scholarly journals Transpolar arc evolution and associated potential patterns

2004 ◽  
Vol 22 (4) ◽  
pp. 1213-1231 ◽  
Author(s):  
J. A. Cumnock ◽  
L. G. Blomberg
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Polar Region ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Auroral Emission ◽  
Field Aligned Current ◽  
Auroral Emissions ◽  
Institute Of Technology ◽  
Electric Fields And Currents

Abstract. We present two event studies encompassing detailed relationships between plasma convection, field-aligned current, auroral emission, and particle precipitation boundaries. We illustrate the influence of the Interplanetary Magnetic Field By component on theta aurora development by showing two events during which the theta originates on both the dawn and dusk sides of the auroral oval. Both theta then move across the entire polar region and become part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the Polar UVI instrument provides measurements of auroral emissions. Utilizing satellite data as inputs, the Royal Institute of Technology model provides the high-latitude ionospheric electrostatic potential pattern calculated at different times during the evolution of the theta aurora, resulting from a variety of field-aligned current configurations associated with the changing global aurora. Key words. Ionosphere (auroral ionosphere; electric fields and currents). Magnetospheric physics (magnetosphereionosphere interactions)

scholarly journals Transpolar aurora: time evolution, associated convection patterns, and a possible cause

2005 ◽  
Vol 23 (5) ◽  
pp. 1917-1930 ◽  
Author(s):  
L. G. Blomberg ◽  
J. A. Cumnock ◽  
I. I. Alexeev ◽  
E. S. Belenkaya ◽  
S. Yu. Bobrovnikov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Auroral Electrons ◽  
Field Lines ◽  
Convection Patterns ◽  
Auroral Emissions ◽  
Set Up

Abstract. We present two event studies illustrating the detailed relationships between plasma convection, field-aligned currents, and polar auroral emissions, as well as illustrating the influence of the Interplanetary Magnetic Field's y-component on theta aurora development. The transpolar arc of the theta aurorae moves across the entire polar region and becomes part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the POLAR UVI instrument provides measurements of auroral emissions. Ionospheric electrostatic potential patterns are calculated at different times during the evolution of the theta aurora using the KTH model. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Paraboloid Model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed. Keywords. Ionosphere (Plasma convection; Polar ionosphere) – Magnetospheric physics (Magnetosphereionosphere interactions)

scholarly journals Astrid-2 and ground-based observations of the auroral bulge in the middle of the nightside convection throat

2001 ◽  
Vol 19 (6) ◽  
pp. 633-641 ◽  
Author(s):  
G. T. Marklund ◽  
T. Karlsson ◽  
P. Eglitis ◽  
H. Opgenoorth
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Current Model ◽  
Energetic Electron ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Magnetometer Data ◽  
Electric Fields And Currents ◽  
Good Agreement

Abstract. Results concerning the electrodynamics of the nightside auroral bulge are presented based on simultaneous satellite and ground-based observations. The satellite data include Astrid-2 measurements of electric fields, currents and particles from a midnight auroral oval crossing and Polar UVI images of the large-scale auroral distribution. The ground-based observations include STARE and SuperDARN electric fields and magnetic records from the Greenland and MIRACLE magnetometer network, the latter including stations from northern Scandinavia north to Svalbard. At the time of the Astrid-2 crossing the ground-based data reveal intense electrojet activity, both to the east and west of the Astrid-2 trajectory, related to the Polar observations of the auroral bulge but not necessarily to a typical substorm. The energetic electron fluxes measured by Astrid-2 across the auroral oval were generally weak being consistent with a gap observed in the auroral luminosity distribution. The electric field across the oval was directed westward, intensifying close to the poleward boundary followed by a decrease in the polar cap. The combined observations suggests that Astrid-2 was moving close to the separatrix between the dusk and dawn convection cells in a region of low conductivity. The constant westward direction of the electric field across the oval indicates that current continuity was maintained, not by polarisation electric fields (as in a Cowling channel), but solely by localized up- and downward field-aligned currents in good agreement with the Astrid-2 magnetometer data. The absence of a polarisation electric field and thus of an intense westward closure current between the dawn and dusk convection cells is consistent with the relatively weak precipitation and low conductivity in the convection throat. Thus, the Cowling current model is not adequate for describing the electrodynamics of the nightside auroral bulge treated here.Key words. Ionosphere (auroral ionosphere; electric fields and currents; plasma convection)

scholarly journals Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field

2000 ◽  
Vol 18 (4) ◽  
pp. 436-444 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester ◽  
S. W. H. Cowley ◽  
M. Brittnacher
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
High Latitude ◽  
Auroral Oval ◽  
Large Field ◽  
Convection Flow ◽  
Plasma Convection ◽  
Flow Measurements ◽  
Auroral Emission ◽  
The Imf

Abstract. We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF) had predominantly a positive Bz component (northward IMF) but varying By. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF By component are especially well correlated, the emission being located in the pre- or post-noon sectors for By < 0 nT or By > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF By \\approx 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.Key words: Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; plasma convection)

Radar studies of high-latitude ionospheric flows

1989 ◽  
Vol 328 (1598) ◽  
pp. 107-118 ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Flow Pattern ◽  
Electric Fields ◽  
Strong Interactions ◽  
Plasma Convection ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Coupling Processes

Strong interactions occur between the solar wind and the Earth’s magnetic field which result in the convection of ionospheric plasma over the polar cap regions. This generally forms a two-cell pattern with westward and eastward flows in the pre- and post-midnight sectors respectively. The flow pattern is sensitive to the flux of the solar wind and the direction of the interplanetary magnetic field. Observations of the flow pattern are thus of considerable value in the interpretation of the magnetosphere-ionosphere coupling processes and in identifying the influence of the solar wind on the Earth’s environment. The plasma convection can be observed by ground-based coherent and incoherent scatter radars and the flow vectors determined. Measurements for a range of flow conditions are presented. These are interpreted in terms of the interactions of the solar wind with the magnetosphere and the resulting electric fields which drive the plasma flows in the ionosphere.

scholarly journals GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector

2015 ◽  
Vol 33 (6) ◽  
pp. 637-656 ◽  
Author(s):  
P. Prikryl ◽  
R. Ghoddousi-Fard ◽  
E. G. Thomas ◽  
J. M. Ruohoniemi ◽  
S. G. Shepherd ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geomagnetic Storms ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Solar Wind Dynamic Pressure ◽  
Polar Cap ◽  
The North ◽  
Auroral Emission ◽  
Ground Magnetic

Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.

scholarly journals Introducing the “VALOR” analysis framework for auroral field-aligned current sheets using observations from Swarm Alpha and Charlie

2021 ◽  
Author(s):  
Leonie Pick ◽  
Joachim Vogt ◽  
Adrian Blagau ◽  
Nele Stachlys
Keyword(s):  
Magnetic Field ◽  
Linear Correlation ◽  
Large Scale ◽  
Spatial Scales ◽  
Time Lag ◽  
Field Vector ◽  
Auroral Oval ◽  
Association Measure ◽  
Field Aligned Current ◽  
Scale Estimate

&lt;p&gt;The investigation of auroral field-aligned current (FAC) sheets is crucial in the context of space weather research since they serve as main transmitters of energy and momentum across geospace domains. Different magnetosphere-ionosphere coupling modes are reflected by the FACs&amp;#8217; multiscale nature with spatial scales, i.e., latitudinal extensions, ranging from below 1 km to hundreds of kilometers. The multiscale property can be addressed conveniently using ESA&amp;#8217;s three-spacecraft mission Swarm. According to common practice a linear correlation analysis is performed on lagged and band-pass filtered scalar FAC density estimates from two nearby spacecraft.&lt;/p&gt;&lt;p&gt;We introduce the framework VALOR (Vectorial Association of Linearly Oriented Residua) which generalizes the common approach in two ways. First, VALOR utilizes the full magnetic field vector primarily observed at both spacecraft without filtering. Second, VALOR allows to test statistical association measures other than linear correlation in dependence of both time and along-track spacecraft lag. The method is further refined by considering the current sheet&amp;#8217;s polarization, i.e., the directional preference of the associated magnetic field perturbation, which additionally constrains the sheet&amp;#8217;s orientation.&lt;/p&gt;&lt;p&gt;Here, we apply VALOR to 1 Hz magnetic field observations from Swarm Alpha and Charlie and base the association measure on a vectorial version of the mean squared deviation. By means of a sample auroral oval crossing event we demonstrate that the incorporation of vectorial and polarization information helps to focus the association measure in the time-lag parameter plane leading to a smaller FAC spatial scale estimate. This result seems to hold in a statistical context including over 9000 quasi-perpendicular auroral oval crossings from 2014 to 2020. The fact that the VALOR derived FAC locations reflect the known ellipsoidal shapes of the auroral ovals speaks to the overall plausibility of the method as well as the independently supported finding that large-scale FACs (&gt;300 km) dominate the dawn and dusk sectors while smaller scale FACs gain importance at noon and midnight. Among the various opportunities for future work are an application to 50 Hz high-resolution Swarm data as well as the investigation of the solar controlling parameters.&lt;/p&gt;

scholarly journals Time development of electric fields and currents in space plasmas

2006 ◽  
Vol 24 (3) ◽  
pp. 1137-1143
Author(s):  
A. T. Y. Lui
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Electric Fields ◽  
Time Development ◽  
Space Plasmas ◽  
Simplifying Assumptions ◽  
Electric Fields And Currents ◽  
Definition Of ◽  
The Magnetic Field ◽  
Made In

Abstract. Two different approaches, referred to as Bu and Ej, can be used to examine the time development of electric fields and currents in space plasmas based on the fundamental laws of physics. From the Bu approach, the required equation involves the generalized Ohm's law with some simplifying assumptions. From the Ej approach, the required equation can be derived from the equation of particle motion, coupled self-consistently with Maxwell's equation, and the definition of electric current density. Recently, some strong statements against the Ej approach have been made. In this paper, we evaluate these statements by discussing (1) some limitations of the Bu approach in solving the time development of electric fields and currents, (2) the procedure in calculating self-consistently the time development of the electric current in space plasmas without taking the curl of the magnetic field in some cases, and (3) the dependency of the time development of magnetic field on electric current. It is concluded that the Ej approach can be useful to understand some magnetospheric problems. In particular, statements about the change of electric current are valid theoretical explanations of change in magnetic field during substorms.

scholarly journals Quantitative modelling of the closure of meso-scale parallel currents in the nightside ionosphere

2004 ◽  
Vol 22 (1) ◽  
pp. 125-140 ◽  
Author(s):  
A. Marchaudon ◽  
J.-C. Cerisier ◽  
O. Amm ◽  
M. Lester ◽  
C. W. Carlson ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Satellite Orbit ◽  
Precipitation Pattern ◽  
Field Gradients ◽  
Southward Shift ◽  
Field Aligned Current ◽  
Electric Field Profile ◽  
Electric Fields And Currents ◽  
Meso Scale

Abstract. On 12 January 2000, during a northward IMF period, two successive conjunctions occur between the CUTLASS SuperDARN radar pair and the two satellites Ørsted and FAST. This situation is used to describe and model the electrodynamic of a nightside meso-scale arc associated with a convection shear. Three field-aligned current sheets, one upward and two downward on both sides, are observed. Based on the measurements of the parallel currents and either the conductance or the electric field profile, a model of the ionospheric current closure is developed along each satellite orbit. This model is one-dimensional, in a first attempt and a two-dimensional model is tested for the Ørsted case. These models allow one to quantify the balance between electric field gradients and ionospheric conductance gradients in the closure of the field-aligned currents. These radar and satellite data are also combined with images from Polar-UVI, allowing for a description of the time evolution of the arc between the two satellite passes. The arc is very dynamic, in spite of quiet solar wind conditions. Periodic enhancements of the convection and of electron precipitation associated with the arc are observed, probably associated with quasi-periodic injections of particles due to reconnection in the magnetotail. Also, a northward shift and a reorganisation of the precipitation pattern are observed, together with a southward shift of the convection shear. Key words. Ionosphere (auroral ionosphere; electric fields and currents; particle precipitation) – Magnetospheric physics (magnetosphere-ionosphere interactions)

scholarly journals Response of ionospheric electric fields to variations in the interplanetary magnetic field

1996 ◽  
Vol 14 (8) ◽  
pp. 794-802 ◽  
Author(s):  
S. P. Mishra ◽  
E. Nielsen
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Electric Fields ◽  
Solar Wind Speed ◽  
Auroral Oval ◽  
Local Times ◽  
Residual Effects ◽  
Magnetospheric Substorms ◽  
The Imf

Abstract. The STARE system (Scandinavian Twin Auroral Radar Experiment) provides estimates of electron drift velocities, and hence also of the electric field in the high-latitude E-region ionosphere between 65 and 70 degrees latitude. The occurrence of drift velocities larger than about 400 m/s (equivalent to an electric field of 20 mV/m) have been correlated with the magnitude of the Interplanetary Magnetic Field (IMF) components Bz and By at all local times. Observation days have been considered during which both southward (Bz<0) and northward (Bz>0) IMF occurred. The occurrence of electric fields larger than 20 mV/m increases with increases in Bz magnitudes when Bz<0. It is found that the effects of southward IMF continue for some time following the northward turnings of the IMF. In order to eliminate such residual effects for Bz<0, we have, in the second part of the study, considered those days which were characterized by a pure northward IMF. The occurrence is considerably lower during times when Bz>0, than during those when Bz is negative. These results are related to the expansion and contraction of the auroral oval. The different percentage occurrences of large electric field for By>0 and By<0 components of the IMF during times when Bz>0, clearly display a dawn-dusk asymmetry of plasma flow in the ionosphere. The effects of the time-varying solar-wind speed, density, IMF fluctuations, and magnetospheric substorms on the occurrence of auroral-backscatter observations are also discussed.

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