Impact of aerosols and turbulence on cloud droplet growth: an in-cloud seeding case study using a parcel–DNS (direct numerical simulation) approach

Chen, Sisi; Xue, Lulin; Yau, M. K.

doi:10.5194/acp-20-10111-2020

Cited by 25 publications

(35 citation statements)

References 47 publications

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“…A one‐dimensional parcel model was used to calculate the evolution of DSDs in the adiabatic region above cloud base, with and without seeding. The parcel model was adopted from Jensen and Nugent (2017) with two modifications (see the detailed description of the modification in Section 2.1 of Chen et al., 2020). First, the collision‐coalescence is excluded for simplicity's sake to emphasize the hygroscopic effect of seeding on the early DSD evolution through condensation.…”

Section: Methodsmentioning

confidence: 99%

“…This assumption is valid for the cloud development near cloud base because cloud droplets with D > 40 µm are too scarce to initiate high collision efficiency (Rogers & Yau, 1989), and an air parcel near the cloud base is close to adiabatic and droplet size spectra may be mostly determined by adiabatic condensational growth (Yum & Hudson, 2005). Second, the hygroscopicity parameter, κ, was used in the droplet diffusional‐growth equation (Equation 1 in Chen et al., 2020). A moving‐bin method was employed to calculate the evolution of the DSDs.…”

Section: Methodsmentioning

confidence: 99%

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The Influence of Hygroscopic Flare Seeding on Drop Size Distribution Over Southeast Queensland

et al. 2021

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Hygroscopic seeding has been explored in various regions of the world with the goal of enhancing rainfall (Bruintjes, 1999; Flossmann et al., 2019; Silverman, 2003). The conceptual model of hygroscopic seeding focuses on increasing the precipitation efficiency of warm-based convective clouds by broadening the droplet spectra to enhance warm rain formation processes. The approach is to introduce large hygroscopic particles that act as efficient cloud condensation nuclei (CCN) or giant CCN (GCCN), which then nucleate large drops that grow more rapidly via condensation and initiate effective collision-coalescence processes. In addition, this process can suppress the activation of small background aerosols via the "competition effect" (Cooper et al., 1997; Ghan et al., 1998; O'Dowd et al., 1999). Even in mixed-phase, deep convective clouds, the concept suggests that more large drops and drizzle produced from warm rain processes would lead to more active mixed-phase ice formation and subsequent increases in the precipitation efficiency (Lawson et al., 2015; Rosenfeld & Woodley, 1993). Only a few studies have directly measured the broadening of the droplet spectra attributed to hygroscopic seeding (Ghate et al., 2007; Mather et al., 1997). While Rosenfeld et al. (2010) also attempted to directly measure droplet broadening from hygroscopic flare seeding, they were unable to detect a distinct change in the drop size distribution (DSD). However, their observational results were only based upon measurements from one seeded cloud. This study uses data collected in Southeast Queensland to examine the impact of hygroscopic seeding on the initial droplet spectra. A decade-long drought in Southeast Queensland, Australia, in the early 2000s, known as the Millennium Drought (van Dijk et al., 2013) prompted the Queensland government to seek ways to create more water resources, which led to a feasibility study to investigate precipitation enhancement via cloud seeding known as the Queensland Cloud Seeding Research Program (QCSRP; Tessendorf et al., 2010; 2012). Scientists from the United States, South Africa, and Australia conducted the feasibility study, which included a randomized hygroscopic cloud-seeding trial, during the summers in 2007-2009. Given the small number of cases and the high level of natural variability in the QCSRP randomized experiment sample, the results were incomplete and not statistically significant (Tessendorf et al., 2010). This is

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

The Influence of Hygroscopic Flare Seeding on Drop Size Distribution Over Southeast Queensland

et al. 2021

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“…The general concept of hygroscopic seeding is based on the notion of introducing large artificial (hygroscopic) particles to compete with smaller naturally occurring aerosols for available cloud LWC. Through this "competition effect", the seeding particles are expected to suppress the activation of smaller background aerosols, rapidly grow into larger drops and trigger C-C (Bruintjes et al, 2012;Cooper et al, 1997). Ghate et al (2007) studied the impact of introducing giant (salt) seeding aerosols (1-5 µm) into marine stratocumulus clouds using in situ aircraft observations off the central coast of California.…”

Section: Implications For Hygroscopic Cloud Seedingmentioning

confidence: 99%

Analysis of aerosol-cloud interactions and their implications for precipitation formation using aircraft observations over the United Arab Emirates

Wehbe¹,

Tessendorf²,

Weeks³

et al. 2021

Preprint

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Abstract. Aerosol and cloud microphysical measurements were collected by a research aircraft during August 2019 over the United Arab Emirates (UAE). The majority of science flights targeted summertime convection along the eastern Hajar mountains bordering Oman, while one flight sampled non-orographic clouds over the western UAE near the Saudi Arabian border. In this work, we study the evolution of growing cloud turrets from cloud base (9 °C) up to the capping inversion level (−12 °C) using coincident cloud particle imagery and particle size distributions from cloud cores under different forcing. Results demonstrate the active role of background dust and pollution as cloud condensation nuclei (CCN) with the onset of their deliquescence in the sub-cloud region. Sub-cloud aerosol sizes are shown to extend from submicron to 100 µm sizes, with higher concentrations of ultra-giant CCN (d >10 µm) from local sources closer to the Saudi border, compared to the eastern orographic region where smaller size CCN are observed. Despite the presence of ultra-giant CCN from dust and pollution in both regions, an active collision-coalescence (C-C) process is not observed within the limited depths of warm cloud (< 1000 m). The state-of-the-art observations presented in this paper can be used to initialize modelling case studies to study the influence of aerosols on cloud and precipitation processes in the region and to better understand the impacts of hygroscopic cloud-seeding on these clouds.

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“…Since turbulence has been shown to strongly influence the collision-coalescence process and thus the formation of drizzle (e.g. Chen et al, 2020), potential deficiencies in the description of the dynamical and thermodynamical environment may therefore result in the weaker seeding effects compared to observations. Moreover, by the same argument, the results presented here are most likely not well generalized to different environments.…”

Section: Discussionmentioning

confidence: 99%

“…It is generally agreed that the seeding particles need to be in the size range of several micrometres in order to be effective in warm clouds (Segal et al, 2004;Rosenfeld et al, 2010). However, the specific outcome will presumably also depend on the properties of the background aerosol as well as on the turbulence characteristics of the cloud (Chen et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Precipitation enhancement in stratocumulus clouds through airborne seeding: sensitivity analysis by UCLALES-SALSA

et al. 2021

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Abstract. Artificial enhancement of precipitation via hygroscopic cloud seeding is investigated with a numerical large-eddy simulation model coupled with a spectral aerosol–cloud microphysics module. We focus our investigation on marine stratocumulus clouds and evaluate our model results by comparing them with recently published results from field observations. Creating multiple realizations of a single cloud event with the model provides a robust method to detect and attribute the seeding effects, which reinforces the analysis based on experimental data. Owing to the detailed representation of aerosol–cloud interactions, our model successfully reproduces the microphysical signatures attributed to the seeding, which were also seen in the observations. Moreover, the model simulations show up to a 2–3-fold increase in the precipitation flux due to the seeding, depending on the seeding rate and injection strategy. However, our simulations suggest that a relatively high seeding particle emission rate is needed for a substantial increase in the precipitation yield, compared with the estimated seeding concentrations from the field campaign. In practical applications, the seeding aerosol is often produced by flare burning. It is speculated that the required number of large seeding particles suggested by our results could pose a technical challenge to the flare-based approach.

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Impact of aerosols and turbulence on cloud droplet growth: an in-cloud seeding case study using a parcel–DNS (direct numerical simulation) approach

Cited by 25 publications

References 47 publications

The Influence of Hygroscopic Flare Seeding on Drop Size Distribution Over Southeast Queensland

The Influence of Hygroscopic Flare Seeding on Drop Size Distribution Over Southeast Queensland

Analysis of aerosol-cloud interactions and their implications for precipitation formation using aircraft observations over the United Arab Emirates

Precipitation enhancement in stratocumulus clouds through airborne seeding: sensitivity analysis by UCLALES-SALSA

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