scholarly journals Ionospheric depletion in auroral downward currents

2007 ◽  
Vol 112 (A10) ◽  
pp. n/a-n/a ◽  
Author(s):  
Alexandra P. Cran-McGreehin ◽  
Andrew N. Wright ◽  
Alan W. Hood
Keyword(s):  
Downward Currents

On Water Circulation in the Valley Reservoir (Krasnodar Reservoir)

2020 ◽  
pp. 87-97
Author(s):  
Anatoly V. Pogorelov ◽  
Andrey A. Laguta
Keyword(s):  
Vertical Movement ◽  
Cyclonic Circulation ◽  
Water Masses ◽  
River Waters ◽  
Westerly Winds ◽  
Delta Formation ◽  
General Dynamics ◽  
The Right ◽  
Downward Currents ◽  
Reservoir Basin

The Krasnodar reservoir has undergone significant transformations during its operation since 1973. As a result of active delta formation of the Kuban and Belaya rivers, the reservoir was divided into two autonomous reservoirs, its area decreased by 35 %. To understand the mechanisms of transformation and the processes of siltation of the reservoir, it is necessary to establish the features of the dynamics of water masses. Based on the results of the ADCP survey carried out in July-August, 2016, the circulation of water masses in the reservoir was analyzed. The distance between survey lines during the survey was 100 m with a total length of 2518 km, the frequency of measurements was 0.28 m-1. The resulting array of data on the velocity vectors (18.6 million values) in combination with the resulting digital model of the reservoir basin was processed in GIS using geostatistical analysis tools. It has been established that the general dynamics of water masses is characterized by cyclonic circulation with a pronounced western runoff current along the right bank of the reservoir. The prevailing velocities of currents are 0.02 ... 0.05 m/s. With steady westerly winds, a shift of the main water jet to the south into the interior of the reservoir was recorded. In the vertical movement of water masses, ubiquitous downward currents were noted in the eastern part of the reservoir, caused by the influx of colder river waters.

scholarly journals Swimming performance of subarctic Calanus spp. facing downward currents

2021 ◽  
Author(s):  
N Weidberg ◽  
C DiBacco ◽  
C Pezzola ◽  
E Rebiffe ◽  
SL Basedow
Keyword(s):  
Swimming Performance ◽  
Downward Currents

scholarly journals THEMIS ground-space observations during the development of auroral spirals

2009 ◽  
Vol 27 (11) ◽  
pp. 4317-4332 ◽  
Author(s):  
A. Keiling ◽  
V. Angelopoulos ◽  
J. M. Weygand ◽  
O. Amm ◽  
E. Spanswick ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Simultaneous Observation ◽  
Model Calculations ◽  
Expansion Phase ◽  
Geocentric Distance ◽  
Field Aligned Current ◽  
Auroral Arcs ◽  
Downward Currents ◽  
A Current ◽  
Space Observations

Abstract. A simultaneous observation of an auroral spiral and its generator region in the near-Earth plasma sheet is rather unlikely. Here we present such observations using the THEMIS spacecraft as well as the THEMIS ground network of all-sky imagers and magnetometers. Two consecutive auroral spirals separated by approximately 14 min occurred during a substorm on 19 February 2008. The spirals formed during the expansion phase and a subsequent intensification, and were among the brightest features in the aurora with diameters of 200–300 km. The duration for the formation and decay of each spiral was less than 60 s. Both spirals occurred shortly after the formation of two oppositely rotating plasma flow vortices in space, which were also accompanied by dipolarizations and ion injections, at ~11 RE geocentric distance. Observations and model calculations also give evidence for a magnetic-field-aligned current generation of approximately 0.1 MA via the flow vortices, connecting the generator region of the spirals with the ionosphere, during the formation of both spirals. In the ionosphere, a pair of equivalent ionospheric current (EIC) vortices with opposite rotations (corresponding to upward and downward currents) was present during both auroral spirals with enhanced EICs and ionospheric flows at the locations of the auroral spirals and along the auroral arcs. The combined ground and space observations suggest that each auroral spiral was powered by two oppositely rotating plasma flow vortices that caused a current enhancement in the substorm current wedge.

scholarly journals Downward auroral currents from the reconnection Hall-region

2011 ◽  
Vol 29 (4) ◽  
pp. 679-685
Author(s):  
R. A. Treumann ◽  
R. Nakamura ◽  
W. Baumjohann
Keyword(s):  
Electromotive Force ◽  
Electron Flow ◽  
Electrons And Ions ◽  
Low Latitudes ◽  
Outflow Region ◽  
Current Region ◽  
Collisionless Reconnection ◽  
Downward Currents ◽  
Auroral Current ◽  
Fast Reconnection

Abstract. We present a simple (stationary) mechanism capable of generating the auroral downward field-aligned electric field that is needed for accelerating the ionospheric electron component up into the magnetosphere and confining the ionospheric ions at low latitudes (as is required by observation of an ionospheric cavity in the downward auroral current region). The lifted ionospheric electrons carry the downward auroral current. Our model is based on the assumption of collisionless reconnection in the tail current sheet. It makes use of the dynamical difference between electrons and ions in the ion inertial region surrounding the reconnection X-line which causes Hall currents to flow. We show that the spatial confinement of the Hall magnetic field and flux to the ion inertial region centred on the X-point generates a spatially variable electromotive force which is positive near the outer inflow boundaries of the ion inertial region and negative in the central inflow region. Looked at from the ionosphere it functions like a localised meso-scale electric potential. The positive electromotive force gives rise to upward electron flow from the ionosphere during substorms (causing "black aurorae"). A similar positive potential is identified on the earthward side of the fast reconnection outflow region which has the same effect, explaining the observation that auroral upward currents are flanked from both sides by narrow downward currents.

scholarly journals Note on the explanation of a so-called "intertraction" phenomenon

1928 ◽  
Vol 118 (779) ◽  
pp. 262-263
Keyword(s):  
Specific Gravity ◽  
Salt Solution ◽  
Filter Paper ◽  
Cover Glass ◽  
Downward Currents ◽  
Upward Current

Sir Almroth Wright observed that a disc of filter paper soaked in coloured albumen solution, fixed to the under side of a cover-glass which was floated upon a salt solution, showed coloured streamers radiating out along the surface. In seeking an explanation, I concluded that the streamers were due to the upper layer of the salt becoming lighter, owing to loss of salt to the filter paper by diffusion, and that this alteration of specific gravity caused currents outwards towards the surface of the solution beyond the cover-glass, which is slightly higher than the under side of the coverglass, and the only region to which upward streaming currents could go. In confirmation of this view, I showed that if the cover-glass was tilted the streamers (which I assumed to indicate the direction of the currents) only went to the upper side of the cover-glass, and if the positions of salt and albumen were reversed, so that the upper layers of solution would become more dense by diffusion, the streamers indicated downward currents. Sir A. Wright has criticised my explanation, and the criticism which seems to have most weight is that the upward currents would be expected to produce a uniform spreading cloud of colour, not a system of radial streamers. I have therefore tested directly whether a slow upward current of water, impinging on a disc of filter paper soaked in dye solution, drives out the colour in a uniform cloud or in streamers. The photograph shows that fine streamers are actually produced. The disc was supported in the surface of water, about 3 mm. above a tube 1 cm. in diameter delivering water at a rate of about 36 c. c. per minute. Variations of the rate of flow slightly altered the appearance of the streamers, but a uniform cloud was never produced.

On the localities affected by hoar-frost, the peculiar currents of air excited by it, and the temperature during its occurrence at high and low stations

1843 ◽  
Vol 4 ◽  
pp. 294-294
Keyword(s):  
Rapid Radiation ◽  
The Earth ◽  
Mean Temperature ◽  
The Mean ◽  
Downward Currents

The author states that he has been accustomed, for the last forty years, to make observations on the occurrence of hoar-frost, and the circumstances under which it takes place, with a view of obtaining a correct explanation of the causes of that phenomenon. It is wellknown, he observes, that the localities chiefly affected with hoar-frost are the bottoms of valleys, and land-locked places of all kinds, whether natural or artificial. The altitude to which its effects reach on the sides of the valleys is dependent on the mean temperature of the day and night at the time of its occurrence: when that temperature is high, the lower places only are affected by the frost; but when low, the frost extends to much higher grounds. Hoar-frost occurs only during a calm state of the air, and when the sky is clear; but the stillness of the air in the bottoms of the valley is invariably accompanied by downward currents of air along all the sloping sides of the valley; and it is to this fact, first noticed by the author, that he wishes more particularly to direct the attention of the Society, as affording a decisive proof of the correctness of the views he entertains, being in accordance with the theory of Dr. Wells. He finds that after sunset, in all seasons of the year, and at all mean temperatures of the air, and whether or not the ground be covered with snow, whenever the sky is clear, although there may be a dead calm at the bottoms of the valleys, currents of air, more or less strong and steady, run downwards on the inclined lands, whatever may be their aspect with reference to the points of the compass. These currents are the result of the sudden depression of temperature sustained by the surface of the earth in consequence of rapid radiation, by which the stratum of air in immediate contact with that surface, becoming specifically heavier by condensation, descends into the valley, and is replaced by air which has not been thus cooled, and which therefore prevents the formation of hoar-frost on the surface of these declivities.

scholarly journals Simulation of the interchange instability in a magnetospheric substorm site

2006 ◽  
Vol 24 (6) ◽  
pp. 1685-1693 ◽  
Author(s):  
O. V. Mingalev ◽  
I. V. Golovchanskaya ◽  
Y. P. Maltsev
Keyword(s):  
Plasma Pressure ◽  
Linear Growth Rate ◽  
Magnetic Flux Tube ◽  
Small Scale ◽  
Inner Magnetosphere ◽  
Magnetospheric Substorm ◽  
Interchange Instability ◽  
Set Up ◽  
Downward Currents ◽  
Nonlinear Deformations

Abstract. We perform modeling of the interchange instability driven by longitudinal pressure asymmetry in the region of the pressure buildup that forms in the inner magnetosphere at the substorm growth phase. The simulation refers to the dawnward side of the Harang discontinuity and times after Bz IMF turning northward. The solution for the equilibrium state indicates tailward flows associated with vortices, which is in agreement with a previous finding of Ashour-Abdalla et al. (1999, 2002). We show that in the regions of equilibrium field-aligned currents (FACs), small initial perturbations in pVγ (p is the isotropic plasma pressure, V is the unit magnetic flux tube volume, γ=5/3 the adiabatic exponent), set up as ripples inclined to azimuth, grow in time. For the background FAC of ~10-6 A/m2, the linear growth rate of the instability is ~6 min. Starting from the 12th min of evolution, the perturbations exhibit nonlinear deformations, develop undulations and front steepening. An interesting peculiarity in the distribution of the associated small-scale FACs is that they become asymmetric with time. Specifically, the downward currents are more localised, reaching densities up to 15×10-6 A/m2 at the nonlinear stage. The upward FACs are more dispersed. When large enough, these currents are likely to produce the aurora. We also run our simulation for the initial perturbations of large transverse scales in order to demonstrate that the interchange instability can be responsible for pressure and cross-tail current spatial variations of great extent.

scholarly journals On the ionospheric coupling of auroral electric fields

2009 ◽  
Vol 16 (2) ◽  
pp. 365-372 ◽  
Author(s):  
G. T. Marklund
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Small Scale ◽  
Scale Size ◽  
Current Voltage ◽  
Current Region ◽  
Scale Structures ◽  
Downward Currents ◽  
Current Voltage Relation ◽  
Small Scale Structures

Abstract. The quasi-static coupling of high-altitude potential structures and electric fields to the ionosphere is discussed with particular focus on the downward field-aligned current (FAC) region. Results are presented from a preliminary analysis of a selection of electric field events observed by Cluster above the acceleration region. The degree of coupling is here estimated as the ratio between the magnetic field-aligned potential drop, ΔΦII, as inferred from the characteristic energy of upward ion (electron) beams for the upward (downward) current region and the high-altitude perpendicular (to B) potential, ΔΦbot, as calculated by integrating the perpendicular electric field across the structure. For upward currents, the coupling can be expressed analytically, using the linear current-voltage relation, as outlined by Weimer et al. (1985). This gives a scale size dependent coupling where structures are coupled (decoupled) above (below) a critical scale size. For downward currents, the current-voltage relation is highly non-linear which complicates the understanding of how the coupling works. Results from this experimental study indicate that small-scale structures are decoupled, similar to small-scale structures in the upward current region. There are, however, exceptions to this rule as illustrated by Cluster results of small-scale intense electric fields, correlated with downward currents, indicating a perfect coupling between the ionosphere and Cluster altitude.

scholarly journals CLUSTER observations of electron outflowing beams carrying downward currents above the polar cap by northward IMF

2007 ◽  
Vol 25 (4) ◽  
pp. 953-969 ◽  
Author(s):  
A. Teste ◽  
D. Fontaine ◽  
J.-A. Sauvaud ◽  
R. Maggiolo ◽  
P. Canu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Beams ◽  
Current System ◽  
Potential Drop ◽  
Careful Analysis ◽  
Auroral Zone ◽  
Polar Ionosphere ◽  
Polar Cap ◽  
Field Lines ◽  
Downward Currents

Abstract. Above the polar cap, at about 5–9 Earth radii (RE) altitude, the PEACE experiment onboard CLUSTER detected, for the first time, electron beams outflowing from the ionosphere with large and variable energy fluxes, well collimated along the magnetic field lines. All these events occurred during periods of northward or weak interplanetary magnetic field (IMF). These outflowing beams were generally detected below 100 eV and typically between 40 and 70 eV, just above the photoelectron level. Their energy gain can be explained by the presence of a field-aligned potential drop below the spacecraft, as in the auroral zone. The careful analysis of the beams distribution function indicates that they were not only accelerated but also heated. The parallel heating is estimated to about 2 to 20 eV and it globally tends to increase with the acceleration energy. Moreover, WHISPER observed broadband electrostatic emissions around a few kHz correlated with the outflowing electron beams, which suggests beam-plasma interactions capable of triggering plasma instabilities. In presence of simultaneous very weak ion fluxes, the outflowing electron beams are the main carriers of downward field-aligned currents estimated to about 10 nA/m2. These electron beams are actually not isolated but surrounded by wider structures of ion outflows. All along its polar cap crossings, Cluster observed successive electron and ion outflows. This implies that the polar ionosphere represents a significant source of cold plasma for the magnetosphere during northward or weak IMF conditions. The successive ion and electron outflows finally result in a filamented current system of opposite polarities which connects the polar ionosphere to distant regions of the magnetosphere.

scholarly journals Sign-Singularity Analysis of Field-Aligned Currents in the Ionosphere

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 708
Author(s):  
Giuseppe Consolini ◽  
Paola De Michelis ◽  
Igino Coco ◽  
Tommaso Alberti ◽  
Maria Federica Marcucci ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Complex Structure ◽  
Singularity Analysis ◽  
Activity Level ◽  
Satellite Mission ◽  
Ionospheric Heating ◽  
Ae Index ◽  
Using Data ◽  
Downward Currents ◽  
Scaling Features

Field-aligned currents (FACs) flowing in the auroral ionosphere are a complex system of upward and downward currents, which play a fundamental role in the magnetosphere–ionosphere coupling and in the ionospheric heating. Here, using data from the ESA-Swarm multi-satellite mission, we studied the complex structure of FACs by investigating sign-singularity scaling features for two different conditions of a high-latitude substorm activity level as monitored by the AE index. The results clearly showed the sign-singular character of FACs supporting the complex and filamentary nature of these currents. Furthermore, we found evidence of the occurrence of a topological change of these current systems, which was accompanied by a change of the scaling features at spatial scales larger than 30 km. This change was interpreted in terms of a sort of symmetry-breaking phenomenon due to a dynamical topological transition of the FAC structure as a consequence of FACs and substorm current wedge intensification during substorms.

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