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Results for “local electric field mapping”

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NASA NTRS1988

Mapping electrodynamic features of the high-latitude ionosphere from localized observations - Technique

This paper describes a novel procedure for mapping high-latitude electric fields and currents and their associated magnetic variations, using sets of localized observational data derived from different types of measurements. The technique provides a formalism for incorporating simultaneously such different classes of data as electric fields from radars and satellites, electric currents from radars, and magnetic perturbations at the ground and at satellite heights; the technique also uses available statistical information on the averages and variances of electrodynamic fields. The technique provides a more rigorous way of quantitatively estimating high-latitude electric field and current patterns than other methods and has a capability to quantify the errors in the mapped fields, based on the distribution of available data, their errors, and the statistical variances of the fields. The technique is illustrated by an application to a substorm which was analyzed by Kamide et al. (1982) by an earlier technique.

Richmond, A. D.↗

NASA NTRS2011

A Multiple Sphere T-Matrix Fortran Code for Use on Parallel Computer Clusters

A general-purpose Fortran-90 code for calculation of the electromagnetic scattering and absorption properties of multiple sphere clusters is described. The code can calculate the efficiency factors and scattering matrix elements of the cluster for either fixed or random orientation with respect to the incident beam and for plane wave or localized- approximation Gaussian incident fields. In addition, the code can calculate maps of the electric field both interior and exterior to the spheres.The code is written with message passing interface instructions to enable the use on distributed memory compute clusters, and for such platforms the code can make feasible the calculation of absorption, scattering, and general EM characteristics of systems containing several thousand spheres.

Mackowski, D. W.↗

NASA NTRS1981

Magnetospherically trapped ions as a source of magnetosheath energetic ions

It has been suggested that energetic ions observed in the magnetosheath may be due to the direct leakage of trapped magnetospheric ions. To test this hypothesis, three-dimensional ion spectra from the energetic particle experiment on ISEE 1 for a magnetopause crossing on Nov. 10, 1977 are utilized to construct three-dimensional distribution functions in the magnetosphere and in the sheath. Using the observed magnetic field, a simple one-dimensional model of the magnetopause is developed. Ions are then followed in the model, starting in the magnetosphere, through the magnetopause and ending up in the sheath. Using Liouville's Theorem a model sheath distribution function is then built up by following the magnetospheric distribution function through the model fields. The model distribution is then compared with the observed sheath distribution. For this case it is found that the main features of the observed ions in the sheath are consistent with direct leakage and with no energization or de-energization processes, and an inward-pointing normal component is required. The energetic particles mapped in this case apparently follow a flux tube which does not penetrate the magnetopause where local tangential electric fields have been reported.

Speiser, T. W.↗

NASA NTRS1984

Electrical structure in the high-latitude middle atmosphere

Large V/m electric fields, both horizontal and vertical, have been observed within bounded regions of the upper stratosphere and lower mesosphere. They seem to occur only in regions where the electrical conductivity is a few times 10 to the -10th S/m or less and appear to be current limited. While low conductivity is necessary, it is not a sufficient condition for occurrence. The observed large horizontal electric fields were found to be anticorrelated with the local neutral wind. Large variations in the conductivity were also observed to occur with fluctuations in magnetic activity, and these were found to be consistent with measured variations in energy deposition during auroral phenomena. Theoretical concepts of mapping of electric fields downward from the thermosphere along equipotential magnetic field lines were shown to hold qualitatively in the D-region at the mV/m level. Perturbations affecting such models were determined to be small.

Maynard, N. C.↗

NASA NTRS1984

Ambipolar diffusion in the middle atmosphere

In the middle atmosphere above 60 km, the electron concentration increases with altitude, reaching values of 10 to the 10th per cu m in the daytime ionospheric E region near 100 km. The electrons are more mobile than the ions and diffuse more rapidly through the neutral atmosphere. The electron diffusion polarizes the medium, causing an electric field to develop that acts to retard the electron diffusion and enhance the conduction current of ions. A global zonally averaged numerical model of atmosheric electricity from the ground to 100 km is used to examine the effect of ambipolar diffusion and the earth's geomagnetic field on the currents and fields in the middle atmosphere. The results show that above about 65 km, ambipolar diffusion generates local electric fields and conduction currents that balance electron diffusion currents. The electric fields and conduction currents are a few orders of magnitude larger than the vertical fields and currents calculated from the downward mapping of the ionospheric potential without taking electron diffusion into account. Ambipolar diffusion does not alter the total current flowing in the global circuit. It is a local effect where enhanced conduction currens flow to balance the electron diffusion current.

Tzur, I.↗

NASA NTRS2023

Editorial: Understanding the Causes of Asymmetries in Earth’S Magnetosphere-Ionosphere System

Geomagnetic activity observed in geospace, the upper atmosphere, and on the ground results from solar-terrestrial interactions. Such interactions correspond to the coupling between the solar wind, magnetosphere, and the thermosphere-ionosphere (MIT) system (Khazanov, 2016). However, given the complexity of the whole system and its large spatial scale and long-term solar variability, effects resulting from this coupling can be asymmetric. For example, inter-hemispherical asymmetric responses can arise when a hemisphere receives more energy than the other (e.g., Knipp et al., 2021; Pakhotin et al., 2021), local time effects can take place due to the occurrence of intense dawn-dusk interplanetary electric fields (e.g.,Haaland et al., 2017), and asymmetric geomagnetic field and mapping are caused by the Earth’s dipole offset and tilt (e.g., Laundal et al., 2017). The drivers that generate asymmetric MIT coupling response are generally recognized as long term: solar activity (Zhang et al., 2022) and dipole offset and tilt (Laundal et al., 2017); middle term: seasons (Lu et al., 2010); and short term: the y and z components of the interplanetary magnetic field (IMF) (Cowley, 1981; Li et al., 2011; Knipp et al., 2021). Thermospheric neutral mass density can present local time asymmetries associated with IMF By (Forster et al., 2017), and inter-hemispheric asymmetries can be generated by cross-hemispheric propagation of large-scale gravity waves (Bruinsma and Forbes, 2007). In addition, forcing from the mesosphere and lower thermosphere can generate inter-hemispheric neutral wind asymmetric patterns that can in turn asymmetrically impact neutral density in different hemispheres (Stober et al., 2021).

magnetosphere-ionophere coupling↗

NASA NTRS1991

Radio sky mapping from satellites at very low frequencies

Wave Distribution Function (WDF) analysis is a procedure for making sky maps of the sources of natural electromagnetic waves in space plasmas, given local measurements of some or all of the three magnetic and three electric field components. The work that still needs to be done on this subject includes solving basic methodological problems, translating the solution into efficient algorithms, and embodying the algorithms in computer software. One important scientific use of WDF analysis is to identify the mode of origin of plasmaspheric hiss. Some of the data from the Japanese satellite Akebono (EXOS D) are likely to be suitable for this purpose.

Storey, L. R. O.↗

NASA NTRS1991

6.7 radio sky mapping from satellites at very low frequencies

Storey, L. R. O.↗

NASA NTRS2010

Plasma IMS Composition Measurements for Europa and the Other Galilean Moons

NASA and ESA are planning the joint Europa Jupiter System Mission (EJSM) to the Jupiter system with specific emphasis to Europa and Ganymede, respectively. The Japanese Space Agency is also planning an orbiter mission to explore Jupiter's magnetosphere and the Galilean satellites. For NASA's Jupiter Europa Orbiter (JEO) we are developing the 3D Ion Mass Spectrometer (IMS) with two main goals which can also be applied to the other Galilean moons, 1) measure the plasma interaction between Europa and Jupiter's magnetosphere and 2) infer the 4 pi surface composition to trace elemental and significant isotopic levels. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second gives information about transfer of material between the Galilean moons, and between the moon surfaces and subsurface layers putatively including oceans. The measurement of the interactions for all the Galilean moons can be used to trace the in situ ion measurements of pickup ions back to either Europa's or Ganymede's surface from the respectively orbiting spacecraft. The IMS instrument, being developed under NASA's Astrobiology Instrument Development Program, would maximally achieve plasma measurement requirements for JEO and EJSM while moving forward our knowledge of Jupiter system composition and source processes to far higher levels than previously envisaged. The composition of the global surfaces of Europa and Ganymede can be inferred from the measurement of ejected neutrals and pick-up ions using at minimum an in situ payload including MAG and IMS also fully capable of meeting Level 1 mission requirements for ocean detection and survey. Elemental and isotopic analysis of potentially extruded oceanic materials at the moon surfaces would further support the ocean objectives. These measurements should be made from a polar orbiting spacecraft about Europa or Ganymede at height 100 km. The ejecta produced by sputtering of the surfaces of Europa and Ganymede has been shown to be representative of the surface composition. Level 2 science on surface geology and composition can then be further enhanced by addition of the following: 3D Ion Neutral Mass Spectrometer (INNS), 3D plasma electron spectrometer (ELS), and hot plasma energetic particle instrument. The measurement approach is to alternate between times measuring pickup ions and times measuring plasma and magnetic field parameters along the spacecraft trajectory. By measuring the pickup ion energy, arrival direction and mass-per-charge, the ion can be traced back along the ejection trajectory to the approximate area of origin if the 3-D electric field and magnetic field are known. In situ observations of plasma flow velocities and vector magnetic fields can be used to determine the local convective electric field (E = -VXB) along the spacecraft trajectory. By combining this information with models of the magnetospheric interaction with Europa, one can generate 3D maps of the electric and magnetic field and compute the trajectories of the pickup ions back to the surface or exospheric points of origin. In the case of Ganymede there is the additional complexity of its own internal dipole magnetic field, while Io's volcanic activity introduces the complexity of a highly structured denser atmosphere. Callisto with its less globally extended exosphere will have a simpler interaction than for Europa (i.e., more like our moon). We will discuss these differences in light of the above proposed technique. Finally, the INNS observations and neutral exosphere models are needed to estimate production rates of pickup ions. The hot plasma measurements are needed to correct for sputtering rates which can be time dependent and electron plasma observations for electron impact ionization rates. Instrument characteristics, field-of-view requirements, modes of operation and effects of radiation on instrument functionality will be discussed.

Sittler, Edward↗

NASA NTRS1990

Electric field measurements during the MAC/EPSILON campaign

The MAC/EPSILON observational campaign in northern Norway involved the taking of three-axis electric field measurements of the middle atmosphere by means of five rocketborne payloads during October and November, 1987. Simultaneous horizontal electric field measurements made by two of the rocket flights were in general agreement in their limited overlap region. The more extensive horizontal E-field measurements exhibited a decreasing mapping function with decreasing altitude, thereby indicating the presence of fields from a local auroral patch. Small-scale variations in the horizontal fields of the lights were similar to observed wavelike variations in the neutral wind field.

Croskey, C. L.↗

NASA NTRS1992

Lunar and Asteroid Composition Using a Remote Secondary Ion Mass Spectrometer

Laboratory experiments simulating solar wind sputtering of lunar surface materials have shown that solar wind protons sputter secondary ions in sufficient numbers to be measured from low-altitude lunar orbit. Secondary ions of Na, Mg, Al, Si, K, Ca, Mn, Ti, and Fe have been observed sputtered from sample simulants of mare and highland soils. While solar wind ions are hundreds of times less efficient than those used in standard secondary ion mass spectrometry, secondary ion fluxes expected at the Moon under normal solar wind conditions range from approximately 10 to greater than 10(exp 4) ions cm(sup -2)s(sup -1), depending on species. These secondary ion fluxes depend both on concentration in the soil and on probability of ionization; yields of easily ionized elements such as K and Na are relatively much greater than those for the more electronegative elements and compounds. Once these ions leave the surface, they are subject to acceleration by local electric and magnetic fields. For typical solar wind conditions, secondary ions can be accelerated to an orbital observing location. The same is true for atmospheric atoms and molecules that are photoionized by solar EUV. The instrument to detect, identify, and map secondary ions sputtered from the lunar surface and photoions arising from the tenuous atmosphere is discussed.

Elphic, R. C.↗

NASA NTRS1990

Observations of ionospheric flux ropes above South Pole

Numerical techniques have been used to investigate two different models of the current flow in ionospheric flux ropes, giving attention to the problem of mapping the electric field from the ionosphere down to balloon altitudes and to the isolated event that occurred at about 1625 UT on January 3, 1986. Also examined are Greenland magnetometer chain and Iqaluit magnetometer data, which imply that the isolated event was localized in longitude as well as 'global', in the sense that it occurred at conjugate points. IMP 8 solar wind plasma and IMF data indicate that the even occurred just as a strong southward turning of the IMF passed the earth.

Lin, Z. M.↗

NASA NTRS1989

Middle Atmosphere Electrodynamics (MAE). Middle atmospheric electrodynamics during MAP

The recent revival and strong motivation for research in middle atmospheric electrodynamics can be attributed, in large part, to the discovery of large (V/m) electric fields within the lower mesosphere during the decade prior to MAP. Subsequent rocket soundings appeared to verify the preliminary findings. During the MAP era, more sophisticated techniques have been employed to obtain measurements which respond positively to criticisms of earlier results, and which provide more insight regarding the character of the fields. The occurrence of mesospheric V/m electric fields now seems to require the presence of aerosols, of local winds and related dynamics, and of an atmospheric electrical conductivity less than 10(-10)S/m. Furthermore, new theoretical ideas describing the origin of the V/m fields are consistent with the measurements. The current status of results regarding V/m fields in the middle atmosphere is reviewed in light of the more widely accepted electric field structure for this region from rocket, balloon and modeling results.

Goldberg, R. A.↗

NASA NTRS1988

Mapping of auroral kilometric radiation sources to the aurora

Auroral kilometric radiation (AKR) and optical auroral emissions are observed simultaneously using plasma wave instrumentation and auroral imaging photometers carried on the DE 1 spacecraft. The DE 1 plasma wave instrument measures the relative phase of signals from orthogonal electric dipole antennas, and from these measurements, apparent source directions can be determined with a high degree of precision. Wave data are analyzed for several strong AKR events, and source directions are determined for several emission frequencies. By assuming that the AKR originates at cyclotron resonant altitudes, a candidate source field line is identified. When the selected source field line is traced down to auroral altitudes on the concurrent DE 1 auroral image, a striking correspondece between the AKR source field line and localized auroral features is produced. The magnetic mapping study provides strong evidence that AKR sources occur on field lines associated with discrete auroral arcs, and it provides confirmation that AKR is generated near the electron cyclotron frequency.

Huff, R. L.↗

NASA NTRS2000

Polar Spacecraft Based Comparisons of Intense Electric Fields and Poynting Flux Near and Within the Plasma Sheet-Tail Lobe Boundary to UVI Images: An Energy Source for the Aurora

In this paper, we present measurements from two passes of the Polar spacecraft of intense electric and magnetic field structures associated with Alfven waves at and within the outer boundary of the plasma sheet at geocentric distances of 4-6 R(sub E), near local midnight. The electric field variations have maximum values exceeding 100 mV/m and are typically polarized approximately normal to the plasma sheet boundary. The electric field structures investigated vary over timescales (in the spacecraft frame.) ranging front 1 to 30 s. They are associated with strong magnetic field fluctuations with amplitudes of 10-40 nT which lie predominantly ill the plane of the plasma sheet and are perpendicular to the local magnetic field. The Poynting flux associated with the perturbation fields measured at these altitudes is about 1-2 ergs per square centimeters per second and is directed along the average magnetic field direction toward the ionosphere. If the measured Poynting flux is mapped to ionospheric altitudes along converging magnetic field lines. the resulting energy flux ranges up to 100 ergs per centimeter squared per second. These strongly enhanced Poynting fluxes appear to occur in layers which are observed when the spacecraft is magnetically conjugate (to within a 1 degree mapping accuracy) to intense auroral structures as detected by the Polar UV Imager (UVI). The electron energy flux (averaged over a spatial resolution of 0.5 degrees) deposited in the ionosphere due to auroral electron beams as estimated from the intensity in the UVI Lyman-Birge-Hopfield-long filters is 15-30 ergs per centimeter squared per second. Thus there is evidence that these electric field structures provide sufficient Poynting flux to power the acceleration of auroral electrons (as well as the energization of upflowing ions and Joule heating of the ionosphere). During some events the phasing and ratio of the transverse electric and magnetic field variations are consistent with earthward propagation of Alfven surface waves with phase velocities of 4000-10000 kilometers per second. During other events the phase shifts between electric and magnetic fields suggest interference between upward and downward propagating Alfven waves. The E/B ratios are about an order of magnitude larger than typical values of C/SIGMA(sub p), where SIGMA(sub p), is the height integrated Pedersen conductivity. The contribution to the total energy flux at these altitudes from Poynting flux associated with Alfven waves is comparable to or larger than the contribution from the particle energy flux and 1-2 orders of magnitude larger than that estimated from the large-scale steady state convection electric field and field-aligned current system.

Wygant, J. R.↗

NASA NTRS1989

Mapping of the solar wind electric field on the earth's polar caps

A quantitative model of a magnetically interconnected (open) magnetosphere is developed as a perturbation of Voight's closed magnetosphere model with a given magnetopause shape. The model is shown to give a reasonable representation of the open magnetosphere configuration and is especially useful in testing the magnetospheric consequences of various merging theories. The convection pattern obtained for southward IMF is in reasonable agreement with observations, especially in the manifestation of a convection 'throat' near noon. For northward IMF, this region of constricted flow is rotated in local time in the direction of the IMF, also in accordance with observations.

Toffoletto, F. R.↗

NASA NTRS1983

A statistical study of large electric field events in the earth's magnetotail

A statistical study of large electric field events, measured on ISEE 1 at geocentric distances of 3 to 23 earth radii, has been performed in order to determine the occurrence frequency and spatial distribution of such events. Large electric fields were seen at all altitudes, with the lowest altitude events occurring on auroral field lines and the higher altitude events occurring on the high latitude boundary of the plasma sheet. The largest events had amplitudes that were approximately proportional to the square root of the local magnetic field strength, in agreement with expectations of a simple mapping model. The apparent concentration of big field events near local midnight is caused, at least in part, by a nonuniform frequency of satellite crossings through the plasma sheet boundary as a function of local time. Thus, the spatial distribution and amplitudes of the large field events are not inconsistent with the mapping of low-altitude electrostatic shocks to the plasma sheet boundary along equipotential magnetic field lines.

Levin, S.↗

NASA NTRS1981

Formation of auroral arcs by plasma sheet processes

It is noted that, in the distant plasma sheet, it is likely that curvature drift is the most important source of drift parallel to the electric field, leading to what is commonly called Fermi acceleration of the particles. The energization mechanism here is proportional to the neutral sheet current density. It is a form of field-aligned acceleration, with rapid lowering of mirror points, caused by the transverse electric field in the plasma sheet. It is noted that the process will work for both negative and positive particles. A filamentation of the neutral current sheet is postulated. Here, the maximum energization by curvature drift and the accompanying intense precipitation will form an auroral band or arc along the sheet of magnetic field lines that maps out to the local enhancement of the crosstail current, explaining inverted V events.

Heikkila, W. J.↗