scholarly journals M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

2014 ◽  
Vol 32 (4) ◽  
pp. 333-351 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
W. F. Denig
Keyword(s):  
Spatial Scales ◽  
Current System ◽  
Auroral Oval ◽  
Local Times ◽  
Type I ◽  
Polar Cap ◽  
Interplanetary Coronal Mass Ejections ◽  
Expansion Phase ◽  
Earth Magnetic Field ◽  
Substorm Activity

Abstract. We study substorms from two perspectives, i.e., magnetosphere–ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δ Bz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50–100 kV enhancements of the cross-polar-cap potential due to inductive electric field coupling.

scholarly journals EISCAT observations of unusual flows in the morning sector associated with weak substorm activity

1994 ◽  
Vol 12 (6) ◽  
pp. 541-553 ◽  
Author(s):  
N. J. Fox ◽  
M. Lockwood ◽  
S. W. H. Cowley ◽  
M. P. Freeman ◽  
E. Friis-Christensen ◽  
...  
Keyword(s):  
Auroral Oval ◽  
Geosynchronous Orbit ◽  
Polar Cap ◽  
Expansion Phase ◽  
Geomagnetic Tail ◽  
Density Depletion ◽  
Significant Difference ◽  
Pi2 Pulsations ◽  
Substorm Activity ◽  
Open Flux

Abstract. A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause.

scholarly journals Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events

2007 ◽  
Vol 25 (8) ◽  
pp. 1865-1876 ◽  
Author(s):  
A. D. DeJong ◽  
X. Cai ◽  
R. C. Clauer ◽  
J. F. Spann
Keyword(s):  
Magnetic Flux ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Polar Cap ◽  
Expansion Phase ◽  
Magnetospheric Convection ◽  
Open Magnetic Flux ◽  
Open Flux ◽  
The Individual

Abstract. Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.

scholarly journals Evidence for thermospheric gravity waves in the southern polar cap from ground-based vertical velocity and photometric observations

2001 ◽  
Vol 19 (5) ◽  
pp. 533-543 ◽  
Author(s):  
J. L. Innis ◽  
P. A. Greet ◽  
P. L. Dyson
Keyword(s):  
Gravity Waves ◽  
Vertical Velocity ◽  
Auroral Oval ◽  
Local Times ◽  
Polar Cap ◽  
Photometric Observations ◽  
Fabry Perot ◽  
Waves And Tides ◽  
Thermospheric Dynamics ◽  
Vertical Winds

Abstract. Zenith-directed Fabry-Perot Spectrometer (FPS) and 3-Field Photometer (3FP) observations of the λ630 nm emission (~240 km altitude) were obtained at Davis station, Antarctica, during the austral winter of 1999. Eleven nights of suitable data were searched for significant periodicities common to vertical winds from the FPS and photo-metric variations from the 3FP. Three wave-like events were found, each of around one or more hours in duration, with periods around 15 minutes, vertical velocity amplitudes near 60 ms–1 , horizontal phase velocities around 300 ms–1 , and horizontal wavelengths from 240 to 400 km. These characteristics appear consistent with polar cap gravity waves seen by other workers, and we conclude this is a likely interpretation of our data. Assuming a source height near 125 km altitude, we determine the approximate source location by calculating back along the wave trajectory using the gravity wave property relating angle of ascent and frequency. The wave sources appear to be in the vicinity of the poleward border of the auroral oval, at magnetic local times up to 5 hours before local magnetic midnight.Key words. Meteorology and atmospheric dynamics (thermospheric dynamics; waves and tides)

scholarly journals Transitions between states of magnetotail–ionosphere coupling and the role of solar wind dynamic pressure: the 25 July 2004 interplanetary CME case

2015 ◽  
Vol 33 (4) ◽  
pp. 427-436 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
W. F. Denig
Keyword(s):  
Solar Wind ◽  
Current System ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Abrupt Increase ◽  
Southern Boundary ◽  
Latitude Range ◽  
Interplanetary Coronal Mass Ejection ◽  
Substorm Activity ◽  
Braking Phase

Abstract. In a case study, we investigate transitions between fundamental magnetosphere–ionosphere (M-I) coupling modes during storm-time conditions (SYM-H between −100 and −160 nT) driven by an interplanetary coronal mass ejection (ICME). We combine observations from the near tail, at geostationary altitude (GOES-10), and electrojet activities across the auroral oval at postnoon-to-dusk and midnight. After an interval of strong westward electrojet (WEJ) activity, a 3 h long state of attenuated/quenched WEJ activity was initiated by abrupt drops in the solar wind density and dynamic pressure. The attenuated substorm activity consisted of brief phases of magnetic field perturbation and electron flux decrease at GOES-10 near midnight and moderately strong conjugate events of WEJ enhancements at the southern boundary of the oval, as well as a series of very strong eastward electrojet (EEJ) events at dusk, during a phase of enhanced ring current evolution, i.e., enhanced SYM-H deflection within −120 to −150 nT. Each of these M-I coupling events was preceded by poleward boundary intensifications and auroral streamers at higher oval latitudes. We identify this mode of attenuated substorm activity as being due to a magnetotail state characterized by bursty reconnection and bursty bulk flows/dipolarization fronts (multiple current wedgelets) with associated injection dynamo in the near tail, in their braking phase. The latter process is associated with activations of the Bostrøm type II (meridional) current system. A transition to the next state of M-I coupling, when a full substorm expansion took place, was triggered by an abrupt increase of the ICME dynamic pressure from 1 to 5 nPa. The brief field deflection events at GOES-10 were then replaced by a 20 min long interval of extreme field stretching (Bz approaching 5 nT and Bx ≈ 100 nT) followed by a major dipolarization (Δ Bz ≈ 100 nT). In the ionosphere the latter stage appeared as a "full-size" stepwise poleward expansion of the WEJ. It thus appears that the ICME passage led to fundamentally different M-I coupling states corresponding to different levels of dynamic pressure (Pdyn) under otherwise very similar ICME conditions. Full WEJ activity, covering a wide latitude range across the auroral oval in the midnight sector, was attenuated by the abrupt dynamic pressure decrease and resumed after the subsequent abrupt increase.

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 Plasma convection jets near the poleward boundary of the nightside auroral oval and their relation to Pedersen conductivity gradients

2010 ◽  
Vol 28 (4) ◽  
pp. 969-976 ◽  
Author(s):  
H. Wang ◽  
H. Lühr ◽  
A. J. Ridley
Keyword(s):  
Auroral Oval ◽  
Flow Speed ◽  
Local Times ◽  
Closed Field ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionospheric Conductivity ◽  
Ion Flow ◽  
One Year ◽  
Conductivity Gradient

Abstract. In this work, we have shown that the ionospheric azimuthal plasma velocity jets near the open-closed field line boundary on the nightside can be associated with the peak in the ionospheric conductivity gradient. Both model and DMSP observations have been utilized to conduct this investigation. The model tests show that when the gradient of conductivity in the poleward boundary becomes sharper, convection peaks appear around the poleward edge of the aurora. The model results have been confirmed by DMSP observations. Hundreds of large ion flow events are identified from one year DMSP observations, with flow speed larger than 500 m/s that occurred poleward of the aurora. Among them, 280 (74%) events are found to be associated with conductivity gradient peaks. Most of the convection jets occur in winter when conductivity gradients are expected to be large. The convection jets tend to occur at later local times (21:00–22:00 MLT) at 70°–72° MLat. These events are preceded by increasing of the merging electric field suggesting that they occur after the expansion of the polar cap. Both observation and model results show that the conductivity gradient at the polar cap boundary are one of the important elements in establishing the convection jets.

Ionospheric convection during the magnetic storm of 20-21 March 1990

1994 ◽  
Vol 12 (12) ◽  
pp. 1174-1191 ◽  
Author(s):  
J. R. Taylor ◽  
T. K. Yeoman ◽  
M. Lester ◽  
M. J. Buonsanto ◽  
J. L. Scali ◽  
...  
Keyword(s):  
Solar Wind ◽  
Response Time ◽  
Magnetic Storm ◽  
Local Times ◽  
Convection Pattern ◽  
Polar Cap ◽  
Flow Measurements ◽  
Ionospheric Convection ◽  
Substorm Activity ◽  
The Imf

Abstract. We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20-21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestrom incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been identified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward turning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. Furthermore, this response time is the same as those previously measured on the dayside. An investigation of the expansion of the polar cap during a substorm growth phase based on Faraday's law suggests that the expansion of the polar cap was nonuniform. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in By and effects due to substorm activity. The second interval, 1200-2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the Bz component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of ~2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.

scholarly journals Monopolar and bipolar auroral electric fields and their effects

2010 ◽  
Vol 28 (11) ◽  
pp. 2027-2046 ◽  
Author(s):  
J. De Keyser ◽  
R. Maggiolo ◽  
M. Echim
Keyword(s):  
High Altitude ◽  
Electric Fields ◽  
Current System ◽  
Analytic Solutions ◽  
Auroral Oval ◽  
Electrostatic Model ◽  
Polar Cap ◽  
Magnetospheric Convection ◽  
Field Aligned Current ◽  
Auroral Current

Abstract. Most of the high-altitude auroral electric fields observed by CLUSTER can be classified into monopolar and bipolar structures. The observations associate monopolar electric fields with polar cap boundary arcs, while bipolar fields tend to be linked to discrete arcs within the auroral oval and to polar cap arcs. The present paper proposes an explanation for this association based on a simple model of the magnetotail configuration and kinetic model computations. The paper introduces a quasi-electrostatic model to describe the auroral current system associated with monopolar and bipolar high-altitude fields. Analytic solutions are presented. The model gives indications about the location of the up- and downward field-aligned current regions, the ionospheric and magnetospheric convection along the arc, the acceleration or deceleration of precipitating particles, and the behaviour of escaping ionospheric ions.

scholarly journals Average thermospheric wind patterns over the polar regions, as observed by CHAMP

2007 ◽  
Vol 25 (5) ◽  
pp. 1093-1101 ◽  
Author(s):  
H. Lühr ◽  
S. Rentz ◽  
P. Ritter ◽  
H. Liu ◽  
K. Häusler
Keyword(s):  
Auroral Oval ◽  
Magnetic Activity ◽  
Local Times ◽  
Polar Regions ◽  
Hemispheric Differences ◽  
Polar Cap ◽  
Seasonal Differences ◽  
Thermospheric Wind ◽  
Wind Distribution ◽  
Wind Patterns

Abstract. Measurements of the CHAMP accelerometer are utilized to investigate the average thermospheric wind distribution in the polar regions at altitudes around 400 km. This study puts special emphasis on the seasonal differences in the wind patterns. For this purpose 131 days centered on the June solstice of 2003 are considered. Within that period CHAMP's orbit is precessing once through all local times. The cross-track wind estimates of all 2030 passes are used to construct mean wind vectors for 918 equal-area cells. These bin averages are presented in corrected geomagnetic coordinates. Both hemispheres are considered simultaneously providing summer and winter responses for the same prevailing geophysical conditions. The period under study is characterized by high magnetic activity (Kp=4−) but moderate solar flux level (F10.7=124). Our analysis reveals clear wind features in the summer (Northern) Hemisphere. Over the polar cap there is a fast day-to-night flow with mean speeds surpassing 600 m/s in the dawn sector. At auroral latitudes we find strong westward zonal winds on the dawn side. On the dusk side, however, an anti-cyclonic vortex is forming. The dawn/dusk asymmetry is attributed to the combined action of Coriolis and centrifugal forces. Along the auroral oval the sunward streaming plasma causes a stagnation of the day-to-night wind. This effect is particularly clear on the dusk side. On the dawn side it is evident only from midnight to 06:00 MLT. The winter (Southern) Hemisphere reveals similar wind features, but they are less well ordered. The mean day-to-night wind over the polar cap is weaker by about 35%. Otherwise, the seasonal differences are mainly confined to the dayside (06:00–18:00 MLT). In addition, the larger offset between geographic and geomagnetic pole in the south also causes hemispheric differences of the thermospheric wind distribution.

scholarly journals GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 2: Interhemispheric comparison

2015 ◽  
Vol 33 (6) ◽  
pp. 657-670 ◽  
Author(s):  
P. Prikryl ◽  
R. Ghoddousi-Fard ◽  
L. Spogli ◽  
C. N. Mitchell ◽  
G. Li ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
Geomagnetic Storms ◽  
Companion Paper ◽  
Auroral Oval ◽  
Ionospheric Scintillation ◽  
High Latitudes ◽  
Polar Cap ◽  
Interplanetary Coronal Mass Ejections ◽  
The North

Abstract. During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7–17 March 2012 caused geomagnetic storms that strongly affected high-latitude ionosphere in the Northern and Southern Hemisphere. GPS phase scintillation was observed at northern and southern high latitudes by arrays of GPS ionospheric scintillation and TEC monitors (GISTMs) and geodetic-quality GPS receivers sampling at 1 Hz. Mapped as a function of magnetic latitude and magnetic local time (MLT), the scintillation was observed in the ionospheric cusp, the tongue of ionization fragmented into patches, sun-aligned arcs in the polar cap, and nightside auroral oval and subauroral latitudes. Complementing a companion paper (Prikryl et al., 2015a) that focuses on the high-latitude ionospheric response to variable solar wind in the North American sector, interhemispheric comparison reveals commonalities as well as differences and asymmetries between the northern and southern high latitudes, as a consequence of the coupling between the solar wind and magnetosphere. The interhemispheric asymmetries are caused by the dawn–dusk component of the interplanetary magnetic field controlling the MLT of the cusp entry of the storm-enhanced density plasma into the polar cap and the orientation relative to the noon–midnight meridian of the tongue of ionization.

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