scholarly journals Observations of the cusp region under northward IMF

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1641-1653 ◽  
Author(s):  
F. Pitout ◽  
J.-M. Bosqued ◽  
D. Alcaydé ◽  
W. F. Denig ◽  
H. Rème
Keyword(s):  
High Altitude ◽  
Boundary Layers ◽  
Plasma Flow ◽  
Field Of View ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Cusp Region ◽  
Time Period ◽  
Lobe Reconnection ◽  
The Imf

Abstract. We present a comparative study of the cusp region using the EISCAT Svalbard Radars (ESR) and the Cluster spacecraft. We focus in this paper on 2 February 2001, over the time period from 07:30 UT to 12:00 UT when the oblique ESR antenna pointing northward at a low elevation recorded latitudinal motions of the cusp region in response to the IMF. Meanwhile, the Cluster satellites were flying over the EISCAT Svalbard Radar field-of-view around local magnetic noon. The spacecraft first flew near ESR, northeast of Svalbard and then passed over the field-of-view of the antenna at about 11:30 UT. From 08:00 UT to 09:00 UT, the IMF remains primarily southward yet several variations in the Z-component are seen to move the cusp. Around 09:00 UT, an abrupt northward turning of the IMF moves the cusp region to higher latitudes. As a result, the Cluster satellites ended up in the northernmost boundary of the high-altitude cusp region where the CIS instrument recorded highly structured plasma due to ion injections in the lobe of the magnetosphere. After 09:00 UT, the IMF remains northward for more than two hours. Over this period, the ESR records sunward plasma flow in the cusp region due to lobe reconnection, while Cluster spacecraft remain in the high-altitude cusp.Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers; plasma convection) Ionosphere (polar ionosphere)

scholarly journals Polar patches observed by ESR and their possible origin in the cusp region

2000 ◽  
Vol 18 (9) ◽  
pp. 1043-1053 ◽  
Author(s):  
A. M. Smith ◽  
S. E. Pryse ◽  
L. Kersley
Keyword(s):  
Energy Distribution ◽  
Electron Density ◽  
Plasma Flow ◽  
Plasma Temperature ◽  
Soft Particle ◽  
Polar Ionosphere ◽  
Polar Cap ◽  
Particle Precipitation ◽  
Cusp Region ◽  
Reconnection Site

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.Key words: Ionosphere (ionosphere-magnetosphere interactions; plasma temperature and density; polar ionosphere)

scholarly journals Simultaneous high- and low-latitude reconnection: ESR and DMSP observations

2002 ◽  
Vol 20 (9) ◽  
pp. 1311-1320 ◽  
Author(s):  
F. Pitout ◽  
P. T. Newell ◽  
S. C. Buchert
Keyword(s):  
High Latitude ◽  
Time Interval ◽  
High Latitudes ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Low Latitude ◽  
Svalbard Archipelago ◽  
Cusp Region ◽  
Ionosphere Plasma ◽  
Particle Measurement

Abstract. We present EISCAT Svalbard Radar and DMSP observations of a double cusp during an interval of predominantly northward IMF on 26 November 2000. In the cusp region, the ESR dish, pointing northward, recorded sun-ward ionospheric flow at high latitudes (above 82° GL), indicating reconnection occuring in the magnetospheric lobe. Meanwhile, the same dish also recorded bursts of poleward flow, indicative of bursty reconnection at the subsolar magnetopause. Within this time interval, the DMSP F13 satellite passed in the close vicinity of the Svalbard archipelago. The particle measurement on board exhibited a double cusp structure in which two oppositely oriented ion dispersions are recorded. We interpret this set of data in terms of simultaneous merging at low- and high-latitude magnetopause. We discuss the conditions for which such simultaneous high-latitude and low-latitude reconnection can be anticipated. We also discuss the consequences of the presence of two X-lines in the dayside polar ionosphere.Key words. Magnetospheric physics (solar wind-magnetosphere interactions) – Ionosphere (polar ionosphere; plasma convection)

scholarly journals Localized electron density enhancements in the high-altitude polar ionosphere and their relationships with storm-enhanced density (SED) plumes and polar tongues of ionization (TOI)

2011 ◽  
Vol 29 (2) ◽  
pp. 367-375 ◽  
Author(s):  
Y. Kitanoya ◽  
T. Abe ◽  
A. W. Yau ◽  
T. Hori ◽  
N. Nishitani
Keyword(s):  
High Altitude ◽  
Electron Density ◽  
Plasma Density ◽  
High Plasma ◽  
Density Increase ◽  
Statistical Characteristics ◽  
Electron Content ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Total Electron

Abstract. Events of localized electron density increase in the high-altitude (>3000 km) polar ionosphere are occasionally identified by the thermal plasma instruments on the Akebono satellite. In this paper, we investigate the vertical density structure in one of such events in detail using simultaneous observations by the Akebono and DMSP F15 satellites, the SuperDARN radars, and a network of ground Global Positioning System (GPS) receivers, and the statistical characteristics of a large number (>10 000) of such events using Akebono data over half of an 11-year solar cycle. At Akebono altitude, the parallel drift velocity is remarkably low and the O+ ion composition ratio remarkably high, inside the high plasma-density regions at high altitude. Detailed comparisons between Akebono, DMSP ion velocity and density, and GPS total electron content (TEC) data suggest that the localized plasma density increase observed at high altitude on Akebono was likely connected with the polar tongue of ionization (TOI) and/or storm enhanced density (SED) plume observed in the F-region ionosphere. Together with the SuperDARN plasma convection map these data suggest that the TOI/SED plume penetrated into the polar cap due to anti-sunward convection and the plume existed in the same convection channel as the dense plasma at high altitude; in other words, the two were probably connected to each other by the convecting magnetic field lines. The observed features are consistent with the observed high-density plasma being transported from the mid-latitude ionosphere or plasmasphere and unlikely a part of the polar wind population.

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 Multi-instrument probing of the polar ionosphere under steady northward IMF

2000 ◽  
Vol 18 (1) ◽  
pp. 90-98 ◽  
Author(s):  
S. E. Pryse ◽  
A. M. Smith ◽  
L. Kersley ◽  
I. K. Walker ◽  
C. N. Mitchell ◽  
...  
Keyword(s):  
Closed Field ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Polar Cap ◽  
Particle Detection ◽  
Plasma Parameters ◽  
Coherent Scatter ◽  
Comprehensive Picture ◽  
Field Lines ◽  
Lobe Reconnection

Abstract. Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere..Key words. Ionosphere (polar ionosphere) · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)

scholarly journals Polar cap influx

2005 ◽  
Vol 23 (5) ◽  
pp. 1755-1761
Author(s):  
J. MacDougall ◽  
P. T. Jayachandran
Keyword(s):  
Magnetic Field ◽  
Magnetospheric Physics ◽  
Plasma Convection ◽  
Polar Cap ◽  
Cusp Region ◽  
Ionosphere Plasma ◽  
Latitude Station ◽  
The Imf

Abstract. This study uses digital ionosonde data from a cusp latitude station (Cambridge Bay, 77° CGM lat.) to study the convection into the polar cap. Days when the IMF magnetic field was relatively steady were used. On many days it was possible to distinguish an interval near noon MLT when the ionosonde data had a different character from that at earlier and later times. Based on our data, and other published measurements, we used the interval 10:00-13:00 MLT as the cusp interval and calculated the convection into the polar cap in this interval. The integrated convection accounted for only ~1/3 of the open polar cap flux. If the convection through the prenoon/postnoon regions on either side of the cusp was calculated the remaining 2/3 of the flux could be accounted for. The characteristics of the prenoon/postnoon regions were different from the cusp region, and we attribute this to transient flank merging versus more steady frontside merging for the cusp. Keywords. Ionosphere (Plasma convection) Magnetospheric physics (Polar cap phenomenon)

scholarly journals Changes in labial capillary density on ascent to and descent from high altitude

F1000Research ◽  
2016 ◽  
Vol 5 ◽  
pp. 2107 ◽  
Author(s):  
Edward Gilbert-Kawai ◽  
Jonny Coppel ◽  
Phillip Hennis ◽  
Michael Grocott ◽  
Can Ince ◽  
...  
Keyword(s):  
High Altitude ◽  
Correlation Coefficient ◽  
Prolonged Exposure ◽  
Haemoglobin Concentration ◽  
Capillary Density ◽  
Vessel Density ◽  
Field Of View ◽  
Rank Test ◽  
Simplified Method

Present knowledge of how the microcirculation is altered by prolonged exposure to hypoxia at high altitude is incomplete and modification of existing analytical techniques may improve our knowledge considerably. We set out to use a novel simplified method of measuring in vivo capillary density during an expedition to high altitude using a CytoCam incident dark field imaging video-microscope. The simplified method of data capture involved recording one-second images of the mucosal surface of the inner lip to reveal data about microvasculature density in ten individuals. This was done on ascent to, and descent from, high altitude. Analysis was conducted offline by two independent investigators blinded to the participant identity, testing conditions and the imaging site.  Additionally we monitored haemoglobin concentration and haematocrit data to see if we could support or refute mechanisms of altered density relating to vessel recruitment. Repeated sets of paired values were compared using Kruskall Wallis Analysis of Variance tests, whilst comparisons of values between sites was by related samples Wilcoxon Signed Rank Test. Correlation between different variables was performed using Spearman’s rank correlation coefficient, and concordance between analysing investigators using intra-class correlation coefficient. There was a significant increase in capillary density from London on ascent to high altitude; median capillaries per field of view area increased from 22.8 to 25.3 (p=0.021). There was a further increase in vessel density during the six weeks spent at altitude (25.3 to 32.5, p=0.017). Moreover, vessel density remained high on descent to Kathmandu (31.0 capillaries per field of view area), despite a significant decrease in haemoglobin concentration and haematocrit. Using a simplified technique, we have demonstrated an increase in capillary density on early and sustained exposure to hypobaric hypoxia at thigh altitude, and that this remains elevated on descent to normoxia. The technique is simple, reliable and reproducible.

scholarly journals Cluster observations of a complex high-altitude cusp passage during highly variable IMF

2004 ◽  
Vol 22 (10) ◽  
pp. 3707-3719 ◽  
Author(s):  
M. G. G. T. Taylor ◽  
M. W. Dunlop ◽  
B. Lavraud ◽  
A. Vontrat-Reberac ◽  
C. J. Owen ◽  
...  
Keyword(s):  
High Altitude ◽  
Northern Hemisphere ◽  
Reasonable Agreement ◽  
Boundary Analysis ◽  
Excellent Opportunity ◽  
Cusp Region ◽  
Magnetic Signatures

Abstract. On 26 February 2001, the Cluster spacecraft were outbound over the Northern Hemisphere, at approximately 12:00 MLT, approaching the magnetosheath through the high-altitude (and exterior) cusp region. Due to macroscopic motions of the cusp, the spacecraft made multiple entries into the exterior cusp region before exiting into the magnetosheath, presenting an excellent opportunity to utilize the four spacecraft techniques available to the Cluster mission. We present and compare 2 methods of 4-spacecraft boundary analysis, one using PEACE data and one using FGM data. The comparison shows reasonable agreement between the techniques, as well as the expected "single spacecraft" plasma and magnetic signatures when associated with propagated IMF conditions. However, during periods of highly radial IMF (predominantly negative BX GSM), the 4-spacecraft boundary analysis reveals a dynamic and deformed cusp morphology.

scholarly journals Wave particle interactions in the high-altitude polar cusp: a Cluster case study

2005 ◽  
Vol 23 (12) ◽  
pp. 3699-3713 ◽  
Author(s):  
B. Grison ◽  
F. Sahraoui ◽  
B. Lavraud ◽  
T. Chust ◽  
N. Cornilleau-Wehrlin ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
High Altitude ◽  
Wave Spectrum ◽  
Alfven Waves ◽  
Wave Activity ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Plasma Convection ◽  
Field Lines ◽  
Kinetic Alfvén Waves

Abstract. On 23 March 2002, the four Cluster spacecraft crossed in close configuration (~100 km separation) the high-altitude (10 RE) cusp region. During a large part of the crossing, the STAFF and EFW instruments have detected strong electromagnetic wave activity at low frequencies, especially when intense field-aligned proton fluxes were detected by the CIS/HIA instrument. In all likelihood, such fluxes correspond to newly-reconnected field lines. A focus on one of these ion injection periods highlights the interaction between waves and protons. The wave activity has been investigated using the k-filtering technique. Experimental dispersion relations have been built in the plasma frame for the two most energetic wave modes. Results show that kinetic Alfvén waves dominate the electromagnetic wave spectrum up to 1 Hz (in the spacecraft frame). Above 0.8 Hz, intense Bernstein waves are also observed. The close simultaneity observed between the wave and particle events is discussed as an evidence for local wave generation. A mechanism based on current instabilities is consistent with the observations of the kinetic Alfvén waves. A weak ion heating along the recently-opened field lines is also suggested from the examination of the ion distribution functions. During an injection event, a large plasma convection motion, indicative of a reconnection site location, is shown to be consistent with the velocity perturbation induced by the large-scale Alfvén wave simultaneously detected.

scholarly journals Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection

2008 ◽  
Vol 26 (11) ◽  
pp. 3279-3293 ◽  
Author(s):  
A. Kullen ◽  
S. Buchert ◽  
T. Karlsson ◽  
T. Johansson ◽  
S. Lileo ◽  
...  
Keyword(s):  
Plasma Flow ◽  
Strong Dependence ◽  
Background Plasma ◽  
Plasma Transport ◽  
Plasma Convection ◽  
Plasma Flows ◽  
Maximum Phase ◽  
Field Peak ◽  
Auroral Arcs

Abstract. The role of intense high-altitude electric field (E-field) peaks for large-scale plasma convection is investigated with the help of Cluster E-field, B-field and density data. The study covers 32 E-field events between 4 and 7 RE geocentric distance, with E-field magnitudes in the range 500–1000 mV/m when mapped to ionospheric altitude. We focus on E-field structures above the ionosphere that are typically coupled to discrete auroral arcs and their return current region. Connected to such E-field peaks are rapid plasma flows directed along the discrete arcs in opposite directions on each side of the arc. Nearly all the E-field events occur during active times. A strong dependence on different substorm phases is found: a majority of intense E-field events appearing during substorm expansion or maximum phase are located on the nightside oval, while most recovery events occur on the dusk-to-dayside part of the oval. For most expansion and maximum phase cases, the average background plasma flow is in the sunward direction. For a majority of recovery events, the flow is in the anti-sunward direction. The net plasma flux connected to a strong E-field peak is in two thirds of the cases in the same direction as the background plasma flow. However, in only one third of the cases the strong flux caused by an E-field peak makes an important contribution to the plasma transport within the boundary plasma sheet. For a majority of events, the area covered by rapid plasma flows above discrete arcs is too small to have an effect on the global convection. This questions the role of discrete auroral arcs as major driver of plasma convection.

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