Engineering topics

Winningham, J. D.

Publications and source records attributed to Winningham, J. D..

At least 37 records · Page 2

NASA NTRS1993

The UARS particle environment monitor

The overall objective of the particle environment monitor (PEM) is to provide comprehensive measurements of both local and global energy inputs into the earth's atmosphere by charged particles and Joule dissipation using a carefully integrated set of instruments. PEM consists of four instruments: the atmospheric X-ray imaging spectrometer (AXIS), the high-energy particle spectrometer (HEPS), the medium-energy particle spectrometer (MEPS), and the vector magnetometer (VMAG). AXIS provides global scale images and energy spectra of 3- to 100-keV bremsstrahlung X-rays produced by electron precipitation into the atmosphere. HEPS and MEPS provide in situ measurements of precipitating electrons in the energy range from 1 eV to 5 MeV and protons in the energy range from 1 eV to 150 MeV. Particles in this energy range deposit their energy in the atmosphere at altitudes extending from several hundred kilometers down to as low as about 30 km. VMAG provides the magnetic field direction needed to indicate and interpret the locations and intensities of ionospheric and field-aligned currents as well as providing a reference for the particle measurements. Examples of data acquired early in the Upper Atmosphere Research Satellite (UARS) mission are presented.

Winningham, J. D.↗

NASA NTRS1993

Observations of the UARS Particle Environment Monitor and computation of ionization rates in the middle and upper atmosphere during a geomagnetic storm

In this paper we present observations made by the Particle Environment Monitor (PEM) instruments during the geomagnetic storm of 8-9 November, 1991. Ionization and energy deposition rates as functions of altitude in the middle and upper atmosphere by incident electrons and positive ions in the storm interval are computed. The suite of PEM instruments provides a systematic measurement of energetic particles and their associated X-rays over an energy range not fully covered by previous satellite missions.

Sharber, J. R.↗

NASA NTRS1993

Atmospheric energy input and ionization by energetic electrons during the geomagnetic storm of 8-9 November 1991

The Atmospheric X-ray Imaging Spectrometer (AXIS) of the Particle Environment Monitor investigation aboard the Upper Atmosphere Research Satellite monitors energy input to the upper atmosphere due to energetic electrons. Analysis of the AXIS data from the major geomagnetic storm of 8-9 November 1991 is presented. During the November storm, electrons above a few keV flowing into a substantially expanded auroral zone provided the bulk of the ionizing power to the upper atmosphere. At the peak of the disturbance the total AXIS-observed power reached 40 GW. On 9 November the whole day average atmospheric ionization rate in the auroral zone at 80 km altitude exceeded the rate due to solar UV and solar X-rays by a factor of over 10 to 100.

Chenette, D. L.↗

NASA NTRS1993

Auroral currents during the magnetic storm of November 8 and 9, 1991 - Observations from the Upper Atmosphere Research Satellite Particle Environment Monitor

The development of the intensity and location of Birkeland currents associated with the magnetic storm of November 8-9, 1991 is reported. Total Birkeland currents exceed 30 MA, more than six times nominal values, indicating Joule heating of about 3 x lO exp 12 W. Birkeland currents below 50 deg, polar cap currents indicative of antisunward convection, and cusp particle signatures of southward IMF all persist at least eight hours into recovery phase of the storm.

Anderson, B. J.↗

NASA NTRS1993

Pickup water group ions at Comet Grigg-Skjellerup

The density and velocity distribution of cometary water group ions was measured by the Giotto spacecraft in the regions upstream and downstream of the 'bow shock' at Comet Grigg-Skjellerup. The results show that the distributions of ions are ring-like until quite close to the shock, the timescales for pitch angle and energy diffusion appear similar and the ion density follows a r exp -2 dependence.

Coates, A. J.↗

NASA NTRS1993

Characterization of the IMF By-dependent field-aligned currents in the cleft region based on DE 2 observations

The magnetic field and plasma data from 47 passes of DE-2 are used to study the IMF By-dependent distribution of field-aligned currents in the cleft region. It is proposed that the low-latitude cleft current (LCC) region is not an extension of the region 1 or region 2 current system and that a pair of LCCs and high-latitude cleft currents (HCCs) constitutes the cleft field-aligned current regime. The proposed pair of cleft field-aligned currents is explained with a qualitative model in which this pair of currents is generated on open field lines that have just been reconnected on the dayside magnetopause. The electric fields are transmitted along the field lines to the ionosphere, creating a poleward electric field and a pair of field-aligned currents when By is positive; the pair of field-aligned currents consists of a downward current at lower latitudes and an upward current at higher latitudes. In the By negative case, the model explains the reversal of the field-aligned current direction in the LCC and HCC regions.

Taguchi, S.↗

NASA NTRS1993

Global atmospheric energy deposition by energetic electrons - Quantitative spatial and temporal characteristics inferred from the Atmospheric X-ray Imaging Spectrometer (PEM/AXIS) on UARS

The primary purpose of PEM/AXIS is to provide a global monitor of the energy input to the upper atmosphere due to energetic electrons. The design, development, and calibration of AXIS are described and an assessment of its excellent on-orbit performance is presented. The unique capabilities of X-ray imaging spectrometers to monitor the global patterns of electron energy deposition in the atmosphere are shown through an analysis of some specific cases during the first year of the UARS mission.

Chenette, D. L.↗

NASA NTRS1993

On the High- and Low- Altitude Limits of the Auroral Electric Field Region

Using measurements from the High Altitude Plasma Instrument (HAPI) on the Dynamics-Explorer 1 (DE-1) spacecraft and the Low Altitude Plasma Instrument (LAPI) on Dynamics Explorer 2 (DE 2), we investigate both die high altitude and low altitude extents of the auroral acceleration region. To infer the high altitude limit, we searched the HAPI data base for evidence of upward-directed auroral electric fields located above the spacecraft when the HAPI spacecraft is above 9000 km altitude. We find that such acceleration is common when DE-1 flies through die auroral oval at an altitude of 9,000-11,000 km. At altitudes above 11,000 km, the fraction of the orbits with evidence of at least a 1000 V potential drop above the spacecraft falls, becoming essentially zero above an altitude of 15,000 km. Above that altitude, small (100 V) potential drops are frequently observed, but only rarely are approx. 1 kV potentials observed, typically associated with polar cap or 'theta' arcs or westward traveling surges. To investigate the low-altitude limit of the auroral acceleration region, we use conjunctions of DE 1 and DE 2 along auroral field lines and match the upgoing fluxes of ionospheric ions observed by DE 2 with the flux of accelerated upgoing ions observed at DE 1. Calculating the ionospheric scale height from the ion and electron temperatures and assuming that the parallel flow velocity is independent of height above 800 km, we calculate the altitude at which the upwelling ionospheric ions are effectively completely lost to upward acceleration. The initial lowest-altitude acceleration process could be either a perpendicular acceleration or a parallel electric field, but it must be sufficient to give the entire distribution escape energy. We find that in the two cases studied, near the region of peak auroral potential drop the altitude of this acceleration was around 1700 km (near the O/H neutral crossover altitude), but was significantly higher (approx. 2000 km) near the edges of the arc, where the potential was lower. The composition of the upgoing ion beam was consistent with these heights, being predominately H(+) near the edges and O(+) near the peak.

Reiff, P. H.↗

NASA NTRS1992

An experimental investigation of thermospheric structure near an auroral arc

The paper compares observations of thermospheric parameters, made from DE-2 spacecraft during three successive orbital crossings of a quiescent dusk sector auroral arc, with the predictions of three fine-grid auroral arc models. DE-2 measured the ion and neutral window, electron and neutral temperatures, neutral composition, and energetic auroral electron spectra (5 eV to 32 keV) at about 320 km altitude. The DE-2 composition measurements showed a local increase of the N2/O ratio in the arc, which is interpreted to be a result of the upward motion of N2-rich air. A reduction in the measured neutral temperature of about 100 K in the arc, relative to temperatures on either side, was found for all three arc crossings. Of the three theoretical models examined, only one shows a tendency for the neutral thermospheric temperature to drop in the auroral arc, and the decrease is significantly less than the observed temperature change.

Eastes, R. W.↗

NASA NTRS1992

The polar cap environment of outflowing O(+)

The properties of the core (0-50 eV) and 'energetic' (0-1 keV) ions, plasma waves, and auroral images obtained from Dynamics Explorer 1 (DE-1) and those of electrons, obtained from DE-2, are examined in the context of the polar cap environment. Results indicate the presence of two populations: high-speed (10-30 eV, or higher, streaming energies) polar beams and low-speed (generally less than 10-eV streaming energies) streams. The high-speed polar beams show an auroral connection (i.e., they are observed on or near the field lines threading auroral arcs), while the low-speed streams are on or near the field lines threading the dark polar cap and may be converted from the cleft ion fountain. Compared to the high-speed streams, the low-speed streams are significantly more stable with respect to energy and flux.

Horwitz, J. L.↗

NASA NTRS1992

Small-scale electrodynamics of the cusp with northward interplanetary magnetic field

Possible low-altitude field signatures of merging occurring at high latitudes during a period of strong northward directed interplanetary magnetic field are reported. Large electric and magnetic field spikes detected at the poleward edge of the magnetosheathlike particle precipitation are interpreted as field signatures of the low-altitude footprint of such merging line locations. A train of phase-shifted, almost linearly polarized electric and magnetic field fluctuations was detected just equatorward of the large electromagnetic spike. It is argued that these may be due to either ion cyclotron waves excited by penetrating magnetosheath ions or transient oscillations in the frame of convecting plasma, brought about by the sudden change in the flow at the magnetospheric end of the field line.

Basinska, Ewa M.↗

NASA NTRS1992

The cyclotron energization through auroral wave experiments (CENTAUR 2B)

The CENTAUR 2B mission, a dual payload program, is in many aspects the same as the previous missions from Cape Perry and Norway in 1985. It was planned that these payloads would be launched from Andoya, Norway, Nov. 1989 from the Universal II launcher. The payloads are identical, but would have been launched at different azimuths as far north and as far west as possible. Particle experiments include the angular resolving energy analyzer (AREA), the fast ion mass spectrometer (FIMS), the spectrographic particle images (SPI), and finally, the differential ion flux probe (DIFP). SwRI was responsible for the scientific payload, which includes the power supplies, the power supply interfacing, the manipulating of the data from the instruments to format it for the telemetry system, all mechanical structure and restraint mechanisms, and the payload subskin. The status of the various components of this program is given.

Winningham, J. D.↗

NASA NTRS1992

Ionospheric simulation compared with Dynamics Explorer observations for November 22, 1981

The present study uses an extensive DE-2 data base to both constrain inputs to a time-dependent ionospheric model (TDIM) for a simulation of the ionosphere and then check the simulated densities. The investigation was carried out for both a quiet period and a substorm period. The quiet-day study produced very good agreement between modeled and observed electron densities in the topside ionosphere with two significant exceptions: First, across the polar region the DE-2 LANG densities showed fine structure in addition to the overall regional density morphology. Second, a surprising discrepancy arose in the presunrise and midlatitude trough. The TDIM densities were an order of magnitude lower than those observed by DE-2. The substorm study showed remarkably good agreement with the observed densities.

Sojka, J. J.↗

NASA NTRS1991

On the auroral current-voltage relationship

The auroral relationship between the upward parallel current and the parallel potential drop is predicted using Knight's (1973) collisionless-plasma kinetic theory, and the results are compared with near-simultaneously carried out measurements by DE 1 and DE 2. The agreement between the calculated and observed data is generally good. However, the Knight current, since it does not include upward ionospheric electrons, is not valid in the downward return current region. It was found that suprathermal electron bursts could be observed in the diffuse aurora at the same invariant latitudes, both at high and at low altitudes, suggesting that these bursts are a spatial rather than temporal phenomenon.

Lu, G.↗

NASA NTRS1990

Ion acceleration at the contact surface of Comet P/Halley

Suprathermal ions form a major component of the plasma within the inner coma of Comet P/Halley. A close inspection of these ions shows them to contain at least two separate populations: one population covers the energy range below about 400 eV, and a second population exists in a narrow energy band centered between 3 and 4 keV. Similar distributions are found in two regions upstream of the contact surface. It is postulated that the suprathermal ions observed upstream of the contact surface were created at the contact surface. Sudden movements of the contact surface, in the cometary frame of reference, in response to changes in the magnetic field pressure, or cometary production rate, give rise to an induction electric field able to accelerate the local thermal cometary ions up into the tens of electron volts range. Higher energies can be attained with the reacceleration of these ions in subsequent movements of the contact surface. Besides creating the ion enhancements observed upstream of the contact surface, this acceleration mechanism wil release large amounts of suprathermal ions into the inner coma.

Gurgiolo, C.↗

NASA NTRS1990

Classification of auroral precipitation fluxes by characteristic parameters and their effects on the coupling of the precipitation to the ambient ionosphere

The spectral shapes of the precipitating auroral electron flux spectra are quantified by an automated fitting procedure which represents each flux spectrum as a superposition of Maxwellian and Gaussian partial fluxes. This makes it possible to represent each spectrum by a set of characteristic parameters which describe the shape of that spectrum. A set of inverted-V events observed by the Low-Energy Plasma Instrument on Dynamics Explorer 2 near the fall 1981 equinox, has been analyzed. The distribution of the peak inverted-V energies in magnetic local time and invariant latitude (IL) has been obtained, and it is shown that by far the highest peak energies occur in the range of IL between 65 and 70 and MLT between 18 and 24 hrs. It is also shown how the difference in spectral characteristics of the precipitation fluxes between the cusp and the nighttime auroral zone determines the thermal coupling of the precipitation to the ambient ionosphere.

Fontheim, E. G.↗

NASA NTRS1990

Energetic photoelectrons and the polar rain

In the daytime midlatitudes, the Low Altitude Plasma Instrument (LAPI) on board the Dynamics Explorer 2 satellite has observed photoelectrons with energies as high as 850 eV. These energetic photoelectrons are an extension of the 'classical' photoelectrons (less than 60 eV) and result from photoionization of neutrals by soft solar X-rays. Since these photoelectrons are produced wherever the solar flux is incident on the earth's atmosphere, they should be present in sunlit polar cap. But in the polar cap, over these same energies, there is a well-known electron population: the polar rain, a low intensity electron flux of magnetospheric origin. Thus, in the sunlit polar cap, an energetic population of electrons should consist of both an ionospheric (photoelectron) and a magnetospheric (polar rain) component. Using numerical solutions of an electron transport equation with appropriate boundary conditions and sunlit polar cap LAPI data, it is shown that the two populations (photoelectron and polar rain) are indeed present and are both needed to explain polar cap observations.

Decker, Dwight T.↗

NASA NTRS1990

DE-2 observations of filamentary currents at ionospheric altitudes

Conjunctive measurements made by the Dynamics Explorer 1 and 2 spacecraft on October 22, 1981, under conditions of southward IMF, suggest the existence of a cusp ion injection from a region at the magnetopause with a scale size of about 1/2 to 1 earth radii. Current signatures observed by the LAPI and MAGB instruments on board DE-2 indicate the existence of a rotation in the magnetic field that is consistent with a filamentary current system. The observed current structure can be interpreted as the ionospheric signature of a flux transfer event (FTE). In addition to this large-scale current structure there exist three small-scale filamentary current pairs. These current pairs close locally and thus, if the present interpretation of this event as an FTE is correct, represent the first reported observations of FTE interior structure at low-altitudes.

Smith, M. F.↗