Antarctic Space Science - Publications
2009
[back]Near-Earth initiation of a terrestrial substorm
Authors: Rae, I. Jonathan; Mann, Ian R.; Angelopoulos, Vassilis; Murphy, Kyle R.; Milling, David K.; Kale, Andy; Frey, Harald U.; Rostoker, Gordon; Russell, Christopher T.; Watt, Clare E. J.; Engebretson, Mark J.; Moldwin, Mark B.; Mende, Stephen B.; Singer, Howard J.; Donovan, Eric F.
Journal: Journal of Geophysical Research, Volume 114, Issue A7, CiteID A07220
Date: Jul 2009
Abstract: Despite the characterization of the auroral substorm more than 40 years ago, controversy still surrounds the processes triggering substorm onset initiation. That stretching of the Earth's magnetotail following the addition of new nightside magnetic flux from dayside reconnection powers the substorm is well understood; the trigger for explosive energy release at substorm expansion phase onset is not. Using ground-based data sets with unprecedented combined spatial and temporal coverage, we report the discovery of new localized and contemporaneous magnetic wave and small azimuthal scale auroral signature of substorm onset. These local auroral arc undulations and magnetic field signatures rapidly evolve on second time scales for several minutes in advance of the release of the auroral surge. We also present evidence from a conjugate geosynchronous satellite of the concurrent magnetic onset in space as the onset of magnetic pulsations in the ionosphere, to within technique error. Throughout this time period, the more poleward arcs that correspond to the auroral oval which maps to the central plasma sheet remain undisturbed. There is good evidence that flows from the midtail crossing the plasma sheet can generate north-south auroral structures, yet no such auroral forms are seen in this event. Our observations present a severe challenge to the standard hypothesis that magnetic reconnection in stretched magnetotail fields triggers onset, indicating substorm expansion phase initiation occurs on field lines that are close to the Earth, as bounded by observations at geosynchronous orbit and in the conjugate ionosphere.
THEMIS observations of extreme magnetopause motion caused by a hot flow anomaly
Authors: Jacobsen, K. S.; Phan, T. D.; Eastwood, J. P.; Sibeck, D. G.; Moen, J. I.; Angelopoulos, V.; McFadden, J. P.; Engebretson, M. J.; Provan, G.; Larson, D.; Fornaçon, K.-H.
Journal: Journal of Geophysical Research, Volume 114, Issue A8, CiteID A08210
Date: Aug 2009
Abstract: On 30 October 2007, the five THEMIS spacecraft observed the cause and consequence of extreme motion of the dawn flank magnetopause, displacing the magnetopause outward by at least 4.8 R E in 59 s, with flow speeds in the direction normal to the model magnetopause reaching 800 km/s. While the THEMIS A, C, D, and E observations allowed the determination of the velocity, size, and shape of a large bulge moving tailward along the magnetopause at a speed of 355 km/s, THEMIS B observed the signatures of a hot flow anomaly (HFA) upstream of the bow shock at the same time, indicating that the pressure perturbation generated by the HFA may be the source of the fast compression and expansion of the magnetosphere. The transient deformation of the magnetopause generated field-aligned currents and created traveling convection vortices which were detected by ground magnetometers. This event demonstrates that kinetic (non-MHD) effects at the bow shock can have global consequences on the magnetosphere.
Searching for ULF signatures of the cusp: Observations from search coil magnetometers and auroral imagers in Svalbard
Authors: Engebretson, Mark J.; Moen, Joran; Posch, Jennifer L.; Lu, Fei; Lessard, Marc R.; Kim, Hyomin; Lorentzen, Dag A.
Journal: Journal of Geophysical Research, Volume 114, Issue A6, CiteID A06217
Date: Jun 2009
Abstract: Spacecraft traveling through the cusp at a variety of altitudes have consistently found the cusp to be filled with intense, often irregular power in the upper ULF frequency range. Some ground-based studies have observed narrowband waves in this same frequency range in the vicinity of the cusp foot point, but it has not been possible with magnetometers alone to either confirm or deny a cusp source for these waves. We report here on the first simultaneous, collocated observations of a set of induction magnetometers installed at three near-cusp sites on Svalbard and an all-sky auroral imager located at Longyearbyen. Data during northern winters of 2006-2007 and 2007-2008, when the cusp foot point was in darkness, showed occasional broadband noise when energetic particle precipitation occurred overhead, but on most days no broadband ULF power was observed above the noise level near noon when only soft cusp precipitation or poleward moving auroral forms occurred overhead. However, on 3 days, including 15 January 2007, several bursts of band-limited Pc 1-2 waves were observed in association with regions of intense soft precipitation that peaked near the poleward edge of the cusp. Their properties are consistent with an origin in the plasma mantle, as observed in a recent satellite-ground study by Engebretson et al. (2005). These observations confirm that even intense cusp precipitation is not effective in generating ion cyclotron waves that penetrate to the ground, if it is embedded within the central regions of the cusp, whereas regions of enhanced precipitation at the poleward edge of the cusp are associated with observed waves.
PENGUIn multi-instrument observations of dayside high-latitude injections during the 23 March 2007 substorm
Authors: Lessard, M. R.; Weatherwax, A. T.; Spasojevic, M.; Inan, U. S.; Gerrard, A.; Lanzerotti, L.; Ridley, A.; Engebretson, M. J.; Petit, N. J.; Clauer, R.; LaBelle, J.; Mende, S. B.; Frey, H. U.; Pilipenko, V. A.; Rosenberg, T. J.; Detrick, D.
Journal: Journal of Geophysical Research, Volume 114, Issue 1, CiteID A00C11
Date: Jan 2009
Abstract: This paper presents ground-based observations from Antarctic stations during a substorm observed on 23 March 2007. Using fluxgate magnetometer data, supported by numerical modeling, the locations of the stations are shown to straddle the open-closed magnetic field boundary. Near these locations (on closed field lines), VLF and riometer signatures are observed to show effects of energetic particle precipitation in the morning sector (extending to the postdawn region), confirmed by observations at geosynchronous orbit. In the VLF data, both the initial injection as well as echoes are observed. The mechanism responsible for such high-latitude injections is thought to be a combination of dynamics of the injection process and drift-shell splitting. Further work will address whether similar observations can be used to infer the dynamics and/or location of the injection region.
Simultaneous observations of Pc 1 micropulsation activity and stratospheric electrodynamic perturbations on 27 January 2003
Authors: Bering, E.; Engebretson, M.; Holzworth, R.; Kadokura, A.; Kokorowski, M.; Reddell, B.; Posch, J.; Yamagishi, H.
Journal: Advances in Space Research, Volume 43, Issue 5, p. 802-818.
Date: Mar 2009
Abstract: The 2nd Polar Patrol Balloon campaign (2nd-PPB) was carried out at Syowa Station in Antarctica during 2002 2003. Identical stratospheric balloon payloads were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. A very pronounced negative ion conductivity enhancement was observed at 32 km in the stratosphere below the auroral zone on 27 January 2003 from 1500 to 2200 UT. During this event, the conductivity doubled for an interval of about 7 h. This perturbation was associated with an extensive Pc 1 or Pi 1 wave event that was observed by several Antarctic ground stations, balloon PPB 10, and the Polar spacecraft. No appreciable X-ray precipitation was observed in association with this event, which would point to >60 Mev proton precipitation as a possible magnetosphere stratosphere coupling mechanism responsible for the conductivity enhancement. Such precipitation is consistent with the wave data. During the latter half of the event, Ez was briefly positive. There was a tropospheric Southern Ocean storm system underneath the balloon during this interval. If the event was associated with this storm system and not energetic proton precipitation, the observations imply an electrified Southern Ocean storm and major perturbations in stratospheric conductivity driven by a tropospheric disturbance. This event represents a poorly understood source for global circuit current. Precipitating energetic proton data from Akebono and NOAA POES spacecraft show significant >16 MeV precipitation was occurring at the location of PPB 8 but not PPB 10, suggesting that proton precipitation was, in fact, the responsible coupling mechanism.
Experimental tests of the generation mechanism of auroral medium frequency burst radio emissions
Authors: Bunch, N. L.; LaBelle, J.; Weatherwax, A. T.; Hughes, J. M.; Lummerzheim, D.
Journal: Journal of Geophysical Research, Volume 114, Issue A9, CiteID A09302
Date: Sep 2009
Abstract: Medium frequency (MF) burst is an impulsive auroral radio emission at 1.3-4.5 MHz commonly detected by ground-based instruments for a few minutes at substorm onsets. It is thought to arise from mode conversion radiation. The Dartmouth College MF radio interferometer at Toolik Field Station, Alaska (68.51° invariant latitude), measured spectra, amplitudes, and directions of arrival (DOA) of 47 MF burst events during 2006-2007 and 49 events during 2007-2008. Statistical analysis of these events shows that they come predominantly from the south and east of Toolik, as expected because propagation conditions are more favorable poleward and westward of the active auroral arcs than equatorward or eastward during premidnight (westward moving) substorm onset activity. Case studies of a selected MF burst event on 20 November 2007 show that motions of the radio emissions qualitatively track the motions of auroral arcs simultaneously observed with all-sky camera. Case studies of DOA data of selected MF burst events on 31 January and 20 November 2007 show that higher-frequency components of MF burst arrive at higher elevation angles than lower-frequency components. Statistical studies confirm this trend. Ray-tracing analysis shows that this trend implies that sources of the higher-frequency components of the MF burst are at higher altitudes than those of the lower-frequency components. The analysis also shows that the MF burst comes from the bottomside F region ionosphere. These observations are consistent with a mechanism of MF burst emission whereby the emissions originate from mode conversion of Langmuir or upper hybrid waves excited over a range of altitudes in the bottomside F region.
Observations of Earth space by self-powered stations in Antarctica
Authors: Mende, S. B.; Rachelson, W.; Sterling, R.; Frey, H. U.; Harris, S. E.; McBride, S.; Rosenberg, T. J.; Detrick, D.; Doolittle, J. L.; Engebretson, M.; Inan, U.; Labelle, J. W.; Lanzerotti, L. J.; Weatherwax, A. T.
Journal: Review of Scientific Instruments, Volume 80, Issue 12, pp. 124501-124501-19 (2009).
Date: Dec 2009
Abstract: Coupling of the solar wind to the Earth magnetosphere/ionosphere is primarily through the high latitude regions, and there are distinct advantages in making remote sensing observations of these regions with a network of ground-based observatories over other techniques. The Antarctic continent is ideally situated for such a network, especially for optical studies, because the larger offset between geographic and geomagnetic poles in the south enables optical observations at a larger range of magnetic latitudes during the winter darkness. The greatest challenge for such ground-based observations is the generation of power and heat for a sizable ground station that can accommodate an optical imaging instrument. Under the sponsorship of the National Science Foundation, we have developed suitable automatic observing platforms, the Automatic Geophysical Observatories (AGOs) for a network of six autonomous stations on the Antarctic plateau. Each station housed a suite of science instruments including a dual wavelength intensified all-sky camera that records the auroral activity, an imaging riometer, fluxgate and search-coil magnetometers, and ELF/VLF and LM/MF/HF receivers. Originally these stations were powered by propane fuelled thermoelectric generators with the fuel delivered to the site each Antarctic summer. A by-product of this power generation was a large amount of useful heat, which was applied to maintain the operating temperature of the electronics in the stations. Although a reasonable degree of reliability was achieved with these stations, the high cost of the fuel air lift and some remaining technical issues necessitated the development of a different type of power unit. In the second phase of the project we have developed a power generation system using renewable energy that can operate automatically in the Antarctic winter. The most reliable power system consists of a type of wind turbine using a simple permanent magnet rotor and a new type of power control system with variable resistor shunts to regulate the power and dissipate the excess energy and at the same time provide heat for a temperature controlled environment for the instrument electronics and data system. We deployed such systems and demonstrated a high degree of reliability in several years of operation in spite of the relative unpredictability of the Antarctic environment. Sample data are shown to demonstrate that the AGOs provide key measurements, which would be impossible without the special technology developed for this type of observing platform.
Global observations of substorm injection region evolution: 27 August 2001
Authors: Spanswick, E.; Donovan, E.; Liu, W.; Liang, J.; Blake, J. B.; Reeves, G.; Friedel, R.; Jackel, B.; Cully, C.; Weatherwax, A.
Journal: Annales Geophysicae, Volume 27, Issue 5, 2009, pp.2019-2025
Date: May 2009
Abstract: We present riometer and in situ observations of a substorm electron injection on 27 August 2001. The event is seen at more than 20 separate locations (including ground stations and 6 satellites: Cluster, Polar, Chandra, and 3 Los Alamos National Laboratory (LANL) spacecraft). The injection is observed to be dispersionless at 12 of these locations. Combining these observations with information from the GOES-8 geosynchronous satellite we argue that the injection initiated near geosynchronous orbit and expanded poleward (tailward) and equatorward (earthward) afterward. Further, the injection began several minutes after the reconnection identified in the Cluster data, thus providing concrete evidence that, in at least some events, near-Earth reconnection has little if any ionospheric signature.
Simultaneous ground-satellite optical observations of postnoon shock aurora in the Southern Hemisphere
Authors: Motoba, T.; Kadokura, A.; Ebihara, Y.; Frey, H. U.; Weatherwax, A. T.; Sato, N.
Journal: Journal of Geophysical Research, Volume 114, Issue A7, CiteID A07209
Date: Jul 2009
Abstract: On 14 June 2005, a transient postnoon shock aurora, induced by an interplanetary (IP) shock, was observed simultaneously with the FUV imager onboard the IMAGE satellite and the all-sky imager (ASI) at the South Pole Station (‑74.3° magnetic latitude (MLAT), ˜15 magnetic local time). The global evolution of the shock aurora was identified by the FUV, whereas the detailed spatial-temporal structure was identified by the ASI. Both optical emissions for the shock aurora showed a reasonable agreement in a common field of view. During the transient auroral brightenings in the dayside oval detected by the FUV, a two-step development of the shock aurora was identified by the ASI in the afternoon sector of the oval. Just after the IP shock, the ASI first observed a diffuse 557.7 nm aurora expanding duskward at the equatorward edge of the oval (‑70° to ‑73° MLAT). About 5 min later, new discrete auroral forms (arcs) were detected in the middle of the oval (‑73° to ‑76° MLAT) by both 557.7 nm and 630.0 nm ASI images. The discrete arcs developed with relatively brighter emissions, and had a lifetime of the order of 10 min, during the main impulse (MI) of geomagnetic sudden commencement. The spectrographic auroral imagers onboard the IMAGE satellite indicated that proton precipitation played an effective role in the first shock auroral emission observed with the ASI, while intense electron precipitation played an effective role in the second one. Mechanisms of the first and second postnoon shock auroras presented here are speculated to be associated with the wave-particle interaction process, and the field-aligned acceleration process in the region of the MI-related upward field-aligned currents, respectively.
Coordinated observation of the dayside magnetospheric entry and exit of the THEMIS satellites with ground-based auroral imaging in Antarctica
Authors: Mende, S. B.; Frey, H. U.; McFadden, J.; Carlson, C. W.; Angelopoulos, V.; Glassmeier, K.-H.; Sibeck, D. G.; Weatherwax, A.
Journal: Journal of Geophysical Research, Volume 114, Issue A3, CiteID A00C23
Date: Jun 2009
Abstract: Data from the five-satellite Time History of Events and Macroscale Interactions during Substorms (THEMIS) constellation suitably located to study solar wind magnetospheric coupling during the austral winter of 2007 were compared to data from ground-based all-sky imagers (ASIs) at South Pole (74° magnetic latitude) and at AGO-1 (80° magnetic latitude). The THEMIS constellation entered and exited the magnetosphere near magnetic midday on 10 and 12 August 2007, respectively. On 12 August interplanetary magnetic field (IMF) (B z > 0) the dayside aurora was located more poleward between AGO-1 and South Pole. The THEMIS satellites traversing the magnetopause saw it move in and out several times during the satellite crossings. The inward motion of the magnetopause was sometimes correlated with equatorward expansions of the aurora and sometimes with solar wind pressure pulses as seen by Geotail. The B z > 0 auroral latitude was consistent with dayside cusp “spot” seen by the IMAGE spacecraft and had been associated with footprints of “steady state” lobe reconnection. The aurora consisted of a continuous stream of poleward moving auroral forms (PMAF) even during a period of slightly B z > 0 and B y = 0. On 10 August 2007 IMF B z < 0 the dayside aurora was located more equatorward, over South Pole, and the THEMIS satellites crossed the bow shock from the magnetosheath into the solar wind. Negative B z pulses observed at the satellite were correlated with large poleward expansions of the dayside aurora consistent with reconnection in the subsolar region accompanied by simultaneous plasma density increases at THEMIS B satellite consistent with outward radial motion of the bow shock.