The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations

Wood, Robert; Mechoso, Carlos R.; Bretherton, Christopher S.; Weller, Robert A.; Huebert, B. J.; Straneo, Fiammetta; Albrecht, Bruce A.; Coe, Hugh; Allen, Grant; Vaughan, G.; Daum, P. H.; Fairall, C. W.; Chand, D.; Gallardo, Laura; Garreaud, René D.; Grados, Carmen; Covert, David S.; Bates, T. S.; Krejci, Radovan; Russell, Lynn M.; Szoeke, Simon de; Brewer, Alan; Yuter, Sandra E.; Springston, Stephen; Chaigneau, Alexis; Toniazzo, Thomas; Minnis, Patrick; Palikonda, Rabindra; Abel, Steven J.; Brown, William O.; Williams, S. F.; Fochesatto, Javier; Brioude, J.; Bower, Keith

doi:10.5194/acp-11-627-2011

Cited by 287 publications

(271 citation statements)

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“…This was one component of the VA-MOS Ocean-Cloud-Atmosphere-Land Systems (VOCALS) project, with the overarching purpose of improving understanding of SEP clouds and their simulation in global climate models (Wood et al, 2011b). One of the specific VOCALS goals was to determine how continental pollution from industrial activity affected droplet size (and presumably, cloud albedo) in the stratocumulus layer offshore.…”

Section: Methods and Objectivesmentioning

confidence: 99%

“…The southeast Pacific Ocean (SEP) is an ideal environment to study stratocumulus clouds because it has one of the world's most persistent and unexplored cloud decks (Huneeus et al, 2006;Wood et al, 2011b). Chile, which borders a large portion of the SEP, has an economy heavily based in mining copper and other metals (Schüller et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Impacts of aerosol particles on the microphysical and radiative properties of stratocumulus clouds over the southeast Pacific Ocean

et al. 2013

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The southeast Pacific Ocean is covered by the world's largest stratocumulus cloud layer, which has a strong impact on ocean temperatures and climate in the region. The effect of anthropogenic sources of aerosol particles on the stratocumulus deck was investigated during the VOCALS field experiment. Aerosol measurements below and above cloud were made with a ultra-high sensitivity aerosol spectrometer and analytical electron microscopy. In addition to more standard in-cloud measurements, droplets were collected and evaporated using a counterflow virtual impactor (CVI), and the non-volatile residual particles were analyzed.

Many flights focused on the gradient in cloud properties on an E-W track along 20° S from near the Chilean coast to remote areas offshore. Mean statistics, including their significance, from eight flights and many individual legs were compiled. Consistent with a continental source of cloud condensation nuclei, below-cloud accumulation-mode aerosol and droplet number concentration generally decreased from near shore to offshore. Single particle analysis was used to reveal types and sources of the enhanced particle number that influence droplet concentration. While a variety of particle types were found throughout the region, the dominant particles near shore were partially neutralized sulfates. Modeling and chemical analysis indicated that the predominant source of these particles in the marine boundary layer along 20° S was anthropogenic pollution from central Chilean sources, with copper smelters a relatively small contribution.

Cloud droplets were smaller in regions of enhanced particles near shore. However, physically thinner clouds, and not just higher droplet number concentrations from pollution, both contributed to the smaller droplets. Satellite measurements were used to show that cloud albedo was highest 500–1000 km offshore, and actually slightly lower closer to shore due to the generally thinner clouds and lower liquid water paths there. Thus, larger scale forcings that impact cloud macrophysical properties, as well as enhanced aerosol particles, are important in determining cloud droplet size and cloud albedo.

Differences in the size distribution of droplet residual particles and ambient aerosol particles were observed. By progressively excluding small droplets from the CVI sample, we were able to show that the larger drops, some of which may initiate drizzle, contain the largest aerosol particles. Geometric mean diameters of droplet residual particles were larger than those of the below-cloud and above cloud distributions. However, a wide range of particle sizes can act as droplet nuclei in these stratocumulus clouds. A detailed LES microphysical model was used to show that this can occur without invoking differences in chemical composition of cloud-nucleating particles

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Section: Methods and Objectivesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impacts of aerosol particles on the microphysical and radiative properties of stratocumulus clouds over the southeast Pacific Ocean

et al. 2013

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“…The VAMOS Ocean-Cloud-Land-Study Regional Experiment (VOCALS-REx), took place in October/November 2008 out of Arica, Chile. The campaign involved 14 research flights aboard the National Center for Aerosol Research (NCAR) C-130, with three distinct flight patterns (Wood et al, 2011b). These included (1) flights along 20 • S with 10 min legs above-cloud, in-cloud and below cloud, (2) flights investigating pockets of open cells (POCs) in the stratocumulus deck (Wood et al, 2011a) A third campaign, the Intercontinental and Megacity Pollution Experiment (IMPEX), also took place aboard the C-130 in April 2006, with 12 research flights from Seattle, WA over the Northeast Pacific Ocean.…”

Section: Field Campaignsmentioning

confidence: 99%

Organic matter and non-refractory aerosol over the remote Southeast Pacific: oceanic and combustion sources

et al. 2012

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(SO 4 ) and organics (Org), during VOCALS and the cruise show lower absolute values than those reported for previous "clean air" studies. In the marine boundary layer, average concentrations for SO 4 were 0.52 µg m −3 for the VOCALS region and 0.85 µg m −3 for the equatorial region while average Org concentrations were 0.10 and 0.07 µg m −3 , respectively. Campaign average Org/SO 4 ratios were 0.19 (VOCALS) and 0.08 (equatorial Pacific). Black carbon (BC) measurements from a single particle soot photometer (SP2) and carbon monoxide (CO) concentrations over the Southeast Pacific provided sensitive indicators of pollution. CO and BC were used to identify the least polluted air, which had average concentrations of SO 4 and Org of 0.14 and 0.01 µg m −3 , respectively, with an average Org/SO 4 of 0.08. Data from IMPEX was constrained to similar clean air criterion, and resulted in an average Org/SO 4 ratio of 0.19. Under the cleanest MBL conditions during VOCALS, identified by CO below 61 ppbv, a robust linear relationship between Org and BC concentrations revealed that even at very low pollution levels, combustion sources dominated organic aerosol, suggesting little to no marine source of submicrometer Org to the atmosphere over the eastern South Pacific. This means marine organics cannot be identified by merely setting a standard for background conditions below which anthropogenic influence can be disregarded. Other methods must be used to exclude nonmarine sources.

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“…Similarly to the subtropical region off the California coast, such conditions lead to a cold well-mixed boundary layer topped by a persistent stratocumulus deck (Rahn and Garreaud, 2010;Toniazzo et al, 2011). Due to a large area of coverage and persistence of stratocumulus clouds, this region significantly affects planetary albedo.…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Limited-are a modelling of stratocumulus over South-Eastern Pacific

et al. 2012

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Abstract. This paper presents application of the Weather Research and Forecasting (WRF) model to limited-area modeling of atmospheric processes over the subtropical southeastern Pacific, with the emphasis on the stratocumulustopped boundary layer. The simulations cover a domain from the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field project conducted in the subtropical south-eastern Pacific in October and November 2008. We focus on a day where the UK's BAe-146 research aircraft encountered Pockets of Open Cells (POCs) at the very western edge of its flight track, rather than on the entire campaign as investigated in previous limited-area modeling studies. Model results are compared to aircraft observations with the main conclusion that the simulated stratocumulus-topped boundary layer is significantly too shallow. This appears to be a combination of an already too shallow boundary layer in the dataset used to provide initial and lateral boundary conditions, and the inability of the WRF model to increase the boundary-layer height. Several sensitivity simulations, applying different subgrid-scale parameterizations available in the model, a larger computational domain and longer simulations, as well as a different dataset providing initial and lateral boundary conditions were all tried to improve the simulation. These changes appeared to have a rather small effect on the results.The model does simulate the formation of mesoscale cloud-free regions that one might consider similar to Pockets of Open Cells observed in nature. However, formation of these regions does not seem to be related to drizzle-induced transition from open-to closed-cell circulations as simulated by LES models. Instead, the cloud-free regions appear to result from mesoscale variations of the lower-tropspheric vertical velocity. Areas of negative vertical velocity with minima (a few cm s −1 ) near the boundary layer top seem to induce direct evaporation of the cloud layer. It remains to be seen in LES studies whether the mechanism seen in the model is realistic or if it is simply an artifact of interactions between resolved and parameterized processes.

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The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations

Cited by 287 publications

References 52 publications

Impacts of aerosol particles on the microphysical and radiative properties of stratocumulus clouds over the southeast Pacific Ocean

Impacts of aerosol particles on the microphysical and radiative properties of stratocumulus clouds over the southeast Pacific Ocean

Organic matter and non-refractory aerosol over the remote Southeast Pacific: oceanic and combustion sources

Limited-are a modelling of stratocumulus over South-Eastern Pacific

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