLACE) 2014 campaign at the Jungfraujoch site in the Swiss Alps with the Weather Research and Forecasting model (WRF). Simulations suggest that droplet shattering is not a significant source of ice crystals at this specific location – but break-up upon collisions between ice particles is quite active, elevating the predicted ICNCs by up to 3 orders of magnitude, which is consistent with observations. The initiation of the ice-ice collisional break-up mechanism is primarily associated with the occurrence of seeder-feeder events from higher precipitating cloud layers. The enhanced aggregation of snowflakes is found to drive secondary ice formation in the simulated clouds, the role of which is strengthened when the large hydrometeors interact with the primary ice crystals formed in the feeder cloud. Including a constant source of cloud ice crystals from blowing snow, through the action of the break-up mechanism, can episodically enhance ICNCs. Increases in secondary ice fragment generation can be counterbalanced by enhanced orographic precipitation, which seems to prevent explosive multiplication and cloud dissipation. These findings highlight the importance of secondary ice and "seeding" mechanisms – primarily falling ice from above and to a lesser degree blowing ice from the surface – which frequently enhance primary ice and determine the phase state and properties of MPCs.

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“…This result is in line with the modeling study of Dedekind et al (2021), who also highlighted the inefficiency of this mechanism in wintertime alpine clouds.…”

Section: Model Simulationssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Secondary ice production processes in wintertime alpine mixed-phase clouds

Georgakaki¹,

Sotiropoulou

Vignon

et al. 2021

Preprint

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Aerosol–cloud–precipitation interactions during a Saharan dust event – A summertime case‐study from the Alps

Eirund

Dusseldorp

Brem

et al. 2022

Quart J Royal Meteoro Soc

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Changes in the ambient aerosol concentration are known to affect the microphysical properties of clouds. Especially regarding precipitation formation, increasing aerosol concentrations are assumed to delay the precipitation onset, but may increase precipitation rates via convective invigoration and orographic spillover further downstream. In this study, we analyse the effect of increased aerosol concentrations on a heavy precipitation event observed in summer 2017 over northeastern Switzerland, an event which was considerably underestimated by the operational weather forecast model. Preceding the precipitation event, Saharan dust was advected towards the Alps, which could have contributed to increased precipitation rates north of the Alpine ridge. To investigate the potential impact of the increased ambient aerosol concentrations on surface precipitation, we perform a series of sensitivity simulations using the Consortium for Small‐scale Modeling (COSMO) model with different microphysical parametrizations and prognostic aerosol perturbations. The results show that the choice of the microphysical parametrization scheme in terms of a one‐ or two‐moment scheme has the relatively largest impact on surface precipitation rates. In the one‐moment scheme, surface precipitation is strongly reduced over the Alpine ridge and increased further downstream. Simulated changes in surface precipitation in response to aerosol perturbations remain smaller in contrast to the impact of the microphysics scheme. Elevated cloud condensation nuclei (CCN) concentrations lead to increased cloud water and decreased cloud ice mass, especially in regions of high convective activity south of the Alps. These altered cloud properties indeed increase surface precipitation further downstream, but the simulated change is too small to explain the observed heavy precipitation event. Additional ice‐nucleating particles (INPs) increase cloud ice mass, but only trigger local changes in downstream surface precipitation. Thus, increased aerosol number concentrations during the Saharan dust outbreak are unlikely to have caused the heavy precipitation event in summer 2017.

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Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds

et al. 2021

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Abstract. The discrepancy between the observed concentration of ice nucleating particles (INPs) and the ice crystal number concentration (ICNC) remains unresolved and limits our understanding of ice formation and, hence, precipitation amount, location and intensity. Enhanced ice formation through secondary ice production (SIP) could account for this discrepancy. Here, in a region over the eastern Swiss Alps, we perform sensitivity studies of additional simulated SIP processes on precipitation formation and surface precipitation intensity. The SIP processes considered include rime splintering, droplet shattering during freezing and breakup through ice–graupel collisions. We simulated the passage of a cold front at Gotschnagrat, a peak at 2281 m a.s.l. (above sea level), on 7 March 2019 with the Consortium for Small-scale Modeling (COSMO), at a 1 km horizontal grid spacing, as part of the RACLETS (Role of Aerosols and CLouds Enhanced by Topography and Snow) field campaign in the Davos region in Switzerland. The largest simulated difference in the ICNC at the surface originated from the breakup simulations. Indeed, breakup caused a 1 to 3 orders of magnitude increase in the ICNC compared to SIP from rime splintering or without SIP processes in the control simulation. The ICNCs from the collisional breakup simulations at Gotschnagrat were in best agreement with the ICNCs measured on a gondola near the surface. However, these simulations were not able to reproduce the ice crystal habits near the surface. Enhanced ICNCs from collisional breakup reduced localized regions of higher precipitation and, thereby, improved the model performance in terms of surface precipitation over the domain.

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Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds

Cited by 3 publications

References 0 publications

Secondary ice production processes in wintertime alpine mixed-phase clouds

Secondary ice production processes in wintertime alpine mixed-phase clouds

Aerosol–cloud–precipitation interactions during a Saharan dust event – A summertime case‐study from the Alps

Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds

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