Tracer Study of Vertical Exchange by Cumulus Clouds

Ching, Jason; Alkezweeny, A.J.

doi:10.1175/1520-0450(1986)025<1702:tsoveb>2.0.co;2

Cited by 42 publications

(19 citation statements)

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“…Measurements dealing with the vertical transport of trace gases were carried out, e.g. by Ehhalt et al (1985), Ching and Alkezweeny (1986), Drummond et al (1988), and Pickering et al (1989). Based on aircraft tracer observations, Ching and Alkezweeny (1986) suggested that mixed-layer pollutants can be lifted above the planetary boundary layer into the overlying free troposphere or cloud c European Geophysical Society 2001 20 Y.…”

Section: Introductionsupporting

confidence: 93%

Simulation of trace gas redistribution by convective clouds - Liquid phase processes

2001

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Abstract.A two-dimensional dynamic cloud model with detailed microphysics and a spectral treatment of gas scavenging was used to simulate trace gas vertical redistribution in precipitating continental and maritime clouds. A general picture of gas transport in such clouds has been developed by examining the sensitivity to a range of parameters, including cloud dynamic and microphysical structure, gas solubility, and the method of calculating gas uptake by droplets. Gases with effective Henry's law constants (H * ) ranging from zero to greater than 10 9 mol dm −3 atm −1 were simulated. The abundance of highly soluble gases in the uppermost parts (top 1 km or so) of continental precipitating clouds was found to be as much as 20-50% of that of the insoluble tracer under conditions where the mixing ratio of the tracer was approximately 5% of its boundary layer value. The abundance of highly soluble gases was approximately 6 times higher in the uppermost parts of the continental cloud than in the maritime cloud, due to differences in wet removal efficiency in the two cloud types. A fully kinetic calculation of gas uptake, as opposed to assuming Henry's law equilibrium, was found to have a significant effect on gas transport, with the abundance of highly soluble gases in the uppermost parts of the cloud being a factor of 5 lower in the equilibrium simulations. The temperature dependence of the Henry's law constant was also found to be an important parameter in determining the abundance of soluble gases at cloud top, with the abundance of moderately soluble gases being as much as 70% lower when the temperature dependence of H * was included. This reduction in abundance was found to be equivalent to increasing the temperature-independent solubility by a factor of 7. The vertical transport of soluble gases could be parameterized in large-scale models by normalizing against the transport of tracers. However, our results suggest that there is no straightforward scaling factor, particularly if small concentrations of Correspondence to: Y. Yin (yan@env.leeds.ac.uk) highly soluble gases in the upper troposphere need to be defined.

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Section: Introductionsupporting

confidence: 93%

Simulation of trace gas redistribution by convective clouds - Liquid phase processes

2001

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“…Several preceding studies have observed vertical transport of trace gases and aerosol from the mixed layer into the cloudinfluenced transition layer during shallow cumulus convection (Angevine, 2005;Ching and Alkezweeny, 1986;Greenhut, 1986;Langford et al, 2010). Our observations are consistent with this earlier work.…”

Section: Discussionmentioning

confidence: 99%

“…The transition layer is intermittently mixed by thermal plumes that originate in the mixed layer and form cumulus clouds that release latent heat within the layer. There have been several observations of vertical transport and redistribution of trace gases by shallow cumulus convection (Angevine, 2005;Ching and Alkezweeny, 1986;Ching et al, 1988;Greenhut, 1986), and a few studies have investigated the vertical transport and aerosol formation during cumulus convection (Ching et al, 1988;Sorooshian et al, 2006Sorooshian et al, , 2007Wonaschuetz et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC<sup>4</sup>RS: observations of a modest aerosol enhancement aloft

et al. 2015

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Abstract. Vertical profiles of submicron aerosol from in situ aircraft-based measurements were used to construct aggregate profiles of chemical, microphysical, and optical properties. These vertical profiles were collected over the southeastern United States (SEUS) during the summer of 2013 as part of two separate field studies: the Southeast Nexus (SENEX) study and the Study of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC 4 RS). Shallow cumulus convection was observed during many profiles. These conditions enhance vertical transport of trace gases and aerosol and create a cloudy transition layer on top of the sub-cloud mixed layer. The trace gas and aerosol concentrations in the transition layer were modeled as a mixture with contributions from the mixed layer below and the free troposphere above. The amount of vertical mixing, or entrainment of air from the free troposphere, was quantified using the observed mixing ratio of carbon monoxide (CO). Although the median aerosol mass, extinction, and volume decreased with altitude in the transition layer, they were ∼10 % larger than expected from vertical mixing alone.This enhancement was likely due to secondary aerosol formation in the transition layer. Although the transition layer enhancements of the particulate sulfate and organic aerosol (OA) were both similar in magnitude, only the enhancement of sulfate was statistically significant. The column integrated extinction, or aerosol optical depth (AOD), was calculated for each individual profile, and the transition layer enhancement of extinction typically contributed less than 10 % to the total AOD. Our measurements and analysis were motivated by two recent studies that have hypothesized an enhanced layer of secondary aerosol aloft to explain the summertime enhancement of AOD (2-3 times greater than winter) over the southeastern United States. The first study attributes the layer aloft to secondary organic aerosol (SOA) while the second study speculates that the layer aloft could be SOA or secondary particulate sulfate. In contrast to these hypotheses, the modest enhancement we observed in the transition layer was not dominated by OA and was not a large fraction of the summertime AOD. Published by Copernicus

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“… Stull [1985] classified fair‐weather cumulus clouds based on the dynamical relationship with the mixed layer for diagnosing tracer transport. Ching and Alkezweeny [1986] observationally examines the vertical exchange of pollutants by cumulus clouds and showed that active clouds carry mixed layer pollutants upward into the cloud layer and force cloud‐layer air downward into the mixed layer. A research interest is then directed to the up‐scale impact of those small‐scale effects on larger‐scale dust cycle in the atmosphere in order to incorporate them as a subgrid‐scale effect in large‐scale numerical prediction models [ Cakmur et al , 2004; Miller et al , 2004].…”

Section: Introductionmentioning

confidence: 99%

Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area

Takemi¹,

Yasui²,

Zhou³

et al. 2006

J. Geophys. Res.

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[1] A series of high-resolution simulations explicitly resolving diurnally varying convective motion is performed for investigating the dynamical processes of dust emission and transport induced by boundary layer and cumulus convection under fair-weather conditions in a midlatitude desert area. The simulation set examines the sensitivity of the dust dynamics to vertical wind shear, upper level wind speed, and moist convection. The simulated results qualitatively capture the diurnal variation of the dust layer observed by lidar in a desert area in northern China. Dry convection plays a primary role in vertically mixing dust within the boundary layer. If cumulus convection also comes into play, mass concentration of dust increases not only within the boundary layer but also in the free troposphere. A coupled effect of dry and moist convection is important because convection is more enhanced with the coupled effect than without moist processes and in addition transports upper level higher momentum down to the surface, intensifying surface winds and hence dust emission. A wind speed exceeding the threshold for surface dust emission is necessary at the upper levels of the daytime boundary layer for the surface wind enhancement. Although the amount of dust lifted is much smaller during a single diurnal cycle of fair weather than is associated with a single case of synoptic disturbances, the total amount of dust emission due to fair-weather processes may not be neglected in a longer timescale. This suggests that a proper parameterization for dry and moist convection in fair weather needs to be employed in large-scale simulations.Citation: Takemi, T., M. Yasui, J. Zhou, and L. Liu (2006), Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area,

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Tracer Study of Vertical Exchange by Cumulus Clouds

Cited by 42 publications

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Simulation of trace gas redistribution by convective clouds - Liquid phase processes

Simulation of trace gas redistribution by convective clouds - Liquid phase processes

In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC<sup>4</sup>RS: observations of a modest aerosol enhancement aloft

Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area

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Tracer Study of Vertical Exchange by Cumulus Clouds

Cited by 42 publications

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Simulation of trace gas redistribution by convective clouds - Liquid phase processes

Simulation of trace gas redistribution by convective clouds - Liquid phase processes

In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC&lt;sup&gt;4&lt;/sup&gt;RS: observations of a modest aerosol enhancement aloft

Role of boundary layer and cumulus convection on dust emission and transport over a midlatitude desert area

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In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC<sup>4</sup>RS: observations of a modest aerosol enhancement aloft