scholarly journals Observations of nightside auroral plasma upflows in the F-region and topside ionosphere

1996 ◽  
Vol 14 (12) ◽  
pp. 1274-1283 ◽  
Author(s):  
C. Foster ◽  
M. Lester
Keyword(s):  
Electric Field ◽  
Plasma Heating ◽  
Leading Edge ◽  
Dominant Factor ◽  
Small Scale ◽  
Topside Ionosphere ◽  
Experimental Conditions ◽  
Ion Flow ◽  
Convection Electric Field ◽  
F Region

Abstract. Observations from the special UK EISCAT program UFIS are presented. UFIS is a joint UHF-VHF experiment, designed to make simultaneous measurements of enhanced vertical plasma flows in the F-region and topside ionospheres. Three distinct intervals of upward ion flow were observed. During the first event, upward ion fluxes in excess of 1013 m–2 s–1 were detected, with vertical ion velocities reaching 300 m s–1 at 800 km. The upflow was associated with the passage of an auroral arc through the radar field of view. In the F-region, an enhanced and sheared convection electric field on the leading edge of the arc resulted in heating of the ions, whilst at higher altitudes, above the precipitation region, strongly enhanced electron temperatures were observed; such features are commonly associated with the generation of plasma upflows. These observations demonstrate some of the acceleration mechanisms which can exist within the small-scale structure of an auroral arc. A later upflow event was associated with enhanced electron temperatures and only a moderate convection electric field, with no indication of significantly elevated ion tem- peratures. There was again some evidence of F-region particle precipitation at the time of the upflow, which exhibited vertical ion velocities of similar magnitude to the earlier upflow, suggesting that the behaviour of the electrons might be the dominant factor in this type of event. A third upflow was detected at altitudes above the observing range of the UHF radar, but which was evident in the VHF data from 600 km upwards. Smaller vertical velocities were observed in this event, which was apparently uncorrelated with any features observed at lower altitudes. Limitations imposed by the experimental conditions inhibit the interpretation of this event, although the upflow was again likely related to topside plasma heating.

Average profile of ion flow and convection electric field in the near-Earth plasma sheet

2000 ◽  
Vol 27 (11) ◽  
pp. 1623-1626 ◽  
Author(s):  
T. Hori ◽  
K. Maezawa ◽  
Y. Saito ◽  
T. Mukai
Keyword(s):  
Electric Field ◽  
Plasma Sheet ◽  
Ion Flow ◽  
Convection Electric Field ◽  
Average Profile

scholarly journals EFFECT OF GAS-DYNAMIC FLOW ON ION TRANSPORT THROUGH THE NOZZLE OF AN ION SOURCE WITH IONIZATION AT ATMOSPHERIC PRESSURE

2020 ◽  
Vol 30 (4) ◽  
pp. 75-83
Author(s):  
P. A. Kupriy ◽  
◽  
M. Z. Muradymov ◽  
N. V. Krasnov ◽  
I. V. Kurnin ◽  
...  
Keyword(s):  
Electric Field ◽  
Ion Transport ◽  
Gas Flow ◽  
Ion Source ◽  
Dynamic Flow ◽  
Experimental Conditions ◽  
Ion Motion ◽  
Ion Flow ◽  
Gas Dynamic ◽  
Research Findings

The effect of the gas flow to the ion transport from the atmosphere to the forevacuum region of the is determined experimentally. Experimental volt-ampere characteristics of the ion flow carried by the gas-dynamic flow behind the nozzle are obtained. It is shown that the fraction of the ion current passing through the nozzle under the influence of the gas flow can be increased several times in relation to the current value due only to the extraction by the electric field. In this case, depending on the magnitude of the electric field penetrating beyond the skimmer, the current is redistributed between the nozzle and the collector. It was found that, under the experimental conditions, the entire ion flux reaches the movable collector at a distance of up to 15 mm at a field strength of 200 V / cm. The diameter of the ionic component of the flow is 1.5 mm. The ion motion in a gas is simulated for conditions close to the experimental ones. Developing research findings, it is possible to consider systems for transporting ions further to the analyzer.

scholarly journals MMS Multipoint electric field observations of small-scale magnetic holes

2016 ◽  
Vol 43 (12) ◽  
pp. 5953-5959 ◽  
Author(s):  
Katherine A. Goodrich ◽  
Robert E. Ergun ◽  
Frederick D. Wilder ◽  
James Burch ◽  
Roy Torbert ◽  
...  
Keyword(s):  
Electric Field ◽  
Small Scale ◽  
Field Observations

scholarly journals Formation conditions and mechanical properties of aggregates produced in tephra–water–snow flows

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Hirofumi Niiya ◽  
Kenichi Oda ◽  
Daisuke Tsuji ◽  
Hiroaki Katsuragi
Keyword(s):  
Mechanical Properties ◽  
Mixing Time ◽  
Testing Machine ◽  
Small Scale ◽  
Scaling Analysis ◽  
Compression Tests ◽  
Ice Slurry ◽  
Experimental Conditions ◽  
Formation Conditions ◽  
Snow And Ice

Abstract The formation of aggregates consisting of snow, water, and tephra has been reported in small-scale experiments on three-phase flows containing tephra, water, and snow, representing lahars triggered by snowmelt. Such aggregates reduce the mobility of mud flow. However, the formation mechanism of such aggregates under various conditions has not been investigated. To elucidate the formation conditions and mechanical properties of the aggregates, we performed mixing experiments with materials on a rotating table and compression tests on the resulting aggregates with a universal testing machine in a low-temperature room at $$0\,^{\circ }\text {C}$$ 0 ∘ C . From experiments with varying component ratios of the mixture and tephra diameter, the following results were obtained: (i) the aggregate grew rapidly and reached maturity after a mixing time of 5 min; (ii) the mass of aggregates increased with snow concentration, exhibiting an approximately linear relationship; (iii) single aggregates with large mass formed at lower and higher tephra concentrations, whereas multiple aggregates with smaller mass were observed at intermediate concentrations; (iv) the shape of the aggregate satisfied the similarity law for an ellipsoid; (v) the compressive mechanical behavior could be modeled by an empirical nonlinear model. The obtained mechanical properties of the aggregates were independent of the experimental conditions; (vi) scaling analysis based on the Reynolds number and the strength of the aggregates showed that the aggregates cannot form in ice-slurry lahars. Our findings suggest that low-speed lahars containing snow and ice are likely to generate aggregates, but snow and ice in the ice-slurry lahars are dispersed without such aggregates.

scholarly journals Numerical Simulation of the Time Evolution of Small-Scale Irregularities in the F-Layer Ionospheric Plasma

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
O. V. Mingalev ◽  
G. I. Mingaleva ◽  
M. N. Melnik ◽  
V. S. Mingalev
Keyword(s):  
Magnetic Field ◽  
Time Evolution ◽  
Ionospheric Plasma ◽  
Debye Length ◽  
Small Scale ◽  
System Of Equations ◽  
Applied Model ◽  
Positive Ions ◽  
F Region ◽  
Small Scale Irregularity

Dynamics of magnetic field-aligned small-scale irregularities in the electron concentration, existing in the F-layer ionospheric plasma, is investigated with the help of a mathematical model. The plasma is assumed to be a rarefied compound consisting of electrons and positive ions and being in a strong, external magnetic field. In the applied model, kinetic processes in the plasma are simulated by using the Vlasov-Poisson system of equations. The system of equations is numerically solved applying a macroparticle method. The time evolution of a plasma irregularity, having initial cross-section dimension commensurable with a Debye length, is simulated during the period sufficient for the irregularity to decay completely. The results of simulation indicate that the small-scale irregularity, created initially in the F-region ionosphere, decays accomplishing periodic damped vibrations, with the process being collisionless.

Numerical Simulation of Impinging Cooling on the Leading Edge of a Turbine Blade

2011 ◽  
Author(s):  
Keyong Cheng ◽  
Xiulan Huai ◽  
Jun Cai ◽  
Zhixiong Guo
Keyword(s):  
Numerical Simulation ◽  
Turbine Blade ◽  
Leading Edge ◽  
Critical Factor ◽  
Main Stream ◽  
Experimental Conditions ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lower Temperature ◽  
Simulation Parameters

In the present study, numerical simulation is carried out for impingement/effusion cooling on the leading edge of a turbine blade similar to an experimental model tested previously. The k-ε turbulence model is used, and simulation parameters are set in accordance with the experimental conditions, including temperature ratio, blowing ratio, and Reynolds number of the main stream. The accuracy and reliability of the simulation is verified by the experimental data, and the influence of various factors on fluid flow and heat transfer is analyzed in detail. The results indicate that the blowing ratio is one critical factor which affects the cooling effectiveness. The greater the blowing ratio is, the higher the cooling effectiveness is. In addition, a staggered-holes arrangement is numerically studied and compared with a line-holes arrangement. The results show that the staggered-holes arrangement has a lower temperature on the outer surface of the leading edge and has improved the cooling effectiveness.

scholarly journals WN4 effect on longitudinal distribution of different ion species in the topside ionosphere at low latitudes by means of DEMETER, DMSP-F13 and DMSP-F15 data

2009 ◽  
Vol 27 (7) ◽  
pp. 2893-2902 ◽  
Author(s):  
L. Bankov ◽  
R. Heelis ◽  
M. Parrot ◽  
J.-J. Berthelier ◽  
P. Marinov ◽  
...  
Keyword(s):  
Density Distribution ◽  
Major Ions ◽  
Local Times ◽  
Longitudinal Distribution ◽  
Topside Ionosphere ◽  
Regular Feature ◽  
Ion Density ◽  
F Region ◽  
Longitudinal Variations ◽  
Ion Species

Abstract. Plasma probe data from DMSP-F13, DMSP-F15 and DEMETER satellites were used to examine longitudinal structures in the topside equatorial ionosphere during fall equinox conditions of 2004 year. Since the launch of DEMETER satellite on 29 June 2004, all these satellites operate close together in the topside ionosphere. Here, data taken from Special Sensor-Ion, Electron and Scintillations (SSIES) instruments on board DMSP-F13, F15 and Instrument Analyser de Plasma (IAP) on DEMETER, are used. Longitudinal variations in the major ions at two altitudes (~730 km for DEMETER and ~840 km for DMSP) are studied to further describe the recently observed "wavenumber-four" (WN4) structures in the equatorial topside ionosphere. Different ion species H+, He+ and O+ have a rather complex longitudinal behavior. It is shown that WN4 is almost a regular feature in O+ the density distribution over all local times covered by these satellites. In the evening local time sector, H+ ions follow the O+ behavior within WN4 structures up to the pre-midnight hours. Near sunrise H+ and later in the daytime, He+ longitudinal variations are out of phase with respect to O+ ions and effectively reduce the effect of WN4 on total ion density distribution at altitudes 730–840 km. It is shown that both a WN4 E×B drift driver and local F-region winds must be considered to explain the observed ion composition variations.

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