Plume Phenomena Research Articles

The effects of the electric field associated with a laser-induced pulsed discharge on the ablation-generated plumes of YBa2Cu3O7−X

The effects of a pulsed discharge on the luminous plume generated during the excimer laser ablation of YBa2Cu3O7−X are investigated in an oxygen environment. A high-voltage capacitor discharge circuit is used to generate a pulsed discharge. The pulsed discharge is initiated by the laser-induced plume. The electric fields are applied along the trajectory of the plume. The time evolution of the discharge current exhibits a distinct dependence on the polarity and magnitude of the electric field and the oxygen background pressure. When an electric field is applied parallel to the plume trajectory two successive plumes may be observed. The first plume, directly induced by the impact of the ablation pulse upon the target, emits bright light, but is electrically neutral. The second plume (reentrant plume), accompanied by a discharge current (charged plume) is observed a few to 100 μs after the first electrically neutral plume. When the parallel field contains a large radial component, i.e., a perpendicular component to the plume trajectory, the charge neutrality of the first plume is lost and only a single charged plume is observed. When the direction of E is reversed (antiparallel field), only a single charged plume is observed directly induced by the laser ablation. The peak current that accompanies the charged plume exceeds 10 A. The time lag of the charged plumes and the minimum voltage required for the discharge are studied as a function of the ambient oxygen pressure. Time-resolved spectra of the plumes are investigated by using a gated intensified diode-array spectrometer. Two-dimensional images of the evolving plume are taken every 100 ns, using a gated, intensified charge-coupled-device camera. A simple model for the observed plume phenomena is proposed.

安定温度成層内のプルームの可視化

A swaying motion of thermal air plume arising from a horizontal line heat source in a stably and thermally stratified fluid is investigated experimentally. Flow and temperature visualizations of the plume were carried out. In the condition of an average heat rate from the line heat source, the amplitude of a swaying motion becomes larger and the plume transits laminar from turbulent state in the top region of the plume. In the condition of a large heat rate from the line heat source, a coherent vortex pair exists in a turbulent region of the plume. From the time-averaged temperature and the swaying spectrum of the plume, influences of the thermal stratification on the plume phenomenon were made clear. Temperature wave measurements are performed. A regular wave occurs in measured temperature profiles of laminar region. It is made clear that swaying spectrum gradients in laminar region are equal to -9/2 and -8.0. Turbulent spectrum gradients are equal to -5/3 and -3.0.

The Plume Phenomenon in Barred Spirals

Barred spirals are well-known to include several ‘distinct components’ or morphological structures in the light distribution (Sandage 1961; de Vaucouleurs 1959; Kormendy 1979). In addition to the bar, spheroid, and disk components, one often observes ring-like enhancements at discrete relative positions within the disk. These inner rings (r), outer rings (R), and nuclear rings (nr) have been the subject of recent, fairly intensive observational (Buta 1984a; Kormendy J979; de Vaucouleurs and Buta 1980a,b; Athanassoula et al. 1982) and theoretical (Schwarz 1979,1981,1984a,b,c; Simkin, Su, and Schwarz 1980) research, and it now seems well-established that most rings are linked to dynamical resonances with the bar.

An Examination of the Formation of Linear Lee Waves Generated by Giant Martian Volcanoes

Abstract The vertical wave displacement generated by a Martian volcano, at heights comparable with and above the altitude of the topography, is investigated in this paper. An examination is made of the leakage of this displacement into atmospheric heights well above the topography, and consideration is given to two large Martian volcanoes, Olympus Mons and Ascraeus Mons. Viking Orbiter imagery portraying wave clouds in the vicinity of these volcanoes is compared with theoretical results obtained by considering a simple one-layer atmosphere in which the ratio of the stability factor to the square of the atmospheric velocity profile is deemed to be constant at all vertical levels. It is found that a wave plume phenomenon is predicted by this theory, and by comparing with visual observations, information can be deduced as to the atmospheric mean structure of velocity and stability when these cloud formations occur.

The role of acoustic gravity waves in the generation of spread- F and ionospheric scintillation

In the aggregate, acoustic gravity waves in the F-region constitute a spectrum of geophysical noise extending from the frequencies involved in diurnal variations up to the Brunt-Väisälä buoyancy frequency. They drive a roughly uniform power spectrum of travelling ionospheric disturbances (TIDs) with vertical scales of the order of the atmospheric scale height H and with horizontal scales extending from the radius of the Earth down to H. It has been known since the 1950s that this permits multiple normals onto the F-region from an ionosonde, thereby creating the multiple-trace type of spread F on ionograms. At shorter scales the spectrum of TIDs decreases in strength and, below the mean free path of the neutral atmosphere, creates a spectrum of plasma turbulence aligned along the Earth's magnetic field. Progressively shorter scales are responsible for phase scintillation, for amplitude scintillation and for blur-type spread F on ionograms. A weak extension of the spectrum to scales less than the ion gyroradius is responsible for spread F and transequatorial propagation in the VHF band. Under evening conditions in equatorial regions a band of TIDs with wavelengths of the order of 600 km can, at times, have a phase velocity that matches the drift velocity of the plasma ( Röttger 1978). This band of TIDs is then amplified until it breaks ( Klostermeyer 1978). The associated explosive increase in plasma turbulence creates the plume phenomenon discovered by Woodmn and La Hoz (1976).

Aerial Investigation of the Ozone Plume Phenomenon

Aerial ozone measurements were obtained during the summer of 1975 in the Northeastern United States. This paper reports on the results of a series of tests conducted upwind and downwind of several major metropolitan and industrial complexes, which include Phila-delphia-Camden-Wilmington and New York City-Northeastern New Jersey-Southeastern Connecticut. Flight patterns consisted of upwind and downwind tranverses perpendicular to the urban plume and vertical profiles. The results indicate significant O3 generation occurs in the urban plumes, but at no time was the difference between the upwind and downwind O3 concentrations greater than 0.08 ppm (maximum 0.078 ppm). However, in several cases when the upwind values were added to the O3 produced by the urban area, this was sufficient to result in violations of the NAAQS downwind. The paper also discusses the results of flights over refineries and petrochemical facilities which yielded a positive contribution to downwind O3 values.