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 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 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.

Radar studies of high-latitude ionospheric flows

1989 ◽  
Vol 328 (1598) ◽  
pp. 107-118 ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Flow Pattern ◽  
Electric Fields ◽  
Strong Interactions ◽  
Plasma Convection ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Coupling Processes

Strong interactions occur between the solar wind and the Earth’s magnetic field which result in the convection of ionospheric plasma over the polar cap regions. This generally forms a two-cell pattern with westward and eastward flows in the pre- and post-midnight sectors respectively. The flow pattern is sensitive to the flux of the solar wind and the direction of the interplanetary magnetic field. Observations of the flow pattern are thus of considerable value in the interpretation of the magnetosphere-ionosphere coupling processes and in identifying the influence of the solar wind on the Earth’s environment. The plasma convection can be observed by ground-based coherent and incoherent scatter radars and the flow vectors determined. Measurements for a range of flow conditions are presented. These are interpreted in terms of the interactions of the solar wind with the magnetosphere and the resulting electric fields which drive the plasma flows in the ionosphere.

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 The pulsed nature of the nightside contribution to polar cap convection: repetitive substorm activity under steady interplanetary driving

2012 ◽  
Vol 30 (10) ◽  
pp. 1539-1553 ◽  
Author(s):  
P. E. Sandholt ◽  
Y. L. Andalsvik ◽  
C. J. Farrugia
Keyword(s):  
Temporal Structure ◽  
Wind Forcing ◽  
Plasma Convection ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Polar Orbit ◽  
Ion Drift ◽  
Flow Phenomena ◽  
Substorm Activity ◽  
Northern And Southern Hemispheres

Abstract. The aim of this study is to investigate the relative contributions of dayside and nightside processes to the spatial and temporal structure of polar cap plasma convection. The central parameter is the cross-polar cap potential (CPCP). Selecting a 10-h-long interval of stable interplanetary driving by an interplanetary CME (ICME), we are able to distinguish between the dayside and nightside sources of the convection. The event was initiated by an abrupt enhancement of the magnetopause (MP) reconnection rate triggered by a southward turning of the ICME magnetic field. This was followed by a long interval (10 h) of steady and strong driving. Under the latter condition a long series of electrojet intensifications was observed which recurred at 50 min intervals. The detailed temporal structure of polar cap convection in relation to polar cap contraction events is obtained by combining continuous ground observations of convection-related magnetic deflections (including polar cap magnetic indices in the Northern and Southern Hemispheres, PCN and PCS) and the more direct, but lower-resolution ion drift data obtained from a satellite (DMSP F13) in polar orbit. The observed PCN enhancements combined with DMSP satellite observations (F13 and F15 data) of polar cap contractions during the evolution of selected substorm expansions allowed us to estimate the CPCP enhancements (25%) associated with individual events in the series. Ground-satellite conjunctions are further used to investigate the spatial structure of polar cap convection, i.e., the homogeneous plasma flow in the centre (Vi ≤ 1 km s−1) versus channels of enhanced antisunward flows (Vi ≥ 1 km s−1) along the periphery of the polar cap. We emphasise the temporal structure of these polar cap flow phenomena in relation to the prevailing solar wind forcing and the repetitive substorm activity.

scholarly journals Dayside flow bursts and high-latitude reconnection when the IMF is strongly northward

2006 ◽  
Vol 24 (8) ◽  
pp. 2227-2242 ◽  
Author(s):  
H. Hu ◽  
T. K. Yeoman ◽  
M. Lester ◽  
R. Liu ◽  
H. Yang ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
High Latitude ◽  
Closed Field ◽  
Flow Data ◽  
Plasma Convection ◽  
Convection Pattern ◽  
Reconnection Rate ◽  
Northern Hemispheric ◽  
Field Lines

Abstract. The characteristics of dayside ionospheric convection are studied using Northern Hemispheric SuperDARN data and DMSP particle and flow observations when the interplanetary magnetic field (IMF) was strongly northward during 13:00–15:00 UT on 2 March 2002. Although IMF Bx was positive, which is believed to favour Southern Hemisphere high-latitude reconnection at equinox, a four-cell convection pattern was observed and lasted for more than 1.5 h in the Northern Hemisphere. The reconnection rate derived from an analysis of the Northern Hemisphere SuperDARN data illustrates that the high-latitude reconnection was quasi-periodic, with a period between 4–16 min. A sawtooth-like and reverse-dispersed ion signature was observed by DMSP-F14 in the sunward cusp convection at around 14:41 UT, confirming that the high-latitude reconnection was pulsed. Accompanying the pulsed reconnection, strong antisunward ionospheric flow bursts were observed in the post-noon LLBL region on closed field lines, propagating with the same speed as the plasma convection. DMSP flow data show that a similar flow pattern and particle precipitation occurred in the conjugate Southern Hemisphere.

scholarly journals A new method to reconstruct the ionospheric convection patterns in the polar cap

1999 ◽  
Vol 17 (6) ◽  
pp. 743-748
Author(s):  
P. L. Israelevich ◽  
A. I. Ershkovich
Keyword(s):  
Stream Function ◽  
New Method ◽  
Satellite Orbits ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Convection Pattern ◽  
Polar Cap ◽  
Minimum Number ◽  
Convection Patterns ◽  
Modelling And Forecasting

Abstract. A new method to reconstruct the instantaneous convection pattern in the Earth's polar ionosphere is suggested. Plasma convection in the polar cap ionosphere is described as a hydrodynamic incompressible flow. This description is valid in the region where the electric currents are field aligned (and hence, the Lorentz body force vanishes). The problem becomes two-dimensional, and may be described by means of stream function. The flow pattern may be found as a solution of the boundary value problem for stream function. Boundary conditions should be provided by measurements of the electric field or plasma velocity vectors along the satellite orbits. It is shown that the convection pattern may be reconstructed with a reasonable accuracy by means of this method, by using only the minimum number of satellite crossings of the polar cap. The method enables us to obtain a reasonable estimate of the convection pattern without knowledge of the ionospheric conductivity.Key words. Ionosphere (modelling and forecasting; plasma convection; polar ionosphere)

scholarly journals A multi-instrument approach to mapping the global dayside merging rate

2002 ◽  
Vol 20 (12) ◽  
pp. 1905-1920
Author(s):  
G. Provan ◽  
T. K. Yeoman ◽  
M. Lester ◽  
S. E. Milan
Keyword(s):  
Electric Fields ◽  
Plasma Flow ◽  
Ionospheric Plasma ◽  
Line Length ◽  
Convection Pattern ◽  
Polar Cap ◽  
Plasma Drift ◽  
Methods Of Calculation ◽  
Wind Measurements ◽  
First Time

Abstract. For the first time three different methods have been used to calculate the global merging rate during the same substorm growth phase. The ionospheric plasma drift was monitored by six of the Northern Hemisphere SuperDARN radars, allowing the convection pattern to be studied over 12 h of magnetic local time. The radars observed reconnection signatures on the dayside simultaneously with substorm signatures on the nightside. The three methods to calculate the global merging rate are: (i) the equatorward expansion of radar backscatter on the nightside, which provides an estimate of the rate of polar cap expansion, while upstream WIND measurements gave an estimate of the reconnection electric fields; (ii) the derivation of the dayside boundary normal plasma flow velocity and an estimate of the extent of the ionospheric merging gap, from radar observation of dayside reconnection; (iii) utilizing the map-potential technique to map the high-latitude plasma flow and cross polar cap potential (Ruohoniemi and Baker, 1998), allowing the global dayside merging rate to be calculated. The three methods support an extensive magnetopause X-line length of between 30 ± 12RE and 35 ± 15 RE (assuming a single X-line and constant merging rate). Such close agreement between the different methods of calculation are unexpected, especially as the length of the magnetopause X-line is not well known.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere – ionosphere interactions; solar-wind magnetosphere interactions)

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)

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