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 Storm Time EMIC Waves Observed by Swarm and Van Allen Probe Satellites

2021 ◽  
Author(s):  
Yangfan He ◽  
Hui Wang ◽  
Lühr Hermann ◽  
Kistler Lynn ◽  
Saikin Anthony ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Recovery Phase ◽  
Early Recovery ◽  
Expansion Phase ◽  
Van Allen Probes ◽  
Substorm Activity ◽  
Temporal And Spatial ◽  
Maximum Occurrence ◽  
Winter Hemisphere ◽  
Emic Waves

<p>The temporal and spatial evolution of electromagnetic ion cyclotron (EMIC) waves during<br>the magnetic storm of 21–29 June 2015 was investigated using high-resolution magnetic field observations<br>from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric<br>EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during<br>the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral<br>regions occurred more frequently in the nighttime than during the day and exhibited less obvious<br>latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere<br>and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were<br>absent in the magnetosphere and ionosphere around the minimum SYM-H. During the early recovery<br>phase, He<sup>+ </sup>band EMIC waves were observed in the ionosphere and magnetosphere. During the late<br>recovery phase, H<sup>+</sup> band EMIC waves emerged in response to enhanced earthward convection during<br>substorms in the premidnight sector. The occurrence of EMIC waves in the noon sector was affected by<br>the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer<br>hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 hr with a<br>duration of less than 186 min from coordinated observations. The results could provide additional insights<br>into the spatial characteristics and propagation features of EMIC waves during storm periods</p>

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.

scholarly journals Substorm behavior of the auroral electrojet indices

2004 ◽  
Vol 22 (6) ◽  
pp. 2135-2149 ◽  
Author(s):  
J. W. Gjerloev ◽  
R. A. Hoffman ◽  
M. M. Friel ◽  
L. A. Frank ◽  
J. B. Sigwarth
Keyword(s):  
Current System ◽  
Three Dimensional ◽  
Recovery Phase ◽  
Auroral Electrojet ◽  
Spatial Behavior ◽  
Early Recovery ◽  
Substorm Current Wedge ◽  
Expansion Phase ◽  
Systematic Behavior ◽  
Current Wedge

Abstract. The behavior of the auroral electrojet indices AU and AL during classical substorms is investigated by the use of global auroral images. A superposition of the 12 AE stations onto global auroral images and identification of the AL and AU contributing stations enable an understanding of the temporal as well as spatial behavior of the indices with respect to the substorm coordinate system and timeframe. Based on this simple technique it was found that at substorm onset the AL contributing station makes a characteristic jump from a location near the dawn terminator to the onset region, typically bypassing one or more AE stations. During the expansion phase this station typically lies at the poleward edge of the surge region. This is the location of the intense substorm current wedge electrojet in the semiempirical self-consistent substorm model of the three-dimensional current system by Gjerloev and Hoffman (2002). This current wedge is fed primarily pre-midnight by an imbalance of the Region 0 and Region 1 field-aligned currents, not from the dawnside westward electrojet. Then during the early recovery phase the AL contributing station jumps back to the dawn sector. The defining AU station does not show any similar systematic behavior. We also find that the dawn side westward electrojet seems to be unaffected by the introduction of the substorm current wedge. According to our model, much of this current is closed to the magnetosphere as it approaches midnight from dawn. Based on the characteristics of the AL station jumps, the behavior of the dawn-side electrojet, and the understanding of the three-dimensional substorm current system from our model, we provide additional experimental evidence for, and an understanding of, the concept of the two component westward electrojet, as suggested by Kamide and Kokubun (1996).

Quantifying the lobe reconnection rate during dominant IMF By periods

2021 ◽  
Author(s):  
Jone Peter Reistad ◽  
Karl Magnus Laundal ◽  
Anders Ohma ◽  
Nikolai Østgaard ◽  
Spencer Hatch ◽  
...  
Keyword(s):  
Transverse Component ◽  
Conceptual Level ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Ionospheric Convection ◽  
Relative Contribution ◽  
Close Proximity ◽  
Lobe Reconnection ◽  
Dipole Tilt ◽  
The Imf

<p>Lobe reconnection is usually considered to play an important role in geospace dynamics only when the Interplanetary Magnetic Field (IMF) is mainly northward. This is because the most common signature of lobe reconnection is the strong sunward convection in the polar cap ionosphere observed during these conditions. During more typical conditions, when the IMF is mainly in a dawn-dusk direction, plasma flows initiated by dayside as well as lobe reconnection map to high latitude ionospheric locations in close proximity to each other. This has been emphasized in the literature earlier, mainly on a conceptual level, but quantifying the relative importance of lobe reconnection to the observed ionospheric convection is highly challenging during these IMF By dominated conditions, since one has to identify and distinguish these regions. By normalizing the ionospheric convection (observed by SuperDARN) to the polar cap boundary (inferred from simultaneous AMPERE observations), we are able to do this separation, allowing us to quantify the relative contribution of both lobe reconnection and dayside/nightisde reconnection to the ionospheric convection pattern. Using this segmentation technique we can get new quantitative insights into the importance of the various mechanisms that affect the lobe reconnection rate. In this presentation we will describe the technique and show results of analysis of periods when the IMF is mainly in the dawn-dusk direction. Our quantification of the average lobe reconnection rate during various conditions yields quantitative knowledge of the importance of the lobe reconnection process, which can act independently in the two hemispheres. We will specifically constrain the influence from parameters such as the dipole tilt angle and the product of IMF transverse component and solar wind velocity.</p>

scholarly journals Magnetospheric Multiscale observations of energetic oxygen ions at the duskside magnetopause during intense substorms

2020 ◽  
Vol 38 (1) ◽  
pp. 123-135 ◽  
Author(s):  
Chen Zeng ◽  
Suping Duan ◽  
Chi Wang ◽  
Lei Dai ◽  
Stephen Fuselier ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Phase 1 ◽  
Density Ratio ◽  
Close Relation ◽  
Recovery Phase ◽  
Expansion Phase ◽  
Absolute Value ◽  
Oxygen Ions ◽  
Magnetospheric Multiscale ◽  
The Imf

Abstract. Energetic oxygen ions (1–40 keV) observed by the Magnetospheric Multiscale (MMS) satellites at the duskside magnetopause boundary layer during phase 1 are investigated. There are 57 duskside magnetopause crossing events identified during intense substorms (AE>500 nT). These 57 events of energetic O+ at the duskside magnetopause include 26 events during the expansion phase and 31 events during the recovery phase of intense substorms. It is found that the O+ density in the duskside magnetopause boundary layer during the recovery phase (0.081 cm−3) is larger than that during the expansion phase (0.069 cm−3). The 26 events of energetic O+ ions at the duskside magnetopause during intense substorm expansion phase are all under the southward interplanetary magnetic field (IMF). There are only seven events under northward IMF, and they all occurred during the intense substorm recovery phase. The density of energetic O+ at the duskside magnetopause ranges from 0.007 to 0.599 cm−3. The maximum density of O+ occurred during the intense substorm recovery phase and under southward IMF. When the IMF is southward, the O+ density shows an exponential increase with the IMF Bz absolute value. Meanwhile, the O+/H+ density ratio shows an exponential growth with the IMF By. These results agree with previous studies in the near-Earth magnetosphere during intense substorm. It is suggested that O+ abundance in the duskside magnetopause boundary layer has a close relation to O+ variations in the near-Earth magnetosphere during intense substorms.

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 Experimental and numerical investigation of plasma parameters in the magnetosheath

2018 ◽  
Vol 145 ◽  
pp. 03003
Author(s):  
Polya Dobreva ◽  
Monio Kartalev ◽  
Olga Nitcheva ◽  
Natalia Borodkova ◽  
Georgy Zastenker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Numerical Investigation ◽  
Euler Equations ◽  
Ideal Gas ◽  
Bow Shock ◽  
Plasma Parameters ◽  
Wind Spacecraft ◽  
The Magnetic Field ◽  
Good Agreement

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.

scholarly journals Electron flux enhancement in the inner radiation belt during moderate magnetic storms

2007 ◽  
Vol 25 (6) ◽  
pp. 1359-1364 ◽  
Author(s):  
H. Tadokoro ◽  
F. Tsuchiya ◽  
Y. Miyoshi ◽  
H. Misawa ◽  
A. Morioka ◽  
...  
Keyword(s):  
Radiation Belt ◽  
Electron Flux ◽  
Recovery Phase ◽  
Magnetic Activity ◽  
Magnetic Storms ◽  
Natural Phenomena ◽  
Early Recovery ◽  
Flux Enhancement ◽  
Angle Scattering ◽  
Order Of Magnitude

Abstract. During moderate magnetic storms, an electron channel (300–1100 keV) of the NOAA satellite has shown sudden electron flux enhancements in the inner radiation belt. After examinating the possibility of contamination by different energetic particles, we conclude that these electron flux enhancements are reliable enough to be considered as natural phenomena, at least for the cases of small to moderate magnetic storms. Here, we define small and moderate storms to be those in which the minimum Dst ranges between −30 and −100 nT. The electron flux enhancements appear with over one order of magnitude at L~2 during these storms. The enhancement is not accompanied by any transport of electron flux from the outer belt. Statistical analysis shows that these phenomena have a duration of approximately 1 day during the period, starting with the main phase to the early recovery phase of the storms. The flux enhancement shows a dawn-dusk asymmetry; the amount of increased flux is larger in the dusk side. We suggest that this phenomenon could not be caused by the radial diffusion but would be due to pitch-angle scattering at the magnetic equator. The inner belt is not in a stationary state, as was previously believed, but is variable in response to the magnetic activity.

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