scholarly journals The high latitude convection response to an interval of substorm activity

1996 ◽  
Vol 14 (5) ◽  
pp. 518-532 ◽  
Author(s):  
T. K. Yeoman ◽  
M. Pinnock
Keyword(s):  
High Latitude ◽  
Neutral Line ◽  
Substorm Onset ◽  
Hf Radar ◽  
The West ◽  
Expansion Phase ◽  
Incoherent Scatter ◽  
Current Disruption ◽  
Substorm Activity ◽  
Substorm Onsets

Abstract. On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB) are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.

CRRES/Ground-based multi-instrument observations of an interval of substorm activity

1994 ◽  
Vol 12 (12) ◽  
pp. 1158-1173 ◽  
Author(s):  
T. K. Yeoman ◽  
H. Lühr ◽  
R. W. H. Friedel ◽  
S. Coles ◽  
M. Grandé ◽  
...  
Keyword(s):  
Current System ◽  
Expansion Phase ◽  
Magnetic Field Data ◽  
Incoherent Scatter ◽  
Magnetic Signature ◽  
Low Latitudes ◽  
E Region ◽  
Substorm Activity ◽  
Substorm Onsets ◽  
Auroral Luminosity

Abstract. Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.

scholarly journals Modulation of nightside polar patches by substorm activity

2009 ◽  
Vol 27 (10) ◽  
pp. 3923-3932 ◽  
Author(s):  
A. G. Wood ◽  
S. E. Pryse ◽  
J. Moen
Keyword(s):  
Spatial Distribution ◽  
High Latitude ◽  
Ionospheric Plasma ◽  
Plasma Convection ◽  
Convection Pattern ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Repetition Time ◽  
Substorm Activity ◽  
European Sector

Abstract. Results are presented from a multi-instrument study showing the influence of geomagnetic substorm activity on the spatial distribution of the high-latitude ionospheric plasma. Incoherent scatter radar and radio tomography measurements on 12 December 2001 were used to directly observe the remnants of polar patches in the nightside ionosphere and to investigate their characteristics. The patches occurred under conditions of IMF Bz negative and IMF By negative. They were attributed to dayside photoionisation transported by the high-latitude convection pattern across the polar cap and into the nighttime European sector. The patches on the nightside were separated by some 5° latitude during substorm expansion, but this was reduced to some 2° when the activity had subsided. The different patch separations resulted from the expansion and contraction of the high-latitude plasma convection pattern on the nightside in response to the substorm activity. The patches of larger separation occurred in the antisunward cross-polar flow as it entered the nightside sector. Those of smaller separation were also in antisunward flow, but close to the equatorward edge of the convection pattern, in the slower, diverging flow at the Harang discontinuity. A patch repetition time of some 10 to 30 min was estimated depending on the phase of the substorm.

scholarly journals The dawn and dusk electrojet response to substorm onset

2000 ◽  
Vol 18 (9) ◽  
pp. 1097-1107 ◽  
Author(s):  
E. Borälv ◽  
P. Eglitis ◽  
H. J. Opgenoorth ◽  
E. Donovan ◽  
G. Reeves ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Information Transfer ◽  
Neutral Line ◽  
Substorm Onset ◽  
Model Case ◽  
Onset Timing ◽  
Storms And Substorms ◽  
Electric Fields And Currents ◽  
Substorm Onsets

Abstract. We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetosphere's reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN) and incoherent (EISCAT) radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.Key words: Ionosphere (auroral ionosphere; electric fields and currents) - Magnetospheric physics (storms and substorms)

scholarly journals Observational evidence for an inside-out substorm onset scenario

2009 ◽  
Vol 27 (5) ◽  
pp. 2129-2140 ◽  
Author(s):  
M. G. Henderson
Keyword(s):  
Neutral Line ◽  
Strong Support ◽  
Linear Increase ◽  
Substorm Onset ◽  
Linear Growth Rate ◽  
Two Phase ◽  
Particle Injection ◽  
Expansion Phase ◽  
The North ◽  
Inside Out

Abstract. We present observations which provide strong support for a substorm expansion phase onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The evolution of the auroral intensity is consistent with an exponential growth with an e-folding time of around 188 s (corresponding to a linear growth rate, γ of 5.33×10−3 s−1). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onset. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called "inside-out" substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

scholarly journals Cluster magnetotail observations of a tailward-travelling plasmoid at substorm expansion phase onset and field aligned currents in the plasma sheet boundary layer

2005 ◽  
Vol 23 (12) ◽  
pp. 3667-3683 ◽  
Author(s):  
N. C. Draper ◽  
M. Lester ◽  
S. W. H. Cowley ◽  
J.A. Wild ◽  
S. E. Milan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Plasma Sheet ◽  
Neutral Line ◽  
Current System ◽  
Onset Time ◽  
Plasma Sheet Boundary Layer ◽  
Expansion Phase ◽  
Magnetometer Data ◽  
Reconnection Site ◽  
Substorm Onsets

Abstract. We present data from both ground- and space-based instruments for a substorm event which occurred on 5 October 2002, with an expansion phase onset time of 02:50 UT determined from the ground magnetometer data. During this substorm, the Cluster spacecraft were located around 15 RE downtail, 8 RE from midnight in the pre-midnight sector and just 2 RE above the equatorial plane (in GSM coordinates). At expansion phase onset the Cluster spacecraft were located in the plasma sheet, tailward of a near-Earth neutral line and detected a significant time delay of 6 min between the tail field Bz component becoming negative and the subsequent detection of Earthward flows. This is explained by the formation of a tailward-directed travelling compression region initially Earthward of the spacecraft; 7 min later the Cluster spacecraft entered the plasma sheet boundary layer; they remained in and close to the plasma sheet boundary layer for around 15 min before exiting to the lobe. The spacecraft then re-entered the plasma sheet 30 min after onset. Earthward then tailward directed currents detected in the plasma sheet boundary layer after onset indicate that the Cluster spacecraft encountered the dawnward and duskward portions of the reconnection flow associated current system with Region 1 sense, respectively. The reconnection site and current system were initially skewed towards the pre-midnight sector, consistent with previous observations that found the majority of substorm onsets located in this sector. At later times the reconnection site and current system had moved towards dawn, to be located more centrally in the midnight sector.

scholarly journals CUTLASS/IMAGE observations of high-latitude convection features during substorms

1997 ◽  
Vol 15 (6) ◽  
pp. 692-702 ◽  
Author(s):  
T. K. Yeoman ◽  
H. Lühr
Keyword(s):  
Time Resolution ◽  
High Latitude ◽  
Geomagnetic Latitude ◽  
Hf Radar ◽  
High Time ◽  
Spatial Extent ◽  
Line Of Sight ◽  
Return Flow ◽  
High Time Resolution ◽  
Substorm Activity

Abstract. The CUTLASS Finland HF radar has been operational since February 1995. The radar frequently observes backscatter during the midnight sector from a latitude range 70–75° geographic, latitudes often associated with the polar cap. These intervals of backscatter occur during intervals of substorm activity, predominantly in periods of relatively quiet magnetospheric activity, with Kp during the interval under study being 2- and ΣKp for the day being only 8-. During August 1995 the radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14 s, and measurement of a full spatial scan of line-of-sight convection velocities every four minutes. Data from such scans reveal the radar to be measuring return flow convection during the interval of substorm activity. For three intervals during the period under study, a reduction in the spatial extent of radar backscatter occurred. This is a consequence of D region HF absorption and its limited extent in the present study is probably a consequence of the high latitude of the substorm activity, with the electrojet centre lying between 67° and 71° geomagnetic latitude. The high time resolution beam of the radar additionally demonstrates that the convection is highly time dependent. Pulses of equatorward flow exceeding ~600 m s–1 are observed with a duration of ~5 min and a repetition period of ~8 min. Their spatial extent in the CUTLASS field of view was 400–500 km in longitude, and 300–400 km in latitude. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. The transient features are interpreted as being due to ionospheric current vortices associated with field aligned current pairs. The relationship between these observations and substorm phenomena in the magnetotail is discussed.

High-latitude crochet (Solar flare effect) as a trigger of pseud-substorm onset

2021 ◽  
Author(s):  
Masatoshi Yamauchi ◽  
Magnar Johnsen ◽  
Shin-Ichi Othani ◽  
Dmitry Sormakov
Keyword(s):  
Solar Flare ◽  
High Latitude ◽  
Current System ◽  
Geomagnetic Latitude ◽  
Geomagnetic Disturbance ◽  
Substorm Onset ◽  
Ionospheric Conductivity ◽  
New Type ◽  
E Region ◽  
Substorm Activity

<p>Solar flares are known to enhance the ionospheric electron density and thus influence the electric currents in the D- and E-region.  The geomagnetic disturbance caused by this current system is called a "crochet" or "SFE (solar flare effect)".  Crochets are observed at dayside low-latitudes with a peak near the subsolar region ("subsolar crochet"), in the nightside high-latitude auroral region with a peak where the geomagnetic disturbance pre-exists during solar illumination ("auroral crochet"), and in the cusp ("cusp crochet").  In addition, we recently found a new type of crochet on the dayside ionospheric current at high latitudes (European sector 70-75 geographic latitude/67-72 geomagnetic latitude) independent from the other crochets.  The new crochet is much more intense and longer in duration than the subsolar crochet and is detected even in AU index for about half the >X2 flares despite the unfavorable latitudinal coverage of the AE stations (~65 geomagnetic latitude) to detect this new crochet (Yamauchi et al., 2020).  </p><p>The signature is sometime s seen in AL, causing the crochet signature convoluting with substorms.  From a theoretical viewpoint, X-flares that enhances the ionospheric conductivity may influence the substorm activity, like the auroral crochet.  To understand the substorm-crochet relation in the dayside, we examined SuperMAG data for cases when the onset of the substorm-like AL (SML) behavior coincides with the crochet.  We commonly found a large counter-clockwise ∆B vortex centered at 13-15 LT, causing an AU peak during late afternoon and an AL peak near noon at higher latitudes than the high-latitude crochet.  In addition, we could recognize a clockwise ∆B vortex in the prenoon sector, causing another poleward ∆B, but this signature is not as clear as the afternoon vortex.  With such strong vortex features, it becomes similar to substorms except for its local time.  In some cases, the vortex expends to the nightside sector, where and when nightside onset starts, suggesting triggering of onset.  Thus, the crochet may behave like pseudo-onset at different latitude than midnight substorms, and may even trigger substorm onset.</p>

scholarly journals A joint Cluster and ground-based instruments study of two magnetospheric substorm events on 1 September 2002

2004 ◽  
Vol 22 (12) ◽  
pp. 4217-4228 ◽  
Author(s):  
N. C. Draper ◽  
M. Lester ◽  
J. A. Wild ◽  
S. E. Milan ◽  
G. Provan ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Neutral Line ◽  
Radar Data ◽  
Hf Radar ◽  
Plasma Sheet Boundary Layer ◽  
Expansion Phase ◽  
Magnetospheric Substorm ◽  
Current Instability ◽  
Ground Magnetic ◽  
Main Region

Abstract. We present a coordinated ground- and space-based multi-instrument study of two magnetospheric substorm events that occurred on 1 September 2002, during the interval from 18:00 UT to 24:00 UT. Data from the Cluster and Polar spacecraft are considered in combination with ground-based magnetometer and HF radar data. During the first substorm event the Cluster spacecraft, which were in the Northern Hemisphere lobe, are to the west of the main region affected by the expansion phase. Nevertheless, substorm signatures are seen by Cluster at 18:25 UT (just after the expansion phase onset as seen on the ground at 18:23 UT), despite the ~5 RE} distance of the spacecraft from the plasma sheet. The Cluster spacecraft then encounter an earthward-moving diamagnetic cavity at 19:10 UT, having just entered the plasma sheet boundary layer. The second substorm expansion phase is preceded by pseudobreakups at 22:40 and 22:56 UT, at which time thinning of the near-Earth, L=6.6, plasma sheet occurs. The expansion phase onset at 23:05 UT is seen simultaneously in the ground magnetic field, in the magnetotail and at Polar's near-Earth position. The response in the ionospheric flows occurs one minute later. The second substorm better fits the near-Earth neutral line model for substorm onset than the cross-field current instability model. Key words. Magnetospheric physics (Magnetosphereionosphere interactions; Magnetic reconnection; Auroral phenomenon)

scholarly journals THEMIS and ground-based observations of successive substorm onsets following a super-long growth phase

2013 ◽  
Vol 31 (5) ◽  
pp. 835-843 ◽  
Author(s):  
J.-M. Liu ◽  
Y. Kamide ◽  
B.-C. Zhang ◽  
H.-Q. Hu ◽  
H.-G. Yang
Keyword(s):  
Magnetic Field ◽  
Growth Phase ◽  
Direct Evidence ◽  
Neutral Line ◽  
Solar Wind Speed ◽  
Time History ◽  
Substorm Onset ◽  
Instability Mechanism ◽  
History Of ◽  
Substorm Onsets

Abstract. We present four successive substorm events, which followed a super-long, as long as 9 h, growth phase on 5 December 2008, observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS) and the GOES 11 satellite with simultaneous coverage by the Alaska and THEMIS ground magnetometers. Several interesting and unique features were found for these cases. The interplanetary magnetic field was steadily southward and the solar wind speed was slow, less than 450 km s−1, which are thought to drive the long growth phase for the following onsets. At least four substorm expansion onsets occurred, including a double-onset event, which appears to be a challenge to the reconnection hypothesis for double-onset substorm and favored an instability mechanism for the onsets and could not be explained by the two neutral line models. For the onsets at 09:32 UT and 09:42 UT, the dipolarization signature was observed by GOES 11, which was located earthward of THEMIS C and THEMIS B. THEMIS C satellite caught a delayed and much weaker signature 1–3 min after GOES 11. THEMIS B observed no relating signature. These observations provide us with direct evidence that these events initiated at the near-earth region. The observations of THEMIS C and THEMIS B around the onsets favor the near-earth instabilities model for substorm onset.

scholarly journals Timing and location of substorm onsets from THEMIS satellite and ground based observations

2009 ◽  
Vol 27 (7) ◽  
pp. 2813-2830 ◽  
Author(s):  
S. Mende ◽  
V. Angelopoulos ◽  
H. U. Frey ◽  
E. Donovan ◽  
B. Jackel ◽  
...  
Keyword(s):  
Large Scale ◽  
Neutral Line ◽  
Rapid Development ◽  
Propagation Speed ◽  
Velocity Model ◽  
Substorm Onset ◽  
Time Of Arrival ◽  
Starting Point ◽  
Field Lines ◽  
Substorm Onsets

Abstract. The unprecedented coverage of the THEMIS GBO station network coupled with high temporal and spatial resolution allowed us to determine the various stages of the global scale developments of the optical aurora at substorm onsets. We identified several steps of the substorm onset auroral phenomena and we suggest that the most rapid development is the starting of the Substorm Poleward Expansion (SPE) and it is most useful for accurate timing of the substorm onset. The physical significance of this step is the start of the large scale substorm energy dissipation in the atmosphere due to particle precipitation and auroral electrojet currents. We also recognized several pre-cursor features. We also measured the time of arrival of magnetic impulses associated with the same substorms at the THEMIS satellites. We used these times and a simple model with assumed iono-acoustic speeds in the range of 300–800 km/s to calculate the location and time of the origin of the magnetic impulses propagating from substorm onset. The assumption was made that the substorm occurred between two THEMIS satellites and the impulses propagated away from a singular starting point in and out along the magneto tail GSM-x axis. This technique is only useful in cases where the ground based signature of the substorm is very close in local time (or longitude) to the foot of the field lines of the THEMIS satellites. The x distance of the calculated origins were naturally highly dependent on the assumed propagation velocity model and the associated magneto-sonic speed. The resulting x distances of the starting point for the three events ranged between 11 and 17.6 RE. denoting a starting region that requires highly stretched field lines to map to the auroral onset latitude but which is generally considered to be too close for neutral line formation. The corresponding start times were in the range of 0 to 170 s prior SPE depending strongly on the assumed propagation speed.

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