Different Approaches for Constraining Global Climate Models of the Anthropogenic Indirect Aerosol Effect

Lohmann, Ulrike; Quaas, Johannes; Kinne, Stefan; Feichter, J.

doi:10.1175/bams-88-2-243

Cited by 71 publications

(41 citation statements)

References 42 publications

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“…Remarkably, the radiative forcing associated with the first indirect effect estimated from remote sensing measurements appears to be relatively small, ∼0.2 W m −2 (Quaas et al, 2008), compared to model derived estimates. This is consistent with other studies that found a weaker relation between aerosol and cloud optical thicknesses when derived from satellites than from models (Menon et al, 2008;Lohmann and Lesins, 2002). It is likely that part of the discrepancy is caused by an underestimation in models of the influence of natural aerosol on clouds, e.g., associated with marine organic aerosol (Roelofs, 2007).…”

Section: Introductionsupporting

confidence: 91%

“…To estimate the magnitude of the radiative forcing due to aerosol indirect effects, global models that simulate activation of aerosol to cloud droplets can be applied (Lohmann et al, 2007;Penner et al, 2006). Due to the complexity of the interactions between aerosol and clouds, involving large variabilities in size, chemical composition and hygroscopicity of particles, current model estimates of the aerosol indirect forcing display a large range, between approximately −0.5 and −1.5 W m −2 (Forster et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

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Cloud processing, cloud evaporation and Angström exponent

Roelofs

Kamphuis

2009

Atmos. Chem. Phys.

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Abstract.With a cloud parcel model we investigate how cloud processing and cloud evaporation modify the size distribution and the Angström exponent of an aerosol population. Our study provides a new explanation for the observed variability of the aerosol optical thickness and Angström exponent in the vicinity of clouds. Cloud processing causes a decrease of aerosol particle concentrations, relatively most efficiently in the coarse mode, and reduces the relative dispersion of the aerosol distribution. As a result the Angström exponent of the aerosol increases. The Angström exponent is very sensitive for changes in relative humidity during cloud evaporation, especially between 90% and 100%. In addition, kinetic limitations delay evaporation of relatively large cloud drops, especially in clean and mildly polluted environments where the coarse mode fraction is relatively large. This hampers a direct relation between the aerosol optical thickness, the Angström exponent and the ambient relative humidity, which may severely complicate interpretation of these parameters in terms of aerosol properties, such as the fine mode fraction.

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Section: Introductionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Cloud processing, cloud evaporation and Angström exponent

Roelofs

Kamphuis

2009

Atmos. Chem. Phys.

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“…To estimate the magnitude of the radiative forcing due to aerosol direct and indirect effects, coupled aerosol-climate models that simulate activation of aerosol to cloud droplets can be applied (Lohmann et al, 2007;Penner et al, 2006). Due to the complexity of aerosol processes and inaccuracies in the representation of the hydrological cycle, current model estimates of the radiative forcing display a large range, between −0.2 and −0.9 W m −2 for the direct effect and between −0.5 and −1.5 W m −2 for the indirect effect (Forster et al, 2007;Quaas et al, 2009).…”

Section: G J Roelofs Et Al: Evaluation Of Simulated Aerosol Propermentioning

confidence: 99%

Evaluation of simulated aerosol properties with the aerosol-climate model ECHAM5-HAM using observations from the IMPACT field campaign

et al. 2010

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Abstract. In May 2008, the measurement campaign IM-PACT for observation of atmospheric aerosol and cloud properties was conducted in Cabauw, The Netherlands. With a nudged version of the coupled aerosol-climate model ECHAM5-HAM we simulate the size distribution and chemical composition of the aerosol and the associated aerosol optical thickness (AOT) for the campaign period. Synoptic scale meteorology is represented realistically through nudging of the vorticity, the divergence, the temperature and the surface pressure. Simulated concentrations of aerosol sulfate and organics at the surface are generally within a factor of two from observed values. The monthly averaged AOT from the model is 0.33, about 20% larger than observed. For selected periods of the month with relatively dry and moist conditions discrepancies are approximately −30% and +15%, respectively. Discrepancies during the dry period are partly caused by inaccurate representation of boundary layer (BL) dynamics by the model affecting the simulated AOT. The model simulates too strong exchange between the BL and the free troposphere, resulting in weaker concentration gradients at the BL top than observed for aerosol and humidity, while upward mixing from the surface layers into the BL appears to be underestimated. The results indicate that beside aerosol sulfate and organics also aerosol ammonium and nitrate sigCorrespondence to: G. J. Roelofs (g.j.h.roelofs@uu.nl) nificantly contribute to aerosol water uptake. The simulated day-to-day variability of AOT follows synoptic scale advection of humidity rather than particle concentration. Even for relatively dry conditions AOT appears to be strongly influenced by the diurnal cycle of RH in the lower boundary layer, further enhanced by uptake and release of nitric acid and ammonia by aerosol water.

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“…Because of their high spatial and temporal coverage, satellite observations are excellent tools to answer these questions (Lohmann et al, 2007). The A-Train satellite constellation offers a unique synergy between a wide range of active and passive instruments (Stephens et al, 2002), such that numerous methods now exist to provide spaceborne retrievals of ice cloud 5 properties.…”

Section: Introductionmentioning

confidence: 99%

Ice crystal number concentration estimates from lidar-radar satellite remote sensing. Part 1: Method and evaluation

Sourdeval¹,

Gryspeerdt²,

Krämer³

et al. 2018

Preprint

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Abstract. The number concentration of cloud particles is a key quantity for understanding aerosol-cloud interactions and describing clouds in climate and numerical weather prediction models. In contrast with recent advances for liquid clouds, few observational constraints exist on the ice crystal number concentration (N i ). This study investigates how combined lidar-radar measurements can be used to provide satellite estimates of N i , using a methodology that constrains moments of a parameterized particle size distribution (PSD). The operational liDAR-raDAR (DARDAR) product serves as an existing base for this method, 5 which focuses on ice clouds with temperatures T c < -30°C.Theoretical considerations demonstrate the capability for accurate retrievals of N i , apart from a possible bias in the concentration in small crystals when T c -50°C, due to the assumption of a monomodal PSD shape in the current method. This is verified by comparing satellite estimates to co-incident in situ measurements, which additionally demonstrates the sufficient sensitivity of lidar-radar observations to N i . Following these results, satellite estimates of N i are evaluated in the context of a 10 case study and a preliminary climatological analysis based on 10 years of global data. Despite of a lack of other large-scale references, this evaluation shows a reasonable physical consistency in N i spatial distribution patterns. Notably, increases in N i are found towards cold temperatures and, more significantly, in the presence of strong updraughts, such as those related to convective or orographic uplifts. Further evaluation and improvements of this method are necessary but these results already constitute a first encouraging step towards large-scale observational constraints for N i . Part two of this series uses this new 15 dataset to examine the controls on N i .

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Different Approaches for Constraining Global Climate Models of the Anthropogenic Indirect Aerosol Effect

Cited by 71 publications

References 42 publications

Cloud processing, cloud evaporation and Angström exponent

Cloud processing, cloud evaporation and Angström exponent

Evaluation of simulated aerosol properties with the aerosol-climate model ECHAM5-HAM using observations from the IMPACT field campaign

Ice crystal number concentration estimates from lidar-radar satellite remote sensing. Part 1: Method and evaluation

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