Ocean–Cloud–Atmosphere–Land Interactions in the Southeastern Pacific: The VOCALS Program

Mechoso, Carlos R.; Wood, R.; Weller, Robert A.; Bretherton, Christopher S.; Clarke, A. D.; Coe, Hugh; Fairall, C. W.; Farrar, J. Thomas; Feingold, Graham; Garreaud, René D.; Grados, Carmen; McWilliams, James C.; Szoeke, Simon P. de; Yuter, Sandra E.; Zuidema, Paquita

doi:10.1175/bams-d-11-00246.1

Cited by 81 publications

(78 citation statements)

References 114 publications

(106 reference statements)

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“…Although our model suggests that even the clean region of the Pacific studied by Koren et al (6) has a different aerosol state and response to parameter perturbations today compared with the PI, it may still behave in a way that is sufficiently similar to the PI to be informative. However, clouds appear to be highly sensitive to aerosols at very low concentrations (3,4,6) and strong regime shifts can occur in some aerosol-cloud systems (8,41), so even small perturbations of the aerosol state away from PI conditions may be important.…”

Section: Discussionmentioning

confidence: 99%

Occurrence of pristine aerosol environments on a polluted planet

Hamilton

Lee

Pringle

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

164

172

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Significance Uncertainty in aerosol forcing of climate since the preindustrial era hampers efforts to quantify the sensitivity of global temperature to radiative perturbations caused by human activity. Because forcings are referenced to preindustrial conditions, a large part of the uncertainty will be reduced only by accurately defining pristine aerosol conditions before air pollution. We show that pristine conditions should still be observable on a few days per month in many regions of the Earth. However, pristine cloudy regions, which are of most importance for forcing uncertainty, occur almost entirely in the Southern Hemisphere. Reduction in uncertainty of predominantly Northern Hemisphere forcing may therefore have to rely on measurements from a different hemisphere, which will limit the extent to which uncertainties can be reduced.

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Section: Discussionmentioning

confidence: 99%

Occurrence of pristine aerosol environments on a polluted planet

Hamilton

Lee

Pringle

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

164

172

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“…An example of such a largescale experiment is the Variability of the American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment, which focused on the stratocumulus cloud deck of the southeast Pacific, its predictability, and its interaction with anthropogenic aerosol from the South American coastal region (73,74). To achieve successful execution of such experiments, interagency and cross-country coordination is important.…”

Section: Observations Of Aerosol−cloud Relationshipsmentioning

confidence: 99%

Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system

Seinfeld

Bretherton

Carslaw

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

593

474

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The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth's clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol−cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.climate | aerosol−cloud effects | general circulation models | radiative forcing | satellite observations Clouds play a key role in Earth's radiation budget, and aerosols serve as the seeds upon which cloud droplets form. Anthropogenic activity has led to an increase in aerosol particle concentrations globally and an increase in those particles that act as cloud condensation nuclei (CCN) and ice nucleating particles (INP). The effect of an increase in aerosols on cloud optical properties, and associated radiative forcing, is the most uncertain component of historical radiative forcing of Earth's climate caused by greenhouse gases (GHGs) and aerosols. The Intergovernmental Panel on Climate Change (IPCC) AR5 assessment of climate forcing factors (Fig. S1) ascribes "high" confidence to the estimate of direct aerosol radiative forcing (mean

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“…Although an excellent site for studying low clouds, Graciosa experiences a much greater degree of meteorological variability than is found in the subtropical stratocumulus sheets and the tropical trades that have been the subject of much recent research (e.g., Rauber et al 2007; Mechoso et al 2014). This is exemplified by a common meteorological metric called the estimated inversion strength (EIS), which is a bulk measure of the strength of the boundary layer capping inversion based on the average static stability between the surface and 700 hPa (Wood and Bretherton 2006).…”

Section: Observationsmentioning

confidence: 99%

Clouds, Aerosols, and Precipitation in the Marine Boundary Layer: An Arm Mobile Facility Deployment

Wood

Wyant

Bretherton

et al. 2015

Bulletin of the American Meteorological Society

127

147

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The Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CAP-MBL) deployment at Graciosa Island in the Azores generated a 21-month (April 2009–December 2010) comprehensive dataset documenting clouds, aerosols, and precipitation using the Atmospheric Radiation Measurement Program (ARM) Mobile Facility (AMF). The scientific aim of the deployment is to gain improved understanding of the interactions of clouds, aerosols, and precipitation in the marine boundary layer. Graciosa Island straddles the boundary between the subtropics and midlatitudes in the northeast Atlantic Ocean and consequently experiences a great diversity of meteorological and cloudiness conditions. Low clouds are the dominant cloud type, with stratocumulus and cumulus occurring regularly. Approximately half of all clouds contained precipitation detectable as radar echoes below the cloud base. Radar and satellite observations show that clouds with tops from 1 to 11 km contribute more or less equally to surface-measured precipitation at Graciosa. A wide range of aerosol conditions was sampled during the deployment consistent with the diversity of sources as indicated by back-trajectory analysis. Preliminary findings suggest important two-way interactions between aerosols and clouds at Graciosa, with aerosols affecting light precipitation and cloud radiative properties while being controlled in part by precipitation scavenging. The data from Graciosa are being compared with short-range forecasts made with a variety of models. A pilot analysis with two climate and two weather forecast models shows that they reproduce the observed time-varying vertical structure of lower-tropospheric cloud fairly well but the cloud-nucleating aerosol concentrations less well. The Graciosa site has been chosen to be a permanent fixed ARM site that became operational in October 2013.

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Ocean–Cloud–Atmosphere–Land Interactions in the Southeastern Pacific: The VOCALS Program

Abstract: New focused measurements, analyses, and modeling of the southeast Pacific climate system are helping to improve our understanding of key atmospheric and oceanic processes and their interactions in the eastern tropical ocean regions.

Cited by 81 publications

References 114 publications

Occurrence of pristine aerosol environments on a polluted planet

Occurrence of pristine aerosol environments on a polluted planet

Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system

Clouds, Aerosols, and Precipitation in the Marine Boundary Layer: An Arm Mobile Facility Deployment

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