Investigation of droplet dynamics in a convective cloud using a Lagrangian cloud model

Abstract

A precipitating convective cloud is simulated successfully using the Lagrangian cloud model, in which the flow field is simulated by large eddy simulation and the droplets are treated as Lagrangian particles, and the results are analyzed to investigate precipitation initiation and to examine the parameterization of cloud microphysics. It is found that raindrops appear initially near the cloud top, in which strong turbulence and broadened droplet spectrum are induced by the entrainment of dry air, but high liquidwater mixing ratio is maintained within cloud parts because of insufficient mixing. Statistical analysis of the downward vertical velocity of a droplet W reveals that the transition from cloud droplets to raindrops occurs in the range 20 lm \ r \ 100 lm, while the variation of W depends on turbulence as well as the droplet radius r. The general pattern of the raindrop size distribution is found to be consistent with the Marshall-Palmer distribution. The precipitation flux can be underestimated substantially, if the terminal velocity w s is used instead of W, but it is not sensitive to the choice of the critical droplet radius dividing cloud drops and raindrops. It is also found that precipitation starts earlier and becomes stronger if the effect of turbulence is included in the collection kernel.

The Parallelized Large-Eddy Simulation Model (PALM) version 4.0 for atmospheric and oceanic flows: model formulation, recent developments, and future perspectives

“…Riechelmann et al (2012) and Lee et al (2014) used the LCM for studying turbulence and droplet dynamics in convective clouds; Hoffmann et al 2 The Barbados Oceanographic and Meteorological EXperiment (2015) investigated cloud droplet activation. Figure 8 shows the spatial distribution of simulated droplets and their respective radius within a simulated cumulus cloud.…”

“…For simulations with hundreds of millions of particles, the LPM consumes more than 95 % of the overall CPU time of PALM and the memory demand of the particles is the limiting factor for these simulations (see high-end applications, e.g., Riechelmann et al, 2012;Lee et al, 2014;Sühring et al, 2015). The present version of the LPM now allows for larger numbers of particles.…”

“…Cloudy boundary layers have been simulated using bulk cloud microphysics for cold-air outbreaks by Gryschka et al (2008) as well as for the analysis of second-order budgets in cloudtopped boundary layers for BOMEX and DYCOMS-II 10 (see Stevens et al, 2005) experiments by Heinze et al (2015). Recently, the embedded LCM has been employed for studying the effect of turbulence on the droplet dynamics and growth (Lee et al, 2014;Riechelmann et al, 2015), and for investigating the entrainment (of aerosols) at the edges of cumulus clouds (Hoffmann et al, 2015(Hoffmann et al, , 2014.…”

Lagrangian Droplet Dynamics in the Subsiding Shell of a Cloud Using Direct Numerical Simulations

“…The study of Seifert et al (2010) is an example of an LES simulation with a spectral bin model including a turbulent collision kernel (Ayala et al 2008). A different approach for representing droplet microphysics in an LES is the Lagrangian cloud model (LCM), which is based on the concept of superdroplets, each representing a large number of real droplets of the same size (e.g., Riechelmann et al 2012;Arabas and Shima 2013;Lee et al 2014). Both a bin microphysics approach and an LCM can provide valuable information on the droplet size distribution but lack the accuracy to represent the turbulence and droplet dynamics down to the smallest scales.…”

libcloudph++ 1.1: aqueous phase chemistry extension of the Lagrangian cloud microphysics scheme

“…The Lagrangian methods are becoming a well known tool for studying cloud microphysics in both warm-clouds (Shima et al (2009), Arabas and Shima (2013), Arabas and Shima (2017), Andrejczuk et al (2010), Andrejczuk et al (2014), Hoffmann (2017, Grabowski et al (2018), Sardina et al (2018)); warm-rain clouds (Riechelmann et al (2012), Junghwa et al (2014), 15 Naumann and Seifert (2015)); and ice-phase clouds (Sölch and Kärcher (2010), Unterstrasser and Sölch (2014)). None of the above however, included description of the aqueous phase chemical reactions happening within cloud droplets.…”