A large‐eddy model for cirrus clouds with explicit aerosol and ice microphysics and Lagrangian ice particle tracking

Sölch, Ingo; Kärcher, B.

doi:10.1002/qj.689

Cited by 115 publications

(144 citation statements)

References 109 publications

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“…This is because each bin needs to be advected separately in the physical space and the computational effort is indepen- dent of whether the entire domain or just its small fraction is filled with droplets. It is worth pointing out that applying Twomey activation to create cloud droplets in the Lagrangian warm-rain thermodynamics bears similarities to the way ice particles are initiated in a particle-based Lagrangian model targeting ice processes (e.g., Sölch and Kärcher, 2010).…”

Section: Super-droplet Initiationmentioning

confidence: 99%

Lagrangian condensation microphysics with Twomey CCN activation

2018

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Abstract. We report the development of a novel Lagrangian microphysics methodology for simulations of warm icefree clouds. The approach applies the traditional Eulerian method for the momentum and continuous thermodynamic fields such as the temperature and water vapor mixing ratio, and uses Lagrangian "super-droplets" to represent condensed phase such as cloud droplets and drizzle or rain drops. In other applications of the Lagrangian warm-rain microphysics, the super-droplets outside clouds represent unactivated cloud condensation nuclei (CCN) that become activated upon entering a cloud and can further grow through diffusional and collisional processes. The original methodology allows for the detailed study of not only effects of CCN on cloud microphysics and dynamics, but also CCN processing by a cloud. However, when cloud processing is not of interest, a simpler and computationally more efficient approach can be used with super-droplets forming only when CCN is activated and no super-droplet existing outside a cloud. This is possible by applying the Twomey activation scheme where the local supersaturation dictates the concentration of cloud droplets that need to be present inside a cloudy volume, as typically used in Eulerian bin microphysics schemes. Since a cloud volume is a small fraction of the computational domain volume, the Twomey super-droplets provide significant computational advantage when compared to the original superdroplet methodology. Additional advantage comes from significantly longer time steps that can be used when modeling of CCN deliquescence is avoided. Moreover, other formulation of the droplet activation can be applied in case of low vertical resolution of the host model, for instance, linking the concentration of activated cloud droplets to the local updraft speed. This paper discusses the development and testing of the Twomey super-droplet methodology, focusing on the activation and diffusional growth. Details of the activation implementation, transport of super-droplets in the physical space, and the coupling between super-droplets and the Eulerian temperature and water vapor field are discussed in detail. Some of these are relevant to the original superdroplet methodology as well and to the ice phase modeling using the Lagrangian approach. As a computational example, the scheme is applied to an idealized moist thermal rising in a stratified environment, with the original superdroplet methodology providing a benchmark to which the new scheme is compared.

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Section: Super-droplet Initiationmentioning

confidence: 99%

Lagrangian condensation microphysics with Twomey CCN activation

2018

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“…Recently, a microphysics module with Lagrangian ice particle tracking was coupled to EULAG and forms the model version EULAG-LCM (Sölch and Kärcher, 2010). For the present study, all microphysical processes are switched off and the simulation particles (representing the passive tracer) are simply advected with the grid point velocity plus an additional turbulent velocity.…”

Section: Eulag-lcmmentioning

confidence: 99%

Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices

et al. 2014

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Abstract. The dispersion of aircraft emissions during the vortex phase is studied using a 3-D LES model with Lagrangian particle tracking. The simulations start with a fully rolled-up vortex pair of a type B747/A340 airplane and the tracer centred around the vortex cores. The tracer dilution and plume extent is studied for a variety of ambient and aircraft parameters until aircraft-induced effects have ceased. For typical upper tropospheric conditions, the impact of stratification is more dominant compared to turbulence intensity or vertical wind shear. Moreover, the sensitivity to the initial tracer distribution was found to be weak. Along the transverse direction, the tracer concentrations can be well approximated by a Gaussian distribution, along the vertical a superposition of three Gaussian distributions is adequate. For the studied parameter range, the vertical plume expansion ranges from 400 m to 550 m and cross-sectional area from 4.0 × 10 4 m 2 to 6 × 10 4 m 2 after six minutes. For validation, selected simulations were compared to an alternative LES model and to in-situ NO-measurements.

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“…This section presents the recently developed microphysics module LCM (Sölch and Kärcher, 2010), originally designed to study the formation of natural cirrus clouds with a thorough, explicit representation of size-resolved nonequilibrium aerosol and ice microphysical processes. In its complete form the LCM comprises explicit aerosol and ice microphysics, covering nonequilibrium growth of liquid supercooled aerosol particles, their homogeneous freezing, heterogeneous ice nucleation of ice nuclei in the deposition or immersion mode, growth of ice crystals by deposition of water vapour, their gravitational sedimentation, aggregation between ice crystals due to differential sedimentation, turbulent dispersion, latent heat release, and radiative impact on particle growth.…”

Section: Lagrangian Particle Tracking Microphysics Module (Lcm)mentioning

confidence: 99%

“…Each SIP represents a number of real ice crystals ranging between 10-10 6 (typically O(10 4 )) usually determined by the conditions prevailing during the formation of ice crystals. In a statistical sense, average ice phase properties per grid box containing N p SIPs converge with increasing sample size ∝1/ N p (Sölch and Kärcher, 2010). In the special case of the simulations in the present work, we only model the deposition/sublimation process, sedimentation, and turbulent dispersion.…”

Section: Lagrangian Particle Tracking Microphysics Module (Lcm)mentioning

confidence: 99%

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Study of contrail microphysics in the vortex phase with a Lagrangian particle tracking model

Unterstraßer

Sölch

2010

Atmos. Chem. Phys.

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Abstract.Crystal sublimation/loss is a dominant feature of the contrail evolution during the vortex phase and has a substantial impact on the later contrail-to-cirrus transition. Previous studies showed that the fraction of crystals surviving the vortex phase depends primarily on relative humidity, temperature and the aircraft type. An existing model for contrail vortex phase simulations (with a 2-moment bulk microphysics scheme) was upgraded with a newly developed state-of-the-art microphysics module (LCM) which uses Lagrangian particle tracking. This allows for explicit processoriented modelling of the ice crystal size distribution in contrast to the bulk approach. We show that it is of great importance to employ an advanced microphysics scheme to determine the crystal loss during the vortex phase. The LCMmodel shows even larger sensitivities to the above mentioned key parameters than previously estimated with the bulk model. The impact of the initial crystal number is studied and for the first time also the initial width of the crystal size distribution. Both are shown to be relevant. This corroborates the need for a realistic representation of microphysical processes and knowledge of the ice phase characteristics.

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A large‐eddy model for cirrus clouds with explicit aerosol and ice microphysics and Lagrangian ice particle tracking

Cited by 115 publications

References 109 publications

Lagrangian condensation microphysics with Twomey CCN activation

Lagrangian condensation microphysics with Twomey CCN activation

Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices

Study of contrail microphysics in the vortex phase with a Lagrangian particle tracking model

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