Simultaneous two hemisphere observations of the presence of polar patches in the nightside ionosphere

1994 ◽  
Vol 12 (7) ◽  
pp. 642-648 ◽  
Author(s):  
A. S. Rodger ◽  
M. Pinnock ◽  
J. R. Dudeney ◽  
J. Waterman ◽  
O. de la Beaujardiere ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Formation Process ◽  
Auroral Oval ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Dayside Magnetopause ◽  
Incoherent Scatter Radars ◽  
High Latitude Ionosphere ◽  
Magnetic Meridian

Abstract. The presence of polar patches as observed simultaneously in the same magnetic meridian of opposite nightside ionospheres by coherent and incoherent scatter radars are described. The patches appear to be related to variations either in the Bz or By component of the interplanetary magnetic field which cause transient merging on the dayside magnetopause. The passage and characteristics of polar patches as they traverse the polar cap into the nightside auroral oval are not significantly affected by the occurrence of small substroms. This study illustrates how the observations of polar patches in the nightside high-latitude ionosphere could be of great value in determining their formation process.

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 Aspect sensitive E- and F-region SPEAR-enhanced incoherent backscatter observed by the EISCAT Svalbard radar

2009 ◽  
Vol 27 (1) ◽  
pp. 65-81 ◽  
Author(s):  
R. S. Dhillon ◽  
T. R. Robinson ◽  
T. K. Yeoman
Keyword(s):  
High Latitude ◽  
Polar Cap ◽  
Electrostatic Waves ◽  
Incoherent Scatter ◽  
F Region ◽  
High Latitude Ionosphere ◽  
Plasma Line ◽  
Sporadic E Layer ◽  
Sporadic E ◽  
Field Aligned Irregularities

Abstract. Previous studies of the aspect sensitivity of heater-enhanced incoherent radar backscatter in the high-latitude ionosphere have demonstrated the directional dependence of incoherent scatter signatures corresponding to artificially excited electrostatic waves, together with consistent field-aligned signatures that may be related to the presence of artificial field-aligned irregularities. These earlier high-latitude results have provided motivation for repeating the investigation in the different geophysical conditions that obtain in the polar cap ionosphere. The Space Plasma Exploration by Active Radar (SPEAR) facility is located within the polar cap and has provided observations of RF-enhanced ion and plasma line spectra recorded by the EISCAT Svalbard UHF incoherent scatter radar system (ESR), which is collocated with SPEAR. In this paper, we present observations of aspect sensitive E- and F-region SPEAR-induced ion and plasma line enhancements that indicate excitation of both the purely growing mode and the parametric decay instability, together with sporadic E-layer results that may indicate the presence of cavitons. We note consistent enhancements from field-aligned, vertical and also from 5° south of field-aligned. We attribute the prevalence of vertical scatter to the importance of the Spitze region, and of that from field-aligned to possible wave/irregularity coupling.

scholarly journals Interplanetary magnetic field control of Saturn's polar cusp aurora

2005 ◽  
Vol 23 (4) ◽  
pp. 1405-1431 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
S. E. Milan
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
High Latitude ◽  
Closed Field ◽  
Vortical Flows ◽  
Dayside Magnetopause ◽  
Closed Field Line ◽  
Lobe Reconnection

Abstract. Dayside UV emissions in Saturn's polar ionosphere have been suggested to be the first observational evidence of the kronian "cusp" (Gérard et al., 2004). The emission has two distinct states. The first is a bright arc-like feature located in the pre-noon sector, and the second is a more diffuse "spot" of aurora which lies poleward of the general location of the main auroral oval, which may be related to different upstream interplanetary magnetic field (IMF) orientations. Here we take up the suggestion that these emissions correspond to the cusp. However, direct precipitation of electrons in the cusp regions is not capable of producing significant UV aurora. We have therefore investigated the possibility that the observed UV emissions are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, akin to flux transfer events seen at the Earth. We devise a conceptual model of pulsed reconnection at the low-latitude dayside magnetopause for the case of northwards IMF which will give rise to pulsed twin-vortical flows in the magnetosphere and ionosphere in the vicinity of the open-closed field-line boundary, and hence to bi-polar field-aligned currents centred in the vortical flows. During intervals of high-latitude lobe reconnection for southward IMF, we also expect to have pulsed twin-vortical flows and corresponding bi-polar field-aligned currents. The vortical flows in this case, however, are displaced poleward of the open-closed field line boundary, and are reversed in sense, such that the field-aligned currents are also reversed. For both cases of northward and southward IMF we have also for the first time included the effects associated with the IMF By effect. We also include the modulation introduced by the structured nature of the solar wind and IMF at Saturn's orbit by developing "slow" and "fast" flow models corresponding to intermediate and high strength IMF respectively. We then consider the conditions under which the plasma populations appropriate to either sub-solar reconnection or high-latitude lobe reconnection can carry the currents indicated. We have estimated the field-aligned voltages required, the resulting precipitating particle energy fluxes, and the consequent auroral output. Overall our model of pulsed reconnection under conditions of northwards and southwards IMF, and for varying orientations of IMF By, is found to produce a range of UV emission intensities and geometries which is in good agreement with the data presented by Gérard et al. (2004). The recent HST-Cassini solar wind campaign provides a unique opportunity to test the theoretical ideas presented here.

scholarly journals A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

2002 ◽  
Vol 20 (11) ◽  
pp. 1769-1781 ◽  
Author(s):  
J.-P. Villain ◽  
R. André ◽  
M. Pinnock ◽  
R. A. Greenwald ◽  
C. Hanuise
Keyword(s):  
High Latitude ◽  
Statistical Study ◽  
Spectral Width ◽  
Auroral Oval ◽  
F Region ◽  
Radar Network ◽  
Period 2 ◽  
Time Period ◽  
High Latitude Ionosphere ◽  
Data Points

Abstract. The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; ionospheric irregularities)

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.

Break up of a polar cap patch in the nightside ionosphere due to a flow channel event

2020 ◽  
Author(s):  
Elizabeth Donegan-Lawley ◽  
Alan Wood ◽  
Gareth Dorrian ◽  
Alexandra Fogg ◽  
Timothy Yeoman ◽  
...  
Keyword(s):  
Electron Density ◽  
Global Navigation Satellite System ◽  
Satellite System ◽  
Flow Channel ◽  
Navigation Satellite ◽  
Polar Cap ◽  
Incoherent Scatter ◽  
Radar Network ◽  
Incoherent Scatter Radars ◽  
Global Navigation Satellite

<p>Flow channel events have previously been observed breaking up polar cap patches on the dayside ionosphere but, to the best of our knowledge, have not been observed on the nightside. We report observations of a flow channel event in the evening of the 9th January 2019 under quiet geomagnetic conditions. This multi-instrument study was undertaken using a combination of multiple EISCAT (European Incoherent Scatter) radars, SuperDARN (Super Dual Auroral Radar Network), MSP (Meridian Scanning Photometer) and GNSS (Global Navigation Satellite System) scintillation data. These data were used to build a picture of the evening’s observations from 1800 to 2359 UT. The flow channel event lasted a total of 13 minutes and was responsible for segmenting a polar cap patch. A decrease in electron density was observed, from a patch value of 1.4x10<sup>11</sup> m<sup>3</sup> to a minimum value of 5x10<sup>10</sup> m<sup>3</sup>. In addition, ion velocities in excess of 1000 ms<sup>-1</sup> and ion temperatures of greater than 2000 K were also observed. </p>

scholarly journals GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector

2015 ◽  
Vol 33 (6) ◽  
pp. 637-656 ◽  
Author(s):  
P. Prikryl ◽  
R. Ghoddousi-Fard ◽  
E. G. Thomas ◽  
J. M. Ruohoniemi ◽  
S. G. Shepherd ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geomagnetic Storms ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Solar Wind Dynamic Pressure ◽  
Polar Cap ◽  
The North ◽  
Auroral Emission ◽  
Ground Magnetic

Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.

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