Engineering topics

Mcpherron, R. L.

Publications and source records attributed to Mcpherron, R. L..

At least 37 records · Page 2

NASA NTRS1988

Multi-point measurements of ULF wave phases using a multi-channel energetic ion detector

The oscillation of differential fluxes of energetic ions modulated by a ULF wave often shows a phase shift between measurements in back-to-back detectors with look directions perpendicular to the ambient magnetic field. In a plasma of a single ion species, the phase difference is caused by displacement of the effective measurement positions by one ion gyroradius to each side of the detector. As the wave phase is periodic, the observed phase shift can correspond to a family of possible wavelengths. Simultaneous measurements of the flux modulations in different energy channels, which are equivalent to measurements of the wave phase at different positions, may make it possible to single out a unique wavelength consistent with all the measurements. Using the medium-energy-particle experiments ISEE-1 and 2, each of which may serve as a back-to-back detector, the above method was applied to a compressional Pc 5 wave observed near the equatorial plane at L between about 7 and 11. The transverse propagation properties of the wave were determined unambiguously.

Lin, N.↗

NASA NTRS1988

Radial Alfven velocity profiles in the magnetosphere and their relation to ULF wave field-line resonances

The radial Alfven velocity, V(A), in the magnetosphere was investigated using magnetic field and plasma data from the ISEE-1 spacecraft. The harmonic frequency structure calculated from these data was compared with the observed resonant wave structure in the frequency range 5-100 mHz and over the region L = 3-9. It was found that the frequency of these resonances depend on the A(V), which is a function of the magnetic field strength and plasma density. The toroidal mode resonance frequency structure was modeled for the first four harmonics, with excellent agreement between the modeled and observed harmonics for a passs which does not show a plasmapause gradient. In the presence of a steep plasmapause gradient, the model was found to predict a correspondingly steep increase in the resonance frequencies at the plasmapause, by about 5 mHz for the first harmonic and by 20 mHz for the fourth harmonic. Special consideration is given to the effect of heavy ion mass loading on the modeling.

Fraser, B. J.↗

NASA NTRS1987

The roles of direct input of energy from the solar wind and unloading of stored magnetotail energy in driving magnetospheric substorms

The contributions to the substorm expansive phase of direct energy input from the solar wind and from energy stored in the magnetotail which is released in an unpredictable manner are considered. Two physical processes for the dispensation of the energy input from the solar wind are identified: (1) a driven process in which energy supplied from the solar wind is directly dissipated in the ionosphere; and (2) a loading-unloading process in which energy from the solar wind is first stored in the magnetotail and then is suddenly released to be deposited in the ionosphere. The pattern of substorm development in response to changes in the interplanetary medium has been elucidated for a canonical isolated substorm.

Rostoker, G.↗

NASA NTRS1986

A storm time, Pc 5 event observed in the outer magnetosphere by ISEE 1 and 2 - Wave properties

The properties of the waves composing a classical storm time Pc 5 event, recorded by the satellite pair ISEE 1,2 during an inbound nearly equatorial pass in the dusk sector on August 21-22, 1978, are described. On the basis of these observations it is concluded that the events of the August 21-22 pass resulted from a combination of sources, namely, distant wideband excitation and ion drift instability, plus a coupling of wave modes. It is suggested that the observed phenomenon was a radial cross section of the type of event reported by Barfield et al. (1972).

Greenstadt, E. W.↗

NASA NTRS1986

Ion cyclotron waves observed near the plasmapause

Pc2 electromagnetic ion cyclotron waves at 0.1 Hz, near the oxygen cyclotron frequency, have been observed by ISEE-1 and -2 between L = 7.6 - 5.8 on an inbound near equatorial pass in the dusk sector. The waves occurred in a thick plasmapause of width about 1 earth radius and penetrated about 1 earth radius into the plasmasphere. Wave onset was accompanied by significant increases in the thermal (0-100 eV) He(+) and the warm (0.1-16 keV/e) O(+) and He(+) heavy ion populations. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by multicomponent cold plasma propagation theory are identified in the wave data. The results are considered as an example of wave-particle interactions occurring during the outer plasmasphere refilling process at the time of the substorm recovery phase.

Fraser, B. J.↗

NASA NTRS1986

Solar wind triggering of substorm expansion onset

A substantial fraction of all substorms with sudden onsets, as identified by minima in the AL index, are found to be triggered by the IMF. Analysis of data from the first six months of 1978 shows auroral zone magnetic records to be disturbed most of the time, with distinct substorms identified in 23 percent of these disturbed hours. For the subset of substorms with sharp onsets and corresponding solar wind data, 44 percent are found to be correlated with northward turnings of the IMF, while 28 percent occur during steady southward IMF. The results suggest that sharp substorm expansion onset is caused by a process internal to the magnetosphere which can be influenced by changes in the solar wind stress applied to the magnetosphere.

Mcpherron, R. L.↗

NASA NTRS1986

Prediction filters for the Dst index and the polar cap potential

The technique of linear prediction filtering is used to create filters relating solar wind parameters to the Dst index and to the polar cap potential. The square root of solar wind dynamic pressure and the solar wind electric field together are found to account for nearly 70 percent of the Dst variance. The prediction filter for the polar cap potential requires the square of the solar wind velocity and the solar wind electric field as inputs. The results suggest that both polar cap potential and ring current injection are primarily controlled by the solar wind, and that substorm expansions do not play a major role in ring current injection.

Fay, R. A.↗

NASA NTRS1985

Magnetospheric impulse response for many levels of geomagnetic activity

The temporal relationship between the solar wind and magnetospheric activity has been studied using 34 intervals of high time resolution IMP 8 solar wind data and the corresponding AL auroral activity index. The median values of the AL index for each interval were utilized to rank the intervals according to geomagnetic activity level. The linear prediction filtering technique was then applied to model magnetospheric response as measured by the AL index to the solar wind input function VB(s). The linear prediction filtering routine produces a filter of time-lagged response coefficients which estimates the most general linear relationship between the chosen input and output parameters of the magnetospheric system. It is found that the filters are composed of two response pulses speaking at time lags of 20 and 60 min. The amplitude of the 60-min pulse is the larger for moderate activity levels, while the 20-min pulse is the larger for strong activity levels. A possible interpretation is that the 20-min pulse represents magnetospheric activity driven directly by solar wind coupling and that the 60-min pulse represents magnetospheric activity driven by the release of energy previously stored in the magnetotail. If this interpretation is correct, the linear filtering results suggest that both the driven and the unloading models of magnetospheric response are important facets of a more comprehensive response model.

Bargatze, L. F.↗

NASA NTRS1985

Dynamics of the 1054 UT March 22, 1979, substorm event - CDAW 6

The Coordinated Data Analysis Workshop (CDAW 6) has the primary objective to trace the flow of energy from the solar wind through the magnetosphere to its ultimate dissipation in the ionosphere. An essential role in this energy transfer is played by magnetospheric substorms, however, details are not yet completely understood. The International Magnetospheric Study (IMS) has provided an ideal data base for the study conducted by CDAW 6. The present investigation is concerned with the 1054 UT March 22, 1979, substorm event, which had been selected for detailed examination in connection with the studies performed by the CDAW 6. The observations of this substorm are discussed, taking into account solar wind conditions, ground magnetic activity on March 22, 1979, observations at synchronous orbit, observations in the near geomagnetic tail, and the onset of the 1054 UT expansion phase. Substorm development and magnetospheric dynamics are discussed on the basis of a synthesis of the observations.

Mcpherron, R. L.↗

NASA NTRS1985

Magnetotail energy storage and release during the CDAW 6 substorm analysis intervals

The concept of the Coordinated Data Analysis Workshop (CDAW) grew out of the International Magnetospheric Study (IMS) program. According to this concept, data are to be pooled from a wide variety of spacecraft and ground-based sources for limited time intervals. These data are to provide the basis for the performance of very detailed correlative analyses, usually with fairly limited physical problems in mind. However, in the case of the CDAW 6 truly global goals are involved. The primary goal is to trace the flow of energy from the solar wind through the magnetosphere to its ultimate dissipation by substorm processes. The present investigation has the specific goal to examine the evidence for the storage of solar wind energy in the magnetotail prior to substorm expansion phase onsets. Of particular interest is the determination, in individual substorm cases, of the time delays between the loading of energy into the magnetospheric system and the subsequent unloading of this energy.

Baker, D. N.↗

NASA NTRS1984

Spectral characteristics of Pc 3 and Pc 4/5 magnetic pulsation bands observed near L = 6

The relationships among Pc 3, Pc 4, and Pc 5 activities observed at ground stations near L = 6 are clarified by comparing their dynamic spectral structures. It is found that there are two predominant spectral bands throughout the daytime with frequencies of about 20-80 mHz and about 3-10 mHz. At synchronous orbit, corresponding spectral bands are seen in the frequency-time spectra of the azimuthal component which generally show a clear harmonic structure when the satellite is located at the off-magnetic equator. The result strongly suggests that the 20-80 mHz band is the higher harmonics of standing shear Alfven waves and the 3-10 mHz band is the fundamental mode. Switching of activity between both bands is frequently observed on magnetically quiet days, indicating that the Pc 3 and Pc 4/5 bands are excited by different external driving sources.

Tonegawa, Y.↗

NASA NTRS1984

Standing hydromagnetic oscillations in the magnetosphere

The mechanisms for generating Alfven waves in the magnetosphere are determined, on the basis of a comprehensive survey of satellite magnetometer data. The mechanisms are classified in terms of the physical properties of standing Alfven waves such as the direction of the major axis of polarization, harmonic mode, and the azimuthal wave number. In an analysis of the statistical organization of the pulsations, it is shown that the most common transverse waves seem to be azimuthally polarized waves involving the fundamental and several harmonics, with radially polarized waves excited at the second harmonic. The former are probably driven externally, while the latter are likely to be excited internally through particle-wave interactions.

Takahashi, K.↗

NASA NTRS1984

The application of dimensional analysis to the problem of solar wind-magnetosphere energy coupling

The constraints imposed by dimensional analysis are used to find how the solar wind-magnetosphere energy transfer rate depends upon interplanetary parameters. The analyses assume that only magnetohydrodynamic processes are important in controlling the rate of energy transfer. The study utilizes ISEE-3 solar wind observations, the AE index, and UT from three 10-day intervals during the International Magnetospheric Study. Simple linear regression and histogram techniques are used to find the value of the magnetohydrodynamic coupling exponent, alpha, which is consistent with observations of magnetospheric response. Once alpha is estimated, the form of the solar wind energy transfer rate is obtained by substitution into an equation of the interplanetary variables whose exponents depend upon alpha.

Bargatze, L. F.↗

NASA NTRS1984

Coupling of the solar wind to measures of magnetic activity

Linear prediction filtering was used to generate empirical response functions relating the solar wind electric field to the magnetic indices, AL, AU, Dst and ASYM. The empirical response functions were convolved with solar wind observations obtained during the International Magnetospheric Study to predict the indices. The predictions are compared with the observed indices during two, 3-day intervals. Differences between the observed and predicted indices are discussed in terms of the linear assumption and in terms of physical processes other than direct solar wind-magnetosphere interaction.

Mcpherron, R. L.↗

NASA NTRS1984

Multispacecraft observations of the harmonic structure of Pc 3-4 magnetic pulsations

Harmonically related Pc 3-4 pulsations (7-100 mHz) are observed simultaneously by the three geosynchronous satellites ATS 6, SMS 1, and SMS 2, which are separated 20 deg from one another. At a given instant the frequency of the same harmonic is different from one spacecraft to another and each spacecraft observes a decrease in the fundamental frequency as it moves from morning (15 mHz) to afternoon (10 mHz). This frequency behavior is explained in terms of standing Alfven waves, for which the frequency is determined by the local magnetic field and plasma density. Occurrence of harmonic Pc 3-4 waves only during daytime hours (0400-2000 LT) and their frequency characteristics suggest a broadband energy source located on the dayside. Possible azimuthal wave number m and azimuthal phase velocity V(phi) of the second through fourth harmonics are determined from an unusual interval during which identical harmonic frequencies were observed at SMS 1 and ATS 6. Under the assumption of tailward propagation of constant-phase fronts at the same velocity for all these harmonics, V(phi) of about 1700 km/s is obtained.

Takahashi, K.↗

NASA NTRS1984

Dependence of the spectrum of Pc 3-4 pulsations on the interplanetary magnetic field

Dependence of the power spectrum of Pc 3-4 magnetic pulsations observed at the ATS 6 geosynchronous satellite on the interplanetary magnetic field (IMF) has been studied. Pulsation events that were observed near noon and exhibited harmonic structure are chosen for analysis. Further selected are pulsation events with identical fundamental frequency to study dependence of the power of pulsations at different harmonic bands on the IMF. A weak negative correlation is observed between the IMF cone angle theta-XB and the power of pulsations in the frequency range 20-70 mHz. Also, a positive correlation between the intensity of the IMF B(IMF) and the power of pulsations at 50-70 mHz is found. This B(IMF) control is present at all ranges of the cone angle. A comparison is conducted of this observation with the frequency of bow shock associated upstream waves predicted from a model of wave generation by a cyclotron resonance of ions reflected at the bow shock. The predicted frequency depends on the IMF as B(IMF) (cos theta-XB)-squared. Although this relation gives a proportionality between the frequency and B(IMF) qualitatively consistent with the observation, it does not explain the most obvious IMF control of the spectrum of the pulsations.

Takahashi, K.↗

NASA NTRS1983

A reexamination of ATS 6 magnetometer data for radially polarized Pc 3 magnetic pulsations

The polarization of Pc 3 (22-100 MHz) magnetic pulsations measured by the ATS 6 fluxgate magnetometer at synchronous orbit has been examined by using dynamic autospectral analysis. In contrast to the result obtained by Arthur et al. (1977) using the same data set, very few cases of radially polarized Pc 3 pulsations are found. It is suggested that satellite noise in the radial component, which depends on frequency f as 0.015/f (nT-squared/Hz), is responsible for this disagreement. In the presence of this type of noise, diagonalization of the spectral matrix can produce an erroneous major axis of polarization. Most Pc 3 pulsations classified as radially polarized by Arthur et al. appear to be a consequence of small amplitude azimuthal pulsations contaminated by satellite noise.

Takahashi, K.↗

NASA NTRS1983

Satellite observations of Pi 2 activity at synchronous orbit

An attempt is made to characterize Pi 2 activity at synchronous orbit, on the basis of magnetic field data recorded in September, 1974. Pi 2 bursts are primarily seen in the nighttime sector, probably near 2100 LT, and are usually simultaneous with the Pi 2 bursts seen at midlatitude ground stations. Three main event types are noted at the data-gathering satellite: a 100-sec irregular oscillation in all field components, an additional 100-sec irregular oscillation which, unlike the first, is not accompanied by high frequency oscillations, and a much rarer, quasi-sinusoidal oscillation in the east-west component of the field. The dominant period of Pi 2 bursts is about 100 sec, and tends to be shorter as the level of activity measured by field changes at the satellite increases.

Sakurai, T.↗