Radiative influences on drop and cloud condensation nuclei equilibrium in stratocumulus

Marquis, James; Harrington, Jerry Y.

doi:10.1029/2004jd005401

Cited by 17 publications

(27 citation statements)

References 33 publications

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“…Marquis and Harrington (2005) pointed out that radiative heating and cooling rates for cloud droplets can vary by 2 to −15 K h -1 , depending on radiative fluxes, droplet diameter and droplet location with reference to cloud top and cloud base. Since the reported measurement flight was conducted between 16:30 and 17:45 CET strong shortwave heating can be neglected.…”

Section: Summary and Discussionmentioning

confidence: 99%

Aerosols-cloud microphysics-thermodynamics-turbulence: evaluating supersaturation in a marine stratocumulus cloud

et al. 2012

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Abstract. This work presents a unique combination of aerosol, cloud microphysical, thermodynamic and turbulence variables to characterize supersaturation fluctuations in a turbulent marine stratocumulus (SC) layer. The analysis is based on observations with the helicopter-borne measurement platform ACTOS and a detailed cloud microphysical parcel model following three different approaches: (1) From the comparison of aerosol number size distributions inside and below the SC layer, the number of activated particles is calculated as 435 ± 87 cm −3 and compares well with the observed median droplet number concentration of N d = 464 cm −3 . Furthermore, a 50 % activation diameter of D p50 ≈ 115 nm was derived, which was linked to a critical supersaturation S crit of 0.16 % via Köhler theory. From the shape of the fraction of activated particles, we estimated a standard deviation of supersaturation fluctuations of σ S = 0.09 %. (2) These estimates are compared to more direct thermodynamic observations at cloud base. Therefore, supersaturation fluctuations (S ) are calculated based on highly-resolved thermodynamic data showing a standard deviation of S ranging within 0.1 % ≤ σ S ≤ 0.3 %. (3) The sensitivity of the supersaturation on observed vertical wind velocity fluctuations is investigated with the help of a detailed cloud microphysical model. These results show highest fluctuations of S with σ S = 0.1 % at cloud base and a decreasing σ S with increasing liquid water content and droplet number concentration. All three approaches are independent of each other and vary only within a factor of about two.

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Section: Summary and Discussionmentioning

confidence: 99%

Aerosols-cloud microphysics-thermodynamics-turbulence: evaluating supersaturation in a marine stratocumulus cloud

et al. 2012

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“…Harrington et al (2000) and Marquis and Harrington (2005) showed that thermal emission enhanced cloud droplet growth by diffusion. An earlier onset of collision and coalescence of cloud droplets was found by Hartman and Harrington (2005a, b) when thermal radiation was considered.…”

Section: Introductionmentioning

confidence: 99%

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

et al. 2017

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Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day −1 . To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations.Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes.The cloud fields in the 100 and 50 m resolution simulations develop similarly...

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“…9 and 10 demonstrate the effect of LW radiant emission in enhancing cloud droplet growth, the opposite effect of SW (solar) radiant absorption could be shown by including it [24][25][26] in the radiation term Q r D, with the possibility that SW radiation could change the sign from negative to positive. This would require estimating absorption of SW radiation, which is more complicated just by the stronger spectral variation of water's absorption coefficient in the SW range compared to the LW range and the smaller absorption efficiency for SW radiation compared with the near unity emission efficiency for LW radiation (different absorption and emission efficiencies would need to be evaluated, as noted previously).…”

Section: Sample Cloud Droplet Radiation Calculationmentioning

confidence: 96%

Evaporation and condensation of water mist/cloud droplets with thermal radiation

Brewster

2015

International Journal of Heat and Mass Transfer

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a b s t r a c tThe role of thermal radiation in water droplet evaporation and condensation is investigated theoretically. The primary droplet size regime considered is that between non-continuum gas effects and gas-liquid velocity-slip effects, nominally 10 À1 -10 2 lm, with mist or clouds (nominally 20-lm diameter) being the primary application of interest. Principles for extending the results to larger droplets are also discussed, even to the radiative-evaporative balance of the oceans. The importance of distributed (volumetric, in-depth) absorption in the droplet, conduction, and advection induced by surface regression are analyzed. It is found that advection within the liquid phase induced by surface regression can be neglected for most conditions and that conduction usually establishes a spatially isothermal droplet. Comparison with experimental results for a laser-irradiated droplet suggests that, due to the isothermal condition, these assumptions are reasonable for predicting evaporation rate. Moreover, it is shown that infrared absorption and emission can be treated as surface phenomena; in-depth effects can be neglected. Extending the analysis to cloud droplets shows that radiation, whether with colder upper layers of the atmosphere, warmer lower layers/ground, or solar radiation, can have a significant influence on cloud droplet growth and stability. For typical ambient conditions the thermal radiation effect near the edge of a cloud can be as strong as the effect of a 0.1% super-or sub-saturation, enough to modify significantly the Kohler curves governing equilibrium droplet size distribution and enough to provide the missing mechanism of warm rain droplet growth between the upper limit of non-radiating, diffusional condensation growth ($30 lm) and the lower limit of turbulent-inertial coalescence growth ($80 lm), the so-called condensation-coalescence ''bottleneck''.

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Radiative influences on drop and cloud condensation nuclei equilibrium in stratocumulus

Cited by 17 publications

References 33 publications

Aerosols-cloud microphysics-thermodynamics-turbulence: evaluating supersaturation in a marine stratocumulus cloud

Aerosols-cloud microphysics-thermodynamics-turbulence: evaluating supersaturation in a marine stratocumulus cloud

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Evaporation and condensation of water mist/cloud droplets with thermal radiation

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