Plume Separation Research Articles

Plume separation effect in pulsed laser ablation deposition

The results of a new geometrical configuration of pulsed laser ablation deposition technique that uses a hemi-cylindrical transparent plastic substrate are presented and discussed. With the new arrangement, two distinct components with different material compositions have been clearly observed. While the first component comprises atoms, ions and molecules and constitutes visible or the so-called “luminous” plume, the second component is formed of fragments, clusters and liquid droplets and is invisible to the naked eye. The latter component constitutes a major part of the ablated material. The luminous plume symmetry axis does not coincide with the mass distribution symmetry axis. In the case of Si ablation and 45° incident beam angle, the maximum deflection angle of the luminous plume reaches 30° with respect to the normal to the target surface, while the deflection angle of the second component is higher than 40°. The change in the target morphology and the dependence of the composition of the ablated material on local fluence, along with the hydrodynamic effects, is sought to explain this previously unexpected and unreported phenomenon.

Plume separation by transient thermohaline convection in porous media

Research on thermohaline convection in porous media has borrowed heavily from the field of viscous liquid thermohaline convection. Transient thermohaline convection in porous media differs dramatically from that in viscous liquids because of thermal retardation. The effects of thermal retardation are well known in geothermal reservoir engineering for forced convection processes such as liquid reinjection. Thermal retardation causes heat to move at approximately the Darcy velocity, while solute moves at the pore velocity. The difference in transport of heat and solute makes transient thermohaline convection in porous media double‐advective rather than double‐diffusive. For upward moving plumes, dense solute is advected in front of the thermal plume and creates a density lid. For downward moving plumes, the dense solute plume separates from the thermal plume.

Observations of the Eastern Maine Coastal Current and its offshore extensions in 1994

Cold surface temperatures, reflecting Scotian Shelf origins and local tidal mixing, serve as a tracer of the Eastern Maine Coastal Current and its offshore extensions, which appear episodically as cold plumes erupting from the eastern Maine shelf. A cold water plume emanating from the Eastern Maine Coastal Current in May 1994 was investigated using advanced very high resolution radiometer (AVHRR) imagery, shipboard surveys of physical and biochemical properties, and satellite‐tracked drifters. Evidence is presented that suggests that some of the plume waters were entrained within the cyclonic circulation over Jordan Basin, while the major portion participated in an anticyclonic eddy at the distal end of the plume. Calculations of the nitrate transported offshore by the plume show that this feature can episodically export significant quantities of nutrients from the Eastern Maine Coastal Current to offshore regions that are generally nutrient depleted during spring‐summer. A series of AVHRR images is used to document the seasonal along‐shelf progression of the coastal plume separation point. We speculate on potential causes and consequences of plume separation from the coastal current and suggest that this feature may be an important factor influencing the patterns and overall biological productivity of the eastern Gulf of Maine.

The Geometric Spreading of Coronal Plumes and Coronal Holes

The geometric spreading in plumes and in the interplume region in coronal holes is calculated, using analytic and numerical theoretical models, between 1.0 and 5.0 R⊙. We apply a two-scale approximation that permits the rapid local spreading at the base of plumes (fl) to be evaluated separately from the global spreading (fg) imposed by coronal hole geometry. We show that fl can be computed from a potential-field model and fg can be computed from global magnetohydrodynamic simulations of coronal structure. The approximations are valid when the plasma beta is small with respect to unity and for a plume separation small with respect to a solar radius.

The Condor Equatorial Spread F Campaign: Overview and results of the large‐scale measurements

During the Condor campaign a number of instruments were set up in Peru to support the rocket experiments. In this series of papers we report on the results of the experiments designed to study the equatorial F region. In this overview paper we summarize the main results as well as report upon the macroscopic developments of spread F as evidenced by data from backscatter radars, from scintillation observations, and from digital ionosonde meaurements. In this latter regard, we argue here that at least two factors other than the classical gravitational Rayleigh‐Taylor plasma instability process must operate to yield the longest‐scale horizontal organization of spread F structures. The horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow, although detailed comparison with theory seems to require shear frequencies a bit higher than observations indicate. On the other hand, the largest‐scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions. Using simultaneous rocket and radar data, we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over Jicamarca are primarily spatial structures advecting overhead. The detailed rocket‐radar comparison verified several other earlier results and speculations, particularly those made in the PLUMEX experiments. In particular, companion papers discuss and extend some of the PLUMEX results to include the role of anomalous diffusion (LaBelle et al., this issue) in the theory of equatorial spread F and to shed light upon the shallow spectral form often observed in the intermediate‐scale regime (LaBelle and Kelley, this issue).

Experimental investigation of conjugate natural convection heat transfer from a horizontal isothermal cylinder with a nonisothermal longitudinal plate fin at various angles

Steady laminar natural convection heat transfer from a horizontal isothermal cylinder in water with a single nonisothermal longitudinal plate fin at various angles is studied experimentally. Results are obtained at a Rayleigh number of approximately 4.0 × 10 5 with a fin length to cylinder diameter ratio of 0.2 and a Prandtl number near 5. Local fin temperatures and heat transfer from the fin and cylinder are obtained using a Mach-Zehnder interferometer. Overall heat transfer measurements are made from thermocouple and multimeter data for comparison. The total heat transfer does not change significantly from the bare cylinder value. The plume separation shifts from above the heated cylinder to the fin tip when the fin is within 50° of the upward vertical position.

Polar coronal plumes

Polar coronal plumes are modeled using concentrations of magnetic flux at 1.01R⊙, and assuming the field is current-free, or a potential field. Identifying the density enhancement of plumes with magnetic flux concentration produces good agreement between 1.01R⊙ and 1.10R⊙, for model conditions of a large background magnetic field and a plume separation of 50 000 to 70 000 km at the base. Beyond 1.10R⊙, both plumes and the potential field diverge very nearly as r2.

Mantle plume separation and the expanding earth : STEWART I. C. F., 1976. Geophys. Jl R. Astr. Soc. 46 (3): 505–511

Mantle plume separation and the expanding earth : STEWART I. C. F., 1976. Geophys. Jl R. Astr. Soc. 46 (3): 505–511