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  • 1
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    Recent research on magnetospheric wave-particle interactions (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Highlights of recent Stanford University VLF research in the Antarctic include new observations of wave-induced particle precipitation and controlled experiments on nonlinear wave growth phenomena. Higher-than-expected levels of burst precipitation have been discovered inside the plasmasphere, near L = 2, using subionospheric signal perturbations called 'Trimpi events'. Studies of burst precipitation have been extended to the region poleward of the plasmapause using the Siple transmitter signal as a waveguide probe. Experiments on the 'coherent wave instability', using the amplitude and frequency modulation capability of the new Siple transmitter, have produced exciting new results. Examples are: (1) better definition of the power threshold for the stimulation of temporal wave growth, (2) generation of strong sidebands by unamplified 'beat' waves and (3) generation of chorus-like elements within a band of simulated hiss. Using a new digital processing technique developed at Stanford, new features of the phase behavior of growing waves have been found. Opportunities for extending these experiments are discussed.
    Keywords: GEOPHYSICS
    Type: National Institute of Polar Research, Memoirs, Special Issue (ISSN 0386-0744); 38, D; 83-98
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  • 2
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    Ozone profile measurements of McMurdo Station, Antarctica, during the spring of 1987 (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ozone and temperature profiles were measured in 50 balloon flights at McMurdo Station (78 deg S) during the spring of 1987. Compared to similar data obtained in 1986, stratospheric temperatures were lower and the spring time Antarctic ozone reduction was greater in magnitude, extended to higher altitude, and proceeded at a higher rate in 1987. Ozone partial pressures reached values as low as 3 nbar (as compared to about 10 nbar in 1986) in the 16- to 18-km region in early and late October, down from about 150 nbar in late August. These low values suggest essentially complete removal of ozone in this region. The upper boundary of the depletion region was observed to be 2-3 km higher than in 1986, extending to altitudes as high as 24 km in mid-September. When averaged over September, the ozone mixing ratio at 18 km decayed with a half-life of only 12.4 days, as compared to about 28 days in 1986. Adiabatic vertical motions over 1- to 2-km intervals between 12 and 20 km with consequent ozone reductions were observed in association with the formation of nacreous clouds, indicating these to be rare events on a local scale probably associated with mountain lee waves.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 16527-16
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  • 3
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    A satellite-ground study of the dynamics of the bulge region of the Earth's magnetosphere (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Data from multiple ground stations and satellites were used to see how the plasmasphere in the dusk sector is modified during magnetic storms. There is clearly some type of erosion process, during which the plasmasphere is diminished in size, and it is believed that the excess plasma is peeled off and carried (convected) away toward the outer boundary of the magnetosphere (the magnetopause). However, very little is know about the physics of the erosion process, and about how the plasmasphere recovers during the quiet periods that follow such disturbances. Case studies from three multiday periods in 1982 produced a number of new findings which are summarized in this two page document.
    Keywords: GEOPHYSICS
    Type: Alabama Univ., Research Reports: 1990 NASA(ASEE Summer Faculty Fellowship Program; 3 p
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  • 4
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    Vlf propagation and noise in the ionosphere observed by sounding rockets final report (1965)
    In:  CASI
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    Publication Date: 2019-05-24
    Description: Aerobee sounding rocket observation of very low frequency propagation and noise in ionosphere
    Keywords: GEOPHYSICS
    Type: NASA-CR-67376
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  • 5
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    A dispersion anomaly in whistlers received on alouette 1. (1965)
    In:  Other Sources
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    Publication Date: 2019-05-24
    Description: Alouette I whistler observations at 1000 km show dispersion anomaly that increases with increasing frequency
    Keywords: GEOPHYSICS
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  • 6
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    Subionospheric VLF/LF phase perturbations produced by lightning-whistler induced particle precipitation (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Rapid phase perturbations of subionospherically propagating VLF/LF signals are associated with lightning-generated whistlers which propagate in the magnetosphere. The perturbations, called 'Trimpi events' or 'Trimpi effects' after their discoverer, are attributed to alterations in the earth-ionosphere waveguide caused by localized enhancements in the ionospheric D region. These enhancements are produced by bursts of high-energy electrons which are precipitated out of the earth's radiation belts by the whistler waves. The present paper has the objective to present and discuss new evidence of whistler-associated phase perturbations of subionospheric signals. Events of this type, called phase Trimpi's were first reported by Lohrey and Kaiser (1979). Attention is given to occurrence statistics in terms of the seasonal distribution and hourly rate of events, possible effects on global VLF/LF navigation, and an interpretive model.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 7457-746
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  • 7
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    A comparison of equatorial electron densities measured by whistlers and by a satellite radio technique (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Magnetospheric equatorial electron densities determined from whistler observations are compared with in situ satellite measurements of electron density along near-equatorial orbits. Whistler data was recorded at Siple and Palmer, Antarctica, while the sweep frequency receiver on ISEE-1 was used to measure plasma densities during passes within about 15 deg of the whistler station longitudes at L values between 3 and 5.2. The whistler and satellite data sets are found to be in good agreement for the three rendezvous considered, suggesting that the diffusive equilibrium model applied to calculate electron densities from whistler measurements was appropriate for the description of electron density distributions along field lines in the outer plasmasphere. Data also indicate that density enhancements within the whistler ducts were not more than about 30% of the mean or interduct level, and that there were no significant east-west density gradients within about 15 deg of whistler station longitudes over the L range of the study.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; Oct. 198
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  • 8
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    Variable frequency VLF signals in the magnetosphere Associated phenomena and plasma diagnostics (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Coherent variable-frequency signals (ramps) extending from 1 to 8 kHz, injected into the magnetosphere from Siple Station, Antarctica (L=4.3), exhibit upper and lower cutoffs when received at the conjugate station, Roberval, Quebec. Ramp group delay measurements and ionospheric sounding data are used to determine the cold plasma density and L shell of the propagation path. Relationships among f, df/dt, and the 'phase equator' for gyroresonance are calculated using second-order resonance equations generalized to relativistic electrons. The concept thereby introduced is used to develop a diagnostic technique which, for an assumed g(alpha)(v exp -n) electron distribution, provides an estimate of the energy dependence n. Additional aspects of the magnetospheric response to ramp injection, such as emission triggering, curvature due to dispersion, and amplitude saturation, are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 1507-152
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  • 9
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    Whistler-triggered VLF noise bursts observed on the DE-1 satellite and simultaneously at Antarctic ground stations (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Simultaneous observations of whistler-triggered very low-frequency noise bursts on the ground at Anarctic stations, Halley and Siple, and on the high-altitude satellite DE-1 are reported. Results of a case study from June 25, 1982 in which the satellite data were recorded near 25 deg south magnetic latitude and the L = 4.7 magnetic shell, are presented. Analysis indicates that the chorus bursts that are triggered in whistler ducts travel downwards in the ducts to low altitudes in the ionosphere, and that propagation to DE-1 is by upward reflection into a nonducted mode. A means of estimating the propagation characteristics of the wave bursts is provided by comparisons of nonducted signals from the Siple transmitter and discrete periodic emissions. The ducted-nonducted mode conversion process is a mechanism for the large-scale spreading into the magnetosphere of coherent whistler-mode wave energy which is generated, amplified, or triggered in small localized ducts. The DE-1 data show that a strong interaction exists between whistler-triggered noise bursts and prevailing hiss levels.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0755-0685); 3; 81-88
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  • 10
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    Perturbations of subionospheric LF and MF signals due to whistler-induced electron precipitation bursts (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Increasing attention is now being devoted to the problem of the pitch angle scattering and resulting precipitation of magnetospheric energetic electrons by coherent waves. The present investigation has the objective to report the first evidence of a correlation between whistlers and amplitude perturbations on low-frequency (LF) signals at 37.2 kHz and medium-frequency (MF) signals at 780 kHz. Whistler-correlated amplitude perturbations were observed on a 780-kHz MF signal propagating on an approximately 1800 km path from South America to Palmer. The observed MF perturbations were of order 50 percent in amplitude and developed much more quickly than other changes of comparable magnitude on the signal.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 9857-986
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