Streamer Flows Research Articles

Interactions of drift wave turbulence with streamer flows in wave-kinetic formalism

Interaction between drift wave turbulence and streamer flow in magnetized plasmas is investigated in the framework of wave-kinetic theory. By performing a wave-kinetic simulation of turbulence coupling with the streamer flow, the role of the phase-space dynamics of turbulence is clarified. Here, the phase-space consists of the real space and wavenumber space. As a consequence of the phase-space dynamics, the turbulence is trapped in the flow and propagates with the streamer. Because of the trapping, the asymmetry of the turbulence intensity with respect to the sign of the flow curvature appears. The trajectories of the turbulence wave-packet, which are the characteristic curves of the wave-kinetic solution, can be categorized by the trapping, passing, and scattering. Therefore, the obtained phase-space structure of the turbulence can be understood by their trajectories. The propagation direction and speed are found to be governed by the turbulence spectrum. The obtained characteristics can be explained by the theoretical analysis.

Scrape‐off layer width set by non‐linear streamer flows in drift wave turbulence

AbstractIn this work, we discuss the physics behind the excitation of non‐linear streamer flows in drift wave turbulence and how to selectively excite these flows. Streamer flows are modelled as a non‐linear, radially elongated convective cell in drift wave turbulence. It is shown that density modulation is key for exciting streamer flows. We show that streamer flows have a finite frequency, albeit smaller than that of drift waves. Streamers propagate in the ion direction. These theoretical predictions are compared against experimental data, which shows reasonable agreement. Finally, the scrape‐off layer width set by streamer flows is calculated, and a scaling law against macroscopic plasma parameters is obtained.

Relating Streamer Flows to Density and Magnetic Structures at the Parker Solar Probe

Abstract The physical mechanisms that produce the slow solar wind are still highly debated. Parker Solar Probe’s (PSP’s) second solar encounter provided a new opportunity to relate in situ measurements of the nascent slow solar wind with white-light images of streamer flows. We exploit data taken by the Solar and Heliospheric Observatory, the Solar TErrestrial RElations Observatory (STEREO), and the Wide Imager on Solar Probe to reveal for the first time a close link between imaged streamer flows and the high-density plasma measured by the Solar Wind Electrons Alphas and Protons (SWEAP) experiment. We identify different types of slow winds measured by PSP that we relate to the spacecraft’s magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when PSP was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. STEREO imaging of the release and propagation of small transients from the Sun to PSP reveals that the spacecraft was continually impacted by the southern edge of streamer transients. The impact of specific density structures is marked by a higher occurrence of magnetic field reversals measured by the FIELDS magnetometers. Magnetic reversals are associated with much stronger density variations inside than outside streamer flows. We tentatively interpret these findings in terms of magnetic reconnection between open magnetic fields and coronal loops with different properties, providing support for the formation of a subset of the slow wind by magnetic reconnection.

Role of density modulation in driving nonlinear streamer flows in drift wave turbulence

The role of density modulation in driving streamer flows in drift wave turbulence is discussed. In contrast to the conventional shearing mechanism, we emphasize the impact of frequency modulation by meso-scale density perturbation. This mechanism is more effective for streamers than for zonal flows. The Reynolds stress and nonlinear growth rate are calculated. The result indicates that the streamer growth is enhanced due to the density modulation. Implications on the selection of streamers and zonal flows are discussed as well.

An Atlantic streamer in stratospheric ozone observations and SD-WACCM simulation data

Abstract. Observation and simulation of individual ozone streamers are important for the description and understanding of non-linear transport processes in the middle atmosphere. A sudden increase in mid-stratospheric ozone occurred above central Europe on 4 December 2015. The GROund-based Millimeter-wave Ozone Spectrometer (GROMOS) and the Stratospheric Ozone MOnitoring RAdiometer (SOMORA) in Switzerland measured an ozone enhancement of about 30 % at 34 km altitude (8.3 hPa) from 1 to 4 December. A similar ozone increase is simulated by the Specified Dynamics Whole Atmosphere Community Climate (SD-WACCM) model. Further, the global ozone fields at 34 km altitude (8.3 hPa) from SD-WACCM and the satellite experiment Aura/MLS show a remarkable agreement for the location and timing of an ozone streamer (large-scale tongue-like structure) extending from the subtropics in northern America over the Atlantic to central Europe. This agreement indicates that SD-WACCM can inform us about the wind inside the Atlantic ozone streamer. SD-WACCM shows an eastward wind of about 100 m s−1 inside the Atlantic streamer in the mid-stratosphere. SD-WACCM shows that the Atlantic streamer flows along the edge of the polar vortex. The Atlantic streamer turns southward at an erosion region of the polar vortex located above the Caspian Sea. The spatial distribution of stratospheric water vapour indicates a filament outgoing from this erosion region. The Atlantic streamer, the polar vortex erosion region and the water vapour filament belong to the process of planetary wave breaking in the so-called surf zone of the northern midlatitude winter stratosphere.

Comparison of interplanetary signatures of streamers and pseudostreamers

AbstractIf the source of the slow solar wind is a web comprising pseudostreamer belts connected to the streamer belt, then one expects the properties of interplanetary pseudostreamer flows to be similar to those of streamer flows. That expectation is tested with data from the slow wind preceding stream interfaces in stream interaction regions at 1 AU, where the interfaces separate what was originally slow and fast wind. Pseudostreamer cases were separated from streamer cases with the aid of the streamer identification tool developed by Owens et al. (), and superposed epoch analysis was performed to compare the patterns of a number of plasma and composition parameters. The results reveal that pseudostreamer flows have all of the slow‐wind characteristics of streamer flows except that they are slightly less pronounced than streamer characteristics when compared to fast wind. The results are consistent with the concept that the solar wind displays a continuum of dynamic states rather than only slow and fast states.

An experimental investigation of modes of flow under conditions of evaporation of liquid on a vertical heating surface

An experimental investigation is performed of the effect of temperature head on the flow of evaporating film of liquid, defined by the wetting line or by ribs, on a vertical heating surface. The experiments are performed under conditions of evaporation of R11 Freon in a medium of own vapor on a vertical copper plate, including the presence of ribbing. The visualization of flow is performed. Analysis is made of the effect of the evaporation intensity in the neighborhood of liquid-vapor-wall contact line on the conditions of film discontinuity and on the pattern of resultant streamer flow. It is demonstrated that, rather than spreading, the liquid in the case of streamer flow on the heating surface contracts downstream even for a close-to-zero equilibrium wetting angle. This is due to intense evaporation of liquid in the region of liquid-vapor-wall contact line, where the liquid film exhibits a minimal thickness, to the variation of curvature of the interface in this region, and to the emergence of thermal contact angle. The dependence of thermal contact angle on temperature head is determined. Dynamic measurements are performed of the local thickness of flowing films of liquid using a capacitance meter, and spectral analysis is performed of waves which arise because of instability of film flow on the evaporating film surface.

Large-scale flows and coherent structure phenomena in flute turbulence

The properties of zonal and streamer flows in the flute mode turbulence are investigated. The stability criteria and the frequency of these flows are determined in terms of the spectra of turbulent fluctuations. Furthermore, it is shown that zonal flows can undergo a further nonlinear evolution leading to the formation of long-lived coherent structures which consist of self-bound wave packets supporting stationary shear layers, and thus can be characterized as regions with a reduced level of anomalous transport.

Non-perturbative models of intermittency in drift-wave turbulence: towards a probabilistic theory of anomalous transport

Two examples of non-perturbative models of intermittency in drift-wave (DW) turbulence are presented. The first is a calculation of the probability distribution function (PDF) of ion heat flux due to structures in ion temperature gradient turbulence. The instanton calculus predicts the PDF to be a stretched exponential. The second is a derivation of a bi-variate Burgers equation for the evolution of the DW population density in the presence of radially extended streamer flows. The PDF of fluctuation intensity avalanches is determined. The relation of this to turbulence spreading, observed in simulations, is discussed.

Mass transfer and dissipation in unipolar electrophoretic flows

Experimental studies of a simple unipolar electrophoretic flow have revealed that, typically, between 10% and 25% of the electrical energy supplied was usefully converted into flow work. Certain experimental uncertainties prevent firm conclusions, but two mechanisms have been proposed to explain low mass transfer efficiency; (i) space charge effects at the collector which reduces the intensity of the 'useful' electric field in the region of the bulk flow and (ii) microscopic shear dissipation arising from the disperse nature of the electrophoretic point forces. The single streamer flows were generated in n-hexane by the localised injection of charge from discs of ion-exchange resin in a parallel plate electrode system. The mass transfer data were collected using a frequency shifted, purpose built laser Doppler anemometer employing specially developed polymethylmethacrylate light-scattering seed particles. Measured velocity profiles within the flow structure provided estimates of mass transfer efficiency at applied field strengths up to 3.75*104 V m-1.