Antarctic Space Science - Publications
2003
[back]Large-scale geomagnetic effects of May 4, 1998
Authors: Farrugia, C. J.; Jordanova, V. K.; Freeman, M. P.; Cocheci, C. C.; Arnoldy, R. L.; Engebretson, M.; Stauning, P.; Rostoker, G.; Thomsen, M. F.; Reeves, G.; Yumoto, K.
Journal: Advances in Space Research, Volume 31, Issue 4, p. 1111-1116.
Date: n/a 2003
Abstract: We study large-scale magnetospheric disturbances elicited by the May 4, 1998 high speed stream by modeling the Dst and studying records from 4 meridional magnetometer chains covering key local time sectors. The quasi-sequential episodes of Bz < < 0 and high dynamic pressure (10-50 nPa) allow a clean separation of their respective geoeffects. Ring current evolution is followed by the kinetic model of Jordanova et al. (1998), which includes both charge exchange and Coulomb collisions of ring current ions H+, He+ and O+ drifting in a Volland-Stern convection electric field. The overall agreement with the temporal variation of the Dst is very good, but the strength of the great storm (min Dst = -280 nT) with its rapid main phase is not reproduced fully. A very asymmetric ring current forms near minimum Dst with maximum energy density located at dusk for all ion species. The data show evidence of (a) a great geomagnetic storm; (b) large enhancements of magnetopause currents; (c) substorm onsets, some of which were triggered; (d) a convection reversal boundary at relatively low latitudes (60-65°) and (e) what might be omega bands at morning local times associated with substorm recovery. An unprecedented measurement at Halley Bay station of an approximately 10% change in the ambient magnetic field strength is related to a sharp 5-fold increase in the dynamic pressure and to a large (~50 nT) variation in IMF Bz
Radial localization of magnetospheric guided poloidal Pc 4-5 waves
Authors: Denton, R. E.; Lessard, M. R.; Kistler, L. M.
Journal: Journal of Geophysical Research (Space Physics), Volume 108, Issue A3, pp. SMP 4-1, CiteID 1105, DOI 10.1029/2002JA009679
Date: Mar 2003
Abstract: The toroidal Alfvén wave, with magnetic field oscillations in the azimuthal direction, exhibits a singularity in the vicinity of the toroidal resonant frequency (field line resonance), so it is not surprising that this wave often exhibits varying frequency as a function of L shell. It is less clear why the poloidal Alfvén wave, with magnetic field oscillations in the radial direction, often exhibits a relatively constant frequency over a range of L shells. So far, the most promising proposal to explain this phenomenon is the theory of Vetoulis and Chen [1994, 1996], who showed that an energetically trapped global poloidal mode can exist in a region where the poloidal Alfvén frequency is lower than the toroidal frequency and where it exhibits a dip (minimum) with respect to L. While this theory is mathematically plausible, it has never been shown that poloidal Alfvén waves actually occur in association with such a dip in poloidal frequency. Here we examine poloidal wave events observed by the AMPTE/IRM spacecraft and calculate the theoretical poloidal frequency as a function of L using the equilibrium parameters obtained from the spacecraft observations. We find that the poloidal Alfvén wave does occur in association with such a dip (or at least a flattening) in poloidal frequency. While Vetoulis and Chen hypothesized that such a dip would occur because of a sharp gradient in plasma pressure, we find that the dip in poloidal frequency may result from the L dependence of the equilibrium density or magnetic field. The observed frequencies are in rough agreement with the theoretical frequencies, though in some cases we must assume that the observed oscillations result from a high harmonic (third or fourth harmonic structure along the magnetic field). We also apply the same analysis to compressional wave events (with oscillations in the direction of the equilibrium magnetic field). Such oscillations may be on the poloidal wave branch or the mirror mode branch. Here also, the observed fluctuations occur in the region of a dip in poloidal frequency. In one case the observed frequency is consistent with the theoretical poloidal frequency, whereas in another case it is not.
Characterizing the long-period ULF response to magnetic storms
Authors: Posch, J. L.; Engebretson, M. J.; Pilipenko, V. A.; Hughes, W. J.; Russell, C. T.; Lanzerotti, L. J.
Journal: Journal of Geophysical Research (Space Physics), Volume 108, Issue A1, pp. SMP 18-1, CiteID 1029, DOI 10.1029/2002JA009386
Date: Jan 2003
Abstract: This study presents an analysis of long-period ULF wave power observed at 44 ground magnetometer stations in the western hemisphere, at latitudes from the equator to the polar caps, during the magnetic storm intervals of May 1997, March 1998, May 1998, September 1998, and October 1998 identified by the GEM research community. Comparison of the long-period pulsations (in the Pc5 frequency range) observed on the ground to the solar wind velocity and solar wind pressure observed by the WIND satellite confirms previous results that high solar wind velocity correlates well with increased Pc5 power. Although some variability was evident among the five storms, solar wind pressure and variability in velocity or pressure exhibited considerably weaker correlations. Each storm exhibited narrow-band Pc5 wave activity during the recovery phase, but only in the dawn-noon sector at each site. During the main phase, and at all other local times during the recovery phase, wave activity was broadband. The strongest Pc5 power was observed at frequencies above 2 mHz at stations in the auroral zone and poleward and below 2 mHz at stations at middle and low latitudes. Comparison to published time profiles of energetic electrons at geosynchronous orbit suggests that if ULF wave activity is responsible for the initial energization of these electrons, broadband activity rather than narrowband (Pc5) waves must play the dominant role. Our data cannot rule out, however, the importance of narrowband waves in providing additional energization during the recovery phase.
Evidence for a discrete spectrum of persistent magnetospheric fluctuations below 1 mHz
Authors: Lessard, M. R.; Hanna, J.; Donovan, E. F.; Reeves, G. D.
Journal: Journal of Geophysical Research (Space Physics), Volume 108, Issue A3, pp. SMP 18-1, CiteID 1125, DOI 10.1029/2002JA009311
Date: Mar 2003
Abstract: Ultralow-frequency waves in the magnetosphere have been observed and widely reported in the literature. One important class of such waves includes field-line resonances, having fundamental frequencies as low as ~1.3 mHz. Fluctuations below this frequency have been reported infrequently, although a few studies note oscillations with periods of approximately 30 min. The nature of these waves is especially interesting because the expected wavelength that would be associated with them should be larger than the scale size of the magnetosphere. In fact, the majority of these observations have been acquired using satellites located in the fairly distant magnetotail. In one of these studies, the only one which finds a discrete spectrum, data was obtained between XGSM = -8 and -18RE. In this paper, we show evidence for the existence of a discrete spectrum of oscillations within the magnetosphere that can persist for up to 2 days and perhaps longer. These observations were acquired at geosynchronous orbit and were observed at all local times simultaneously with a signature that is clearest in energetic electron data but can also be seen in the GOES magnetometer data. These facts suggest that a global-scale magnetic fluctuation, perhaps one that originates in the magnetotail, resonates with energetic electron drift orbits via an E × B force.
Statistical identification of solar wind origins of magnetic impulse events
Authors: Kataoka, Ryuho; Fukunishi, Hiroshi; Lanzerotti, Louis J.
Journal: Journal of Geophysical Research, Volume 108, Issue A12, pp. SMP 13-1, CiteID 1436, DOI 10.1029/2003JA010202
Date: Dec 2003
Abstract: We have compiled a complete list of magnetic impulse events (MIEs) during the 8-year period of 1995-2002 covering solar minimum to solar maximum using fluxgate magnetometer data obtained at the South Pole. Wavelet analysis enables us to detect 825 distinct MIEs automatically with high confidence. Interplanetary magnetic field (IMF) discontinuities are also detected automatically for the same period from Wind and ACE satellite data. From an examination and comparison of the two lists, we find that monthly and seasonal variations in IMF discontinuity occurrences have a significant correlation (0.4-0.5) with those of MIEs. We also find that MIEs tend to occur during intervals of low density, high-speed solar wind streams, and/or radial IMF. No preferences for MIE occurrences are found for solar wind pressure jumps or IMF Bz southward turnings. From detailed minimum variance analysis of 36 IMF discontinuities with one-to-one correspondence to MIEs, ~70% of the IMF discontinuities are found to be tangential discontinuities. The hot flow anomaly (HFA) mechanism can explain at most ~50% of the MIEs; bursty reconnection and pressure pulses can explain the production of at most ~30% and ~20% of the MIEs, respectively. All of the observations and associations are consistent with HFAs or foreshock cavities being the main cause of MIEs.
Multistation studies of the simultaneous occurrence rate of Pc 3 micropulsations and magnetic impulsive events
Authors: Shields, D. W.; Bering, E. A.; Alaniz, A.; Mason, S. E. M.; Guo, W.; Arnoldy, R. L.; Engebretson, M. J.; Hughes, W. J.; Murr, D. L.; Lanzerotti, L. J.; Maclennan, C. G.
Journal: Journal of Geophysical Research Space Physics, Volume 108, Issue A6, pp. SMP 2-1, CiteID 1225, DOI 10.1029/2002JA009397
Date: Jun 2003
Abstract: This study reports simultaneous observations of two different phenomena whose sources may be either near the magnetopause or in the solar wind: Pc 3 micropulsations and high-latitude magnetic impulsive events (MIEs), whose best studied subset comprises traveling current vortices (TCVs). Isolated Pc 3 emissions that occurred simultaneously with MIE or TCV events and appeared to have the same horizontal speed as the TCVs have been reported. This observation suggests that these events were on the same geomagnetic field lines and may share a common source. The current study reports a search of existing databases for simultaneous Pc 3-MIE observations. The databases that were searched are the South Pole search coil magnetometer data during 1985-1986 and the Magnetometer Array for Cusp and Cleft Studies (MACCS) database from 1992 to 1993. The rate of occurrence of joint Pc 3 bursts and high-latitude impulsive events has been consistently found to be ~70-90%, depending on the database. The rate of coincidence is so high that it suggests that search algorithms based on ground-based data that seek ``clean'' MIE signals may be omitting some events owing to the presence of large-amplitude ULF emissions. A reverse search for candidate MIEs occurring during dayside Pc 3 bursts doubled the number of candidate MIEs in the database. The final results show that 91% of all MIEs were accompanied by Pc 3 emissions, and 43% of all 10-30 min bursts or banded enhancements in Pc 3 emission were accompanied by an MIE. A statistical analysis confirms that the correlation rates are statistically significant. The observed dependence of the properties of the MIE-concurrent Pc 3s on the solar wind and interplanetary magnetic field is consistent with previous studies of Pc 3s of solar wind origin.