scholarly journals Spatial structure of summertime ionospheric plasma near magnetic noon

2005 ◽  
Vol 23 (1) ◽  
pp. 25-37 ◽  
Author(s):  
R. W. Sims ◽  
S. E. Pryse ◽  
W. F. Denig
Keyword(s):  
High Latitude ◽  
Ionospheric Plasma ◽  
Local Times ◽  
Soft Particle ◽  
Supporting Evidence ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionospheric Electron Density ◽  
Plasma Distribution

Abstract. Results are presented from a multi-instrument study of the spatial distribution of the summertime, polar ionospheric electron density under conditions of relatively stable IMF Bz<0. The EISCAT Svalbard radar revealed a region of enhanced densities near magnetic noon that, when comparing radar scans from different local times, appeared to be spatially confined in longitude. This was identified as the tongue-of-ionisation (TOI) that comprised photoionisation of sub-auroral origin that is drawn poleward into the polar cap by the anti-sunward flow of the high-latitude convection. The TOI was bounded in longitude by high-latitude troughs; the pre-noon trough on the morning side with a minimum near 78° N and the post-noon trough on the afternoon side with a minimum at 80° N. Complementary measurements by radio tomography, the SuperDARN radars, and a DMSP satellite, together with comparisons with earlier modelling work, provided supporting evidence for the interpretation of the density structuring, and highlighted the role of plasma convection in the formation of summertime plasma distribution. Soft particle precipitation played only a secondary role in the modulation of the large summertime densities entering the polar cap.

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 Evidence for solar-production as a source of polar-cap plasma

2004 ◽  
Vol 22 (4) ◽  
pp. 1093-1102 ◽  
Author(s):  
S. E. Pryse ◽  
R. W. Sims ◽  
J. Moen ◽  
L. Kersley ◽  
D. Lorentzen ◽  
...  
Keyword(s):  
High Latitude ◽  
Extended Period ◽  
Soft Particle ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
F Region ◽  
Modelling Studies ◽  
Restricted Region ◽  
Radio Tomographic Imaging

Abstract. The focus of the study is a region of enhanced ionospheric densities observed by the EISCAT Svalbard radar in the polar F-region near local magnetic noon under conditions of IMF Bz<0. Multi-instrument observations, using optical, spacecraft and radar instrumentation, together with radio tomographic imaging, have been used to identify the source of the enhancement and establish the background ionospheric conditions. Soft-particle precipitation was ruled out as a candidate for the production. Tomographic observations identified a latitudinally restricted region of enhanced densities at sub-auroral latitudes, distinct from the normal mid-latitude ionosphere, which was likely to be the source. The evidence suggested that the increased sub-auroral densities were photoionisation produced at the equatorward edge of the afternoon high-latitude cell, where the plasma is exposed to sunlight for an extended period as it flows slowly sunward toward magnetic noon. It is proposed that this plasma, once in the noon sector, was drawn antisunward by the high-latitude convection toward polar latitudes where it was identified by the EISCAT Svalbard radar. The observations are discussed in terms of earlier modelling studies of polar patch densities. Key words. Ionosphere (polar ionosphere; plasma temerature; plasma convection)

scholarly journals High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

2008 ◽  
Vol 26 (9) ◽  
pp. 2685-2700 ◽  
Author(s):  
M. Förster ◽  
S. E. Haaland ◽  
G. Paschmann ◽  
J. M. Quinn ◽  
R. B. Torbert ◽  
...  
Keyword(s):  
High Latitude ◽  
Cell Structure ◽  
Reference Plane ◽  
Convection Cell ◽  
Gradual Transition ◽  
Plasma Convection ◽  
Convection Pattern ◽  
Polar Cap ◽  
Small Shift ◽  
Magnetic Latitude

Abstract. In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007), and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward) convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum) potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South) Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the other intensifies and merges with the opposite main cell of the same polarity to form the large "round-shaped" convection cell when approaching a well-known IMFBy-dominated configuration. Opposite scenarios with interchanged roles of the respective cells occur for the opposite turning of the clock angle and at the Southern Hemisphere. The high-latitude dayside cells become more pronounced with increasing magnitude of the IMF vector.

scholarly journals Modelling the tongue-of-ionisation using CTIP with SuperDARN electric potential input: verification by radiotomography

2009 ◽  
Vol 27 (3) ◽  
pp. 1139-1152 ◽  
Author(s):  
S. E. Pryse ◽  
E. L. Whittick ◽  
A. D. Aylward ◽  
H. R. Middleton ◽  
D. S. Brown ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Electric Potential ◽  
Convective Flow ◽  
Ionospheric Plasma ◽  
The Other ◽  
High Latitudes ◽  
Polar Cap ◽  
Radar Network ◽  
Plasma Distribution ◽  
Good Agreement

Abstract. Electric potential patterns obtained by the SuperDARN radar network are used as input to the Coupled Thermosphere-Ionosphere-Plasmasphere model, in an attempt to improve the modelling of the spatial distribution of the ionospheric plasma at high latitudes. Two case studies are considered, one under conditions of stable IMF Bz negative and the other under stable IMF Bz positive. The modelled plasma distributions are compared with sets of well-established tomographic reconstructions, which have been interpreted previously in multi-instrument studies. For IMF Bz negative both the model and observations show a tongue-of-ionisation on the nightside, with good agreement between the electron density and location of the tongue. Under Bz positive, the SuperDARN input allows the model to reproduce a spatial plasma distribution akin to that observed. In this case plasma, unable to penetrate the polar cap boundary into the polar cap, is drawn by the convective flow in a tongue-of-ionisation around the periphery of the polar cap.

scholarly journals Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

2002 ◽  
Vol 20 (10) ◽  
pp. 1577-1601 ◽  
Author(s):  
A. Grocott ◽  
S. W. H. Cowley ◽  
J. B. Sigwarth ◽  
J. F. Watermann ◽  
T. K. Yeoman
Keyword(s):  
Flow Pattern ◽  
High Latitude ◽  
Large Scale ◽  
Local Times ◽  
Closed Field ◽  
Plasma Convection ◽  
Expansion Phase ◽  
Ionospheric Conductivity ◽  
Large Scale Flow ◽  
Open Flux

Abstract. We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ~40 kV prior to expansion phase onset, grew to ~80 kV over a ~15 min interval during the expansion phase, and then decayed to ~35 kV over ~10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ~65– 75 kV, compared with continuing dayside reconnection rates of ~30–45 kV. The net closure of open flux during the sub-storm was thus ~0.4–0.6 × 108 Wb, representing ~15–20% of the open flux present at onset, and corresponding to an overall contraction of the open-closed field line boundary by ~1° latitude.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection)

scholarly journals Impact of Storm-Enhanced Density (SED) on Ion Upflow Fluxes During Geomagnetic Storm

2021 ◽  
Vol 8 ◽  
Author(s):  
Shasha Zou ◽  
Jiaen Ren ◽  
Zihan Wang ◽  
Hu Sun ◽  
Yang Chen
Keyword(s):  
Geomagnetic Storm ◽  
Critical Role ◽  
Auroral Zone ◽  
High Density ◽  
Soft Particle ◽  
Event Analysis ◽  
Polar Cap ◽  
Holistic Understanding ◽  
The Impact

The impact of the dynamic evolution of the Storm-Enhanced Density (SED) on the upward ion fluxes during the March 06, 2016 geomagnetic storm is studied using comprehensive multi-scale datasets. This storm was powered by a Corotating Interaction Region (CIR), and the minimum Sym-H reached ∼−110 nT. During the ionospheric positive storm phase, the SED formed and the associated plume and polar cap patches occasionally drifted anti-sunward across the polar cap. When these high-density structures encountered positive vertical flows, large ion upward fluxes were produced, with the largest upward flux reaching 3 × 1014 m−2s−1. These upflows were either the type-1 ion upflow associated with fast flow channels, such as the subauroral polarization stream (SAPS) channel, or the type-2 ion upflow due to soft particle precipitations in the cusp region. The total SED-associated upflow flux in the dayside cusp can be comparable to the total upflow flux in the nightside auroral zone despite the much smaller cusp area compared with the auroral zone. During the ionospheric negative storm phase, the ionospheric densities within the SED and plume decreased significantly and thus led to largely reduced upward fluxes. This event analysis demonstrates the critical role of the ionospheric high-density structures in creating large ion upward fluxes. It also suggests that the dynamic processes in the coupled ionosphere-thermosphere system and the resulting state of the ionospheric storm are crucial for understanding the temporal and spatial variations of ion upflow fluxes and thus should be incorporated into coupled geospace models for improving our holistic understanding of the role of ionospheric plasma in the geospace system.

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.

scholarly journals A multi-diagnostic approach to understanding high-latitude plasma transport during the Halloween 2003 storm

2008 ◽  
Vol 26 (9) ◽  
pp. 2739-2747 ◽  
Author(s):  
P. Yin ◽  
C. N. Mitchell ◽  
P. Spencer ◽  
I. McCrea ◽  
T. Pedersen
Keyword(s):  
Electron Density ◽  
High Latitude ◽  
Extreme Event ◽  
Time History ◽  
Diagnostic Approach ◽  
Plasma Transport ◽  
Storm Event ◽  
Soft Particle ◽  
Polar Cap ◽  
Optical Images

Abstract. During the Halloween 2003 storm event, significant electron density enhancements at elevated F-layer altitudes were recorded by the EISCAT and ESR radars in northern Europe between 20:00 and 24:00 UT on 30 October. At the same time, a sequence of optical images from Qaanaaq in northern Greenland captured a series of eastward-propagating polar cap patches. In this paper, an advanced 4-D tomographic method based on the assimilation of global GPS data, coupled to a predictive Kalman filtering technique, has been used to reveal the linkage between these ionospheric structures. The combination of the various data sources has clearly established the time history of this extreme event, in which high-density plasma was uplifted in the dayside ionosphere and convected anti-sunward across the polar cap to European high latitudes at an elevated F-layer. Using this multi instrument approach, we can differentiate between those density structures observed at the ESR which occurred as a result of cross-polar transport and those more likely to have been produced by in-situ soft particle precipitation, a distinction which is supported by the ESR and EISCAT data. The multi-diagnostic approach reported here has the potential significantly to extend our current understanding of high latitude plasma transport and the origin of electron density enhancements.

scholarly journals Variations in the polar cap area during two substorm cycles

2003 ◽  
Vol 21 (5) ◽  
pp. 1121-1140 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester ◽  
S. W. H. Cowley ◽  
K. Oksavik ◽  
M. Brittnacher ◽  
...  
Keyword(s):  
Hf Radar ◽  
Local Times ◽  
Convection Flow ◽  
Closed Field ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Dayside Magnetopause ◽  
Magnetospheric Configuration And Dynamics ◽  
Open Flux

Abstract. This study employs observations from several sources to determine the location of the polar cap boundary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral images from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the magnetosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, allowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and decreases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to decrease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap boundary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times supports this finding.Key words. Ionosphere (plasma convection; polar ionosphere) – Magnetospheric physics (magnetospheric configuration and dynamics)

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