Antarctic Space Science - Publications

2001

ULF wave damping in the auroral acceleration region

Authors: Fedorov, E.; Pilipenko, V.; Engebretson, M. J.

Journal: Journal of Geophysical Research, Volume 106, Issue A4, p. 6203-6212

Date: Apr 2001

Abstract: The width of a resonant peak in the spatial distribution of the ULF Pc5 pulsation amplitude at high latitudes is controlled by the dominant dissipation mechanism of Alfven waves in the ionosphere-magnetosphere system. Among possible mechanisms, mostly Joule dissipation and dispersive effects are considered to terminate the growth and narrowing of a resonant peak pumped by an external source. We estimate the width of the resonance which may be provided by the field-aligned electric field in a thermal, mirror-confined collisionless plasma. We consider a simple case, in which a potential drop is confined within a narrow region above the ionosphere, called the auroral acceleration region. Theoretical estimates show that the mirror-force mechanism can dominate over the ionospheric dissipation and dispersive effects in auroral regions with a sufficiently large field-aligned potential drop. Therefore ground-based monitoring of the resonance width (e.g., with the gradient method) may be used as an indicator of the occurrence of large-scale parallel electric fields in the outer magnetosphere.

Simultaneous satellite and ground observations of transient events near the morningside magnetopause

Authors: Kim, K.-H.; Lin, N.; Cattell, C. A.; Song, Y.; Lee, D.-H.; Engebretson, M. J.; Kawano, H.; Kokubun, S.; Mukai, T.; Tsuruda, K.

Journal: Journal of Geophysical Research, Volume 106, Issue A4, p. 5743-5760

Date: Apr 2001

Abstract: We present observations of transient events on April 13, 1996, using simultaneous measurements in the solar wind, near the magnetopause, at geosynchronous orbit, and on the ground at high latitudes. On this day, Geotail passed outbound through the morningside magnetopause. When Geotail was in the magnetosphere, a clear bipolar perturbation in the magnetic field component normal to the nominal magnetopause and transient outbound (from the magnetosphere to the magnetosheath)/inbound (from the magnetosheath to the magnetosphere) magnetopause crossings were observed. When Geotail was in the magnetosheath, inbound/outbound crossings were observed. During the bipolar magnetic field signature, Geotail observed asymmetric bipolar (less inward/more outward) flow normal to the nominal magnetopause accompanied by sunward flow. Inward flow was observed when the total magnetic field of the event was enhanced, whereas outward flow was observed when the total magnetic field was depressed. We observed that some of the transient outbound/inbound crossings show significantly different signatures in the plasma flow and magnetic field, that is, weak inward flow and enhanced magnetic field before the outbound crossing and strong outward flow and decreased magnetic field after the inbound crossing. The field and flow variations during the transient outbound/inbound crossings are qualitatively similar to those during the bipolar magnetic field signature. These observations suggest that the bipolar field signature and the transient magnetopause crossings would be similar phenomena on the magnetopause. We discuss whether the observed field and flow variations during the transient events are caused by inward/outward magnetopause motion due to compression/expansion of the magnetosphere by comparing the data sets obtained from different regions of the solar wind-magnetosphere system.

Coordinated ground-based, low altitude satellite and Cluster observations on global and local scales during a transient post-noon sector excursion of the magnetospheric cusp

Authors: Opgenoorth, H. J.; Lockwood, M.; Alcaydé, D.; Donovan, E.; Engebretson, M. J.; van Eyken, A. P.; Kauristie, K.; Lester, M.; Moen, J.; Waterman, J.; Alleyne, H.; André, M.; Dunlop, M. W.; Cornilleau-Wehrlin, N.; Masson, A.; Fazerkerley, A.; Rème, H.; André, R.; Amm, O.; Balogh, A.; Behlke, R.; Blelly, P. L.; Boholm, H.; Borälv, E.; Bosqued, J. M.; Buchert, S.; Candidi, M.; Cerisier, J. C.; Cully, C.; Denig, W. F.; Eglitis, P.; Greenwald, R. A.; Jackal, B.; Kelly, J. D.; Krauklis, I.; Lu, G.; Mann, I. R.; Marcucci, M. F.; McCrea, I. W.; Maksimovic, M.; Massetti, S.; Décréau, P. M. E.; Milling, D. K.; Orsini, S.; Pitout, F.; Provan, G.; Ruohoniemi, J. M.; Samson, J. C.; Schott, J. J.; Sedgemore-Schulthess, F.; Stamper, R.; Stauning, P.; Strømme, A.; Taylor, M.; Vaivads, A.; Villain, J. P.; Voronkov, I.; Wild, J. A.; Wild, M.

Journal: Annales Geophysicae, vol. 19, Issue 10, pp.1367-1398

Date: Oct 2001

Abstract: On 14 January 2001, the four Cluster spacecraft passed through the northern magnetospheric mantle in close conjunction to the EISCAT Svalbard Radar (ESR) and approached the post-noon dayside magnetopause over Green-land between 13:00 and 14:00 UT. During that interval, a sudden reorganisation of the high-latitude dayside convection pattern occurred after 13:20 UT, most likely caused by a direction change of the Solar wind magnetic field. The result was an eastward and poleward directed flow-channel, as monitored by the SuperDARN radar network and also by arrays of ground-based magnetometers in Canada, Greenland and Scandinavia. After an initial eastward and later poleward expansion of the flow-channel between 13:20 and 13:40 UT, the four Cluster spacecraft, and the field line footprints covered by the eastward looking scan cycle of the Söndre Strömfjord incoherent scatter radar were engulfed by cusp-like precipitation with transient magnetic and electric field signatures. In addition, the EISCAT Svalbard Radar detected strong transient effects of the convection reorganisation, a poleward moving precipitation, and a fast ion flow-channel in association with the auroral structures that suddenly formed to the west and north of the radar. From a detailed analysis of the coordinated Cluster and ground-based data, it was found that this extraordinary transient convection pattern, indeed, had moved the cusp precipitation from its former pre-noon position into the late post-noon sector, allowing for the first and quite unexpected encounter of the cusp by the Cluster spacecraft. Our findings illustrate the large amplitude of cusp dynamics even in response to moderate solar wind forcing. The global ground-based data proves to be an invaluable tool to monitor the dynamics and width of the affected magnetospheric regions.

Coordinated Cluster, ground-based instrumentation and low-altitude satellite observations of transient poleward-moving events in the ionosphere and in the tail lobe

Authors: Lockwood, M.; Opgenoorth, H.; van Eyken, A. P.; Fazakerley, A.; Bosqued, J.-M.; Denig, W.; Wild, J. A.; Cully, C.; Greenwald, R.; Lu, G.; Amm, O.; Frey, H.; Strømme, A.; Prikryl, P.; Hapgood, M. A.; Wild, M. N.; Stamper, R.; Taylor, M.; McCrea, I.; Kauristie, K.; Pulkkinen, T.; Pitout, F.; Balogh, A.; Dunlop, M.; Rème, H.; Behlke, R.; Hansen, T.; Provan, G.; Eglitis, P.; Morley, S. K.; Alcaydé, D.; Blelly, P.-L.; Moen, J.; Donovan, E.; Engebretson, M.; Lester, M.; Watermann, J.; Marcucci, M. F.

Journal: Annales Geophysicae, vol. 19, Issue 10, pp.1589-1612

Date: Oct 2001

Abstract: During the interval between 8:00-9:30 on 14 January 2001, the four Cluster spacecraft were moving from the central magnetospheric lobe, through the dusk sector mantle, on their way towards intersecting the magnetopause near 15:00 MLT and 15:00 UT. Throughout this interval, the EISCAT Svalbard Radar (ESR) at Longyearbyen observed a series of poleward-moving transient events of enhanced F-region plasma concentration ( polar cap patches ), with a repetition period of the order of 10 min. Allowing for the estimated solar wind propagation delay of 75 ( +/- 5) min, the interplanetary magnetic field (IMF) had a southward component during most of the interval. The magnetic footprint of the Cluster spacecraft, mapped to the ionosphere using the Tsyganenko T96 model (with input conditions prevailing during this event), was to the east of the ESR beams. Around 09:05 UT, the DMSP-F12 satellite flew over the ESR and showed a sawtooth cusp ion dispersion signature that also extended into the electrons on the equatorward edge of the cusp, revealing a pulsed magnetopause reconnection. The consequent enhanced ionospheric flow events were imaged by the SuperDARN HF backscatter radars. The average convection patterns (derived using the AMIE technique on data from the magnetometers, the EISCAT and SuperDARN radars, and the DMSP satellites) show that the associated poleward-moving events also convected over the predicted footprint of the Cluster spacecraft. Cluster observed enhancements in the fluxes of both electrons and ions. These events were found to be essentially identical at all four spacecraft, indicating that they had a much larger spatial scale than the satellite separation of the order of 600 km. Some of the events show a correspondence between the lowest energy magnetosheath electrons detected by the PEACE instrument on Cluster (10-20 eV) and the topside ionospheric enhancements seen by the ESR (at 400-700 km). We suggest that a potential barrier at the magnetopause, which prevents the lowest energy electrons from entering the magnetosphere, is reduced when and where the boundary-normal magnetic field is enhanced and that the observed polar cap patches are produced by the consequent enhanced precipitation of the lowest energy electrons, making them and the low energy electron precipitation fossil remnants of the magnetopause reconnection rate pulses.

Modeling ionospheric absorption modified by anomalous heating during substorms

Authors: Milikh, G. M.; Dimant, Y. S.; Shao, X.; Guzdar, P. N.; Sharma, A. S.; Papadopoulos, K.; Burns, E. M.; Goodrich, C. C.; Rosenberg, T. J.; Weatherwax, A. T.; Wiltberger, M. J.; Lyon, J. G.; Fedder, J. A.

Journal: Geophysical Research Letters, Volume 28, Issue 3, p. 487-490

Date: Feb 2001

Abstract: Riometers monitor the changes in ionospheric conductivity by measuring the absorption of very high frequency radio noise of galactic origin passing through the ionosphere. In this Letter the absorption of radio signals by a thin layer of ionospheric plasma, produced by ionization due to energetic precipitating electrons, is modeled by taking into account strong turbulent heating caused by instabilities. The precipitating electron population is obtained from a global MHD simulation of the magnetosphere, along with the electric fields which excite the Farley-Buneman instability and lead to turbulent electron heating. A comparison, the first of its kind, of the data from polar and sub-auroral riometers for the magnetic cloud event of January 10, 1997 shows good agreement. The ionospheric conductance modified by turbulent electron heating can be used to improve the magnetosphere-ionosphere coupling in the current global MHD models.

Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Authors: Lockwood, M.; Fazakerley, A.; Opgenoorth, H.; Moen, J.; van Eyken, A. P.; Dunlop, M.; Bosqued, J.-M.; Lu, G.; Cully, C.; Eglitis, P.; McCrea, I. W.; Hapgood, M. A.; Wild, M. N.; Stamper, R.; Denig, W.; Taylor, M.; Wild, J. A.; Provan, G.; Amm, O.; Kauristie, K.; Pulkkinen, T.; Strømme, A.; Prikryl, P.; Pitout, F.; Balogh, A.; Rème, H.; Behlke, R.; Hansen, T.; Greenwald, R.; Frey, H.; Morley, S. K.; Alcaydé, D.; Blelly, P.-L.; Donovan, E.; Engebretson, M.; Lester, M.; Watermann, J.; Marcucci, M. F.

Journal: Annales Geophysicae, vol. 19, Issue 10, pp.1613-1640

Date: Oct 2001

Abstract: We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ( [ XGSM, YGSM, ZGSM ] <approx> [ 2, 7, 9 ] RE). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is welldefined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10-15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 RE in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.

Correlation of solar energetic protons and polar cap absorption

Authors: Patterson, J. D.; Armstrong, T. P.; Laird, C. M.; Detrick, D. L.; Weatherwax, A. T.

Journal: Journal of Geophysical Research, Volume 106, Issue A1, p. 149-164

Date: Jan 2001

Abstract: This study shows the results of a model of polar cap absorption events (PCAs) using solar energetic proton flux as an input. The proton data are recorded by the Charged Particle Measurement Experiment (CPME) on board the IMP 8 satellite and are collected by the Applied Physics Laboratory at Johns Hopkins University. The IMP 8 satellite orbits the Earth at distances between 30 and 35 Earth radii, which places it in the solar energetic particle environment throughout most of its orbit. It has been shown in previous studies that these solar energetic particles have direct and immediate access to the polar atmosphere [Reid, 1970]. Our model shows that the majority of the ionization resulting from the influx of solar energetic protons occurs in the altitude range from ~50-90 km. Excess ionization at these altitudes causes enhanced absorption of cosmic HF radio waves. The levels of absorption used for comparison in this study were measured directly by the riometer at South Pole station, Antarctica. The results show a very strong correlation between the incident proton flux and measured path-integrated cosmic HF radio noise absorption for significant events, involving absorptions greater than 1.0 dB. For absorption levels lower than this it is obvious that other phenomena dominate. For HF radio waves the primary contributors to PCA are protons with energies near 20 MeV. This study extends the correlated observations of interplanetary particles and PCA throughout a 9-year period. The close quantitative agreement between the measured and calculated values of absorption supports the validity of the assumptions and suppositions made by this model. The data also suggest a method by which the path-integrated cosmic noise absorption may be used to probe the E and D layers of the ionosphere to determine the effective ion-electron recombination coefficients within these regions.

Magnetic impulse event: A detailed case study of extended ground and space observations

Authors: Kataoka, R.; Fukunishi, H.; Lanzerotti, L. J.; Maclennan, C. G.; Frey, H. U.; Mende, S. B.; Doolittle, J. H.; Rosenberg, T. J.; Weatherwax, A. T.

Journal: Journal of Geophysical Research, Volume 106, Issue A11, p. 25873-25890

Date: Nov 2001

Abstract: Analysis of conjugate data from extended magnetometer networks in northern and southern high latitudes is used to elucidate the initiation and the evolution of a magnetic impulse event (MIE) on June 6, 1997. In addition, data from all-sky imagers, imaging riometers, and Super Dual Auroral Radar Network radars in Antarctica are investigated to confirm the energy content, motion, and electrical current structure of the MIE. The MIE was accompanied by traveling convection vortices (TCVs) that began at ~10 MLT and moved eastward (toward dusk) and slightly equatorward at 1-3 km/s across the noon meridian with north-south conjugacy. The MIE had upward field-aligned currents with soft electron precipitation that was located near the trailing edge of the Hall current loop. During the MIE interval the interplanetary magnetic field (IMF) was directed strongly outward from the Sun (Bx=-5nT), with a slightly positive (1-2 nT) Bz, and a nearly zero By. Since abrupt solar wind pressure changes are unlikely under this IMF orientation (and none was, in fact, observed), classical mechanisms for MIE generation, such as a pressure pulse or dayside reconnection, are excluded. It is speculated that an abrupt IMF cone angle change from 60° to 20°, ~30 min prior to the MIE onset, may have been an indirect trigger of this event via the interaction between the solar wind and the bow shock.

Determining the mass density along magnetic field lines from toroidal eigenfrequencies: Polynomial expansion applied to CRRES data

Authors: Denton, R. E.; Lessard, M. R.; Anderson, R.; Miftakhova, E. G.; Hughes, J. W.

Journal: Journal of Geophysical Research, Volume 106, Issue A12, p. 29915-29924

Date: Dec 2001

Abstract: Because the harmonics of toroidal Alfvén wave eigenmodes have a different response to mass density at different points along a magnetic field line, the frequencies of these harmonics can, in principal, be used to infer the distribution of mass density along the field line. Here we present several improvements to the methodology and test our method using magnetic and plasma wave data from the CRRES spacecraft. Our method includes the calculation of toroidal frequencies in a Tsyganenko magnetic field assuming a polynomial expansion for the logarithm of the mass density with respect to a coordinate related to distance along the field line. We use a Monte Carlo distribution of frequencies about the observed peaks in order to infer an uncertainty for the mass density. The method only works well if the frequencies of the fundamental and second harmonic are known. We compare the inferred mass density at the spacecraft location with the electron density determined from the plasma wave experiment onboard CRRES. The observed electron density is about a factor of 2 lower than the mean of the inferred mass density for an ensemble of frequency combinations based on the uncertainties of the measured spectral peaks but is close to or within the error bars of the inferred mass density. In one of the cases examined, the inferred mass density had a local maximum at the equator, while in the other case the inferred mass density increased monotonically away from the equator.

Interplanetary magnetic field: Statistical properties and discrete modes

Authors: Thomson, D. J.; Lanzerotti, L. J.; Maclennan, C. G.

Journal: Journal of Geophysical Research, Volume 106, Issue A8, p. 15941-15962

Date: Aug 2001

Abstract: We report here detailed statistical studies of power spectra of 1 hour average interplanetary magnetic field (IMF) data that were acquired by the magnetometer instrument on the Ulysses spacecraft in the ecliptic plane of the heliosphere during Ulysses' cruise phase from Earth to Jupiter (October 1990 through January 1992). We have pursued these studies in order to examine in a critical manner our previously published conclusions [Thomson et al., 1995] that energetic particle fluxes in the interplanetary medium carried signatures of discrete modes. We attributed these signatures to the existence of solar acoustic and gravitational modes (p and g modes, respectively) in the heliosphere. Here we first examine the statistical distributions of g modes (less than ~200 μHz) that are predicted by a theoretical model of the solar interior. With this background information we formulate the time series and statistical analysis procedures that must be used in order to provide information on possible modal signals in the IMF, independent of the source. We show from the statistical analyses that the modal components that are present in the IMF fluctuations can amount to ~20% to ~70% of the IMF fluctuation power in the frequency range of ~10-140 μHz. We discuss these findings in the context of previously published work on searches for optical signatures of solar g modes in the solar photosphere as well as published research papers that have called into question some of the conclusions of Thomson et al. [1995]. We conclude that the interplanetary medium is not a totally chaotic medium, but can sustain high power levels of discrete, low-frequency modes, probably of solar origin, over a long interval of time.

Correlation studies of compressional Pc5 pulsations in space and Ps6 pulsations on the ground

Authors: Vaivads, A.; Baumjohann, W.; Georgescu, E.; Haerendel, G.; Nakamura, R.; Lessard, M. R.; Eglitis, P.; Kistler, L. M.; Ergun, R. E.

Journal: Journal of Geophysical Research, Volume 106, Issue A12, p. 29797-29806

Date: Dec 2001

Abstract: Compressional Pc5 pulsations in space and Ps6 pulsations on the ground are common features observed in the morning sector. Here we use a conjunction study of Equator-S, Geotail, and ground stations in Canada to show that Ps6 pulsations can be the ground counterpart of compressional Pc5 pulsations observed by satellites. Because strong Ps6 pulsations are associated with optical omega-band signatures, we also suggest that the omega-band counterparts in space might be compressional pulsations on the Pc5 scale. We also discuss the magnetic field configuration that makes all these observations consistent.

Compressional Pc5 type pulsations in the morningside plasma sheet

Authors: Vaivads, A.; Baumjohann, W.; Haerendel, G.; Nakamura, R.; Kucharek, H.; Klecker, B.; Lessard, M. R.;  

Journal: Annales Geophysicae, vol. 19, Issue 3, pp.311-320

Date: Mar 2001

Abstract: We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000 1700 UT on 9 March 1998, and 0200 0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode), and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.

Ionospheric reflection of small-scale Alfvén waves

Authors: Lessard, M. R.; Knudsen, D. J.

Journal: Geophysical Research Letters, Volume 28, Issue 18, p. 3573-3576

Date: Sep 2001

Abstract: The transfer of energy from the magnetosphere to the ionosphere occurs through complex mechanisms that often involve shear Alfvén waves, implying that the interaction of these waves with the ionosphere is fundamental to our understanding of the coupling process. Indeed, a variety of problems that involve magnetosphere-ionosphere coupling assume that the ionosphere acts as a perfectly reflecting boundary, although we know that this is not the case in general. In this work, we calculate the reflection coefficient of shear Alfvén waves incident on the ionosphere under three different ionospheric profiles. Our results indicate that 1) under all profiles considered, reflection of shear Alfvén waves with perpendicular lengths of ~1 km or less is negligible and 2) under a profile that might be typical of a nightside ionosphere, reflection of shear Alfvén waves is significant only for waves with frequencies below ~0.4 Hz and λx above ~2 km; reflection of waves with λx less than ~2 km is poor.