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Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as ''ship tracks.'' Airborne measurements are used to derive emission factors of SO 2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were 15-89 and 2-25 g kg 1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO 2 emission factor of 6 g kg 1. Various types of ships, burning both MFO and navy distillate fuel, emitted from 4 10 15 to 2 10 16 total particles per kilogram of fuel burned (4 10 15-1.5 10 16 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (0.03-0.05 m) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius 0.02 m). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis. The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO 2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN. The fluxes of heat and water vapor from ships are estimated to be 2-22 MW and 0.5-1.5 kg s 1 , respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

Results are presented from analyses of high-precision time series of measurements of temperature and total heat transport obtained in a high-Prandtl-number (Pr = 26) fluid contained in a rotating, cylindrical annulus subject to a horizontal temperature gradient. Emphasis is placed on regions of parameter space close to the onset of irregular and/or chaotic behaviour. Two distinct transitions from oscillatory to apparently chaotic flow have been identified. The first occurs in an isolated region of parameter space at moderate to high Taylor number in association with a transition to a lower azimuthal wavenumber, in which a quasi-periodic (m = 3) amplitude vacillation (on a 2-torus) gives way to a low-dimensional (D ∼ 3) chaotically modulated vacillation at very low frequency (apparently organized about a 3-torus). The spatial structure of the chaotic flow exhibits the irregular growth and decay of azimuthal sidebands suggestive of a nonlinear competition between adjacent azimuthal wavenumbers. The other main transition to aperiodic flow occurs at high Taylor number as the stability parameter Θ is decreased, and is associated with the onset of ‘structural vacillation’. This transition appears to be associated with the development of small-scale instabilities within the main m = 3 baroclinic wave pattern, and exhibits a route to chaos via intermittency. The nature of the apparent chaos in these two aperiodic regimes is discussed in relation to possible mechanisms for deterministic chaos, apparatus limitations, and to previous attempts to model nonlinear baroclinic waves using low-order spectral models.

International audienceCLOUDYCOLUMN is one of the 6 ACE-2 projects which took place in June-July 1997, between Portugal and the Canary Islands. It was specifically dedicated to the study of changes of cloud radiative properties resulting from changes in the properties of those aerosols which act as cloud condensation nuclei. This process is also refered to as the aerosol indirect effect on climate. CLOUDYCOLUMN is focused on the contribution of stratocumulus clouds to that process. In addition to the basic aerosol measurements performed at the ground stations of the ACE-2 project, 5 instrumented aircraft carried out in situ characterization of aerosol physical, chemical and nucleation properties and cloud dynamical and microphysical properties. Cloud radiative properties were also measured remotely with radiometers and a lidar. 11 case studies have been documented, from pure marine to significantly polluted air masses. The simultaneity of the measurements with the multi-aircraft approach provides a unique data set for closure experiments on the aerosol indirect effect. In particular CLOUDYCOLUMN provided the 1st experimental evidence of the existence of the indirect effect in boundary layer clouds forming in polluted continental outbreacks. This paper describes the objectives of the project, the instrumental setup and the sampling strategy. Preliminary results published in additional papers are briefly summarized

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