Comparison of different droplet measurement techniques in the Braunschweig Icing Wind Tunnel

Knop, Inken; Bansmer, Stephan; Hahn, Valerian; Voigt, Christiane

doi:10.5194/amt-14-1761-2021

Cited by 26 publications

(18 citation statements)

References 58 publications

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“…Data from the following instruments were used: condensation particle counter (CPC; TSI model 3772) for number concentration of particles with diameter > 10 nm; scanning mobility particle sizer (SMPS; TSI model 3081) for aerosol size distribution data between 3.2 and 89.1 nm; laser aerosol spectrometer (LAS; TSI model 3340) for aerosol size distribution data between diameters of 0.09 and 5 μm; two-dimensional optical array imaging probe (2DS; SPEC Inc.) ( Lawson et al, 2006 ) for rain water content (RWC) quantified by integrating raindrop size distributions between diameters of 39.9 and 1464.9 μm; and fast cloud droplet probe (FCDP; SPEC Inc.) ( Knop et al, 2021 ) for cloud liquid water content (LWC) calculated by integrating drop size distributions between diameters of 3 and 50 μm. With the exception of SMPS data (45 s resolution), all airborne data were at 1 s resolution.…”

Section: Reanalysis Datamentioning

confidence: 99%

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

et al. 2021

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Abstract. North American pollution outflow is ubiquitous over the western North Atlantic Ocean, especially in winter, making this location a suitable natural laboratory for investigating the impact of precipitation on aerosol particles along air mass trajectories. We take advantage of observational data collected at Bermuda to seasonally assess the sensitivity of aerosol mass concentrations and volume size distributions to accumulated precipitation along trajectories (APT). The mass concentration of particulate matter with aerodynamic diameter less than 2.5 µm normalized by the enhancement of carbon monoxide above background (PM2.5/ΔCO) at Bermuda was used to estimate the degree of aerosol loss during transport to Bermuda. Results for December–February (DJF) show that most trajectories come from North America and have the highest APTs, resulting in a significant reduction (by 53 %) in PM2.5/ΔCO under high-APT conditions (> 13.5 mm) relative to low-APT conditions (< 0.9 mm). Moreover, PM2.5/ΔCO was most sensitive to increases in APT up to 5 mm (−0.044 µg m−3 ppbv−1 mm−1) and less sensitive to increases in APT over 5 mm. While anthropogenic PM2.5 constituents (e.g., black carbon, sulfate, organic carbon) decrease with high APT, sea salt, in contrast, was comparable between high- and low-APT conditions owing to enhanced local wind and sea salt emissions in high-APT conditions. The greater sensitivity of the fine-mode volume concentrations (versus coarse mode) to wet scavenging is evident from AErosol RObotic NETwork (AERONET) volume size distribution data. A combination of GEOS-Chem model simulations of the 210Pb submicron aerosol tracer and its gaseous precursor 222Rn reveals that (i) surface aerosol particles at Bermuda are most impacted by wet scavenging in winter and spring (due to large-scale precipitation) with a maximum in March, whereas convective scavenging plays a substantial role in summer; and (ii) North American 222Rn tracer emissions contribute most to surface 210Pb concentrations at Bermuda in winter (∼ 75 %–80 %), indicating that air masses arriving at Bermuda experience large-scale precipitation scavenging while traveling from North America. A case study flight from the ACTIVATE field campaign on 22 February 2020 reveals a significant reduction in aerosol number and volume concentrations during air mass transport off the US East Coast associated with increased cloud fraction and precipitation. These results highlight the sensitivity of remote marine boundary layer aerosol characteristics to precipitation along trajectories, especially when the air mass source is continental outflow from polluted regions like the US East Coast.

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Section: Reanalysis Datamentioning

confidence: 99%

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

et al. 2021

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“…More recent work by Knop et al . (2021) which involved an intercomparison between the PDI and laser spectroscopy with a fast cloud droplet probe (FCDP) found good agreement in the mean droplet diameter between FCDP and PDI (for the size range of 8 to 35

μ

m) with up to 14% deviation. This deviation is well within the range of other instrument intercomparisons (Braga et al ., 2017; Faber et al ., 2018).…”

Section: Methodsmentioning

confidence: 99%

Analyzing cloud droplet spatial tendencies on the millimetre and centimetre scales in stratocumulus clouds

Dodson¹,

Griswold²

2022

Quart J Royal Meteoro Soc

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It is well known that fluid turbulence can affect cloud droplet motion, leading to droplet clustering, which in turn can impact precipitation formation through influences on collision-coalescence. Previous work suggests that droplet clustering, or preferential concentration, of cloud droplets occurs on the order of the Kolmogorov length-scale (𝜂), with the magnitude of this clustering depending on the Stokes number (St). However, the accuracy of these theories remains largely unquantified for in situ atmospheric clouds. Therefore, data gathered from a weakly turbulent marine stratocumulus (Sc) deck during the Variability of the American Monsoons (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) are used to analyze the spatial statistics of cloud droplets by means of one-dimensional pair correlation functions 𝜂(l). Cloud droplet arrival times were recorded onboard the CIRPAS Twin-Otter aircraft over a two-week analysis period using the Artium Flight phase-Doppler Interferometer. Results from 2431 subsets of droplet arrival data indicate that droplet clustering occurs in 95% of cases from analyzing 𝜂(l), with the magnitude of the clustering becoming significant in the turbulence dissipation range, at a length-scale of ∼ 2𝜂. Analyzing 𝜂(l) as a function of in-cloud normalized height (Z * ) indicates that a maximum in the magnitude of average droplet clustering occurs near the Sc middle, at Z * = 0.47. Droplet clustering and St are also found to be strongly correlated at a statistically significant rate.

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“…The Fast Cloud Droplet Probe (FCDP) (O'Connor et al, 2008;Knop et al, 2021) manufactured by Stratton Park Engineering Company Incorporated (SPEC Inc.) is a forward-scattering probe, which counts single particles in the diameter size range of 1.5 − 50 µm. In this analysis we use only particles with diameters larger than 3µm.…”

Section: Cloud Measurements: the Fast Cloud Droplet Probementioning

confidence: 99%

Seasonal updraft speeds change cloud droplet number concentrations in low level clouds over the Western North Atlantic

Kirschler

Voigt

Anderson

et al. 2022

Preprint

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Abstract. Low level clouds over the Western North Atlantic show a seasonal cycle in cloud properties which anticorrelates to aerosol concentrations. To determinate the impact of dynamic and aerosol processes within marine low clouds we examine the seasonal impact of updraft speed w and cloud condensation nuclei concentration at 0.43 % supersaturation (NCCN0.43 %) on the cloud droplet number concentration (NC) of low level clouds over the Western North Atlantic Ocean. Aerosol and cloud properties were measured with instruments on board the NASA LaRC Falcon HU-25 during the ACTIVATE (Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment) mission in summer (August) and winter (February-March) 2020. The data are grouped in different NCCN0.43 % loadings and the density functions of NC and w near the cloud bases are compared. For low updrafts (w < 1.3 m s-1), NC in winter are mainly limited by the updraft speed and in summer additionally by aerosols. At larger updrafts (w > 3 m s-1), NC are impacted by the aerosol population, while at clean marine conditions cloud nucleation is aerosol limited and for high pollution it is influenced by aerosols and updraft. The aerosol size distribution in winter shows a bimodal distribution in clean marine environments, which transforms to a unimodal distribution in high pollution levels due to altering processes, whereas unimodal distributions prevail in summer with a significant difference in their aerosol concentration and composition. The increase in pollution level is accompanied with an increase of organic aerosol and sulfate compounds in both seasons. We demonstrate that NC can be explained by cloud condensation nuclei activation through upwards processed air masses with varying fractions of activated aerosols. The activation highly depends on w and thus supersaturation between the different seasons, while the aerosol size distribution additionally affects NC within a season. Our results quantify the seasonal influence of w and NCCN0.43 % on NC and can be used to improve the representation of low marine clouds in models.

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Comparison of different droplet measurement techniques in the Braunschweig Icing Wind Tunnel

Cited by 26 publications

References 58 publications

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

Analyzing cloud droplet spatial tendencies on the millimetre and centimetre scales in stratocumulus clouds

Seasonal updraft speeds change cloud droplet number concentrations in low level clouds over the Western North Atlantic

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