Engineering topics

Coley, W. R.

Publications and source records attributed to Coley, W. R..

At least 19 records

NASA NTRS2011

Observations of Low-Latitude Plasma Density Enhancements and their Associated Plasma Drifts

Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed +/- 15 deg away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous observations have shown that the peak change in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the 1results in this paper show that the peak change in parallel fl ow typically occurs 25-100 km to the east of the peak perpendicular ow. We discuss this and other aspects of the observations in relation to the characteristics of the plasma depletions formed near the magnetic equator detected by the same probes on the C/NOFS satellite and to previous observations and theories.

Klenzing, J. H.↗

NASA NTRS1999

Polar UVI Observations of Auroral Oval Intensifications during a Transpolar Arc Event on December 7, 1996

The evolution of the northern hemisphere aurora is examined during a time when the Interplanetary Magnetic Field (IMF) makes three brief southward excursions after an extended period of northward IMF. POLAR UltraViolet Imager (UVI) provides images of the aurora while DMSP provides in situ measurements of precipitating particles, ionospheric plasma flows and ion density. Substorm-like events are correlated with northward turnings of the IMF, while the intensity of the ionospheric response is correlated with the duration of the southward IMF period prior to the northward turning. Observations indicate that when the transpolar arc reaches the highest latitudes it is located on a spatially narrow region of closed field lines which extends along the noon-midnight meridian. UV observations indicate a connection between the transpolar arc and the nightside auroral enhancements. Precipitating particles associated with both features are attributed to a plasma sheet boundary layer source in the magnetotail implying a magnetospheric connection between the transpolar arc and the nightside auroral oval intensification.

Cumnock, J. A.↗

NASA NTRS1995

Adaptive Identification and Characterization of Polar Ionization Patches

Dynamics Explorer 2 (DE 2) spacecraft data are used to detect and characterize polar cap 'ionization patches' loosely defined as large-scale (greater than 100 km) regions where the F region plasma density is significantly enhanced (approx greater than 100%) above the background level. These patches are generally believed to develop in or equatorward of the dayside cusp region and then drift in an antisunward direction over the polar cap. We have developed a flexible algorithm for the identification and characterization of these structures, as a function of scale-size and density enhancement, using data from the retarding potential analyzer, the ion drift meter, and the langmuir probe on board the DE 2 satellite. This algorithm was used to study the structure and evolution of ionization patches as they cross the polar cap. The results indicate that in the altitude region from 240 to 950 km ion density enhancements greater than a factor of 3 above the background level are relatively rare. Further, the ionization patches show a preferred horizontal scale size of 300-400 km. There exists a clear seasonal and universal time dependence to the occurrence frequency of patches with a northern hemisphere maximum centered on the winter solstice and the 1200-2000 UT interval.

Coley, W. R.↗

NASA NTRS1995

Gravity Waves Near 300 km Over the Polar Caps

Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

Johnson, F. S.↗

NASA NTRS1994

Spacecraft potential effects on the Dynamics Explorer 2 satellite

The relationship between the plasma environment and spacecraft potential is examined for the Dynamics Explorer 2 (DE 2) spacecraft in an attempt to improve the accuracy of ion drift measurements by the retarding potential analyzer (RPA). Because of the DE 2 orbit characteristics (apogee near 1000 km and perigee near 300 km) and the configuration of conducting surfaces on the spacecraft, thermal electrons and ions constituted the only significant contributions to the charging currents to the spacecraft surface for the majority of geophysical conditions encountered. The geomagnetic field had considerable effect on the spacecraft potential due to magnetic field confinement of the electrons as well as to the V x B electric field resulting from the movement of the spacecraft across magnetic field lines. Using a database of inferred spacecraft potentials from the RPA, measured electron temperatures from the Langmuir probe (LANG), and calculated V x B electric fields, we derive an algorithm for determining the spacecraft potential (at the location of the RPA on the spacecraft) for any point of the DE 2 orbit. Knowledge of the spacecraft potential subsequently allows us to retrieve relatively accurate ion drifts from the RPA data.

Anderson, P. C.↗

NASA NTRS1994

Comparison of low-latitude ion and neutral zonal drifts using DE 2 data

We have used data from the ion drift meter and the wind and temperature spectrometer on the DE 2 spacecraft to make statistical comparisons of the zonal ion and neutral drifts at dip latitudes (DLAT) in the +/- 35 deg range over all local times. Fourier analysis indicates that the superrotation and the diurnal components of both flows are strongly peaked at the dip equator, with the superrotation term becoming negative for the absolute value DLAT greater than or equal 20 deg. One interesting feature is the presence of a period (2200-0500 solar local time) in the 300-400 km altitude region near the dip equator where the ion drift is more strongly eastward than the neutral flow. This would seem to indicate the presence of an electric field source of greater strength than the F region dynamo elsewhere along the geomagnetic field line. Model calculations indicate that a possible mechanism for this source lies in the vertical shear in the zonal neutral wind in the 100-200 km altitude region.

Coley, W. R.↗

NASA NTRS1993

A comparison of in situ measurements of vector-E and - vector-V x vector-B from Dynamics Explorer 2

Dynamics Explorer-2 provided the first opportunity to make a direct comparison of in situ measurements of the high-latitude convection electric field by two distinctly different techniques. The vector electric field instrument (VEFI) used antennae to measure the intrinsic electric fields and the ion drift meter (IDM) and retarding potential analyzer (RPA) measured the ion drift velocity vector, from which the convection electric field can be deduced. The data from three orbits having large electric fields at high latitude are presented, one at high, one at medium, and one at low altitudes. The general agreement between the two measurements of electric field is very good, with typical differences at high latitudes of the order of a few millivolts per meter, but there are some regions where the particle fluxes are extremely large (e.g., the cusp) and the disagreement is worse, probably because of IDM difficulties. The auroral zone potential patterns derived from the two devices are in excellent agreement for two of the cases, but not in the third, where bad attitude data may be the problem. At low latitudes there are persistent differences in the measurements of a few millivolts per meter, though these differences are quite constant from orbit to orbit. This problem seems to arise from some shortcoming in the VEFI measurments. Overall, however, these measurements confirm the concept of `frozen-in' plasma that drifts with velocity vector-E x vector-B/B(exp 2) within the measurement errors of the two techniques.

Hanson, W. B.↗

NASA NTRS1992

East-west ion drifts at mid-latitudes observed by Dynamics Explorer 2

The effects of the dynamo electric fields and the penetration of high-latitude electric fields on zonal ion drifts were investigated by examining east-west ion drifts at mid-latitudes observed during magnetically quiet and disturbed periods by the polar orbiting DE-2 spacecraft. The influences of the electric field sources can be summarized as follows: (1) semidiurnal and terdiurnal tides are most important during quiet times between 25 deg and 55 deg magnetic local time, (2) the influence of the disturbance dynamo and magnetospheric penetration field are seen on average down to 45 deg during quiet times and down to 35 deg during disturbed times, and (3) direct influence of the auroral zone electric field is important on average down to 60 deg during quiet times and down to 50 deg during disturbed times.

Heelis, R. A.↗

NASA NTRS1992

Three-dimensional ionospheric plasma circulation

Examination of the ion drift velocity vector measured on the DE2 spacecraft reveals the significance of ionospheric flows both perpendicular and parallel to the magnetic field at high latitudes. During periods of southward directed interplanetary magnetic field the familiar two-cell convection pattern perpendicular to the magnetic field is associated with field-aligned motion predominantly upward in the dayside auroral zone and cusp, and predominantly downward in the polar cap. Frictional heating by convection through the neutral gas and heating by energetic particle precipitation are believed to be responsible for the bulk of the upward flow with downward flows resulting from subsequent cooling of the plasma. Some of the upward flowing plasma is apparently given escape energy at altitudes above about 800 km. The average flow of ions across the entire high-latitude region at 400 km is outward and comparable to the energetic ion outflow observed at much higher altitudes by DE 1.

Heelis, R. A.↗

NASA NTRS1992

Remote-sensing observations of F-region ion drift velocities using Dynamics Explorer-2 Doppler measurements of the O+(2P) 732.0 nm emission

Limb-scan observations of Doppler line profiles from the O+(2P) 732.0 nm emission at F-region altitudes, made with the Fabry-Perot interferometer (FPI) on the Dynamics Explorer-2 (DE-2) spacecraft, have been analyzed to provide measurements of the meridional component of the ion convection velocity along the instrument line-of-sight. The initial DE-2 results presented here demonstrate the first spaceborne use of the remote-sensing Doppler technique for measurements of ionospheric convection. The FPI meridional ion drift measurements have been compared with nearly simultaneous in situ ion drift measurements from the Retarding Potential Analyzer on DE 2. Once allowance is made for the temporal lag between the in situ and remote measurements, the results from the two techniques are in good agreement. The results of a simulation study demonstrate that the spaceborne interferometric technique has future utility for 2D imaging of the quasi-instantaneous ion convection pattern.

Carr, S. S.↗

NASA NTRS1990

Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes

Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.

Basu, Sunanda↗

NASA NTRS1989

Low-latitude zonal and vertical ion drifts seen by DE 2

Horizontal and vertical ion drift data from the DE 2 spacecraft have been used to determine average zonal and vertical plasma flow (electric field) characteristics in the +/- 26-deg dip latitude region during a time of high solar activity. The 'average data' local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time ((SLT) with a maximum westward velocity of 80 m/s in the early afternoon. There is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m/s. A secondary nighttime maximum exists at 0430 SLT preceeding the reversal to westward flow. This profile is in good agreement with Jicamarca, Peru, radar measurements made under similar solar maximum conditions. Haramonic analysis indicates a net superrotation which is strongest at lower apex altitudes. The diurnal term is dominant, but higher order terms through the quatradiurnal are significant.

Coley, W. R.↗

NASA NTRS1988

Case study of polar cap scintillation modeling using DE 2 irregularity measurements at 800 km

High-resolution in situ Dynamics Explorer 2 data on thermal plasma densities are used here to study the small-scale irregularity structure of the F layer patches. It is shown that spatially discrete density structures associated with polar cap patches can be detected fairly high in the topside by an in situ irregularity sensor and that they correspond to temporally discrete scintillation patches. It is also shown that it is possible to model phase and amplitude scintillation occurrence from a knowledge of irregularity amplitude at a satellite altitude of about 800 km provided that independent measurements of the peak density and scale height of the F region are available.

Basu, Sunanda↗

NASA NTRS1988

Global and local Joule heating effects seen by DE 2

In the altitude region between 350 and 550 km, variations in the ion temperature principally reflect similar variations in the local frictional heating produced by a velocity difference between the ions and the neutrals. Here, the distribution of the ion temperature in this altitude region is shown, and its attributes in relation to previous work on local Joule heating rates are discussed. In addition to the ion temperature, instrumentation on the DE 2 satellite also provides a measure of the ion velocity vector representative of the total electric field. From this information, the local Joule heating rate is derived. From an estimate of the height-integrated Pedersen conductivity it is also possible to estimate the global (height-integrated) Joule heating rate. Here, the differences and relationships between these various parameters are described.

Heelis, R. A.↗

NASA NTRS1988

Simultaneous density and electric field fluctuation spectra associated with velocity shears in the auroral oval

A detailed study is presented of simultaneous density and electric field fluctuation spectra over a large-scale length range seen in association with large structured convective plasma flows, field-aligned currents, and particle precipitation at high latitudes. The data were obtained for two Dynamics Explorer 2 orbits at two different altitudes within the F region and the topside ionosphere. The observations are compared with results of nonlinear simulations of shear flow-driven instabilities and predictions based on two-dimensional turbulence arguments, with particular reference to the Kelvin-Helmholtz process.

Basu, Sunanda↗

NASA NTRS1987

Ionospheric convection signatures and magnetic field topology

A statistical study of signatures of the high-latitude ionospheric convection pattern and the simultaneously observed energetic electron precipitation is presented. Most often found are convection cells in which the sunward flowing region contains auroral particle precipitation but the antisunward flowing region does not. However, observations also show the frequent occurrence of convection cells in which neither the antisunward nor the sunward flowing plasma region contains auroral particle precipitation. These findings may appear within the dawnside or duskside convection pattern and strongly suggest that such convection cells may be associated with open magnetic field lines that thread the magnetotail lobes.

Coley, W. R.↗

NASA NTRS1986

Studies of dynamo field structure and related effects: DE satellite project guest investigator program

The establishment of the latitudinal and longitudinal structure of the low latitude dynamo electric (DE) field was initiated using data primarily from the Unified Abstract (UA) files of the Atmosphere Explorer E (AE-E) satellite. Mass plots of the vertical ion drift values were made for 1977, 1978, and 1979. The average diurnal variation of V sub v within 20 degrees of the dip equator is remarkably similar to that obtained at Jicamarca in the same years. The average meridional ion drift velocity vectors, obtained as a function of latitude by combining the average vertical and horizontal (nearly north-south) ion drift values from the AE-E, showed the expected variations with local time and season based on the well known equatorial fountain effect theory. The average diurnal variation of the vertical drift was found for four different ranges of dip latitude for a northern solstice season. The effect of the transequatorial neutral winds was as evident in this plotting format as in the meridional or fountain effect format. Finally, the average vertical drift velocity V sub v, not the east-west electric field E sub ew, was found to be approximately independent of longitude, as expected from the dynamo theory.

Coley, W. R.↗

NASA NTRS1986

Medium and large-scale variations of dynamo-induced electric fields from AE ion drift measurements

Current models of the low latitude electric field are largely based on data from incoherent scatter radars. These observations are extended through the addition of the rather extensive high quality electric field measurements from the Ion Drift Meter (IDM) aboard the Atmosphere Explorer (AE) spacecraft. Some preliminary results obtained from the Unified Abstract files of satellite AE-E are presented. This satellite was active from the end of 1975 through June 1981 in various elliptical and circular orbits having an inclination near 20 deg. The resulting data can be examined for the variation of ion drift with latitude, longitude, season, solar cycle, altitude, and magnetic activity. The results presented deal primarily with latitudinal variations of the drift features. Diagrams of data are given and briefly interpreted. The preliminary results presented here indicate that IDM data from the AE and the more recent Dynamics Explorer B spacecraft should continue to disclose some interesting and previously unobserved dynamical features of the low latitude F region.

Coley, W. R.↗