Earth system science: Putting together the “big picture” puzzle

The Earth behaves as a highly coupled, interdependent system of components and processes – all of which operate on a multitude of time and spatial scales. Humans – rather than simply affecting or being affected by the natural environment – are a central component in the Earth system. Within the Earth system, there are feedbacks and teleconnections that operate on a planetary scale, and in which humans are directly involved. This article presents examples of such feedback systems and of human interactions in the Earth system, and describes some of the research infrastructure necessary to pursue Earth System Science

Single particle analysis of aerosols, observed in the marine boundary layer during the Monterey Area Ship Tracks Experiment (MAST), with respect to cloud droplet formation

The chemical composition of individual particles >0.2 µm sampled during the MAST-experiment were analysed by SEM-EDX, in combination with multivariate techniques. The objective of this experiment was to identify the mechanisms responsible for the modification of marine stratocumulus clouds by emissions from ships and in a wider sense to provide information on the global processes involved in atmospheric modification of cloud albedo. Aerosols were examined under different MBL pollution levels (clean, intermediately polluted and moderately polluted) in five different reservoirs: background below-cloud and above-cloud aerosol; background cloud droplet residual particles; below-cloud ship plume aerosol and ship track cloud droplet residual particles. In this study a relation was provided between the aerosol emitted from the ship's stack to an effect in cloud. Additionally, a large fraction of the ambient aerosol was found to be composed of organic material or other compounds, consisting of low Z-elements, associated with chlorine. Their number fraction was largest in clean marine boundary layers, and decreased with increasing pollution levels. The fraction of 'transformed sea salt' (Na, Cl, S), on the other hand, increased with the pollution level in the MBL. Only 20% of the particles fell within the detectable range of the analysis

Influence of humidity on the aerosol scattering coefficient and its effect on the upwelling radiance during ACE-2

Tellus (ACE-2 Special Issue), 52B, 546-567

Evolution of the aerosol, cloud and boundary-layer dynamic and thermodynamic characteristics during the 2nd Lagrangian experiment of ACE-2

We present observations from the 2nd Aerosol Characterisation Experiment where over a 29‐h period between 16–18 July 1997 a tagged column of air was followed by a fully instrumented aircraft. The Lagrangian framework this offered made it possible to measure the evolution of the aerosol size distribution, the cloud structure and microphysics, and the dynamic and thermodynamic structure of the marine boundary layer within a polluted airmass advecting off northwest Europe over the sub‐tropical North Atlantic Ocean. The salient observations are presented and analysed. Processes responsible for the evolution are suggested, but quantification of their respective rates must be taken up by future modelling studies. Stratocumulus capped the boundary layer throughout the period that produced negligible washout of aerosol. This implies that the conversion of a continental to a maritime airmass within the cloud‐capped sub‐tropical marine boundary layer is not controlled by the drizzle process but by entrainment from the free troposphere. We find evidence of processing of aerosol particles by stratocumulus cloud, in particular by aqueous‐phase reactions. The processing of the aerosol, realised by modification of the aerosol size distribution in the particle diameter range 0.1–0.5 μm, was complicated by rapid changes in boundary layer height and structure, and also by entrainment of both polluted and relatively clean aerosol from the free troposphere. The cloud microphysics was affected by these changes in the boundary layer aerosol through changes in the cloud condensation nuclei activation spectra. The cloud microphysics was also strongly affected by changes in the dynamics of the boundary layer which included variations (e.g., diurnal) in cloud thickness and an increase in vertical wind speed. Thermodynamic changes within the boundary layer included decoupling due to an increasing sea‐surface temperature and a change in the subsidence rate in the free troposphere superimposed on diurnal decoupling. Hypotheses have been devised so that future modellers can focus their efforts to either validate or invalidate potentially important processes

Regional aerosol properties from satellite observations: ACE-1, TARFOX, and ACE-2 results

Recent field programs designed to study aerosol properties have produced interesting contrasts across diverse regions of the globe..

Microphysics of clouds: Model vs measurements

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