Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model

Seifert, Axel; Хаин, А.; Blahak, Ulrich; Beheng, K.D.

doi:10.1175/jas3432.1

Cited by 67 publications

(59 citation statements)

References 26 publications

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“…As found and suggested in Rosenfeld et al (2008) and Seifert et al (2005), increased cloud liquid due to increased aerosols can increase the freezing of cloud liquid when it is transported to the freezing level. This increased freezing increases the latent heat release, intensifying convection (and thus updrafts) which can lead to further increases in cloud liquid.…”

Section: Summary and Discussionsupporting

confidence: 57%

Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period

2009

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Abstract. Cloud and aerosol effects on radiation in two contrasting cloud types, a deep mesoscale convective system (MCS) and warm stratocumulus clouds, are simulated and compared. At the top of the atmosphere, 45-81% of shortwave cloud forcing (SCF) is offset by longwave cloud forcing (LCF) in the MCS, whereas warm stratiform clouds show the offset of less than ∼20%. 28% of increased negative SCF is offset by increased LCF with increasing aerosols in the MCS at the top of the atmosphere. However, the stratiform clouds show the offset of just around 2-5%. Ice clouds as well as liquid clouds play an important role in the larger offset in the MCS. Lower cloud-top height and cloud depth, characterizing cloud types, lead to the smaller offset of SCF by LCF and the offset of increased negative SCF by increased LCF at high aerosol in stratocumulus clouds than in the MCS. Supplementary simulations show that this dependence of modulation of LCF on cloud depth and cloud-top height is also simulated among different types of convective clouds.

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Section: Summary and Discussionsupporting

confidence: 57%

Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period

2009

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“…We use 73 bins to express a range of radii (from 1 µm to 4 mm) for activated cloud droplets and raindrops. In addition, we adopt the coalescence efficiency proposed by Seifert et al (2005) and a breakup scheme based on that of Feingold et al (1988) to estimate the collision-breakup of raindrops. Collision-coalescence and collision-breakup are calculated separately.…”

Section: Model Descriptionmentioning

confidence: 99%

Effect of hygroscopic seeding on warm rain clouds – numerical study using a hybrid cloud microphysical model

Kuba

Murakami²

2010

Atmos. Chem. Phys.

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Abstract. The effect of hygroscopic seeding on warm rain clouds was examined using a hybrid cloud microphysical model combining a Lagrangian Cloud Condensation Nuclei (CCN) activation model, a semi-Lagrangian droplet growth model, and an Eulerian spatial model for advection and sedimentation of droplets. This hybrid cloud microphysical model accurately estimated the effects of CCN on cloud microstructure and suggested the following conclusions for a moderate continental air mass (an air mass with a large number of background CCN). (1) Seeding can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount and radius of seeding particles are appropriate. (2) The optimal radius of monodisperse particles to increase rainfall becomes larger with the increase in the total mass of seeding particles. (3) Seeding with salt micro-powder can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount of seeding particles is sufficient. (4) Seeding by a hygroscopic flare decreases rainfall in the case of large updraft velocity (shallow convective cloud) and increases rainfall slightly in the case of small updraft velocity (stratiform cloud). (5) Seeding with hygroscopic flares including ultragiant particles (r>5 µm) hastens the onset of surface rainfall but may not significantly increase the accumulated surface rainfall amount. (6) Hygroscopic seeding increases surface rainfall by two kinds of effects: the "competition effect" by Correspondence to: N. Kuba (kuba@jamstec.go.jp) which large soluble particles prevent the activation of smaller particles and the "raindrop embryo effect" in which giant soluble particles can immediately become raindrop embryos. In some cases, one of the effects works, and in other cases, both effects work, depending on the updraft velocity and the amount and size of seeding particles.

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“…To counter numerical diffusivity in the discrete approach, Bott (1998) proposed a flux correction method that was tested by Khain et al (2000) for solving the SCE. However, for combined coalescence breakup (SCE-SBE), the adaptation of Bott's method would be both computationally prohibitive and a challenge to implement because of the difficult estimation of the breakup function under this discretization scheme (Seifert et al 2005). In addition, in the case of combined coalescence-breakup (SCE-SBE), the numerical diffusivity problem caused by the evolution of the DSD toward larger sizes driven by coalescence is alleviated by simultaneous breakup that erodes the front tail of the distribution.…”

Section: Casementioning

confidence: 99%

A Robust Numerical Solution of the Stochastic Collection–Breakup Equation for Warm Rain

Prat

Barros

2007

Journal of Applied Meteorology and Climatology

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The focus of this paper is on the numerical solution of the stochastic collection equation-stochastic breakup equation (SCE-SBE) describing the evolution of raindrop spectra in warm rain. The drop size distribution (DSD) is discretized using the fixed-pivot scheme proposed by Kumar and Ramkrishna, and new discrete equations for solving collision breakup are presented. The model is evaluated using established coalescence and breakup parameterizations (kernels) available in the literature, and in that regard this paper provides a substantial review of the relevant science. The challenges posed by the need to achieve stable and accurate numerical solutions of the SCE-SBE are examined in detail. In particular, this paper focuses on the impact of varying the shape of the initial DSD on the equilibrium solution of the SCE-SBE for a wide range of rain rates and breakup kernels. The results show that, although there is no dependence of the equilibrium DSD on initial conditions for the same rain rate and breakup kernel, there is large variation in the time that it takes to reach steady state. This result suggests that, in coupled simulations of in-cloud motions and microphysics and for short time scales (Ͻ30 min) for which transient conditions prevail, the equilibrium DSD may not be attainable except for very heavy rainfall. Furthermore, simulations for the same initial conditions show a strong dependence of the dynamic evolution of the DSD on the breakup parameterization. The implication of this result is that, before the debate on the uniqueness of the shape of the equilibrium DSD can be settled, there is critical need for fundamental research including laboratory experiments to improve understanding of collisional mechanisms in DSD evolution.

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Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model

Cited by 67 publications

References 26 publications

Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period

Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period

Effect of hygroscopic seeding on warm rain clouds – numerical study using a hybrid cloud microphysical model

A Robust Numerical Solution of the Stochastic Collection–Breakup Equation for Warm Rain

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