A proposal to continue studying low frequency hydromagnetic waves using ATS-1 data
Correlation between frequency of magnetic oscillations and geomagnetic disturbances, and low frequency oscillation of earth magnetic field
Cummings, W. D.↗
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Investigation of the association of magnetopause instability with interplanetary sector structure
The variation of the solar wind parameters (speed, magnetic field intensity, and proton density) and geomagnetic disturbance with location within the interplanetary sector structure is well established. The Kelvin-Helmholtz instability of the magnetopause provides a mechanism for the initiation of worldwide geomagnetic disturbance. Since the Kelvin-Helmholtz mechanism depends on an integration of several of the solar wind parameters, it was considered of interest to see how it varies within the sector structure. Support is given to the idea that the integration of the solar wind parameters via Kelvin-Helmholtz instability is an important concept in understanding geomagnetic disturbance.
Boller, B. R.↗
Ionosonde observations of the northern magnetospheric cleft during December 1974 and January 1975
During December 1974 and January 1975, the northern magnetospheric cleft was monitored by ionosondes at Cape Parry and Sachs Harbor, Northwest Territories, Canada, in support of rocket shots into the cleft. Ionograms were taken nominally at 15-min intervals but as rapidly as two per minute during times of particular interest. Analysis of 5 days of data shows the ionosphere at cleft latitudes to be very complex and dynamic. The ionograms often show considerable structure and can change appearance significantly in a minute or two. The cleft at times appears to move equatorward in response either to a southward turning of the interplanetary magnetic field or to the occurrence of geomagnetic disturbances. This response is in agreement with the conclusions of previous satellite studies. Behavior contrary to this generalization is not uncommon, however, and therefore it may not always hold on time scales considerably shorter than the satellite orbital period of at least 1 hour. The rate of the cleft's motion may vary from about 0.05 to 0.5 deg/min.
Stiles, G. S.↗
A decameter type II burst associated with a behind-the-limb flare
The characteristics of a decametric type II burst associated with a possible behind-the-limb flare are discussed. The burst source had an unusually high velocity. Assuming that the disturbance propagated as an MHD wave, the magnetic field strength at the 40-MHz plasma level is estimated to be 5.6 gauss.
Gergely, T. E.↗
Parallel acceleration and transport of ions from polar ionosphere to plasma sheet
The effect of the convection electric field in accelerating ions that escape from the polar ionosphere is investigated. It is shown that at high altitudes the velocity component of the ions along the magnetic field may be increased by more than an order of magnitude. The highest velocities are acquired by ions that escape from the region of the ionosphere that is connected along magnetic field lines to the dayside cusps. During disturbed times, ions from that region intercept the center plane of the magnetotail in one to two hours at radial distances exceeding about 6 earth radii. Investigation of the resulting O(+) properties in the center plane, viz., their locations, number densities, and energies, indicates that the polar ionosphere near the cusps is the principal source of the O(+) observed in the plasma sheet. Moreover, a study of the ion motion at quiet and disturbed times indicates that the increase of O(+) in the plasma sheet with increasing AE values (Lennartsson and Shelley, 1986) is due mainly to an increase in the source of O(+) rather than alteration of its transport path.
Cladis, J. B.↗
A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution
A broad class of astronomical accretion disks is presently shown to be dynamically unstable to axisymmetric disturbances in the presence of a weak magnetic field, an insight with consequently broad applicability to gaseous, differentially-rotating systems. In the first part of this work, a linear analysis is presented of the instability, which is local and extremely powerful; the maximum growth rate, which is of the order of the angular rotation velocity, is independent of the strength of the magnetic field. Fluid motions associated with the instability directly generate both poloidal and toroidal field components. In the second part of this investigation, the scaling relation between the instability's wavenumber and the Alfven velocity is demonstrated, and the independence of the maximum growth rate from magnetic field strength is confirmed.
Balbus, Steven A.↗
Regions of negative Bz in the Tsyganenko 1989 model neutral sheet
A disturbing feature of the Tsyganenko (1989) model magnetic field, namely the occurrence of negative Bz in the model neutral sheet is pointed out. On the basis of observations of Bz in the neutral sheet it is concluded that this is an artifact of the model and not a real effect. This feature of the model should be considered when the model is used either to infer mappings from the ionosphere to the vicinity of the neutral sheet or as a tool in theoretical studies. It is proposed that in the development of future models, it would be useful for the distribution of Bz in the neutral sheet to be imposed as a constraint on the model.
Donovan, E. F.↗
Remote sensing of two-dimensional magnetopause structures
The study presents a technique for analyzing remote measurements made by a single spacecraft of 2D disturbances in the ambient magnetosheath or magnetospheric magnetic field caused, for example, by flux transfer events or pressure pulses. The methodology is based on a recent linear theory for isentropic field-aligned MHD flow over gently sloping 2D obstacles. The technique uses only magnetic field measurements and can provide information about the orientation and actual cross-sectional shape of the event, as well as information about the spacecraft trajectory relative to the bulge. Analysis of two sample events, one recorded by the AMPTE/IRM spacecraft in the magnetosheath and the other by AMPTE/CCE in the magnetosphere, indicates that the bulges on the magnetopause surface causing the magnetic field and flow perturbations for these events did not have the semicircular cross section suggested in previous work; instead they had a more elongated shape, the dimension tangential to the magnetopause being substantially larger than that normal to it.
Walthour, D. W.↗
Interplanetary magnetic field enhancements - Evidence for solar wind dust trail interactions
Magnetic disturbances related to the passage of the asteroid 2201 Oljato are described. It is pointed out that the process leading to these disturbances must be associated with material in the orbit of Oljato and not the Oljato asteroid itself. Using data from latest space observations, the statistical association of these disturbances with the orbit of 2201 Oljato is updated, and the possible mechanisms for causing the disturbances are discussed. The phenomenon is considered to be associated with comet-like processes in the solar wind.
Russell, C. T.↗
On the prediction of magnetospheric configuration
A simple model of magnetic flux transfer is reviewed along with empirical expressions for flux transfer rates based upon the auroral AL index and the eastward component of the interplanetary electric field. It is shown that the magnitude of the time integral of the AL index over isolated intervals of geomagnetic disturbance can be predicted from the the observed flux of southward interplanetary magnetic field lines incident on the front of the magnetosphere. Difficulties in the quantitative prediction of substorm onset time and intensity are discussed and magnetospheric stress index on both solar wind and ground based observations is proposed for this purpose. Finally, caveats concerning the use of both the AL index and interplanetary medium data in predicting the response of the magnetosphere to solar wind conditions are considered.
Slavin, J. A.↗
Improved State Estimation in Distorted Magnetic Fields
The magnetic field of the Earth – besides varying naturally – may be disturbed locally by the (man-made) environment. State estimation and corresponding navigation frameworks that use magnetometers on-board of mobile platforms suffer from severe performance loss or failure upon local magnetic distortions if these are not detected and mitigated adequately. Advanced estimators include the magnetic variation in the state vector. However, Cartesian coordinates, although widely used in the literature, suffer from observability issues when it comes to disturbance detection. This paper shows the importance of representing the magnetic variation in a spherical coordinate system and subsequent improvements with respect to the common representation in Cartesian coordinates. The spherical representation improves estimator consistency and allows for accurate and fast mitigation of magnetic disturbances through consistent statistical tests which leads to better system state estimates in magnetically distorted areas. The approach is validated by performing tests with simulated and real-world data on embedded hardware.
Brommer, Christian↗
Effects of thermospheric motions on the polar wind - A time-dependent numerical study
This paper presents the results of a numerical study investigating the effects of low-altitude short-duration plasma heating episodes (such as horizontal frictional heating) on transient heavy ion outflows from the polar ionosphere using a time-dependent model. In a previous set of calculations, where the effects of high-altitude transient heat sources were investigated, the low-altitude neutral atmosphere (z less than 800 km) acted as a very efficient heat sink, absorbing most of the energy conducted to this region and thus preventing large differences between the ion and neutral temperatures. One purpose of the present study was to investigate whether realistic, specified low-altitude frictional heating rates, based on published experimental data, can result in elevated ion temperatures and lift a part of the heavy ion population over the gravitational barrier before the extra energy is lost to the neutral atmosphere. In these model calculations the specified heating generated an upflowing O(+) disturbance (with a normalized peak flux of about 100 million/sq cm per sec) moving upward along the open magnetic field line with a velocity of about 2 km/s. The spatial extent of the disturbance was approximately equal to the disturbance velocity times the duration of the heat source. The model results provide a possible mechanism to explain recent European Incoherent Scatter observations of high-latitude O(+) upwellings.
Gombosi, T. I.↗
Average high latitude magnetic field - Variation with interplanetary sector and with season. II
Average high-latitude magnetic-field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1- to 1+, 2- to 3+ and greater than or equal to 4-. Except for 0 to 0800 hr MLT, 55 to 78 deg invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance. Other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems and nonionospheric sources are present in addition to latitudinally narrow electrojet currents.
Langel, R.↗
Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, George Williams College, Lake Geneva, Wis., September 30-October 4, 1974, Proceedings
The papers deal with solar-wind and magnetospheric interactions with the moon, ancient and present-day lunar surface magnetic and electric fields, the dynamics and evolution of the lunar atmosphere, the lunar record of solar radiation, and nonmeteoric transport of lunar surface materials. Topics discussed include bow-shock protons in the lunar environment, energetic ion events during the lunar night, mapping of the lunar surface magnetic field from orbital observations of mirrored electrons, geomagnetic disturbances induced by the moon, the relationship between lunar topography and limb compressions, measurements of lunar sky brightness, atmospheric supply and loss mechanisms on the moon, the nature and composition of the lunar atmosphere, molecular gas species in that atmosphere, and vacuum-UV spectroscopic measurements of the surface properties of lunar materials. Individual items are announced in this issue.
Source record↗
Observations of Lunar Swirls by the Diviner Lunar Radiometer Experiment
The presence of anomalous, high albedo markings on the lunar surface has been known since the Apollo era. These features, collectively known as lunar swirls, occur on both the mare and highlands. Some swirls are associated with the antipodes of major impact basins, while all are associated with magnetic field anomalies of varying strength. Three mechanisms have been proposed for the formation of the swirls: (1) solar wind standoff due to the presence of magnetic fields, (2) micrometeoroid or comet swarms impacting and disturbing the lunar surface, revealing unweathered regolith, and (3) transport and deposition of fine-grained feldspathic material. Diviner s unique capabilities to determine silicate composition and degree of space weathering of the lunar surface, in addition to its capabilities to determine thermophysical properties from night-time temperature measurements, make it an ideal instrument to examine the swirls and help differentiate among the three proposed formation mechanisms.
Glotch, T. D.↗
Exploring the Use of Alfven Waves in Magnetometer Calibration at Geosynchronous Orbit
An Alfven wave is a type magnetohydrodynamicwave that travels through a conducting fluid under the influence of a magnetic field. Researchers have successfully calculated offset vectors of magnetometers in interplanetary space by optimizing the offset to maximize certain Alfvenic properties of observed waves (Leinweber, Belcher). If suitable Alfven waves can be found in the magnetosphere at geosynchronous altitude then these techniques could be used to augment the overall calibration plan for magnetometers in this region such as on the GOES spacecraft, possibly increasing the time between regular maneuvers. Calibration maneuvers may be undesirable because they disrupt the activities of other instruments. Various algorithms to calculate an offset using Alfven waves were considered. A new variation of the Davis-Smith method was derived because it can be mathematically shown that the Davis-Smith method tolerates filtered data, which expands potential applications. The variant developed was designed to find only the offset in the plane normal to the main field because the overall direction of Earth's magnetic field rarely changes, and theory suggests the Alfvenic disturbances occur transverse to the main field. Other variations of the Davis-Smith method encounter problems with data containing waves that propagate in mostly the same direction. A searching algorithm was then designed to look for periods of time with potential Alfven waves in GOES 15 data based on parameters requiring that disturbances be normal to the main field and not change field magnitude. Final waves for calculation were hand-selected. These waves produced credible two-dimensional offset vectors when input to the Davis-Smith method. Multiple two-dimensional solutions in different planes can be combined to get a measurement of the complete offset. The resulting three dimensional offset did not show sufficient precision over several years to be used as a primary calibration method, but reflected changes in the offset fairly well, suggesting that the method could be helpful in monitoring trends of the offset vector when maneuvers cannot be used.
calibration↗
Understanding the impact of an applied axial magnetic field on efficient current coupling on the Z machine
Magnetized liner inertial fusion (MagLIF) is an attractive concept for producing thermonuclear fusion reactions. The MagLIF platform involves the operation of Helmholtz coils to apply a 15 Tesla axial magnetic field to the load region, where a cylindrical, fuel-filled metal liner is imploded by a ∼ 2 0 MA current pulse. The fringe field from these coils extends into the transmission line that delivers the current to the target. We investigated the extent to which this applied field disturbs the nominal power flow within that transmission line. A simplified model of the geometry shows that adding the applied magnetic field results in magnetic field lines that connect the cathode to the anode, suggesting electrons may not be magnetically insulated in this region. Particle-in-cell simulations indicated the addition of the applied magnetic field would not significantly impact the current delivery to the load. Velocimetry was used to experimentally assess the current delivery with and without the applied magnetic field. We find no measurable effects of the applied field on current delivery in the configuration investigated in this study. Published by the American Physical Society 2024
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Solar Cycle Predictions Near Sunspot Minimum
Observations of solar magnetic activity and the dynamics of the solar convection zone have produced severe constraints on models of the Sun's magnetic dynamo. These constraints are so severe that, at present, we do not have numerical models that can accept the current conditions and then march forward in time to predict future activity. Given this state of solar dynamo theory we are forced to examine previous behavior to discover patterns and trends that afford us some measure of predictability. Here we examine the behavior of several indicators of solar activity near solar minimum that are well correlated with the amplitude of the following solar maximum to predict the level of solar activity over cycle 23. Sunspot numbers, areas, and positions are useful for characterizing solar cycle behavior due to the extent of the data (12 cycles or more). These data exhibit several patterns that relate future activity to past behavior. With the Odd-Even effect the odd numbered cycles have been larger than their even numbered predecessors for each of the last six cycle pairs. With the Amplitude-Period effect short period cycles have been followed by large amplitude cycles and long period cycles have been followed by small amplitude cycles for 10 of the last 13 cycles. With the Maximum-Minimum effect the sunspot number at minimum is directly correlated with the sunspot number at maximum for a given cycle. The geomagnetic indices aa and Ap are also related to solar activity by the connections between disturbances in the solar wind and variations in the Earth's magnetic field. Like the Maximum-Minimum effect for sunspots, the size of the aa and Ap indices at minimum are directly related to the amplitude of the following maximum. The number of geomagnetically disturbed days (days with Ap >= 25) over the course of a cycle is another indicator for the size of the next cycle. The aa and Ap indices can each be separated into a component in phase with the current sunspot cycle and an "extended cycle" component that is directly related to the following cycle. Individually each of these indicators provides some measure of predictive ability for the amplitudes of previous cycles. Taken in combination we find that the predictions are much more accurate. Our multi-variate analysis indicates that a maximum sunspot number of 160 +/- 20 should occur near the end of 1999 for cycle 23.
Hathaway, David H.↗