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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 91 records · Page 5
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NASA NTRS1972

The responses of the thermosphere due to a geomagnetic storm: A MHD model

A magnetohydrodynamics theory was used to study the dynamic response of the neutral atmosphere to a geomagnetic storm. A full set of magnetohydrodynamic equations appropriate for the present problem is derived and their various orders of approximation are discussed in some detail. In order to demonstrate the usefulness of this theoretical model, the May 1967 geomagnetic storm data were used in the resulting set of nonlinear, time dependent, partial differential magnetohydrodynamic equations to calculate variations of the thermosphere due to the storm. The numerical results are presented for wind speeds, electric field strength, and amount of joule heating at a constant altitude for the data recorded. Data show that the strongest thermospheric responses are at the polar region becoming weaker in the equatorial region. This may lead to the speculation that a thermospheric wave is generated in the polar region due to the geomagnetic storm which propagates towards the equator.

Wu, S. T.↗
NASA NTRS1973

The relation between the azimuthal component of the interplanetary magnetic field and the geomagnetic field in the polar caps

The recently discovered relation between the azimuthal component of the interplanetary magnetic field and magnetic variations in the earth's polar caps is reviewed. When the IMF azimuthal component is positive (typical of an interplanetary sector with magnetic field directed away from the sun) geomagnetic perturbations directed away from the earth are observed within 8 deg from the corrected geomagnetic pole. When the IMF azimuthal component is negative (typically within toward sectors) the geomagnetic perturbations are directed towards the earth at both poles. These perturbations can also be described by an equivalent current flowing at a constant magnetic latitude of 80 - 82 deg clockwise around the magnetic poles during toward sectors and counterclockwise during away sectors. This current fluctuates in magnitude and direction with the azimuthal component of the IMF, with a delay time of the order of 20 minutes. The importance of this effect for understanding of both solar magnetism and magnetospheric physics is stressed in view of the possibility for investigating the solar sector structure during the last five sunspot cycles.

Svalgaard, L.↗
NASA NTRS1973

Drift shell splitting by internal geomagnetic multipoles.

Computations on an 80-coefficient model of the earth's field illustrate the 'topography' of the magnetic equatorial surface and the geometry of the drift shells of geomagnetically trapped particles. Individual terms in the spherical harmonic expansion of the geomagnetic scalar potential V(r, theta, phi) are either even or odd in cos theta, where theta = 90 deg denotes the dipole equator. Terms that are even in cos theta tend to 'warp' the equatorial surface, but do not (in first order) distort particle drift shells radially nor split the drift shells of particles having different equatorial pitch angles. Azimuthally asymmetric terms that are odd in cos theta do cause shell splitting in first order. Shell splitting at large L values (neglecting deformation of the earth's field by the solar wind) is found to be dominated by the geomagnetic octupole. At L approximately equal to 1, shell splitting is strongly enhanced by the South American and South African anomalies. When combined with pitch angle diffusion caused by atmospheric scattering, these results may be able to account for anomalous radial diffusion of inner zone electrons.

Roederer, J. G.↗
NASA NTRS1973

Magnetospheric mapping with quantitative geomagnetic field models

The Mead-Fairfield geomagnetic field models were used to trace field lines between the outer magnetosphere and the earth's surface. The results are presented in terms of ground latitude and local time contours projected to the equatorial plane and into the geomagnetic tail. With these contours various observations can be mapped along field lines between high and low altitudes. Low altitudes observations of the polar cap boundary, the polar cusp, the energetic electron trapping boundary and the sunward convection region are projected to the equatorial plane and compared with the results of the model and with each other. The results provide quantitative support to the earlier suggestions that the trapping boundary is associated with the last closed field line in the sunward hemisphere, the polar cusp is associated with the region of the last closed field line, and the polar cap projects to the geomagnetic tail and has a low latitude boundary corresponding to the last closed field line.

Fairfield, D. H.↗
NASA NTRS1974

Error enhancement in geomagnetic models derived from scalar data

Models of the main geomagnetic field are generally represented by a scalar potential gamma expanded in a finite number of spherical harmonics. Very accurate observations of F were used, but indications exist that the accuracy of models derived from them is considerably lower. One problem is that F does not always characterize gamma uniquely. It is not clear whether such ambiguity can be encountered in deriving gamma from F in geomagnetic surveys, but there exists a connection, due to the fact that the counterexamples of Backus are related to the dipole field, while the geomagnetic field is dominated by its dipole component. If the models are recovered with a finite error (i.e. they cannot completely fit the data and consequently have a small spurious component), this connection allows the error in certain sequences of harmonic terms in gamma to be enhanced without unduly large effects on the fit of F to the model.

Stern, D. P.↗
NASA NTRS1974

Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind

The polar semiannual oscillation in zonal wind can explain midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summar easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that polar wind oscillations are caused by the semiannual maxima in magnetic storm activity which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and thereby inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.

Belmont, A. D.↗
NASA NTRS1974

Geomagnetic responses to the solar wind and to solar activity

A unified overview of present knowledge of the geomagnetic response to the dynamic solar wind is reported. The formation of the magnetosphere and the magnetospheric tail is discussed the importance of electric fields is stressed, and the magnetospheric convection of plasma and frozen-in magnetic field lines under the influence of large scale magnetospheric electric fields is outlined. Ionospheric electric fields and currents are intimately related to electric fields and currents in the magnetosphere and the strong coupling between the two regions is discussed. The energy input of the solar wind to the magnetosphere and upper atmosphere is discussed in terms of the reconnection model where interplanetary magnetic field lines merge or connect with the terrestrial field on the sunward side of the magnetosphere. The merging model emphasizes the importance of the interplanetary magnetic field and especially the north-south component. The solar sector structure with its organized magnetic field and embeeded high speed plasma streams is identified as the source of recurrent geomagnetic disturbances while flare associated interplanetary shock waves are the source of most violet and sporadic geomagnetic storms.

Svalgaard, L.↗
NASA NTRS1974

Solar coronal holes as sources of recurrent geomagnetic disturbances

Observations of the solar corona by Oso 7 have been used in a superposed epoch analysis to study the relationships between classes of coronal features and geomagnetic activity. Both bright coronal regions and regions of less than average brightness were investigated. It was found that for the period from January 1972 through January 1973, a significant enhancement in geomagnetic activity occurred 2-3 days after central meridian passage of large coronal holes that extended to within 5 deg of the solar subearth point when they were on the meridian. Large coronal holes appear to satisfy the requirements for 'M regions' which were hypothesized to be responsible for recurrent geomagnetic disturbances (Bartels, 1934). If solar wind high-speed streams originate preferentially in these regions, their velocity at the base of the corona will be substantially higher than that expected from an axisymmetric solar wind model.

Neupert, W. M.↗
NASA NTRS1975

Possible isotopic shifts with changes in the geomagnetic field

The geomagnetic fields of the past geological epochs are studied on the basis of observations on the rock residual magnetization. This paper evaluates the shifts in the isotopic composition of the same elements in the rocks affected by cosmic rays. The possibility of using the shifts in the isotopic composition for revealing geomagnetic field inversions is discussed. Geomagnetic field inversion periods traced by the rock residual magnetization are in good agreement with the periods of the greatest qualitative changes in the animal world throughout the last 500 million years.

Bulashevich, Y. P.↗
NASA NTRS1975

A study of geomagnetic storms

Twenty-one geomagnetic storm events during 1966 and 1970 were studied by using simultaneous interplanetary magnetic field and plasma parameters. Explorer 33 and 35 field and plasma data were analyzed on large-scale (hourly) and small-scale (3 min.) during the time interval coincident with initial phase of the geomagnetic storms. The solar-ecliptic Bz component turns southward at the end of the initial phase, thus triggering the main phase decrease in Dst geomagnetic field. When the Bz is already negative, its value becomes further negative. The By component also shows large fluctuations along with Bz. When there are no clear changes in the Bz component, the By shows abrupt changes at the main phase onet. On the small-scale behavior of the magnetic field and electric field (E=-VxB) studied in details for the three events, it is found that the field fluctuations in By, Bz and Ey and Ez are present in the initial phase. These fluctuations become larger just before the main phase of the storm begins. In the largescale behavior field remains quiet because the small scale variations are averaged out.

Patel, V. L.↗
NASA NTRS1975

Magnetospheric mapping with a quantitative geomagnetic field model

Mapping the magnetosphere on a dipole geomagnetic field model by projecting field and particle observations onto the model is described. High-latitude field lines are traced between the earth's surface and their intersection with either the equatorial plane or a cross section of the geomagnetic tail, and data from low-altitude orbiting satellites are projected along field lines to the outer magnetosphere. This procedure is analyzed, and the resultant mappings are illustrated. Extension of field lines into the geomagnetic tail and low-altitude determination of the polar cap and cusp are presented. It is noted that while there is good agreement among the various data, more particle measurements are necessary to clear up statistical uncertainties and to facilitate comparison of statistical models.

Fairfield, D. H.↗
NASA NTRS1975

Using the moon to probe the geomagnetic tail lobe plasma

We have detected the presence of plasma in the lobes of the geomagnetic tail from observations of magnetic induction in the moon forced by time variations of the earth's magnetotail lobe field. The magnitude of the moon's tangential electromagnetic transfer function when the moon is in the lobes of the geomagnetic tail is less than that when the moon is in the solar wind or geomagnetic tail plasma sheet. The tangential transfer function when the moon is in the magnetotail lobes decreases at frequencies above about 8 mHz due to finite wavelength effects. This shows that the waves in the magnetotail lobes which drive the lunar magnetic induction must have speeds far less than the speed of light and wavelengths comparable to the size of the moon.

Schubert, G.↗
NASA NTRS1975

Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind

The polar semiannual oscillation in zonal wind explains midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summer easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that the polar wind oscillations are caused by the semiannual maxima in magnetic storm activity, which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.

Belmont, A. D.↗
NASA NTRS1976

Comparison of periodic and other characteristics of geomagnetic and meterological rocket data

The temporal variations in stratospheric winds and temperatures with the geomagnetic field elements were compared. From a periodic analysis of the geomagnetic field elements the amplitude and phase of the quasibiennial, annual, and semiannual waves are given for stations from 1 degree S to 89 degree N. These results are then compared with corresponding waves reported in rocketsonde wind and temperature data. The annual waves are found to be coupled as a result of the annual variation in the dynamo effect of the wind in the lower ionosphere. The semiannual waves are also found to be coupled and three possible causes for the extra tropical stratospheric semiannual wind wave are discussed. Time variance spectra for the interval from 4 days to 44 days in both zonal winds and horizontal geomagnetic field intensity are compared for years when major midwinter warmings occur and years when only minor warmings occur. The noted differences are suggested to arise from upward propagating planetary waves which are absorbed or refracted in varying amounts depending on the prevailing circulation.

Nastrom, G. D.↗
NASA NTRS1976

Search for correlation between geomagnetic disturbances and mortality

A search is conducted for a possible correlation between solar activity and myocardial infarction and stroke in the United States. A statistical analysis is performed using data on geomagnetic activity and the daily U.S. mortality due to coronary heart disease and stroke for the years 1962 through 1966. None of the results are found to yield any evidence of a correlation. It is concluded that correlations claimed by Soviet workers between geomagnetic activity and the incidence of various human diseases are probably not statistically significant or probably are not due to a causal relation between geomagnetic activity and disease.

Lipa, B. J.↗
NASA NTRS1977

Solar generated quasi-biennial geomagnetic variation

The existence of highly correlated quasi-biennial variations in the geomagnetic field and in solar activity is demonstrated. The analysis uses a numerical filter technique applied to monthly averages of the geomagnetic horizontal component and of the Zurich relative sunspot number. Striking correlations are found between the quasi-biennial geomagnetic variations determined from several magnetic observatories located at widely different longitudes, indicating a worldwide nature of the obtained variation. The correlation coefficient between the filtered Dst index and the filtered relative sunspot number is found to be -0.79 at confidence level greater than 99% with a time-lag of 4 months, with solar activity preceding the Dst variation. The correlation between the unfiltered data of Dst and of the sunspot number is also high with a similar time-lag. Such a timelag has not been discussed in the literature, and a further study is required to establish the mode of sun-earth relationship that gives this time delay.

Sugiura, M.↗
NASA NTRS1977

Geomagnetic activity: Dependence on solar wind parameters

Current ideas about the interaction between the solar wind and the earth's magnetosphere are reviewed. The solar wind dynamic pressure as well as the influx of interplanetary magnetic field lines are both important for the generation of geomagnetic activity. The influence of the geometry of the situation as well as the variability of the interplanetary magnetic field are both found to be important factors. Semi-annual and universal time variations are discussed as well as the 22-year cycle in geomagnetic activity. All three are found to be explainable by the varying geometry of the interaction. Long term changes in geomagnetic activity are examined.

Svalgaard, L.↗
NASA NTRS1976

Quasi-biennial geomagnetic variation caused by the sun

Clear evidence for the existence of a quasi-biennial geomagnetic variation is shown by an analysis of annual averages of the horizontal (H) component of the geomagnetic field observed at five observatories. The analysis uses a numerical filter, which is equivalent to taking the second order time derivative of the time series. The cause for the variation is external to the earth because its amplitude depends on magnetic activity. The second order time derivative of H is well correlated with the corresponding time derivatives of the relative sunspot number and 10.7 cm solar flux. It is suggested that quasi-biennial oscillations observed in the geomagnetic field, cosmic rays, stratospheric zonal wind and temperature, total ozone, and other meteorological parameters could be produced by a common cause on the sun.

Sugiura, M.↗