Antarctic Space Science - Publications
2000
[back]Spatiotemporal characteristics of cusp latitude spectra
Authors: Szuberla, Curt A. L.; Olson, John V.; Engebretson, Mark J.; McHarg, M. Geoff; Hughes, W. Jeffrey
Journal: Journal of Geophysical Research, Volume 105, Issue A4, p. 7695-7706
Date: Apr 2000
Abstract: In this study we analyze the spatiotemporal characteristics of spectra generated from 754 days of cusp latitude magnetometer data (Longyearbyen and selected Magnetometer Array for Cusp and Cleft Studies (MACCS) stations). In order to distinguish between the presence of spatial (fixed in magnetic local time) and temporal (fixed in universal time) signatures in cusp latitude spectra we develop a simple test using trace power, polarization, and ellipticity spectra. On the basis of this test we find evidence for both spatial and temporal signatures in cusp latitude spectra. We find that the trace power spectrum is dominated by temporal information; however, the polarization and ellipticity spectra contain unambiguous spatial structure. Temporal information in cusp latitude spectra is carried primarily by broadband Pc3 (10-50 mHz) noise, while spatial information is carried by polarized Pc5 (1-10 mHz) pulsations. Additionally, we establish a state-space measure as a quantitative means of discriminating the spatial passage of the cusp and boundary regions by ground-based magnetic means. The measure is based on the difference between daily polarization spectra (centered on local magnetic noon) and the mean polarization spectra for a given station. This procedure replaces previous determinations which were made from spectra ``by-eye.''
VERITAS: the Very Energetic Radiation Imaging Telescope Array System
Authors: Vassiliev, V.; Lessard, R.; The VERITAS Collaboration
Journal: Nuclear Physics B Proceedings Supplements, Vol. 80, Proceedings of the Texas Symposium on Relativistic Astrophysics and Cosmology held in Paris, France, 14-18 December, 1998. CDROM contents., p.01/29
Date: Jan 2000
Abstract: Not Available
Poleward progressing quasiperiodic disturbances at cusp latitudes: The role of wave processes
Authors: Pilipenko, V. A.; Fedorov, E. N.; Engebretson, M. J.; Papitashvili, V. O.; Watermann, J. F.
Journal: Journal of Geophysical Research, Volume 105, Issue A12, p. 27569-27588
Date: Dec 2000
Abstract: Observations from various magnetometer networks, including Magnetomer Array for Cusp and Cleft Studies (MACCS), Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS), the Greenland Coastal Chain, and the U.S./Russia Antarctic Array, made on January 5, 1995, show an event of very long period pulsations (30- to 40-min period) in the cusp region. Pulsations were driven by quasiperiodic Interplanetary Magnetic Field (IMF) By variations which were observed by the Wind spacecraft. Disturbances of this type are commonly interpreted as poleward moving, east-west oriented ionospheric currents (e.g., intensification of the DPY current system), stimulated by reconnection processes at the dayside magnetopause. However, the temporal/spatial, ground-based structure of such disturbances can better be described if this picture is augmented by the inclusion of transient wave processes, for example, distortions of the Alfven phase front, transmitting a disturbance from an assumed reconnection region to the ionosphere. In general, this type of disturbance, which we suggest calling PDPY6 pulsations, is shown to be a manifestation of the modulation of the high-latitude ionosphere electrodynamics by a large-scale Alfven wave in the solar wind under favorable IMF orientation.
Relationship between the Northern Hemisphere Joule heating and geomagnetic activity in the southern polar cap
Authors: Ballatore, P.; Lanzerotti, L. J.; Lu, G.; Knipp, D. J.
Journal: Journal of Geophysical Research, Volume 105, Issue A12, p. 27167-27178
Date: Dec 2000
Abstract: One of the most important effects from the coupling of the solar wind to the magnetosphere-ionosphere system is the Joule heating (JH) of the atmosphere that is produced by the energy dissipation of ionospheric currents and geomagnetic field-aligned precipitating particles. At present, the most commonly used technique to estimate the global JH rate is the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. Here we describe a study of the relationship of the Northern Hemisphere JH and the Southern Hemisphere polar geomagnetic index AES-80 during a magnetic storm on October 18-23, 1995 (when both quantities are available). The purpose is to study the effects of the Northern-Southern Hemispherical asymmetry on the correlation between JH and geomagnetic indices. Our results confirm a higher contribution to JH from regions associated with eastward currents. Moreover, we find that the best correspondence between the northern JH and the AES-80 occurs during negative interplanetary magnetic field (IMF) Bz and By conditions. We discuss how this result is in agreement with the magnetospheric-ionospheric model that considers, during negative IMF Bz and By, an increase of conductance in the regions associated with eastward currents in the Northern Hemisphere. Our observations related to the best estimation of Southern Hemisphere JH are in agreement with the same model too. We also find a ``saturation'' effect for large values of northern JH: the JH-AES-80 correlation breaks down for intervals with JH>190gigawatt (GW), during the highest geomagnetic perturbations, and a negative IMF Bz that exceeds -20 nT. This ``saturation'' is in part attributed to the onset of hemispherical asymmetry due to the solar wind pressure with respect to the Earth-dipole orientation under severe storm conditions.
The distention of the magnetosphere on May 11, 1999: High latitude antarctic observations and comparisons with low latitude magnetic and geopotential data
Authors: Weatherwax, A. T.; Rosenberg, T. J.; Lanzerotti, L. J.; Maclennan, C. G.; Frey, H. U.; Mende, S. B.
Journal: Geophysical Research Letters, Volume 27, Issue 24, p. 4029-4032
Date: Dec 2000
Abstract: We examine the Earth's ionospheric response on May 11, 1999, to an unusually tenuous solar wind, focusing on magnetometer, riometer, and optical data from high geomagnetic latitudes in Antarctica. Comparisons are also made with POLAR satellite data during a perigee pass over Antarctica, and with geomagnetic data collected at low latitudes. It is shown that the southern hemisphere was geophysically active, even though the Kp index on May 11 ranged only from 0 to 0+. Furthermore, despite the fact that the IMF and solar wind conditions favored northern hemisphere polar rain, low energy electron precipitation did occur in the southern polar cap. Geomagnetic power levels at low, cusp, and polar cap latitudes were also lower on May 11 than on surrounding days. Although this might be expected, discrete millihertz peaks in ULF power were still evident, especially at cusp latitudes.
High-latitude ionospheric response to a sudden impulse event during northward IMF conditions
Authors: Moretto, T.; Ridley, A. J.; Engebretson, M. J.; Rasmussen, O.
Journal: Journal of Geophysical Research, Volume 105, Issue A2, p. 2521-2532
Date: Feb 2000
Abstract: A high-density structure under northward interplanetary magnetic field BZ conditions is identified at the Wind and IMP 8 satellites, both in the solar wind on August 22, 1995. A compression of the magnetosphere is observed by the GOES 7 magnetometer within a few minutes of the pressure increase encountering the magnetopause. The response of the high-latitude ionosphere is analyzed on the basis of ground-based magnetometer data. A comprehensive description of this response in the Northern Hemisphere is provided by more than 70 ground magnetometers. This data set is interpreted in terms of high-latitude ionospheric potential patterns by means of the assimilative mapping of ionospheric electrodynamics technique. Convection cells in the polar cap are formed and disappear on minute timescales in accordance with previous results. However, the high-latitude ionospheric ground magnetic signature does not match the interpretation as events of traveling convection vortices, as has been suggested by past studies.
Solar wind control of polar chorus
Authors: Salvati, M. A.; Inan, U. S.; Rosenberg, T. J.; Weatherwax, A. T.
Journal: Geophysical Research Letters, Volume 27, Issue 5, p. 649-656
Date: n/a 2000
Abstract: The intensity of chorus as observed at several high latitude ground stations in the Antarctic is highly correlated with the solar wind dynamic pressure exerted on the magnetopause boundary. In two different cases, intense chorus and associated precipitation measured as riometer absorption were abruptly interrupted by several minutes of deep quieting. Satellite measurements of solar wind dynamic pressure showed the intensity of chorus to rapidly respond to magnetospheric compression and relaxation over an extended region as evidenced by the fact the effect was observed at multiple sites.
A programmable riometer for Earth and Mars
Authors: Fry, C. D.; Rosenberg, T. J.; Lutz, L.; Detrick, D. L.; Weatherwax, A. T.; Knouse, E.; Breden, H.; Giganti, J.
Journal: Radio Science, Volume 35, Issue 1, p. 263-274
Date: n/a 2000
Abstract: We have developed a miniature radio receiver designed to operate as a relative ionospheric opacity meter (riometer). This project was funded by NASA as an enabling technology for future planetary radio science missions. We sought to reduce the instrument's size, mass, and power so that it would be practical for a Mars lander or rover mission. A recent study by our group indicates that a riometer might work well on Mars and offers a potentially rich science return. The technology also has immediate terrestrial applications. For example, the University of Maryland operates a chain of imaging riometers at the Automatic Geophysical Observatories (AGOs) in Antarctica. Our riometer includes features that are desirable for extended autonomous operation such as those with AGOs: low power consumption, wide dynamic range and linearity, computer command and data interface, and the ability to be remotely reconfigured. The receiver design provides significant improvements over previous implementations used in riometers. The high degree of system linearity, combined with a digital feedback loop (including a low-duty calibration cycle), allows more time for viewing the radio sky. We implemented several of the receiver subsystems in a field-programmable gate array, including the receiver detector, the control logic, and the data acquisition and processing blocks. Considerable efforts were made to eliminate or minimize RF noise and spurious emissions generated by the receiver's digital circuitry. Results of laboratory and field tests are presented and discussed.
Energetic Electron and Ion Dynamics and Polar Aurora during Magnetospheric Substorm of March 10, 1994
Authors: Kuznetsov, S.; Lazutin, L.; Gotselyuk, Yu.; Rosenburg, T.; Weatherwax, A.; Borovkov, L.; Reeves, G.
Journal: Fifth International Conference on Substorms. Held 16-20 May, 2000, at the Congress Centre of the Arctic and Antarctic Research Institute, St. Petersburg, Russia. Edited by A. Wilson. European Space Agency, ESA SP-443, 2000. ISBN: 92-9092-772-0., p.511
Date: Jul 2000
Abstract: Not Available
Discrete electrostatic eigenmodes associated with ionospheric density structure: Generation of auroral roar fine frequency structure
Authors: Yoon, P. H.; Weatherwax, A. T.; LaBelle, J.
Journal: Journal of Geophysical Research, Volume 105, Issue A12, p. 27589-27596
Date: Dec 2000
Abstract: Radio emissions emanating from the Earth and other planets are often characterized by discrete frequency structures. For example, recent ground-based observations of auroral roar, an auroral radio emission which occurs near the second and third harmonic of the electron cyclotron frequency, show that it consists of fine frequency structure similar to that of auroral kilometric radiation and other planetary radio emissions. These auroral roar fine structures, sometimes as narrow as a few hertz, often occur in multiplets separated by the order of <=1 kHz which drift up and down in frequency. Theoretical and experimental efforts to explain the generation of auroral roar suggest that in the source region near the F region peak, the quasi-electrostatic Z mode (or upper-hybrid) waves are first excited, partly converted to free-space radio waves and subsequently observed on the ground. Using WKB-type calculations of the wave mechanics of upper-hybrid modes in a cylindrical field-aligned density structure, we show that discrete frequency eigenmodes are a natural consequence of such density structures. Discrete eigenmodes can exist within density enhancements but not within depletions. Cylindrical field-aligned structures the order of 100 m to several kilometers diameter result in eigenmodes spaced by a few hundred hertz as observed for auroral roar. Since structure of this scale size often occurs in the Earth's auroral ionosphere at F region altitudes, it seems possible that the observed auroral roar fine structure results from this mechanism.