Atmospheric sulfur and deep convective clouds in tropical Pacific: A model study

Andronache, C.; Donner, Leo; Seman, Charles J.; Ramaswamy, V.; Hemler, Richard S.

doi:10.1029/1998jd200085

Cited by 15 publications

(14 citation statements)

References 72 publications

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“…In the reference case, a fixed coefficient for β equal to 1.12 over both land and ocean is used to account for the relationship between the effective radius and the volume mean radius. However, alterations in the linear relationship between r e and r v are expected in the presence of entrainment, precipitation, and ice particles (Andronache et al, 1999). Recently, Liu and Daum (2002) showed that the dispersion of the cloud droplet spectrum is related to the cloud droplet number concentration.…”

Section: Sources Of Uncertaintymentioning

confidence: 99%

Uncertainty analysis for estimates of the first indirect aerosol effect

2005

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Abstract. The IPCC has stressed the importance of producing unbiased estimates of the uncertainty in indirect aerosol forcing, in order to give policy makers as well as research managers an understanding of the most important aspects of climate change that require refinement. In this study, we use 3-D meteorological fields together with a radiative transfer model to examine the spatially-resolved uncertainty in estimates of the first indirect aerosol forcing. The global mean forcing calculated in the reference case is −1.30 Wm −2 . Uncertainties in the indirect forcing associated with aerosol and aerosol precursor emissions, aerosol mass concentrations from different chemical transport models, aerosol size distributions, the cloud droplet parameterization, the representation of the in-cloud updraft velocity, the relationship between effective radius and volume mean radius, cloud liquid water content, cloud fraction, and the change in the cloud drop single scattering albedo due to the presence of black carbon are calculated. The aerosol burden calculated by chemical transport models and the cloud fraction are found to be the most important sources of uncertainty. Variations in these parameters cause an underestimation or overestimation of the indirect forcing compared to the base case by more than 0.6 Wm −2 . Uncertainties associated with aerosol and aerosol precursor emissions, uncertainties in the representation of the aerosol size distribution (including the representation of the pre-industrial size distribution), and uncertainties in the representation of cloud droplet spectral dispersion effect cause uncertainties in the global mean forcing of 0.2∼0.6 Wm −2 . There are significant regional differences in the uncertainty associated with the first indirect forcing with the largest uncertainties in industrial regions (North America, Europe, East Asia) followed by those in the major biomass burning regions.

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Section: Sources Of Uncertaintymentioning

confidence: 99%

Uncertainty analysis for estimates of the first indirect aerosol effect

2005

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“…3.2 Aerosol effects on deep convective clouds (thermodynamic effect) Andronache et al (1999) showed that an increase in sulfate loading during the TOGA-COARE experiment causes a significant decrease of the effective radius of cloud droplets (changes up to 2 µm on average) and an increase in the number concentration of cloud droplets of 5-20 cm −3 over a limited domain of 500 km. The change in the average net shortwave radiation flux above the clouds was estimated to be on average −1.5 W m −2 , with significant spatial and temporal variations.…”

Section: Aerosol Effects On Large-scale Mixed-phase Cloudsmentioning

confidence: 99%

Global indirect aerosol effects: a review

2005

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Abstract. Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.

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“…place in association with deep convection updrafts, and an unresolved issue is the degree to which precipitation scavenging suppresses the convective cloud venting of water-soluble gases [Andronache et al, 1999;Flossmann and Wobrock, 1996;Barth, 1994]. We present here an analysis of this issue.…”

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confidence: 99%

Transport and scavenging of soluble gases in a deep convective cloud

Mari¹,

Jacob²,

Bechtold³

2000

J. Geophys. Res.

252

246

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(1.9) for CO, 11 (9.5) for CH3OOH, 2.9 (3.1) for CH20, 1.9 (1.2) for H202, and 0.8 (0.4) for HNO3. Simulated scavenging efficiencies in the convective column are 5% for CH3OOH, 23% for CH20, 66% for H202, 77% for HNO3, and 28% for SO2. The large CEF for CH3OOH reflects its low solubility and its boundary layer enrichment relative to the upper troposphere. The Henry's law constant for CH20 puts it at the threshold for etficient scavenging. Scavenging of SO2 is limited by the rate of aqueous phase reaction with H•O•, as H•O2 is itself efficiently scavenged by Henry's law equilibrium; efficient scavenging of SO2 requires unusually high cloud water pH (pH > 6) to enable fast aqueous phase oxidation by Oa. Both HNO3 and HaOa are efficiently scavenged in the lower (warm) part of the cloud, but H202 is released as the cloud freezes due to low retention efficiency during timing. Significant scavenging of H202 still takes place by cocondensation with ice in the glaciated cloud but is less efficient than in the warm cloud. Inefficient scavenging of H202 in glaciated clouds may explain the observation, in TRACE-A and elsewhere, that HaO2 is enhanced in deep convective outflows while HNOa is depleted. Model results indicate little direct transfer of air from the boundary layer to the cloud anvil in the convective plume, because of low-level detrainment in the warm cloud and high-level entrainment in the glaciated cloud. We find instead a convective ladder effect where midlevel outflow during the growing phase of the storm is teentrained into the convective plume as the storm matures.

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Atmospheric sulfur and deep convective clouds in tropical Pacific: A model study

Cited by 15 publications

References 72 publications

Uncertainty analysis for estimates of the first indirect aerosol effect

Uncertainty analysis for estimates of the first indirect aerosol effect

Global indirect aerosol effects: a review

Transport and scavenging of soluble gases in a deep convective cloud

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