Nucleation Scavenging of Smoke Particles and Simulated Drop Size Distributions over Large Biomass Fires

Chuang, Catherine C.; Penner, Yoyce E.; Edwards, Leslie L.

doi:10.1175/1520-0469(1992)049<1264:nsospa>2.0.co;2

Cited by 19 publications

(12 citation statements)

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“…The activated particle fractions are substantially higher than assumed in earlier model studies of pyro-convective clouds (5%, . However, the linear extrapolation of our results to extreme pyro-convective conditions (N CN =4×10 5 cm −3 , w=20 m s −1 ) is consistent with the results of Chuang et al (1992: S max =0.15%, N CD /N CN =16%).…”

Section: Different Regimes Of Ccn Activationsupporting

confidence: 91%

Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN)

et al. 2009

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Abstract.We have investigated the formation of cloud droplets under pyro-convective conditions using a cloud parcel model with detailed spectral microphysics and with the κ-Köhler model approach for efficient and realistic description of the cloud condensation nucleus (CCN) activity of aerosol particles. Assuming a typical biomass burning aerosol size distribution (accumulation mode centred at 120 nm), we have calculated initial cloud droplet number concentrations (N CD ) for a wide range of updraft velocities (w=0.25-20 m s −1 ) and aerosol particle number concentrations (N CN =200-10 5 cm −3 ) at the cloud base. Depending on the ratio between updraft velocity and particle number concentration (w/N CN ), we found three distinctly different regimes of CCN activation and cloud droplet formation:(1) An aerosol-limited regime that is characterized by high w/N CN ratios (>≈10 −3 m s −1 cm 3 ), high maximum values of water vapour supersaturation (S max >≈0.5%), and high activated fractions of aerosol particles (N CD /N CN >≈90%). In this regime N CD is directly proportional to N CN and practically independent of w.(2) An updraft-limited regime that is characterized by low w/N CN ratios (<≈10 −4 m s −1 cm 3 ), low maximum values of water vapour supersaturation (S max <≈0.2%), and low activated fractions of aerosol particles (N CD /N CN <≈20%). In this regime N CD is directly proportional to w and practically independent of N CN .Correspondence to: H. Su (hsu@mpch-mainz.mpg.de) (3) An aerosol-and updraft-sensitive regime (transitional regime), which is characterized by parameter values in between the two other regimes and covers most of the conditions relevant for pyro-convection. In this regime N CD depends non-linearly on both N CN and w.In sensitivity studies we have tested the influence of aerosol particle size distribution and hygroscopicity on N CD . Within the range of effective hygroscopicity parameters that is characteristic for continental atmospheric aerosols (κ≈0.05-0.6), we found that N CD depends rather weakly on the actual value of κ. A compensation of changes in κ and S max leads to an effective buffering of N CD . Only for aerosols with very low hygroscopicity (κ<0.05) and also in the updraft-limited regime for aerosols with higher than average hygroscopicity (κ>0.3) did the relative sensitivities ∂lnN CD /∂lnκ≈ ( N CD /N CD )/( κ/κ) exceed values of ∼0.2, indicating that a 50% difference in κ would change N CD by more than 10%.The influence of changing size distribution parameters was stronger than that of particle hygroscopicity. Nevertheless, similar regimes of CCN activation were observed in simulations with varying types of size distributions (polluted and pristine continental and marine aerosols with different proportions of nucleation, Aitken, accumulation, and coarse mode particles). In general, the different regimes can be discriminated with regard to the relative sensitivities of N CD against w and N CN (∂lnN CD /∂lnw and ∂lnN CD /∂lnN CN ). We propose to separate the different regimes by rel...

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Section: Different Regimes Of Ccn Activationsupporting

confidence: 91%

Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN)

et al. 2009

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“…Furthermore, in this study we have not attempted to estimate the indirect effects of the smoke. There is evidence from other studies of biomass burning events to suggest that a substantial proportion of such smoke can act as CCN [Chuang et al, 1992], and that the indirect effects associated with it may thus be important [Penner et al, 2003]. Figure 9.…”

Section: Discussionmentioning

confidence: 99%

Estimating the direct radiative forcing due to haze from the 1997 forest fires in Indonesia

et al. 2004

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[1] The El Niño event of 1997-1998 caused a severe reduction of rainfall in Indonesia that promoted the spread of forest fires, leading to a pervasive haze in the region. Here we use fire coverage data from the 1997 World Fire Atlas with a review of other available data and literature to estimate the distribution of particulate emissions from August to November 1997 and the particle size and radiative properties. Our preferred estimate of the total particulate emissions is approximately 41 Tg. The emissions have been used to drive an atmospheric model to simulate the distribution of the haze and its direct radiative effect, with and without allowing for the effects of the smoke on the atmospheric evolution. Model diagnostics of the aerosol and its radiative impact are compared with measurements and output from other models. Large decreases in the incident solar flux at the surface are obtained in the region. The simulated global mean shortwave radiative forcing at the top of the atmosphere, averaged over the 4 months, is À0.32 Wm À2 . The accuracy of this calculation is discussed, and the importance of the Indonesian fires in particular and of biomass burning in general is assessed.

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“…Differentiation of the separate effects of dust, sea salt, and natural sulfates is the subject of a new parameterization that is still under development. The detailed microphysical model described by Chuang et al [1992] is used to develop the parameterization for the interrelationship between anthropogenic sulfate, aerosol number concentration and cloud drop nucleation.…”

Section: Cloud Drop Parameterizationmentioning

confidence: 99%

Cloud susceptibility and the first aerosol indirect forcing: Sensitivity to black carbon and aerosol concentrations

et al. 2002

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[1] Present-day global anthropogenic emissions contribute more than half of the mass in submicron particles primarily due to sulfate and carbonaceous aerosol components derived from fossil fuel combustion and biomass burning. These anthropogenic aerosols increase cloud drop number concentration and cloud albedo. Here, we use an improved version of the fully coupled climate/chemistry models to investigate cloud susceptibility and the first indirect effect of anthropogenic aerosols (the Twomey effect). We examine the correspondence between the model simulation of cloud susceptibility and that inferred from satellite measurements to test whether our simulated aerosol concentrations and aerosol/cloud interactions give a faithful representation of these features. This comparison provides an overall measure of the adequacy of cloud cover and drop concentrations. We also address the impact of black carbon absorption in clouds on the first indirect forcing and examine the sensitivity of the forcing to different representations of natural aerosols. We find that including this absorption does not change the global forcing by more than 0.07 W m À2 , but that locally it could decrease the forcing by as much as 0. Citation: Chuang, C. C., J. E. Penner, J. M. Prospero, K. E. Grant, G. H. Rau, and K. Kawamoto, Cloud susceptibility and the first aerosol indirect forcing: Sensitivity to black carbon and aerosol concentrations,

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Nucleation Scavenging of Smoke Particles and Simulated Drop Size Distributions over Large Biomass Fires

Cited by 19 publications

References 0 publications

Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN)

Aerosol- and updraft-limited regimes of cloud droplet formation: influence of particle number, size and hygroscopicity on the activation of cloud condensation nuclei (CCN)

Estimating the direct radiative forcing due to haze from the 1997 forest fires in Indonesia

Cloud susceptibility and the first aerosol indirect forcing: Sensitivity to black carbon and aerosol concentrations

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