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Results for “GEOMAGNETIC PULSATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Kelvin-Helmholtz instability and the variation of geomagnetic pulsation activity

It is shown that the observed local time variation of dayside geomagnetic micropulsations is consistent with the Kelvin-Helmholtz generation mechanism operating at the magnetopause. The variation of the angle between the interplanetary magnetic field and the magnetopause around the magnetosphere causes variations in the magnetosheath magnetic field, which in turn lead to local time variations in micropulsation amplitudes. Morning sector pulsations are expected to be larger than afternoon sector pulsations. Furthermore, large-amplitude pulsations are expected to be more frequently observed when the angle between the interplanetary magnetic field and the solar wind velocity in front of the bow shock is small.

Lee, L. C.↗
NASA NTRS1978

Geomagnetic pulsations observed simultaneously on three geostationary satellites

Simultaneous observations of magnetic pulsations have been made by three geostationary satellites carrying similar magnetometers and acting as an azimuthal array. Autospectral and cross-spectral analysis yields coherence and phase differences between the pulsations at the satellite positions. The majority of the data fit the Kelvin-Helmholtz generation mechanism. The azimuthal wave number changes sign near noon and corresponds to propagation away from noon. Usually, the wave number is less than 10 deg per degree of longitude. Later in the afternoon, however, strong pulsations are observed with low coherence, implying large wave numbers. This suggests an instability driven by a gradient in the intensity of energetic protons, which may be expected at this local time. The data also suggest that some of the observed phase difference between the azimuthal components is due to small separations in magnetic shell, whereas this is not the case for the radial components. This implies a localized field-line resonance.

Hughes, W. J.↗
NASA NTRS1990

The AMPTE lithium releases in the solar wind - A possible trigger for geomagnetic pulsations

Shortly after the AMPTE/IRM satellite had released Lithium ions into the solar wind, magnetometers on the ground and in the frontside magnetosphere observed deflections of a type similar to those associated with solar wind pressure pulses. Since the natural solar wind was very stable during this event and did not exhibit pressure changes, the magnetic deflections have likely been caused by the artificially injected Lithium cloud when it hit the magnetosphere. Order of magnitude estimates show that 300 g of Lithium vapor released in the solar wind are indeed able to produce a 300 nT magnetic deflection on the ground under favorable conditions.

Luehr, Hermann↗
NASA NTRS1990

Ultra-low-frequency magnetic pulsations in the earth's magnetosphere

Spacecraft observations have shown that geomagnetic pulsations originating in magnetospheric processes, in spite of their small amplitude on the ground, have amplitudes in space relative to the local magnetic field of 5-10 percent and occasionally up to about 50 percent. It is noted that by studying geomagnetic pulsations, a detailed comparison can be made between plasma physics theory and observations that are not possible in laboratory experiments. Also geomagnetic pulsations play a role in magnetospheric dynamics and energy transport, and their study forms an integral part of enhancing the knowledge of the magnetosphere. The importance of spacecraft observations are discussed and attention is given to such topics as waves in the magnetosphere, field-line resonances, the quantitative analysis of a dipole field, plasma instabilities, and energy flow.

Anderson, Brian J.↗
NASA NTRS1989

Relationships between SC- and SI-associated ULF waves and ionospheric HF Doppler oscillations during the great geomagnetic storm of February 1986

The SC- and SI-associated ionospheric Doppler velocity oscillations and geomagnetic pulsations during the great geomagnetic storm of February 1986 are interpreted. This is done by considering the 'dynamo-motor' mechanism of ionospheric E-field and the global compressional oscillations of the magnetosphere and the ionosphere, respectively.

Yumoto, K.↗
NASA NTRS1989

SC- and SI-associated ULF and HF-Doppler oscillations during the great magnetic storm of February 1986

Results are presented of an investigation of SC- and SI-associated ULF and HF-Doppler pulsations observed during the great geomagnetic storm of February 1986, which began with a sudden commmencement on February 6 at about 13:12 UT, developed slowly over the next two days, and, after a rapid intensification late on February 8, reached a minimum. It is shown that these ULF and geomagnetic pulsations can be explained by the dynamo-motor mechanism of ionospheric electric fields and by global compressional oscillations in the magnetosphere and ionosphere, respectively.

Yumoto, K.↗
NASA NTRS1982

Multisatellite observations of resonant hydromagnetic waves

Long period geomagnetic pulsations with periods between about 10 and 600 s have been observed by ground magnetometers for over 100 years. Dungey (1954) suggested that these pulsations might be hydromagnetic waves resonating on geomagnetic field lines. One of the most recent techniques employed to examine pulsations and to test pulsation theory has been that of multispacecraft observations. A review is attempted to show how multisatellite observations have been used to provide new insight in the generation mechanisms, propagation characteristics, and resonant properties of magnetospheric pulsations. Some studies show how measurements of the plasma environment both in the vicinity of the waves and elsewhere have enabled tests of resonance theory in ways which were not previously possible with single satellite measurements.

Singer, H. J.↗
NASA NTRS1997

Sounding of the Cleft Ion Fountain Energization Region

The objectives of the ground-based observations in support of the SCIFER are: Acquire and display ionospheric conditions prior to launch to aid in the establishment of launch criteria in real time. Observers at both stations participated in real-time visual interpretation. Solar wind data from IMP-8 and WIND were acquired and interpreted in real time. Telephonic and data links were established at the observatory for the launch window period. Ground-based observatory countdown and launch criteria were developed. 2) Relate optical and magnetic ionospheric signatures observed from the ground to magnetospheric boundaries in the energetic particle flux measured at the payload. The energetic electron trapping boundary was found to correspond to the equatorward edge of the discrete auroral arcs forming the dayside aurora. The energetic electron trapping boundary was found to correspond to the poleward edge of pulsating aurora. The pulsating aurora was found to correspond to one second bursts of energy-dispersed electrons originating in the equatorial plane. Pulsations at larger intervals corresponded to travel times to the conjugate region and return. The pulsating aurora was also directly linked to the geomagnetic pulsations and traveling magnetic vortices, all occurring equatorward of the trapping boundary. 630 nm emission corresponding to less than 10 eV electron precipitation was observed equatorward of the trapping boundary (L=15) and ascribed to photoelectrons from the sunlit conjugate region. 3) Aid in the interpretation of time/space incongruities in the rocket data. The motion of the payload conjugate across the aurora showed that the payload passed over three distinct arc systems on the poleward side of the trapping boundary. These results were reported in a series of articles to be printed in Geophysical Research Letters on June 15, l996.

Kintner, P.↗
NASA NTRS1975

Search for correlation between geomagnetic disturbances and mortality

Statistical evaluation of death rates in the U.S.A. from heart diseases or stroke did not show any correlation with measured geomagnetic pulsations and thus do not support a claimed relationship between geomagnetic activity and mortality rates to low frequency fluctuations of the earth's magnetic field.

Lipa, B. J.↗
NASA NTRS1981

Pulsations in total columnar electron content

Radio signals from the ATS 6 beacon received at Boulder reveal small-amplitude, quasi-sinusoidal fluctuations with periods in the range of 10 to 50 s. Visual comparisons of these data (116 events for October 1974 to April 1975) shows a good correspondence with simultaneous geomagnetic pulsations at Boulder in two thirds of the cases for which Boulder magnetograms were available, but they do not necessarily correspond with magnetic pulsations on ATS 6. Spectral analyses, by the method of maximum entropy, were made on sample records. The principal results are the following: (1) The occurrence of the pulsations is higher on magnetically disturbed days. (2) The maximum likelihood of occurrence is around 2100 UT (1400 LT). (3) The dominant spectrum peaks of the radio fluctuations and geomagnetic field on the ground generally coincide. Cases are found also in which temporal characteristics of the spectra are similar. These results indicate a close association of the radio fluctuations with the Pc 3-4 type pulsations of the geomagnetic field on the ground. It is suggested that the radio fluctuations originate mainly in the F region of the ionosphere, while some of them could be due to plasmapause effects.

Okuzawa, T.↗
NASA NTRS1985

Frequency spectra of short-period variations of cosmic ray

Frequency spectra for different periods of solar activity were calculated by 5-minutes data of a neutron super-monitor, (altitude 3340 m, cutoff rigidity is 6, 7 GV, counting rate is about 4.5.10 per hour). It was shown that shifting of the spectrum power from low-frequency range to high-frequency range takes place from minimum to maximum of the solar activity. It was reliably distinguished the peak with 160-minutes period coincided with the period of the Sun's atmosphere oscillation and some types of geomagnetic pulsation by the method of accumulation of the frequency spectra. It was conducted the comparison of cosmic ray spectra with spectra of geomagnetic field for the same point of the registration and at the same period.

Antonova, V. P.↗