scholarly journals Polar cap patches observed during the magnetic storm of November 2003: observations and modeling

2015 ◽  
Vol 33 (9) ◽  
pp. 1117-1133 ◽  
Author(s):  
C. E. Valladares ◽  
T. Pedersen ◽  
R. Sheehan
Keyword(s):  
Magnetic Storm ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Polar Cap ◽  
Throat Region ◽  
Incoherent Scatter ◽  
Cross Correlation Analysis ◽  
Convection Patterns ◽  
Airglow Intensity ◽  
Good Agreement

Abstract. We present multi-instrumented measurements and multi-technique analysis of polar cap patches observed early during the recovery phase of the major magnetic storm of 20 November 2003 to investigate the origin of the polar cap patches. During this event, the Qaanaaq imager observed elongated polar cap patches, some of which containing variable brightness; the Qaanaaq digisonde detected abrupt NmF2 fluctuations; the Sondrestrom incoherent scatter radar (ISR) measured patches placed close to but poleward of the auroral oval–polar cap boundary; and the DMSP-F13 satellite intersected topside density enhancements, corroborating the presence of the patches seen by the imager, the digisonde, and the Sondrestrom ISR. A 2-D cross-correlation analysis was applied to series of two consecutive red-line images, indicating that the magnitude and direction of the patch velocities were in good agreement with the SuperDARN convection patterns. We applied a back-tracing analysis to the patch locations and found that most of the patches seen between 20:41 and 21:29 UT were likely transiting the throat region near 19:41 UT. Inspection of the SuperDARN velocities at this time indicates spatial and temporal collocation of a gap region between patches and large (1.7 km s−1) line-of-sight velocities. The variable airglow brightness of the patches observed between 20:33 and 20:43 UT was investigated using the numerical Global Theoretical Ionospheric Model (GTIM) driven by the SuperDARN convection patterns and a variable upward/downward neutral wind. Our numerical results indicate that variations in the airglow intensity up to 265 R can be produced by a constant 70 m s−1 downward vertical wind.

scholarly journals IMF effect on the polar cap contraction and expansion during a period of substorms

2013 ◽  
Vol 31 (6) ◽  
pp. 1021-1034 ◽  
Author(s):  
A. T. Aikio ◽  
T. Pitkänen ◽  
I. Honkonen ◽  
M. Palmroth ◽  
O. Amm
Keyword(s):  
Recovery Phase ◽  
Bow Shock ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Early Recovery ◽  
Mhd Simulation ◽  
Expansion Phase ◽  
Contraction And Expansion ◽  
Good Agreement ◽  
The Imf

Abstract. The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase. In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

scholarly journals EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

2008 ◽  
Vol 26 (1) ◽  
pp. 87-105 ◽  
Author(s):  
A. T. Aikio ◽  
T. Pitkänen ◽  
D. Fontaine ◽  
I. Dandouras ◽  
O. Amm ◽  
...  
Keyword(s):  
Neutral Line ◽  
Broad Band ◽  
Low Frequency ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Polar Cap ◽  
Early Recovery ◽  
F Region ◽  
Cluster Data ◽  
Cluster Satellite

Abstract. The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat) and Longyearbyen (75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5° cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 RE mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2° during ~5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.

Extended period of polar cap auroral display: auroral dynamics and relation to the IMF and the ionospheric convection

1995 ◽  
Vol 13 (8) ◽  
pp. 854-862 ◽  
Author(s):  
V. G. Vorobjev ◽  
S. V. Leontyev ◽  
Ya. I. Feldstein
Keyword(s):  
Large Scale ◽  
Interplanetary Space ◽  
Extended Period ◽  
Auroral Oval ◽  
Polar Cap ◽  
Substorm Activity ◽  
Convection Patterns ◽  
Northern And Southern Hemispheres ◽  
Birkeland Currents ◽  
The Imf

Abstract. An unusually extended period (5 h) of polar cap auroral display on 3 August 1986 is examined. Auroras have been investigated using ground-based data as well as measurements from the IMP-8 spacecraft in interplanetary space and simultaneous observations from the polar-orbiting satellites Viking and DE-1 in the northern and southern hemispheres, respectively. It is found that visible Sun-aligned arcs are located inside the transpolar band of the θ-aurora observed from the satellite in ultraviolet wavelengths. The transpolar band can contain several Sun-aligned arcs that move inside the band toward the morning or evening side of the auroral oval independent of the direction of the band movement. Intensifications of polar cap auroras with durations of up to about 30 min are observed. No change has been found in either IMF parameters or substorm activity that can be related to these intensifications. The θ-aurora occurred during a 2-h period when the B z-component of the IMF was negative. A tendency is noted for dawnward (duskward) displacement of the transpolar band when By>0 (By<0) in the southern hemisphere. Simultaneous observations of auroral ovals during interplanetary Bz<0, By<0 and Bx>0 in both hemispheres and convection patterns for Bz<0 and By<0 have been displayed using satellite and ground-based measurements. It was found that the transpolar band of the <theta>-aurora in the sunlit hemisphere was situated in the region of large-scale downward Birkeland currents.

scholarly journals Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm

2000 ◽  
Vol 18 (9) ◽  
pp. 1067-1072 ◽  
Author(s):  
H. Liu ◽  
K. Schlegel ◽  
S.-Y. Ma
Keyword(s):  
Strong Electric Field ◽  
Dynamic Pressure ◽  
Time Lag ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Soft Particle ◽  
Polar Cap ◽  
Ion Flow ◽  
Storms And Substorms

Abstract. The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min.Key words: Ionosphere (auroral ionosphere; polar ionosphere) - Magnetospheric physics (storms and substorms)

Effect of field-aligned currents in the polar cap at the recovery phase of a magnetic storm

1981 ◽  
Vol 29 (12) ◽  
pp. 1315-1318 ◽  
Author(s):  
Sh.Sh. Dolginov ◽  
Y.I. Feldstein ◽  
L.V. Strunnikova
Keyword(s):  
Magnetic Storm ◽  
Recovery Phase ◽  
Polar Cap

scholarly journals Polar cap convection patterns inferred from EISCAT observations

1997 ◽  
Vol 15 (4) ◽  
pp. 403-411 ◽  
Author(s):  
C. Peymirat ◽  
D. Fontaine
Keyword(s):  
Statistical Models ◽  
Order Differential Equation ◽  
Magnetic Activity ◽  
Analytical Models ◽  
Convection Flow ◽  
Convection Pattern ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Convection Patterns ◽  
Steady Convection

Abstract. From data of the European incoherent scatter radar EISCAT, and mainly from its tristatic capabilities, statistical models of steady convection in the auroral ionosphere were achieved for various levels of magnetic activity. We propose here to consistently extend these models to the polar cap, by avoiding the use of a pre-defined convection pattern. Basically, we solve the second-order differential equation governing the polar cap convection potential with the boundary conditions provided by these models. The results display the classical twin-vortex convection pattern, with the cell centres around 17 MLT for the evening cell and largely shifted towards midnight (3–3.5 MLT) for the morning cell, both slightly moving equatorward with activity. For moderate magnetic activities, the convection flow appears approximately oriented along the meridian from 10:00 MLT to 22:00 MLT, while in more active situations, it enters the polar cap at prenoon times following the antisunward direction, and then turns to exit around 21:00 MLT. Finally, from these polar cap patterns combined with the auroral statistical models, we build analytical models of the auroral and polar convection expected in steady magnetic conditions.

scholarly journals Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm

2009 ◽  
Vol 27 (5) ◽  
pp. 2157-2171 ◽  
Author(s):  
T. Pitkänen ◽  
A. T. Aikio ◽  
A. Kozlovsky ◽  
O. Amm
Keyword(s):  
Electric Field ◽  
Growth Phase ◽  
Continuation Method ◽  
Recovery Phase ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Closed Field ◽  
Polar Cap ◽  
Vhf Radar ◽  
The North

Abstract. The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager. The location of the polar cap boundary (PCB) is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42 m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE) boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7° of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB) is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1° equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines. East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD) region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet. The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs) in the same MLT sector. The results suggest that PBIs (typically 1.5 h MLT wide) are a consequence of temporarily enhanced longitudinally localized magnetic flux closure in the magnetotail.

Simultaneous two hemisphere observations of the presence of polar patches in the nightside ionosphere

1994 ◽  
Vol 12 (7) ◽  
pp. 642-648 ◽  
Author(s):  
A. S. Rodger ◽  
M. Pinnock ◽  
J. R. Dudeney ◽  
J. Waterman ◽  
O. de la Beaujardiere ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Formation Process ◽  
Auroral Oval ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Dayside Magnetopause ◽  
Incoherent Scatter Radars ◽  
High Latitude Ionosphere ◽  
Magnetic Meridian

Abstract. The presence of polar patches as observed simultaneously in the same magnetic meridian of opposite nightside ionospheres by coherent and incoherent scatter radars are described. The patches appear to be related to variations either in the Bz or By component of the interplanetary magnetic field which cause transient merging on the dayside magnetopause. The passage and characteristics of polar patches as they traverse the polar cap into the nightside auroral oval are not significantly affected by the occurrence of small substroms. This study illustrates how the observations of polar patches in the nightside high-latitude ionosphere could be of great value in determining their formation process.

scholarly journals Studying the dynamics of electric currents and polar caps in ionospheres of two hemispheres during the August 17, 2001 geomagnetic storm

2019 ◽  
Vol 5 (2) ◽  
pp. 15-27
Author(s):  
Сергей Лунюшкин ◽  
Sergey Lunyushkin ◽  
Владимир Мишин ◽  
Vladimir Mishin ◽  
Юрий Караваев ◽  
...  
Keyword(s):  
Magnetic Storm ◽  
Geomagnetic Storm ◽  
Electric Fields ◽  
Large Scale ◽  
Hall Current ◽  
Auroral Oval ◽  
Polar Cap ◽  
Advanced Technique ◽  
Current Function ◽  
Polar Caps

The magnetogram inversion technique (MIT), developed at ISTP SB RAS more than forty years ago, has been used until recently only in the Northern Hemisphere. In recent years, MIT has been improved and extended to make instantaneous calculations of 2D distributions of electric fields, horizontal and field-aligned currents in two polar ionospheres. The calculations were carried out based on one-minute ground-based geomagnetic measurements from the worldwide network of stations in both hemispheres (SuperMAG). In this paper, this extended technique is used in the approximation of uniform ionospheric conductance and is applied for the first time to calculations of equivalent and field-aligned currents in two hemispheres through the example of the August 17, 2001 geomagnetic storm. We have obtained the main and essential result: the advanced MIT-ISTP can calculate large-scale distributions of ionospheric convection and FACs in the Northern (N) and Southern (S) polar ionospheres with a high degree of expected hemispheric similarity between these distributions. Using the said event as an example, we have established that the equivalent and field-aligned currents obtained with the advanced technique exhibit the expected dynamics of auroral electrojets and polar caps in two hemispheres. Hall current intensities in polar caps and auroral electrojets, calculated from the equivalent current function, change fairly synchronously in the N and S hemispheres throughout the magnetic storm. Both (westward and eastward) electrojets of the N hemisphere are markedly more intense than respective electrojets of the S hemisphere, and the Hall current in the north polar cap is almost twice as intense as that in the south one. This interhemispheric asymmetry is likely to be due to seasonal conductance variations, which is implicitly contained in the current function. From FAC distributions we determine auroral oval boundaries and calculate magnetic fluxes through the polar caps in the N and S hemispheres. These magnetic fluxes coincide with an accuracy of about 5 % and change almost synchronously during the magnetic storm. In the N hemisphere, the magnetic flux in the dawn polar cap is more intense that that in the dusk one, and vice versa in the S hemisphere. These asymmetries (dawn–dusk and interhemispheric) in the polar caps are consistent with the theory of reconnection for IMF By>0 and with satellite images of auroral ovals; both of these asymmetries decrease during the substorm expansion phase.

scholarly journals Studying the dynamics of electric currents and polar caps in ionospheres of two hemispheres during the August 17, 2001 geomagnetic storm

2019 ◽  
Vol 5 (2) ◽  
pp. 17-29
Author(s):  
Сергей Лунюшкин ◽  
Sergey Lunyushkin ◽  
Владимир Мишин ◽  
Vladimir Mishin ◽  
Юрий Караваев ◽  
...  
Keyword(s):  
Magnetic Storm ◽  
Geomagnetic Storm ◽  
Electric Fields ◽  
Large Scale ◽  
Hall Current ◽  
Auroral Oval ◽  
Polar Cap ◽  
Advanced Technique ◽  
Current Function ◽  
Polar Caps

The magnetogram inversion technique (MIT), developed at ISTP SB RAS more than forty years ago, has been used until recently only in the Northern Hemisphere. In recent years, MIT has been improved and extended to make instantaneous calculations of 2D distributions of electric fields, horizontal and field-aligned currents in two polar ionospheres. The calculations were carried out based on one-minute ground-based geomagnetic measurements from the worldwide network of stations in both hemispheres (SuperMAG). In this paper, this extended technique is used in the approximation of uniform ionospheric conductance and is applied for the first time to calculations of equivalent and field-aligned currents in two hemispheres through the example of the August 17, 2001 geomagnetic storm. We have obtained the main and essential result: the advanced MIT-ISTP can calculate large-scale distributions of ionospheric convection and FACs in the Northern (N) and Southern (S) polar ionospheres with a high degree of expected hemispheric similarity between these distributions. Using the said event as an example, we have established that the equivalent and field-aligned currents obtained with the advanced technique exhibit the expected dynamics of auroral electrojets and polar caps in two hemispheres. Hall current intensities in polar caps and auroral electrojets, calculated from the equivalent current function, change fairly synchronously in the N and S hemispheres throughout the magnetic storm. Both (westward and eastward) electrojets of the N hemisphere are markedly more intense than respective electrojets of the S hemisphere, and the Hall current in the north polar cap is almost twice as intense as that in the south one. This interhemispheric asymmetry is likely to be due to seasonal conductance variations, which is implicitly contained in the current function. From FAC distributions we determine auroral oval boundaries and calculate magnetic fluxes through the polar caps in the N and S hemispheres. These magnetic fluxes coincide with an accuracy of about 5 % and change almost synchronously during the magnetic storm. In the N hemisphere, the magnetic flux in the dawn polar cap is more intense that that in the dusk one, and vice versa in the S hemisphere. These asymmetries (dawn–dusk and interhemispheric) in the polar caps are consistent with the theory of reconnection for IMF By>0 and with satellite images of auroral ovals; both of these asymmetries decrease during the substorm expansion phase.

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