Recirculation and growth of raindrops in simulated shallow cumulus

Naumann, Ann Kristin; Seifert, Axel

doi:10.1002/2016ms000631

Cited by 24 publications

(24 citation statements)

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“…Second, the in-cloud circulations which are better resolved at higher resolution increase the in-cloud residence time of the rain drops and therefore their overall growth by self-collection and accretion. The latter effect has recently been emphasized as an important growth mechanism for raindrops in shallow cumulus clouds (Naumann and Seifert, 2016). Although it remains questionable whether a two-moment bulk scheme can represent recirculation properly, the strong increase of accretion observed in Fig.…”

Section: Sensitivity To Grid Resolutionmentioning

confidence: 86%

Turbulence effects on warm-rain formation in precipitating shallow convection revisited

Seifert

Onishi

2016

Atmos. Chem. Phys.

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Abstract. Two different collection kernels which include turbulence effects on the collision rate of liquid droplets are used as a basis to develop a parameterization of the warmrain processes autoconversion, accretion, and self-collection. The new parameterization is tested and validated with the help of a 1-D bin microphysics model. Large-eddy simulations of the rain formation in shallow cumulus clouds confirm previous results that turbulence effects can significantly enhance the development of rainwater in clouds and the occurrence and amount of surface precipitation. The detailed behavior differs significantly for the two turbulence models, revealing a considerable uncertainty in our understanding of such effects. In addition, the large-eddy simulations show a pronounced sensitivity to grid resolution, which suggests that besides the effect of sub-grid small-scale isotropic turbulence which is parameterized as part of the collection kernel also the larger turbulent eddies play an important role for the formation of rain in shallow clouds.

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Section: Sensitivity To Grid Resolutionmentioning

confidence: 86%

Turbulence effects on warm-rain formation in precipitating shallow convection revisited

Seifert

Onishi

2016

Atmos. Chem. Phys.

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“…Thus, the raindrop growth during shallow convective rains is more significant than deep convection. In addition to the collision-coalescence process due to the convective updraft, two other processes determine raindrop growth, that is, accretion of bulk cloud water and self-collection among raindrops [35]. The updraft is generally weaker over ocean than over land [36].…”

Section: Engineering and Mathematical Topics In Rainfall 78mentioning

confidence: 99%

Seasonal and Diurnal Variations of Vertical Profile of Precipitation over Indonesian Maritime Continent

Marzuki¹,

Hashiguchi²,

Vonnisa³

et al. 2018

Engineering and Mathematical Topics in Rainfall

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This chapter presents variabilities in the vertical structure of precipitation over the Indonesian maritime continent (IMC), which were inferred from the gradients of the radar reflectivity (dBZ) below the freezing level and were gathered from the latest 2A25 TRMM-Precipitation Radar product over a 17-year time span (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). In general, the downward increasing (DI) pattern of dBZ toward the surface is more dominant than the downward decreasing (DD) pattern, which has a ratio of 1.3. The DI is frequently observed over the ocean, and the higher prevailing rain top heights over land are associated with DD, in most cases. Shallow convective rains have the largest ratio of DI to DD (>4), followed by deep convective rains. The largest ratio is observed during DecemberJanuary-February (DJF) when wetter conditions are dominant over the IMC, which is a favorable condition for raindrop growth. The stratiform rains show a dominant DD in which the ratio of DD to DI is greater than 1.6 for each season. The spatial distribution of the stratiform gradient is more complex than that of convective rain and does not show a robust land-ocean contrast. The diurnal variation in the reflectivity gradient for stratiform rain is less pronounced. With convective rain, DD is more dominant in the afternoon and evening over a large island, indicates a decrease in the raindrop concentration due to the evaporation and updraft associated with the intense convection.

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“…This number is called multiplicity or weighting factor. These models have been used successfully to investigate various aspects of aerosol-cloud interactions (e.g., Andrejczuk et al, 2010;Hoffmann et al, 2015;Hoffmann, 20 2017) or precipitation processes (e.g., Naumann and Seifert, 2016;Hoffmann et al, 2017;Dziekan and Pawlowska, 2017). Unterstrasser et al (2017) have reviewed all three currently available LCM collection algorithms, from which the so-called all-or-nothing algorithm (Shima et al, 2009;Sölch and Kärcher, 2010) exhibits the generally best performance.…”

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confidence: 99%

Improving Collisional Growth in Lagrangian Cloud Models: Development and Verification of a New Splitting Algorithm

Schwenkel¹,

Hoffmann²,

Raasch³

2018

Preprint

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Abstract. Lagrangian cloud models (LCMs) are used increasingly in the cloud physics community. They not only enable a very detailed representation of cloud microphysics but also lack numerical errors typical for most other models. However, insufficient statistics, caused by an inadequate number of Lagrangian particles to represent cloud microphysical processes, can limit the applicability and validity of this approach. This study presents the first use of a splitting and merging algorithm designed to improve the warm cloud precipitation process by deliberately increasing or decreasing the number of Lagrangian 5 particles under appropriate conditions. This new approach and the details of how splitting is executed are evaluated in box and single-cloud simulations, as well as a shallow cumulus test case. The results indicate that splitting is essential for a proper representation of the precipitation process. Moreover, the details of the splitting method (i.e., identifying the appropriate conditions) become insignificant for larger model domains as long as a sufficiently large number of Lagrangian particles is produced by the algorithm. The accompanying merging algorithm is essential to constrict the number of Lagrangian particles in or-10 der to maintain the computational performance of the model. Overall, splitting and merging did not affect the life cycle and domain-averaged macroscopic properties of the simulated clouds. This new approach is a useful addition to all LCMs since it is able to significantly increase the number of Lagrangian particles in appropriate regions of the clouds, while maintaining a computationally feasible total number of Lagrangian particles in the entire model domain.

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Recirculation and growth of raindrops in simulated shallow cumulus

Cited by 24 publications

References 50 publications

Turbulence effects on warm-rain formation in precipitating shallow convection revisited

Turbulence effects on warm-rain formation in precipitating shallow convection revisited

Seasonal and Diurnal Variations of Vertical Profile of Precipitation over Indonesian Maritime Continent

Improving Collisional Growth in Lagrangian Cloud Models: Development and Verification of a New Splitting Algorithm

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