A study of inverted‐V auroral acceleration mechanisms using Polar/Fast Auroral Snapshot conjunctions

Janhunen, P.; Olsson, Annika; Peterson, W. K.; Laakso, H.; Pickett, J. S.; Pulkkinen, Tuija; Russell, C. T.

doi:10.1029/2001ja900012

Cited by 14 publications

(13 citation statements)

References 21 publications

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“…Also in this region, no particle data are available from Cluster, but the small-scale arcs and adjacent cavities are well known to be associated with downward and upward flowing electrons, respectively (e.g. Marklund et al, 1997;Karlsson and Marklund, 1998;McFadden et al, 1999;Janhunen et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations

et al. 2003

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Abstract. We analyse a conjunction event of the Cluster II spacecraft with the MIRACLE ground-based instrument network in northern Fennoscandia on 6 February 2001, between 23:00 and 00:00 UT. Shortly after the spacecraft were located at perigee, the Cluster II satellites' magnetic footpoints move northwards over Scandinavia and Svalbard, almost perfectly aligned with the central chain of the IMAGE magnetometer network, and cross a morning sector ionospheric shear zone during this passage. In this study we focus on the mesoscale structure of the ionosphere. Ionospheric conductances, true horizontal currents, and field-aligned currents (FAC) are calculated from the ground-based measurements of the IMAGE magnetometers and the STARE coherent scatter radar, using the 1-D method of characteristics. An excellent agreement between these results and the FAC observed by Cluster II is reached after averaging the Cluster measurements to mesoscales, as well as between the location of the convection reversal boundary (CRB), as observed by STARE and by the Cluster II EFW instrument. A sheet of downward FAC is observed in the vicinity of the CRB, which is mainly caused by the positive divergence of the electric field there. This FAC sheet is detached by 0.5 • -2 • of latitude from a more equatorward downward FAC sheet at the poleward flank of the westward electrojet. This latter FAC sheet, as well as the upward FAC at the equatorward flank of the jet, are mainly caused by meridional gradients in the ionospheric conductances, which reach up to 25 S in the electrojet region, but only ∼5 S poleward of it, with a minimum at the CRB. Parti-cle measurements show that the major part of the downward FAC is carried by upward flowing electrons, and only a small part by downward flowing ions. The open-closed field line boundary is found to be located 3 • -4 • poleward of the CRB, implying significant errors if the latter is used as a proxy of the former.

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Section: Discussionmentioning

confidence: 99%

Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations

et al. 2003

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“…If the waves are producing the anisotropies, then there should exist a correlation between them, as is recently found in an event study by Janhunen et al (2001).…”

Section: Summary and Discussionmentioning

confidence: 88%

“…One way to produce ion shell distributions is by time of flight effects of ions injected from the reconnection X line. (2) Middle-energy electrons (the present paper) are energised by the waves in the parallel direction with a Landau resonance mechanism (Janhunen et al, 2001(Janhunen et al, , 2003a. (3) The parallel energisation of electrons leads to charge separation effects and auroral potential structure formation taking place below ∼ 4 R E radial distance (Janhunen et al, 1999;Janhunen and Olsson, 2002a).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Thus, one could think that giving the temperature ratio T /T ⊥ , perhaps multiplied by the electron density, would be a good way of quantifying the magnitude of the anisotropy. However, in practice, this approach has a severe difficulty: it will turn out that almost always the electron plasma cannot be modelled by a single Maxwellian or kappa distribution, but one needs at least two such distributions (examples are given by Janhunen et al, 2001). The anisotropy usually exists in only one of these distributions.…”

Section: Data Processingmentioning

confidence: 99%

“…Another viewpoint is that wave-particle interactions might also produce electron anisotropies directly (Janhunen et al, 2001(Janhunen et al, , 2003a. In this case the waves are the cause of the anisotropies, and the anisotropies might, in turn, be related to other auroral processes, such as potential structure formation.…”

Section: Introductionmentioning

confidence: 99%

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Middle-energy electron anisotropies in the auroral region

et al. 2004

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Abstract. Field-aligned anisotropic electron distribution functions of T > T ⊥ type are observed on auroral field lines at both low and high altitudes. We show that typically the anisotropy is limited to a certain range of energies, often below 1 keV, although sometimes extending to slightly higher energies as well. Almost always there is simultaneously an isotropic electron distribution at higher energies. Often the anisotropies are up/down symmetrical, although cases with net upward or downward electron flow also occur. For a statistical analysis of the anisotropies we divide the energy range into low (below 100 eV), middle (100 eV-1 keV) and high (above 1 keV) energies and develop a measure of anisotropy expressed in density units. The statistical magnetic local time and invariant latitude distribution of the middleenergy anisotropies obeys that of the average auroral oval, whereas the distributions of the low and high energy anisotropies are more irregular. This suggests that it is specifically the middle-energy anisotropies that have something to do with auroral processes. The anisotropy magnitude decreases monotonically with altitude, as one would expect, because electrons have high mobility along the magnetic field and thus, the anisotropy properties spread rapidly to different altitudes.

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Multiprobe estimation of field line curvature radius in the equatorial magnetosphere and the use of proton precipitations in magnetosphere‐ionosphere mapping

et al. 2013

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[1] Nonadiabatic, chaotic motion of ions under a curved geomagnetic field geometry is well recognized as a key mechanism that leads to the pitch angle scattering of protons in the equatorial magnetosphere. The efficiency of such proton pitch angle scattering process is energy dependent and controlled by the radius of curvature of the magnetic field line (RCMFL). The protons scattered into the loss cone will precipitate into the ionosphere and excite proton auroras there. In this study, we propose techniques to calculate the RCMFL based upon multiprobe measurements under different probe geometries. We also demonstrate how to use the obtained RCMFL to evaluate the proton precipitation fluxes, and further use the proton precipitation features to help estimate the magnetosphereionosphere mapping. Our procedures are summarized as follows: (1) We calculate the RCMFL using Time History of Events and Macroscale Interactions during Substorms (THEMIS) multiprobe measurements. (2) With the obtained RCMFL, we evaluate the scattering efficiency and in turn the loss cone fluxes of the magnetospheric protons at different energy levels. (3) The above evaluation of the in situ loss cone fluxes is compared to the ionospheric measurements of proton precipitation fluxes in various energy ranges and/ or the optical proton auroras to estimate the possible footprint of THEMIS probes in the ionosphere.Citation: Liang, J., E. Donovan, E. Spanswick, and V. Angelopoulos (2013), Multiprobe estimation of field line curvature radius in the equatorial magnetosphere and the use of proton precipitations in magnetosphere-ionosphere mapping,

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A study of inverted‐V auroral acceleration mechanisms using Polar/Fast Auroral Snapshot conjunctions

Abstract: Abstract.We present observations of electrons and ions that have been affected by an auroral plasma acceleration mechanism. In the nine events studied, nearly simultaneous and magnetically conjugate measurements were made by instruments on the Fast Auroral Snapshot (

Cited by 14 publications

References 21 publications

Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations

Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations

Middle-energy electron anisotropies in the auroral region

Multiprobe estimation of field line curvature radius in the equatorial magnetosphere and the use of proton precipitations in magnetosphere‐ionosphere mapping

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