scholarly journals Combined optical, EISCAT and magnetic observations of the omega bands/Ps6 pulsations and an auroral torch in the late morning hours: a case study

2005 ◽  
Vol 23 (5) ◽  
pp. 1821-1838 ◽  
Author(s):  
V. Safargaleev ◽  
T. Sergienko ◽  
H. Nilsson ◽  
A. Kozlovsky ◽  
S. Massetti ◽  
...  
Keyword(s):  
Interplanetary Medium ◽  
Plasma Convection ◽  
Helmholtz Instability ◽  
Magnetic Signature ◽  
Magnetic Pulsations ◽  
Spatially Periodic ◽  
Interchange Instability ◽  
Auroral Phenomena ◽  
Image Network

Abstract. We present here the results of multi-instrument observations of auroral torch and Ps6 magnetic pulsations, which are assumed to be the magnetic signature of the spatially periodic optical auroras known as omega bands. Data from TV and ASC cameras in Barentsburg and Ny Ålesund, EISCAT radars in Longyearbyen and Tromsø, as well as IMAGE network were used in this study. The auroral phenomenon which was considered differed from that previously discussed, as it occurred both in an unusual place (high latitudes) and at an unusual time (late morning hours). We show that this might occur due to specific conditions in the interplanetary medium, causing the appropriate deformation of the magnetosphere. In such a case, the IMF turned out to be an additional factor in driving the regime of Ps6/omega bands, namely, only by acting together could a substorm onset in the night sector and Bz variations result in their generation. Since the presumable source of Ps6/omega bands does not co-locate with convection reversal boundaries, we suggest the interpretation of the phenomena in the frame of the interchange instability instead of the Kelvin-Helmholtz instability that is widely discussed in the literature in connection with omega auroras. Some numerical characteristics of the auroral torch were obtained. We also emphasize to the dark hole in the background luminosity and the short-lived azimuthally-restricted auroral arc, since their appearance could initiate the auroral torch development. Keywords. Magnetospheric physics (Auroral phenomena; Plasma convection; Solar wind-magnetosphere interaction)

scholarly journals Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(<i>B<sub>y</sub></i> <u>~</u> |<i>B<sub>z</sub></i>|) IMF orientation

2003 ◽  
Vol 21 (2) ◽  
pp. 539-558 ◽  
Author(s):  
P. E. Sandholt ◽  
J. Moen ◽  
C. J. Farrugia ◽  
S. W. H. Cowley ◽  
M. Lester ◽  
...  
Keyword(s):  
Central Feature ◽  
Plasma Convection ◽  
Polar Cap ◽  
Westward Expansion ◽  
Equatorward Boundary ◽  
Dayside Magnetopause ◽  
On Line ◽  
Auroral Emissions ◽  
Auroral Phenomena

Abstract. In a case study we demonstrate the spatiotemporal structure of aurora and plasma convection in the cusp/polar cap when the interplanetary magnetic field (IMF) Bz < 0 and By ~ | Bz | (clock angle in GSM Y - Z plane: ~ 135°). This IMF orientation elicited a response different from that corresponding to strongly northward and southward IMF. Our study of this "intermediate state" is based on a combination of ground observations of optical auroral emissions and ionospheric plasma convection. Utilizing all-sky cameras at NyAlesund, Svalbard and Heiss Island (Russian arctic), we are able to monitor the high-latitude auroral activity within the ~10:00–15:00 MLT sector. Information on plasma convection is obtained from the SuperDARN radars, with emphasis placed on line of sight observations from the radar situated in Hankasalmi, Finland (Cutlass). A central feature of the auroral observations in the cusp/polar cap region is a ~ 30-min long sequence of four brightening events, some of which consists of latitudinally and longitudinally separated forms, which are found to be associated with pulsed ionospheric flows in merging and lobe convection cells. The auroral/convection events may be separated into different forms/cells and phases, reflecting a spatiotem-poral evolution of the reconnection process on the dayside magnetopause. The initial phase consists of a brightening in the postnoon sector (~ 12:00–14:00 MLT) at ~ 73° MLAT, accompanied by a pulse of enhanced westward convection in the postnoon merging cell. Thereafter, the event evolution comprises two phenomena which occur almost simultaneously: (1) westward expansion of the auroral brightening (equatorward boundary intensification) across noon, into the ~ 10:00–12:00 MLT sector, where the plasma convection subsequently turns almost due north, in the convection throat, and where classical poleward moving auroral forms (PMAFs) are observed; and (2) auroral brightening at slightly higher latitudes (~ 75° MLAT) in the postnoon lobe cell, with expansion towards noon, giving rise to a clear cusp bifurcation. The fading phase of PMAFs is accompanied by a "patch" of enhanced (~ 1 km/s) poleward-directed merging cell convection at high latitudes (75–82° MLAT), e.g. more than 500 km poleward of the cusp equatorward boundary. The major aurora/convection events are recurring at ~ 5–10 min intervals. Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

scholarly journals Excitation of transient lobe cell convection and auroral arc at the cusp poleward boundary during a transition of the interplanetary magnetic field from south to north

2001 ◽  
Vol 19 (5) ◽  
pp. 487-493 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
S. W. H. Cowley ◽  
M. Lester ◽  
J.-C. Cerisier
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Large Scale ◽  
Intermediate Phase ◽  
Bright Spot ◽  
Convection Cell ◽  
Plasma Convection ◽  
Cell Pattern ◽  
Auroral Phenomena ◽  
Lobe Reconnection

Abstract. We document the activation of transient polar arcs emanating from the cusp within a 15 min long intermediate phase during the transition from a standard two-cell convection pattern, representative of a strongly southward interplanetary magnetic field (IMF), to a "reverse" two-cell pattern, representative of strongly northward IMF conditions. During the 2–3 min lifetime of the arc, its base in the cusp, appearing as a bright spot, moved eastward toward noon by ~ 300 km. As the arc moved, it left in its "wake" enhanced cusp precipitation. The polar arc is a tracer of the activation of a lobe convection cell with clockwise vorticity, intruding into the previously established large-scale distorted two-cell pattern, due to an episode of localized lobe reconnection. The lobe cell gives rise to strong flow shear (converging electric field) and an associated sheet of outflowing field-aligned current, which is manifested by the polar arc. The enhanced cusp precipitation represents, in our view, the ionospheric footprint of the lobe reconnection process.Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

scholarly journals <i>Letter to the Editor</i> Simultaneous observations of the ionospheric footprint of flux transfer events and dispersed ion signatures

2002 ◽  
Vol 20 (2) ◽  
pp. 281-287 ◽  
Author(s):  
G. Provan ◽  
S. E. Milan ◽  
M. Lester ◽  
T. K. Yeoman ◽  
H. Khan
Keyword(s):  
Boundary Layers ◽  
High Latitude ◽  
Spectral Width ◽  
Field Of View ◽  
Magnetospheric Physics ◽  
Plasma Convection ◽  
Coherent Scatter ◽  
Flux Transfer Events ◽  
Letter To The Editor

Abstract. We perform a case study of a favourable conjunction of overpasses of the DMSP F11 and F13 spacecraft with the field of view of the Hankasalmi HF coherent scatter. At the time, pulsed ionospheric flows (PIFs) were clearly observed at a high-latitude in the radar field of view. The PIFs were associated with medium spectral width values and were identified as the fossilized signatures of pulsed dayside reconnection. Simultaneously, DMSP spectrograms from the two spacecraft showed dispersed ion signatures, observed equatorwards of the PIF signatures. We identified dayside high-latitude magnetosphere boundaries; these boundaries agreed well with those defined using the algorithm on the JHU/APL auroral particle website (Haerendel et al., 1978; Newell and Meng, 1988, 1995; Newell et al., 1991a, 1991b, 1991c; Traver et al., 1991). We conclude that in this case study the dispersed ion signatures map to regions of very newly-opened flux. It is only when this flux has convected polewards that the signatures of the PIFs with medium spectral widths are observed by the HF radars. These particular PIF signatures map to regions of mantle precipitation, i.e. recently reconnected flux.Key words. Ionosphere (ionosphere-magnetosphere interaction) – Magnetospheric physics (magnetopause, cusp and boundary layers; plasma convection)

scholarly journals Ultra Low Frequency Waves at the Ground Driven by the Kelvin-Helmholtz Instability Associated with Reconnection: A Case Study

2020 ◽  
Author(s):  
Jamie Gorman ◽  
Elena A. Kronberg ◽  
Katariina Nykyri ◽  
Artem Smirnov ◽  
Jesper W Gjerloev ◽  
...  
Keyword(s):  
Low Frequency ◽  
Helmholtz Instability ◽  
Low Frequency Waves

Detection of Kelvin-Helmholtz instability with the Indian mesosphere-stratosphere-troposphere radar: A case study

1999 ◽  
Vol 104 (D4) ◽  
pp. 3937-3945 ◽  
Author(s):  
Sachchidanand Singh ◽  
K. K. Mahajan ◽  
R. K. Choudhary ◽  
O. P. Nagpal
Keyword(s):  
Helmholtz Instability

scholarly journals Velocity of auroral arcs drifting equatorward from the polar cap

1998 ◽  
Vol 16 (10) ◽  
pp. 1322-1331 ◽  
Author(s):  
P. J. S. Williams ◽  
C. F. del Pozo ◽  
I. Hiscock ◽  
R. Fallows
Keyword(s):  
Electric Fields ◽  
Drift Velocity ◽  
Major Change ◽  
Recovery Phase ◽  
Plasma Velocity ◽  
Plasma Convection ◽  
Expansion Phase ◽  
F Region ◽  
Auroral Phenomena ◽  
Auroral Arcs

Abstract. The drift velocity of an auroral arc is compared with the component of F-region plasma velocity in the same direction for ten cases where the arc is seen to move steadily equatorward for several minutes without any major change in appearance or orientation. In most cases the two velocities are close, but on two occasions the drift velocity of the arc is much higher than the plasma velocity. From the cases studied it appears that during the growth and recovery phase of the substorm cycle the arc moves with a velocity close to the convection velocity, but during the expansion phase this is not the case.Key words. Magnetospheric physics (auroral phenomena; electric fields; plasma convection)

scholarly journals Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 2009

2018 ◽  
Vol 123 (9) ◽  
pp. 7486-7497 ◽  
Author(s):  
T. Pitkänen ◽  
A. Kullen ◽  
Q. Q. Shi ◽  
M. Hamrin ◽  
A. De Spiegeleer ◽  
...  
Keyword(s):  
Electric Field ◽  
Plasma Convection ◽  
Convection Electric Field
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